Electromyographic studies on the ovine uterus : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy at Massey University

(1)Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author..

(2) ELECTROMYOGRAPHIC STUDIES ON THE OVINE UTERUS. A THESIS PRESENTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF PHILOSOPHY AT MASSEY UNIVERSITY. Li Yuemin _January. 1991.

(3) TABLE O F CONTENTS. ELECTR O MYOGRAPHIC STUDIES ON THE OVINE UTER U S. A b s tra ct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii Lis t o f Ta b l e s v List o f Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi Acknowl e dg m en ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v i ii .. I.. .. .. .. .. .. INTR O D U CTION. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. 11 . LITERATURE REVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 II.1. The Repro d u c t i ve Cyc l e o f S h e e p. . . . . . . . . . . . . ... . ... . . . . 3. Il . l .A . The b reeding seaso n . . . . . . . . . . Il . l . B . Th e o estro u s cycle i n ewes . . . . . Il . l . C. Pregn ancy a n d part u r i t i o n i n ewes Il . l . D .The post- partu m period i n ewes . . . 11 . 2. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. 3 5 7 9. Myo m e tri a l Acti v i ty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3. I I . 2 . A . Stru c t u re a n d o rgan isation o f t h e myom etrial cont r act i l e u n i t . . . . . . . . . . . . . . . . . . . . . . . . . I I . 2 . B . Speci a l featu res o f t h e u l tr as tr ucture o f t h e fu n c t io na l u n i t s o f the m y o m e t rui m . . . . . . . . . . . (a) (b) (c) (d). The c o n tract i l e apparat u s . P lasm a membrane . . . . . . The sarcoplasmic reticu l u m Th e g a p j u nctions . . . . . . .. . . . . . . . . (SR) . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. 13 14. . . . . . . . .. 14 14 15 15. I I . 2 . C . Myo metrial con traction . . . . . . . . . . . . . . . . . . . . . . . . 1 6 II.2.D. E l e c t r o p h y s i o l o g y of myo m e t r i a l con t racti l i ty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 6. 11 .3.. E ffe c t s of Horm o n e s on Emg Activity. 11 . 3 . A . 11 . 3 . B . 11 . 3 . C . 11 . 3 . D . 11 . 3 . E. 11 . 3 . F. 11 .4.. O e strogen . . . . . . . Progesterone . . . . . Oxytoci n . . . . . . . . Prostagl an d i n s . . . . Relaxin . . . . . . . . Vasoactive i n t es t i n al .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . pepti d e. . . . . . . . . . . . . . . . . . . . 19. . . . . . . . . . . . . . . . . . . . . . . . . (VIP) .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. Uteri n e Moti l i ty S t u d i e s with Pa r ticu l ar Refe r e n c e t o t he Ewe .. .. .. •. .. .. •. •. .. .. .. .. .. .. .. .. •. .. .. .. .. •. .. .. .. .. .. .. .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. .. .. .. .. •. .. .. .. .. .. 19 22 24 28 30 30. 31. 11 . 4 .A. Methods o f studying u te r i n e motility . . . . . . . . . . . . . . 3 1 11 . 4 . B . Uterin e motil ity observations recorded from t h e uterus o f t h e i n t act ewe . . . . . . . . . . . . . . . . . . 33 .. ..

(4) 11 . 4 . C . Uter i n e motility observations recorded fro m t h e u terus o f t h e ovariecto m i s e d ewe . . . . . . . . . . . . . Ill.. 11 ! . 1 . 111 . 2 . 11! . 3 . 111 .4. III.5. III.6.. GEN ERAL MATERIALS AND M ETHODS. .. •. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. •. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. M y o m e t r i a l E m g A c t i v i ty i n t h e Inta c t Ewe d u ri n g A n o e s tr u s . . . . . . . . . . . . . . . . . . .. IV .l .A. IV .LB .. IV .l . C . IV .l . D . I V. LE.. 48. 48 48 48 54 54 60. 62. 62. Th e r esting emg of t h e u t e r u s . Th e e ffect o f exogen o u s o xytoci n on restin g e m g o f the u t e r u s d u ri n g anoestru s . . . . . . . . . . . . . Th e e ffect o f exogeno u s o estrogen o n t h e resting emg of t h e uterus d u ri n g anoestrus . . . . . . . . . . . . . Th e e ffect of oxytocin on o estrogen i n d u c ed emg a c t i v i ty during a noestrus . . . . . . . . . . . . . . . . . . . Th e effect of P G F21X on o estrogen i n d u c ed emg a c t i v i ty during anoestrus . . . . . . . . . . . . . . . . . . Th e chan ges in myometr ial activity �hen st i m u l ated by a secon d i n jection o f oestrogen . . . . . . . . . . .. I V. l . F.. IV. 2 .. .. A n i m al . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electrodes ....................... . ........... . . . . . . Su rgery a n d an aesthesia . . Recordi ngs . . . . . . . . . . . . . . . . . . . . . . . . . . Th e Electromyograms . . . . . . . . . . . . . . . . . . . Q u a n t itative a n alysis o f the Electromyograms . .. IV. R E S U LTS IV. l .. .. 41. 62 the . . . . . . . . . 62 . . . . . . . . . . . . 62 . . . . . . . . . . . . 62. . . . . .. .. . . . . .. .. 66. . . . . . . . . . . . . 66. M y o m e t r i a l Acti v i ty i n t h e O v a r i e c to m i zed Ewe d u ri n g t h e A n o e s tr u s S e a s o n .. . ... . .. . ... . . . .. . . . . . . . . . .. . . . . 7 2. I V. 2 .A.. Specific features of the design o f t h i s experiment . . . . . . . . . . . . . . . . . . . . . 72 I V. 2 . B . The gen eral patterns o f electrical activity . . . . . . . . . . . 73 (a) Resting emg activity a n d t h e e ffects of exogeno u s oxytoci n a n d PGF21X o n it . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 (b) O estrogen i n duced e m g activity i n the ovariectomized e w e and t h e e ffects o f oxytocin a n d P GF21X o n it . . . . . . . . . . . . . . . . . . . . . . . . . 73 (c) Th e e ffects o f progesterone o n 77 oestrogen i n duced e m g activity (d) Th e reduced responsiven ess of t h e uterus i n regime two o f t h e experiment . . . . . . . . . . . . . . . . . . . 83 .. .. .. .. ..

(5) (e) Th e d irection o f propagation o f e m g a ctio n pot e n t i a ls . . . . . . .. .. .. .. .. .. .. .. .. .. . .. .. I V. 2 . C . S o m e q u a n t i t a t iv e aspect s of the e l e c t r o myograms recorded from the ovariectom ized ewes . . . . . . . . . . . . . . . . . . . (a) A m p l i t u de . . . . . . (b ) B u rst frequency . . . . (c) Spikes per burst . . . . . . . . . . . . . . . . . . . ( d ) M o t i l i ty in dex . . . . . . . . . . . . . . . . . . . . . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ·.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. IV.3.. V. V. 2 .. V.3 . V.4 . V.S .. .. 84. . . . . . . . . . . . . . . . . . . . . .. 85 85 85 85 85. .. .. .. .. .. .. .. .. .. .. .. .. .. Th e E m g A c t i v i ty o f the Ute r u s o f the Cycl i n g Ewe .......... 93. DISCU S S ION. .. .. .. .. .. . .. .. .. . . .. .. .. .. .. .. .. . .. .. .. . . .. Emg Activity d u r i n g Anoestrus and i n t h e Ovar i ec t o m ized Ewe . . . . . . Th e D irection o f Pro pagation of t h e Act i o n Poten t i a l s . . . . . . . . . . . . . . . . . . . . . Th e I n fl u en c e o f O estrogen . . . . . . . . . . . Th e I n fl u e n c e o f Progestero n e . . . . . . . U te r in e r e fractoriness . . . . . . . . . . . . . . .. V .2 .. .. .. .. .. .. .. .. .. .. .. 104. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 1 04. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . . . . . . . . . . .. 1 06 1 10 1 12 116. REFER E N C E S ........................................ 1 1 7. A P P E NDIX I. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 130.

(6) ii. A B S TRACT. There a re many repo r t s in t h e l i t er a t u re, u s i n g a variety of t e c h n i qu es , i n dicating t h at h ormonally i n du ced m ovem en t s o f t h e u terus play a m aj o r r o l e i n t h e reproduction process. Th e pu rpose o f t h is study w a s to explore some of t h ese p h enomena by measuring electro-myographical respons es from t h e u terus o f i n t act a n d ovariectom i zed ewes b o t h b e fore a n d during t h ei r n o r m a l b reeding seaso n .. Six h e a l t h y non-pregn a n t Rom n ey ewes o f abou t 5 0 kg body w e i g h t were selected for the i nvestigations which were carried out b etween September 1 987 and Feb r ua ry 1 988. Electrodes, u sually in gro u p s of t h ree, were surg ically impl a n t e d a t pre­ s elected s i t es (cervix, u t er i n e b o dy, u t erine h o r n , oviduct) on t h e reproductiv e t ract o f t he ewes, le a d s plugged i n t o a u n iversal AC a m p l i fier, a n d the o u t p u t recorded o n a fo ur c h a n n e l i n k wri t i n g c h a r t r ecorder. Four o f t h e six ewes were ovariect omized at the time o f implan t a t i o n o f t h e electrodes.. I n dwelling silastic cat h eters were inserted into t h e ext er n a l. j ug u l ar veins o f t h ese ewes t o e n a b l e oxytocin to be injected wi t h o u t disturb i n g t h e animal. A l l ewes were h o u sed i n dividu ally i n doors i n p e n s t h a t all owed t h em t o moy e freely during reco r d i n g session s .. Recordi n gs b eg an. abo u t 1 0 days after su rgery h ad been carried o u t . Th e electromyographs (emgs) were described u si ng generally accepted ter m s such as t he presence o f s pik es , t h e i r ampl i t u de, t h e presence o f b u rs ts a n d o f episodes o f activity, w h e t h e r el ectr ical activit y was co-ordi nat ed o r u n co­ ordinat e d , and t h e direction o f propagat i o n o f t h e act ivity. A m o t il i ty i n dex (MI) was derived as a m e t h o d of meas u r ing electrical activity of t h e u te r u s over prolonged periods o f t i m e . D uring t h e anoestro u s p e r i o d i n b o t h i n tact a n d ovariectomized e w e s a n emg pattern o f myo electrical complexes c h aracterised by alternating p h ases o f co­ ordina t ed b u rst s o f electrical activity a n d q u i escent periods were ob served. Th i s b asic pa ttern of activi ty, and respon s iv e n e ss to u t erine s t im u lan t s s u c h a s oxytocin and Glandin N (a P GF2oc an al og u e), was greater i n t h e i n t ac t.

(7) iii. ewes a s compared to t h e ovariec t o mized ewes a t t h i s t i m e . A l t h o u gh s u ch a d i ffer e n c e c o u l d be anticipated, a clear answer as to w h e t h er i t i s a general p h e n o m e n o n , or whether seaso n al d i ffere n c es exist, cou ld not be det e r m i n ed b ec a u se o f t h e l i m i t ations i n design o f t h i s s t u dy. A d i s t i n c t pattern o f emg activity was also i d e n t i fied d u r i n g d i ffer e n t p h ases of t h e o estro u s cycle in the ewe d u r i n g the n a t u ral b r e e d i n g season .. Th i s. p a t t er n cou l d b e m imicked by a d m i n i s tr a t i o n of th e exogen o u s steroid h o r m o n es oestrogen and proges t ero ne i n the ovariect o m ized ewes. Fou r days a fte r daily oes tradiol- 1 7b i njec t i o n s (50J..Lg s . c . ) t h e emgs of t h e ovariec t o m ized ewes s h owed a marked i n crease in ampl i t u d e and i n b u rs t frequency a n d a c o n s i d erably inc reased respo ns e to oxytocin a n d Gla n d i n N . W h e n t h i s was follo w e d by progestero ne a d m i n i st r a t i o n (50mg. s.c.), even wit h o estrogen i nj e c t i o n s c o n t i n u ing, i n h i b i t ion of activi ty a n d redu ced respon siveness to oxy t o c i n and Glan din N was e q u a l ly m arked. W i t h drawal o f progesteron e , b u t with co n t i n u i ng oest rogen a d m i n is tr at io n , r e s u l t e d i n a recovery fro m t h e i n h i b i t i o n a n d a respo n se t h a t w a s even greater t h an before t he progestero n e h a d been given . Th i s s u ggests both an i n h i b i t i n g and a poten t i a t i n g action o f progestero n e o n u t eri n e electrical ac t ivity, a fin di n g which adds s ome suppo r t to Csapo's c l assical w i t h d r awal of the 'progeste ron e block' as one o f t h e pre-requ isi tes fo r i n i t i at i o n of normal p ar t u r i t io n in sh eep. _. W h i l e o estrogen h as a clear role t o play as a s t i m u l a t o r o f electrical activity it a l so seem s c apable of exh i b i t i n g a b iph asic resp o n s e with a period of depressed a c t ivity occurri n g befo r e the pos i t ive stimu l u s occurs. W h e t h e r t h i s i s a fu n c t io n o f dose o r s o m e o t h er factor c o u l d n o t b e e s t ab l i s h e d i n t h i s s t u dy . I t s poten t i a ti n g e ffec t on t h e action o f both oxytocin a n d G l a n d i n N i n t h e s e experiments adds fu r t h er sign i ficance t o t h e a t t e n t io n t h a t s h o u l d b e p a i d t o t h e reproductive s t a t u s o f t h e a n i m a l when c l i n i c a l u se i s m a d e o f t h es e s u bstances.. Th e d i rection of propagation of action pot e n tials recorded in t h ese s t u di e s d ep e n d ed o n t h e general l evel o f emg activity.. W h e n t h is was l o w t h e. directi o n o f propagation w a s cervico- t u b a l , when h i g h , t h e proportion o f a c t i o n poten ti a l s i s i n both d i rections fro m t h e t u b a l e n d o f t h e u terus. A.

(8) iv. c l e a r u n derst a n d i n g o f such a m e c h a n i sm , a n d i t s sig n i fi c a n c e, m u s t await fu r t h er s t u dy..

(9) V. LIS T O F TAB LES. Tab l e 1 :. Th e e ffect o f oxytocin both o n spo n t an e o u s a n d . . . . . . . 67 oestradiol i n duced e m g activity (Ewe 329) .. Tab l e 11 :. Th e e ffec t of oxytocin on spo n t aneo u s a n d oestradiol i n d u c ed e m g activity 1 3 days a ft er l a s t oest radiol i nject i o n o f ewe 329 (compare w i t h Tab l e I ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69. Tab l e I l l :. Th e d i fferences i n emg activity b etween a n i m a l s du r i n g stage 2 o f regime o n e . . . . . . . . . . . . . . . . . . . . . . 9 1. Tab l e I V:. Th e e ffect o f oxytocin a n d P GF2cx: o n t h e o e s t radiol i n d u c e d electrical act ivity du r i n g stage 2 of regi m e one . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.

(10) vi. L I S T O F F IGURE S. Fig. 1 :. Th e pos i t i o n s of electrodes s u t u r e d a t pre- s elec t e d sites o n t h e u teru s a m o n g 6 ewes . . . . . . . . . . . . . 50. Fig. 2 :. Active a n d qu iesce n t periods of emg d u r i n g a noestr u s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 6. Fig. 3 :. An e x a m ple o f t h e m e t h o d o f m easu r i n g th e du rat i o n o f bu rsts, th e i n t erval b etween b u rs t s , t h e b u rs t frequ ency, spike frequ ency a n d am p l i t u d e o f t h e spike . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 7. Fig. 4 (a & b): Fig. 5 :. A n example showi n g t h e propagative direc t i o n o f b ursts a n d episodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 8 A n example o f co-o r d in at e d a n d u n co-o r d i n a t e d patterns o f elect rical a c t iv i ty . . . . . . . . . . . . .. Fig. 6 :. An exam ple of calc u l a t i n g t h e m o t i l i ty i n dex. Fig. 7 :. Oxytocin effect o n durin g a n oestrus. .. 59 61. spo n t a n eo u s emg activity . . . . . . . 63. Fig. 8 :. Oestradiol benzoate b o t h i n h i b i t s a n d s t i m u l at es myo m et r i a l activity in ewe 329 d u r i n g a n o e s t r u s . . . . . . . . 64. Fig. 9:. The e ffect o f oxytoci n on oestradiol i n du ce d emg activi ty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65. Fig. 1 0:. Th e effect o f P GF2oc on oestr ad iol i n d u c e d emg activity. during anoes t r us . . . . . . . . . . . . . . . . . . . . . . . . . 68. Fig. 1 1 :. Characteristics o f t h e emg recorded 13 days a ft er the i n i t i a l injec t i o n o f oes trogen . . . . . . . . . . . . . . . . 70. Fig. 1 2 :. Th e e ffects o f oes trogen and oxytocin on ampl i t u de, burst fre q u e n cy and m o t i l i ty i n dex during two expe r i m en t s on i n t a c t anoestro u s ewe 329. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1. Fig. 1 3 :. Th e patter n o f emg a c t iv i ty i n ovariec t o m i z e d ewe 247 d u r i n g the a n o es t r o u s season . . . . . . . . . . . . . . . . . . 74. Fig. 1 4 :. Th e pattern of emg activity i n d u c e d by o e s t r a d i o l 1 7b (50JLg g i v e n s . c. daily) on ovariec t o m i z e d ewes during the anoestrou s season . . . . . . . . . . . . . . . . . . . . . 75. Fig. 1 5 :. Th e e ffect s o f oxyto c i n (500 m u given i.v.) on t h e oestrogen i n d uced e m g activity o f ovariecto mi z e d ewes d u r i n g t h e anoestrous season . . . . . . . . . . . . . . . . . . 76.

(11) vii. Fig. 1 6a :. Th e d evelopment o f i n hi b it i o n a fter progestero n e a d m i n istration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 8. Fig. 1 6b :. Th e e ffect of oxytoc i n a n d P GF2<x: w h e n t h e uterus i s i n h ibited by progest e r o n e . . . . . . . . . . . . . . 79. Fig. 1 6c :. T h e e m g pattern observed d u r i n g t h e recovery from progesteron e i n h ib it i o n . . . . . . . . . . . . . . . . . . . . . . 8 1. Fig. 1 6d :. Th e pattern of oestrogen i n d u c e d emg i n ewe 1 0 b efor e progesteron e admi n i stration (A) a n d i n t h e sa m e ewe 1 1 5 h after a large dose o f progesterone ( 1 00mg given i . m . ) h ad b e e n g iven when th e ewe h a d recovered from t h e progestero n e tr eatm ent a d m i n istered during reg ime o n e (E) . . . . . . . . . . . . . . . . 82. Fig. 1 7 :. Th e difference i n amplit u d e a n d b u rst frequency b etween 4 electrode positio n s o n t h e reproduct ive . . . . . . . 86 trace. Fig. 1 8 :. Em g amplitu des d u r i n g treatment i n regime o n e .. di fferent. stages. of . . . . . . . 87. Fig. 1 9 :. Di fferences i n bu rst fre q u e n c y at each tr eatm ent stage o f regime one . . . . . . . 88. Fig. 20:. Nu mber of spikes i n a b u r st during the p eriod o f oestradiol i n duced emg activity i n regi me one . . . . . . . 89. Fig . 2 1 :. Th e n u mber of spikes in a bu rst d u r i n g each treatm ent stage of regime one . . . . . . . . . . . . . . . . . . . . . 9 0. Fig. 2 2:. Th e motility i n dex du r i n g stages 2 a n d 4 o f reg i m e o n e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94. Fig. 2 3 :. Th e c h aracteristics of emg act ivity during st ages 2, 3 and 4 of both reg i m es . . . . . .. 95. Fig. 24:. Ewe 661 during dioest r u s. 96. Fig. 2 5 :. Ewe 661 during pro-oest r u s .. Fig. 2 6 :. Ewe 661 during oest r u s . . . . . . . . . . .. Fig. 2 7 :. Ewe 661 du ring metoestru s/early dioestru s. 1 00. Fig. 28:. Ewe 661 during early dioestr u s . . . . . . . . . . . . .. 101. Fig. 29:. Ewe 6 6 1 recorded at m id-oe st r u s 8.4. 88. 102. Fig. 30:. Ewe 6 6 1 recorded at l ate o estr u s 9.4.88. .. . . . . . 97 . . . . . . . . . 98. 103.

(12) viii. ACKNOWLEDGME NTS. I ta ke t h i s opportun ity to t h a n k t h e m an y people who h ave g iv e n me enc o u rage m en t , h elp and advic e d u r i n g my M . P h i l . stu dy . M y s i n c e r e t h an ks g o to m y su pervisors Prof. E . D . Fielden a n d D r . D . H . C a r r for t h ei r u n fa l t e r i n g e n th u siasm a n d g u i da n ce d u r i n g t h e proj e c t . e n c o u r agem e n t ,. e n t h u siasm,. constructive. suggest ions. and. Th eir. assistance. t h r o u gh o u t the project were as important as t h ei r advice on the fi n al draft of t h i s thesis. My t h a n k s a l so go to the Tech n i cal Sta ff o f the Depart ment o f P h ysio logy and Anatomy, pa r t ic u l arly that of Debbie Anthony for h el p i n preparat ion of figu r es, J . C . Pedl ey for making the recor d i n g faci l i t ies u sed in t h is st udy ava i l ab l e t o m e , N . I . B roomfi e l d for givi n g v a l u able advice d u r i n g t h e cou rse o f the exp e r i m e n t s and helping m e i n the u se o f the word processo r , and I r e n e H a l l for a ssist a nc e during the surgical procedures.. I a m also i n debted to Mr Cedric B a r n ett and Rose Law for their w i l l i n g h el p with t h e sh eep, a n d with obtai n i n g t h e drugs a n d disposables u se d . T. Law's assistance w i t h t h e photography of all emg records i n gratefu l ly a c k n owledged.. F i n a l ly I w i l l for ever , a ppreciate t h e su pport and forb earance o f m y fam i ly a n d of Xinj i a n g S h i h ezi Agricu ltu ral College, w i t h o u t whose h elp t h i s s t u dy wo u l d n o t h ave b ee n po ssib le..

(13) 1 ELECTROMYOGRAPHIC STUDIES ON THE OVINE UTERUS. I.. INTRODUCTION. I t has l ong been r e c ogn i sed that the movement of spe rm f r o m the si t e of e j acul a t i on to the ovi du c t is due not only t o the mo t i l i ty of sperm c e l l s but a l so t o c ont ra c t i ons o f the f emale reproduc t i ve t r ac t ; i n al l spe c i es in whi ch i t has been t imed i t has been f ound that onl y a f ew minutes a r e requi red from de posi t i on of sperm i n the vag i na;c e rv i x unt i l they r e a c h t h e fal l op i an tube . Fur thermore the r e seems t o be no r e l a t i onship be twe en the rate a t whi c h semen is prope l l ed through the ute rus and the d i stance sepa ra t ing the c e r v i x and the vagina f r om the ovi duc ts ( Nal bando v ,. 1 9 76 ) .. The pr obabl e i mportance of hormones in this proc ess was i nd i c a t e d by. Nal bandov ( 1 976 ) who found ,. in c ows , t h a t ma ting c aused a r i se i n. i ntra - mammary pressure and that strong ut e r i ne c ontrac t i ons we r e i nduc ed by the st imulus o f natural ma t ing , a r t i f i c ia l insemina t i on , man i pul a t i on of the vulva ,. or even by the sight of a bul l .. Thi s same auth o r r e p o r ted. t hat inc reased a c t i v i ty was noted in isol a t e d uteri perfused w i th oxyt o c i n and , even i n such pre parations , semen deposi t ed in the c e rvix was t ransported t o the oviduc t s in fi� m i nutes . Al l these obse rva t i ons t aken t ogethe r were i nte rpre ted to mean that c o i tus induc es ne rvous i mpul ses that r ea c h the post e r i or l obe of the p i tui tary v i a the hypothal amus a c t i vat ing the r e l e ase o f oxy t o c in; this then c auses the u t e r ine and oviduc t c ontra c t i ons tha t are r e sponsi b l e f o r the r a p i d movement of semen f r om the sit e o f e j acul a t i on to the oviduc t ( Nal bandov , Pusey. 1 9 76 ) . et. al.. ( 1 9 80 ) demonst ra t e d i n the rat that myome t r i al. a c t ivi ty al so pl ays a r o l e i n the d i st r i but i on of bl astocyc t s throughout the ute rus . Thi s p r o c ess had earl i e r been suggested by Haf e z ( 1 9 6 4) t o p l ay a rol e i n the proc e ss o f spac ing and t r ans -ut e r ine m i g r a t i on o f bl astocysts i n the ewe . The c ontrol of myome t r i al a c t i vi t y around o e st rus i s v e r y c ompl ex . In the ewe , Naaktgeboren and Van Der Weyd e n ( 1 973) f i rst d e monst ra t e d ,.

(14) 2 by r e c ording the e l e c t r i c al ac t iv i ty of the myome tr ium , that the c hanges i n the c ontrac t i on pat t e rn o f the ute rus ar e c aused by the chan g ing progeste rone : o e st r ogen rat i o .. Quinl i van and Robi nson ( 1 9 6 9 ) r e p o r t e d. r e duc ed fert i l i ty i n ani mal s t r e at ed w i th progesterone i mpregnat ed intravaginal sponges to synchroni z e oest rus .. This reduc t i on i n. f e rt i l i ty can b e at t r i buted , a t l e ast i n par t , t o decr eased spe rm t ransport to the oviduc t r e sul t ing from reduced ute r i ne mot i l i ty . I n many spe c i e s progeste rone i s c onsidered essent i al f o r t he maintenanc e of ut e r ine quiesc en c e dur ing pregnancy and progest e rone wi thdrawal is c onsidered essent i al for the normal evol ut i on of u t e r ine c on t rac t i l i ty assoc i a t ed w i th both natural ( Thorburn et al . , induc ed partur i t i on ( Cur r i e e t al . ,. 1 9 77 ) and. 1 9 73).. I t thus seems c l ear that hormonal l y i nduc ed movements o f the ute rus play a ma j o r role in the r e produc t i on proc ess . The purp o se o f t h i s study the r e f o r e was t o exp l o r e some o f these phenomena b y measur i ng e l e c t r o-myogr aph i c al r esponses f r om the ute rus of both intac t and ovar i e c tomi zed ewe s . E l e c tr o - myograms ( emgs ) were rec orded f ro m an intact ewe before , during and af t e r a p e r i od of natural o e st rus .. S tud i e s. were al so made o f the emg o f the ute rus o f an intact ewe in the ano e st r ous st at e and o f ovar i e c t om i z e d ewe s : expe r i mental. in both types of. pre parat i ons c ommonl y use d e xogenous hormones w e r e. admi n i stered t o the ewe be ing i nve st i gat ed and the r e sponses r e c orded . The r e sul ts of these stud i es f orm the basis o f this thesi s ..

(15) 3 II. LITERATURE REVIEW II.l.. The Reproduc t ive Cyc l e of Sheep.. II.l.A.. The breeding season. Ewes are seasona l l y pol y - o e st r ous animal s .. The annual. r e produc t i ve cyc l e c onsists of a br e eding ( oe st rus ) season and a non­ breed i ng ( anoest rus ) season .. The breed ing season i n New Z e a l and usua l l y. begins i n March and i s c harac t e r i zed by suc c e ssive 1 6- 1 7 day oestrous c ycl e s .. The dur a t i on of oestr us is about 36 h with ovul a t i on oc curring. 24 h after i t s onse t .. I n June/Jul y , the ova r i an cyc l e s c e ase and the. anoe strous season beg ins ( Ward ,. 1 9 86 ) .. This seasona l i ty ensures the young are born a t a t i me o f year when they have the best c hanc e o f growing to matur i t y but i t does p l a c e r e st r a ints on mod e rn far me rs who w i sh t o maximi z e farm out put .. W i th a. cycl e of 5 months p r e gnancy and 3 months l ac t a t i on ,. i t i s theore t i c al l y. possibl e t o pr oduc e 3 sets o f l ambs every 2 years .. Howeve r , the ve ry. str ong seasonal phot o - p e r i o d i c infl uence upon f e rt i l i t y makes this d i f f i cul t t o achi eve .. Whe ther the o b j e c t i ve i s to max i m i z e t he. ef f i c i ency of l abour - int ensi ve management systems as i n Europe ,. or t o. maximise the e ff i c i ency of l abour - ext ensive farming syst e ms as i n Aust ral i a and New Z e a l a nd , ma t i ng management st rategi e s r e qui r e be t t e r c ontrol o f the onse t o f bre ed i ng a c t iv i ty ( Kennaway. et. a l ., 1 9 87 ) .. Nume rous p r o c e dures have be en used to induc e out of season br e e ding ( McDona l d ,. 1 986 ) , but al l have f a i l ed to a c c ount for the. persist ing i nh i b i t o r y phot o - pe r i octic signal s the she e p r e c e ive dur i ng anoestrus . The f i rst a t t empts to inf luence she e p breed i ng by mani pul a t ing day l engt h appear to be those p e r f o rmed by Yeates ( 1 949), who demonstrated that decre asing pe r i ods of l ight a t a t ime o f year when she e p were norma l l y anoest rus i nduc ed oest rous cycl es . This r e ma ins a me thod of produc ing more than one c r o p o f l a mbs a year i n housed she e p . Yea t e s also found that t h e a c tual l ength o f the da i l y l i ght per i od was not i mp o rt ant , thus showing that breed ing was not dependent upon a c r i t i c al.

(16) 4 t o t al amount o f l ight . More r e c ent l y i t was reported that bl inded she ep we re abl e t o r e spond t o ar t i f i c i al changes in l i ght pe r i od onl y when housed w i th a s i ghted ram ( Le gan and Karsch , 19 80). Fur t h e r advanc es in our understanding o f se asonal i ty have c ome w i t h the rec ogni t i on of the v i t al r o l e that the pineal gl and and i t s hormone m e l atonin pl ays i n r e l ay i ng photo - pe r i od i c info rmat i on to the endocr ine syst em ;. t r eatment w i t h. m e l atonin c an be used t o bring f o rward t h e b e g inning o f t h e bre eding se ason ( Arendt e t a l . , 19 8 3) . Dur ing seasonal an oestrus the p i tu i t ary c ontains l arge amount s o f f o l l i c l e - st i mul at ing ho rmone ( FS H ) and l ut e i n i z ing hormone ( LH ) , and the ovar i e s c ontain smal l numbers of l arge fol l i c l es . Corpora l ut e a ( i nd i c a t i ng ovul at i on ) a r e found o n l y a t the e nd of t h e ano est rous p e r iod ( Ward ,. 1 9 8 6) .. Th i s inc rease in gonad o t r o phins in the p i tu i t ary. g l and may be due t o a h i gher sensi t iv i t y o f t he pi tui tary t o the negat ive f e e dback o f o e st rad i o l dur ing ano e st rus .. Changes i n annual. pho to - pe r i od modul ates the negat i ve fe edback of oestrad i o l - l ib on t he t on i c LH se c r e t i on i n the ewe ( Legan and Karsc h , 19 80) .. The durat i on o f. se c ret i on of the p i neal hormone me l atonin i s r e sponsi bl e f o r the changes in oest rad i o l f e edback ( Bi ttman et al . ,. 1983) .. The br e e d i ng season o f. ewes i s the re f ore c harac t e r i zed b y l ower o e st rad iol negat ive sensi t i v i ty at the hypothal am i c jp i tui tary l evel and t h i s permits the LH pul se f r e quency to increase dur ing the pe r i - ovul a t o ry pe r i od , r e sul t ing i n an LH surge and ovul at i on ( Legan et al . ,. 1 977) .. The deve l opment of b i o l o g i c al l y ac t i ve , b i odegradabl e , c ont i nuous r e l ease f o rmul at i ons o f melatonin shoul d al l ow she ep produc e r s to gain al most c ompl e t e c on t r o l of the t ime the i r ani mals c an c on c e ive and thus maximi z e the i r l amb produc t i on .. However, there are st i l l many que st i ons. to be answe r e d c on c e rn i ng how me l atonin ac t s at the neuro e nd o c r ine l ev e l t o promo t e c yc l i c ovar i an ac t i v i ty and max i m i z e the number o f ova shed by the ewes ( Ke nnaway et al . , 1 9 8 7 ) ..

(17) 5 II.l. B.. The oe s trous c ycl e in ewe s .. The principal s t e ro ids s e c r e t e d in the cycl ic e we are prog e s t e r one and o e s t rad i ol - 1 7b ( Pant e t al . ,. 197 7 ) .. On the day b e f o r e o e s t rus one. o r more f ol l i c l e s grow rapidl y and the c oncent ra t i on o f o e s t r ad i o l - 17 b i n t h e bl o od incre a s e s f r om about 1 0 to 2 0 pg/ml . behavi oural o e s t rus .. The o e s t r ogen cau s e s. A pos i t i ve f e e dback f r o m o e s t radi ol , al ong w i th. hypo thal a m i c GnRH , s t imul a t e s r e l e a s e of LH and FSH from the p i tuitary . The c onc entrat i on of LH in the bl ood r i s e s t o a peak of about 80 ngjml 1 0 h a f t e r the beginning of o e s t rus , and then both LH and e s t radiol c on c e ntra t i ons. fal l rapidl y . LH s t imul a t e s ovul a t i on , whi c h occurs. about 14 h after the LH p e ak , i . e . about 2 4 h a f t e r the beg inning of o e s t rus. Thr oughout the r e s t of the o e s t rous cycl e , the LH c onc entra t i on r e ma i ns ve ry l ow ( 2 to 3 ng/ml ) .. At the s ame t ime a s the LH peaks , F S H. r e a c h e s a maxi mum of about 1 7 0 ng/ m l and t h e n fal l s rapidl y . LH ,. it r i s e s to a s e c ond peak 24 h a f t e r the f i r s t .. Unl ike. Af t e r o e s trus , F S H. c oncentra t i on i s el evated a t day 3 and f r o m d a y 8 t o 1 2 i t r i s e s t o a bout 8 0 ng/ml and then d e c l ine s t o about 40 ngjml b e f o r e t h e next o e s t rus .. At ovul a t i on , s t i mul ated by LH and prola c t in ,. the granul o s a. c e l l s f o r m the corpus lut eum ( CL) , whi c h s e c r e t e s proge s t e r one . Max imum c onc ent r a t i ons of proge s t e r one a r e re ached in the blood at days 8 - 9 of the cyc l e and rema in high unt i l days 1 3 -14 when the c o rpus l uteum s t a r t s t o r e gre s s ( Ward , 1 98 6 ) . On the twel t h day i n the nonpre gnant ( and pregnant ) ewe , p r o s t agl and in F2a ( PGF2a ) i nc r e a s e s in c onc entra t i on and r e a c he s a peak o n the fourte enth day at a c onc entrat i on i n the ute r ine ve i n o f about l Ongjml . PGF2a , whi c h i s e s tabl i shed<. s. the l u t e o l y s i n in the she e p ,. r e ache s the c orpus lut eum by means of the cl o s e appo s i t i on of the u t e r ine ve in and ova r i an a r t e ry ( Ward ,. 1986 ) .. The r e l e a s e by the ovary o f oxyt o c i n ,. i n amount s that are grea t e s t. a t the t i me o f luteal r e g r e s s i o n , sugge s t s a rol e i n l u t e o l ys i s ; howeve r hys t e r e c tomy d e pl e t e s the ovary of oxyt o c i n w i thout prevent ing l u t e ol y s i s by the pros t agl and i n anal ogue , c l op r o s t enol ( She l dr i ck and Fl int ,. 1983 ).. Wathe s e t al . ,. ( 1 9 8 6 ) sugg e s t that ova r i an oxytoc in. s t i mul at e s the r e l e a s e o f endome t r i a l PGF2 a , which in turn d e c r ea s e s.

(18) 6. l u t e a l prog e s te rone p roduc t i on and al s o c aus e s the r e l e a s e o f fur the r oxytoc in . I t i s not ye t cle a r whe ther the appearance of endome t r i a l oxy t o c i n r e c e pt ors t r igge r s thi s c ha in of events o r whe the r t h e fal l i n proge s t erone s e c r e t i on i s i nduc ed b y s ome other factor.. In the ewe the. c oncentrat i on of endome t r i al oxyt o c in r e c e p t o r s chang e s from a max i mum a t o e s trus to an almo s t und e t e c tabl e l eve l dur i ng the m i d - luteal phas e b e f o r e inc r e a s i ng aga i n o n day 1 5 o f the cyc l e ( Robe r t s and Mc Cracken , 1976).. I n both the ewe and the c ow , PGF2a i t s e l f i s not lut e olyt i c. dur ing the f i r s t f ew days of the c yc l e ( Rowson e t al . , 1978 ) .. 1972 ;. Har e s i gn ,. The pe r i od be tween days 3 and 6 when oxytocin does induce. l ut e ol ys i s in c ows and g o a t s is the r e fore p r e s umed to r e f l e c t a t i me when suf f i c i ent r e c e p t o r s of the appro p r i a t e type are pre s ent for oxy t o c i n t o a c t on the endome trium and f o r P G F 2 a to a c t on the c orpus l u t eum ;. such a s i tua t i on may not o c cur in the ewe ( Wa the s. et. al . ,. 1986) . The c or pus lut eum shows hi s t ol o g i c al e v i dence o f regr e s s i on on the 1 5 th day and by day 16 the c oncent r a t i on of p r o g e s t e r one is basal ( l e s s than 0. 2ngjml ) .. FSH r e l e a s e d from the p i tu i t a ry becaus e of a reduc t i on. i n negat i ve f e edback from p r oge s t e r one s t imul a t e s oe s trad i o l produc t i on f r om growing f o l l i cl e s .. The inc r e a s ed o e s t r ad i o l in turn a c t s as a. p o s i t ive f e e dback on the hypothal amicjp i tu i t ar y axi s l e ad ing to a p e ak o f LH .. Thi s LH peak s t imul a t e s ovul a t i on ( Ha f e z , 1 9 8 0 ) . Proge s t e rone i s be l i eved to be a ne c e s s ary precursor f o r the. p r oduc t i on of o e s trous behavi our by the oe s t r a d i ol ( Ha fe z ,. 1 9 80 ) .. Synthe t i c GnRH s t i mul a t e s r e l e a s e of phy s i ol og i cal amount s o f LH and FSH ( Ward , 1 9 8 6 ) .. The s e pa r a t e r e l e a s e o f FSH wi thout LH at t he end. of o e s t rus may be exp l a ined by the e f f e c t o f the previous h i gh c oncentrat i ons of o e s t ra d i o l depl e t ing LH in the p i tui t a ry by the p o s i t ive f e edback me chan i s m re sul t i ng i n ovul a t i on .. Thi s t r eatment c an. a l s o caus e r e l e a s e of F S H ( and n o t LH ) in ano e s trous e w e s be c ause o f the h i gher s ens i t i v i ty of the s e ewe s t o the negat i v e f e e dback of o e s t r ad i o l on the r e l e a s e o f LH when they a r e in the s ta t e of ano e s t rus ( Whe a t on al . , 1 98 2 ) .. et.

(19) 7 II.l. C.. Pregnancy and partur i t i on in ewe s. I f pr e gnancy fol l ows f e r t i l i za t i on i n the ewe , ova rema i n i n. the. f a l l op i an tube s for about 4 days and ent e r the uterus at the 8 to 1 6 c e l l s tage .. Attachment occurs between 1 4 and 1 8 day s , whi ch means that. the bl a s t oc y s t is abl e to pr e ve nt the cycl i c a l r e gre s s i on of the c o rpus l u t e um before be ing attache d .. Thi s may be br ought about by i nhi b i t i on. o f the r e l e a s e of the ut e r i ne l u t e o l y s i n ( PGF 2 a ) ( Fi t z patr i ck ,. 1986 ) .. Fol l owing concept i on the c or pus l ut e um p e r s i s t s and peak d i ­ o e s t rous val ue s of proge s t e r one a r e ma intained and gradual l y inc r e a s e t o about 60 days o f ge stat i on when there i s a fur the r inc r e a se .. Thi s l a t e r. r i s e i s due t o the pl ac ental c ont r i bu t i on t o proges t e rone produc t i on ( t he pl acenta takes over the r o l e of proge s t e rone produc t i on i n the ewe by about day 5 0 of gesta t i on ) .. Leve l s remain h i gh unt i l the l a s t w e e k. o f pre gnancy when they d e c l ine r a p i d l y ( Ar thur. et. al . , 1 9 8 2 ) .. The c oncentra t i on o f proge s t e rone i s s i gn i f icant l y highe r in mul t i pl e pregnanc i e s ( Ba s s e t. et. al . ,. 1969 ) .. Maximum proge s t e r one. c oncent ra t i on in the pe r i pheral bl o od o f ewe s w i th a s ingl e l amb was 3 . 7 8 ng/ml b e tween days 1 0 5-1 1 0 , and 5 . 0 9 ngjml betwe en days 1 2 5 - 1 3 0 i n ewe s w i th twins ( Emady. et. al . ,. 1 9 74 ) .. O e s t r ogen c oncent ra t i on in the pe r i phe ral ci rcul a t i on r e ma ins l ow unt i l a few days be fore partu r i t i o n when i t s t a r t s to r i s e and then suddenl y i n c r e a s e s to about 400 pgjml at the t ime of l ambing. Thi s i s f o l l owed b y a rapid fal l ( Chal l i s , 1 9 7 4 ) . Dur ing pr egnancy pro l a c t i n c oncentrat i on s fluctuate betwe en about 2 0 and 80 ngjml ; howeve r , they s ta r t t o i nc r e a s e and reach a p e ak ( be tw e en 4 0 0 and 700 ngjml ) on the day of l �mbing ( Kann and Denamur , 1974) . I t i s now we l l e s tabl i s hed that the f o e tu s i nf l uenc e s the t im e o f i t s own b i rth ( Li ggins , 1 9 7 7 ) .. The s e quence o f events s tarts w i t h. a c t i va t i on o f the hypotha l amus and p i tui tary o f the f o etus by a mechan i sm that i s , as ye t , unknown .. It i s however c e r tain that about 5. days before b i rth adreno c ort i c o tr o ph i c hormone ( ACTH ) i s s e c r e t e d and s t i mul a t e s the foetal adrenal gl ands to l i berate cort i so l .. C or t i s o l. a c t s o n t h e s te ro i d - s e c r e t ing c e l l s o f the f o e tal c otyl edon , whi c h f o r.

(20) 8 mo s t of pregnancy have b e e n s e c re t i ng the proge sterone e s s ent i a l f o r the maintenance of pregnanc y .. C o r t i s ol inc r e a s e s a c t i v i t y o f the e nzyme 1 7 a­. hydr oxyl ase , and the r e by c au s e s a decrease in proge s t e r one s e c r e t i on . S i m i l arly , c o r t i s ol a c t s on the i n c r e a s e in s t e r o id - 1 7 ,. mate rnal she e p pl a c enta to c au s e an. 2 0 - l y a s e , which , in the face of i nc r e a s ed. s t e ro i d 17a - hydroxyl a s e a c t i v i t y r e sul t s in an incr e a s e i n the p r oduc t i on o f androstene d i one , the precursor of o e s t r ogen ( Ca s ey and Ma c Donal d , 1 9 8 6 ) .. F o e t a l o e s t r ogen c r o s s e s the placenta , whe r e i t. b e c ome s unc onjugated o e s t r ad i o l . proge s t erone i nc r e a s e s ( Fl int. A t the s ame t ime the c l earance rate o f. et. al . , 1 9 7 5 ) .. The change to o e s t r ogen dominanc e over proge s t e r one i s i mp o r t ant in s e ve ral r e s p e c t s but pa r t i cul arly in the produc t i on o f pro s t agl and i n s i n the ce l l s o f the myome t r i um and mat e rnal p l a c ent a .. Unc onjuga ted. o e s t r ogen i s m o s t c l o s e l y r e l a t ed t o the increased synthe s i s of p r o s tagland ins , s inc e there is a ma rked inc r e a s e in the c oncentrat i on o f p r o s tagl andins in u t e r i n e venous bl ood a f t e r the admi n i s t rat i on o f o e s t radiol t o the pr egnant e w e ( Liggins. et. al . , 19 7 2 ) .. P G E 2 are powerful s t i mul ant s o f u t e r i ne mus c l e .. Both P G F 2 a and. Ut e r ine c ontrac t i ons. thems e l ves fac i l i t a t e the further r e l e a s e of intra - c e l l ul ar l ys o s omal e nzyme s that synthe s i z e pr o s tagl and ins and the whol e pr o c e s s b e c om e s s e l f - pe rpe tua t i ng . The ul t i ma t e e f f e c t o f t he uter ine c ont r a c t i ons ,. i n c ombina t i on. w i th c e rvical r e l axat i on and o ther change s , i s to advance the f o e tus i nt o the c e rvix and ant e r i or vag ina , wher e it s t imul a t e s sens o ry r e c e ptors and ini t i a t e s F e r gu s on ' s refl ex , with the r e l e a s e o f l arge amount� of oxytoc in from the p o s te r i o r p i tui tary .. Thi s augments the. myome t rial c ontrac t i ons , and r e sul t s in the l i berat i on of even mo r e p r o s tagland i ns s o that t he who l e s e quenc e bec ome s a c a s c ade w i th a p o s i t i ve f e edback .. The s igni f i c ance of s e c ond stage c on t ra c t i ons w i t h. r e f l exly synchronized a bdominal e f fort i s t o i ncrea s e t h e e f f i c i ency and d e c r e a s e the dur a t i on of s e c ond s t age l a bour , when the r i sks o f anox i a and o ther hazard s are maxi ma l .. Each u t e r ine c ontrac t i on out l a s t s the. a c c ompanying abdominal s p a s m and i s i mportant in mai n t a i n i ng u t e r ine " t one " ( F i t zpatr i ck ,. 1 9 86 ) ..

(21) 9 Partur i t i on invol ve s more than mere c ontrac t i on of the ute rus howeve r .. The i nc r e a s e in expul s ive for c e mus t be coinc ident with a. d e c r e a s e in r e s i stanc e whi ch for pra c t i ca l purpos e s , means sof t ening of the c ol l agen of the c e rvix , and r e l axa t i on of the u t e r ine , vaginal and p e l v i c l i gament s .. S tud i e s on the she e p c e rvix by F i t z pa t r i ck ( 1 9 7 9 ) have. reveal ed that the dense c onne c t ive t i s sue of the wal l softens drama t i c a l l y a t the end of pre gnancy and ul t i ma t e l y b e c ome s g e l - l i ke ,. so. t h a t the c e r v i x i s held t ogethe r during t h e pa s s age o f t he foe tus b y t h e e x t e rnal mus c l e l aye r and t h e mucosa al one .. Both the total amount of. c ol l agen and i t s c onc e nt r a t i on fal l and the r e i s a marked i nc r e a s e in the wa t e r cont ent .. H i s tol og i c a l l y ,. the col l agen bundl e s become de­. s e gr e gated and the f i br i l s di s p e r s ed .. Thi s is a s soc i at e d with. d e t e c t abl e i nc r e a s e s in the proteogl ycan con s t i tuent s . Tog e ther the s e c hange s , whi ch a r e infl uenc e d b y the d e c l ine i n proge s t e rone s e c r e t i on and i nc re a s e i n oes trogens , prostagl andins and r e l ax i n ,. inc r e a s e the. d i s t ens i bi l i ty of the c e rvix ove r a pe r i od of 1 2 - 1 8 hour s . II.l.D.. The p os t - partum p e r i od in ewe s. C i r cul a t i ng conc entra t i ons of LH are l ow dur ing the e a r l y pos t ­ partum pe r i od i n ewe s ( Re s t a l l and S ta r r ,. 197 7 ) .. e xpl ana t i on for thi s wa s off e r ed by Ne t t ( 1 9 8 7 ) .. The fol l owing Dur i ng pregnancy the. hypotha l amo - hypophys ial axi s i s suppre s s ed by the h i gh conc ent r a t i ons of prog e s t e rone and oe s t rad i ol in the c i rcul a t i on .. The h i gh conc entrat i on. of the s e s t e roids i nhi b i t s s e c re t i on of GnRH f r om the hypothal amus , r e sul t ing in i nadequa t e s t i mul a t i on of the p i tu i tary gonadotrophs to ma intain synthe s i s of LH.. The depl e t e d s tore s of LH in the ant e r ior. p i tu i t a ry g l and mus t be re s t ored a f t e r partur i t i on be f ore normal oe s t r ous cycl e s c an begin. however. ( Mos s e t al . ,. C onc entrat i ons of. F S H a r e not suppre s s e d. 1 9 8 5 ) , a phenomenon that may be due t o the. r e l a t ive l ack of f ol l i cu l a r deve l opment dur i ng l a t e ge s t a t i on and the absence of n e ga t i ve f e e dback f rom fol l i cul os t a t in f r om the f ol l i c l e s ( Mi l l e r e t a l . , 1 9 8 2 ) . The impor tance of suckl ing on the durat i on of pos t - par t um anoe s t rus i s demon s t r a t ed in she e p by the r e s pons e to exp e r i menta l l y.

(22) 10 induc e d p r e gnancy during s e a s onal ano e s t rus s o that l ambi ng o c curs dur i ng the b r e ed ing s e a s on . a f t e r a bout one month , s om e w e e k s l a t e r ( Hafez ,. D r i e d - off ewe s u sual l y r e turn t o o e s t rus. whi l e suckled ewe s p r e sent the f i r s t o e s t rus 1 9 80 ) .. Expul s i on of the f o e t a l - pl a c ental uni t at pa rtur i t i on i s a c c o mpan i ed by a drama t i c d e c r e a s e in the c oncent r at i on and proge s t e r one in the c i rcul a t i on ( Burd. et. al . ,. 1976 ) .. o f o e s t rad i ol Thi s l eads t o. t h e r e moval o f the i r nega t ive f e edback ac t i on s o n the hypotha l amo ­ hyp o phy s i al axi s .. From an end o c r inol o g i c a l v i ewpo int , once thi s pha s e. i s c ompl e t e , t h e f e mal e shoul d be ready t o re sume no r ma l o e s t rous c y c l e s . H oweve r , even though the func t i on of the hypo thal amo - hypophys i a l a x i s r e turns t o normal w i thin a r e l at i ve l y sho r t per i o d of t i me a f t e r par tur i t i on ( about 3 5 days i n t h e ewe - - W i s e. et. al . ,. 1 9 8 6 ) , dur i ng thi s. p e r i od three change s occur permi t t ing a gradual r e cove ry in gonadotroph func t i on : (a). an inc r e a s e in the f r e quency of LH pul s e s i nduced by an i nc re a s e i n the c oncentra t i on o f mRNAs f o r the subun i t s o f L H i n t h e axi s ;. (b). an inc r e a s e the c oncent r a t i on of r e c e pt o r s. for oe s t r ad i o l in the. hypothal amus and p i tu i t a ry gl and whi c h bec ome s ens i t ive to the po s i t i ve f e edback e f f e c t s of o e s t ra d i o l t o r e l e a s e LH ; and (c). t he mo rphol ogy of the gonadotrophs a l s o re turns t o a s t a t e s i mi l a r t o tha t obse rved i n cycl i ng ewe s .. Even a f t e r thi s r e c ove ry o f func t i on the f a c t that f r e quent suckl i ng , and o the r env i r onmental fac tors , w i l l suppr e s s pul s a t i l e s e c re t i on o f LH sugge s t s that during the po s t - partum p e r i od , a two-phas e r e c ov e ry o f the hypothal amo - hypophy s i a l - gonadal axi s oc cur s ( Ne t t , 1 9 87 ) .. The f i r s t phas e , whi ch la s t s from 2 t o 5 weeks a f t e r. partur i t i on ,. i s charac t e r i z e d b y infre quent d i s charge s ( e . g . o n e pul s e. e v e r y 4 - 8 h ) o f GnRH i n t o the hypothal amo - hypophys i a l portal c i rc ul a t i on .. Thi s mode o f GnRH s e c re t i on s t i mul a t e s the b i o synthe t i c. mac h i ne ry i n the gonad o t r o ph and the rate o f synthe s i s o f LH i n c r e as e s . Howeve r , the pul s e s. o f GnRH a r e suf f i c i ently spaced that onl y a s ma l l. p o r t i on o f t h e newly synthe s i s e d LH i s s ec re t ed i n t o the c i rcul a t i on ..

(23) 11 The inc r ea s ed r a t e of synthe s i s o f LH c oup l e d with i t s r e l a t i vely s l ow r a t e o f r e l e a s e c r e a t e s a s i tua t i on in whi ch p i tui tary s t or e s o f LH are r e p l eni shed.. S inc e the magn i tude o f the pul s e i s dependent on the. quant i ty of LH s t o red in the ant e r i or p i tui tary the e a r l y part of thi s pha s e o f. r e covery fa i l s t o induc e f o l l i cu l a r maturat i on.. Only a f t e r. p i t u i t a ry s t or e s of L H have re turned t o the i r normal l evel are the pul s e s of LH t ha t are rel e a s ed into the c i r c ul at i on of suf f i c i ent amp l i tud e t o s t imul a t e f o l l i cul ar growth .. Thi s marks the beg inning o f. t h e s e c ond pha s e o f the r e c overy proc e s s .. Dur ing thi s pha s e the. inc r e a s ed c i rcul at ing conc entrati ons of LH s t imul ate growth of ovarian f ol l i c l e s and the s e c r e t i on of oe s t rad i ol . An i mportant e f f e c t o f oe s t rad i o l i s to s t imul a t e produc t i on o f i t s own r e c e pt o r s i n the hypo thal amus and ant e r i o r p i t u i t ary gl and thus inc r e a s ing the sens i t i vity of the s e t i s sue s to the po s i t i ve f e edback e f f e c t s of i t s e l f . Thi s po s i t ive f e edback e ff e c t of o e s tradiol is the re s ul t of smal l inc r e a s e s i n c i rcul a t i ng c onc entrat i ons for short pe r i od s o f t im e i n c ont rast t o the pr o l onged p e r i ods of. very high. c on c e nt r a t i ons dur ing l a t e g e s t a t i on that pr oduce a powe rful nega t ive f e e dback e f f e c t . incr e a s e s ,. At thi s p o i nt , the f r e quency of d i s charge s of GnRH. in turn produc ing more frequent pul s e s o f LH .. l e ad t o the f i nal s tage s o f f o l l i cul ar deve l o pment and ovul a t i on ( Ne t t ,. 1987 ) .. Thi s author a l s o proposed. The s e event s culminate in. that the f i r s t s t age. o f thi s re covery proc e s s ( i . e . e vent s l eading t o inc r e a s e d pi tui tary s t o r e s of LH ) i s r e l ative l y independent o f the suckl i ng s t imul us and e nv i r onmental s t r e s s ors .. The s e c ond pha s e of the r e c ove ry ( i . e. event s. l e ad i ng t o an increased f r e quency o f d i s charge s of LH) , howeve r , appears to be t i ght l y c oupl ed to the suckl ing s t i mul us and e nv i ronmental s t r e s s or s . As s e s sment of the l i t e rature sugg e s t s that the e nv i r onmental s t r e s s o r s in ewe s may be the pe r s i s t ing inhi b i t o ry pho t o - pe r i o d i c s i gnal s they r e c e ived dur i ng ano e s trus.. The s e s i gnal s a f f e c t the pine a l. g l and and inf l uenc e mel atonin produc t i on whi c h in turn a f f e c t s the e ndo c r i ne sys t e m . Thi s may be achieved by a mechan i s m s im i l a r to that whi ch o p e r at e s in the s e c ond pha s e of Ne t t 's " two pha s e r e c ove ry".

(24) 12 the o ry .. If thi s i s c orre c t ,. Legan and Ka r s ch's ( 1 9 8 0 ) sugge s t i on that. the p i tuit ary ha s a higher s en s i t i vi t y t o negat ive f e e dback of o e s t rad i ol dur ing the anoe s t r ou s pha s e may be inc orr e c t ..

(25) 13 II. 2 . Myometrial Ac t ivi ty. Myometrium c ontrac t i li ty is affected by the und e r l yi ng end o c r i ne event s of the oes trous c y c le , pregnancy and partur i t i on .. Dur i ng. pre gnancy , the myome tr ium r e l ax e s to acc ommodate the deve l oping f oe tus and pr oduc t s of conc e p t i on whi l e at the end of pregnanc y ,. it prov i d e s. the rhythmic t onic c ontra c t i ons o f pa rtur i t i on whi ch f ac i l i ta t e the expul s i on of the ute r ine c ontent s .. The s e uter ine event s oc cur in. r e s ponse t o the rele a s e o f oxyt o c in , PG , and othe r ho rmone s , and r e fl e c t change s i n the c e l l ul ar c omponent s o f the myome tr ium such a s the forma t i on of gap junc t i ons ,. synthe s i s of rec e ptors and c ontra c t i l e. prote i n , and the gene rat i on o f enhanc e d e l e c t r i cal a c t i v i t y .. II. 2 . A .. S t ruc ture and organ i z a t i on of the myomet r i al cont r ac t i l e uni t. In mos t spe c i e s the u t e r ine wal l i s c ompo s e d o f thr e e d i s t i nc t l aye r s .. An inne r endome t r i um l ine s the l umen of the organ , whi l e the. myome t r ium i t s e l f c ompr i s e s two laye r s , an oute r l ongi tudinal l ay e r ove r l y ing an i nner c i rcul ar l aye r .. The l ongi tudinal lay e r c ons i s t s of. bundles o f smooth mus c l e c e l l s t hat are gene ral ly or i ented along the l ong axi s of the u t e rus .. The bundl e s int e r c onne c t to f o rm a ne twork on. the surface of the uterus ( C sapo ,. 1 96 2 ) .. C ontra c t i on of the. l ongi tudinal mus c l e t end s to shorten the uterus and c ons t r i c t i t s lume n . Mus c l e c e l l s of the c i r c ul ar mus c l e layer are a r rang<d c oncentrical l y around the l ongi tudinal axi s of the u t e ru s . The s e mus c l e c e l l s are arranged more d i f fu s e l y and the bundle arrangement i s not a s apparent a s w i th the l on g i tud i na l l aye r s . mus c le l ayer cons t r i c t s the ut e r ine lumen .. C ontrac t i on of the c i rcular Mus c l e c e l ls of both mus c l e. laye r s occupy a ma j o r part o f the ut e r i ne wall , but the myome t r i um i s not an homogeneous mus c le t i s sue .. I t i s composed of mus c le c e ll s that. are e mbedded i n conne c t i v e t i s sue as a mat r ix which c ons i s t s of c ol l agen , gap junc t i ons and othe r c e ll s such as f i b robl a s t s , blood and.

(26) 14 l ympha t i c ve s s e l s , and nerve s .. Eve ry myome t r ial mus c l e c e l l , t og e ther. w i t h its ma t r i x o f c onne c t ive t i s sue e l ement s , is the func t i onal uni t f o r u t e r ine c on t ra c t i l i t y ( Ve rhoe f f and Garf i e l d , 1 9 8 6 ) . II.2 .B.. S pe c i al features of the ul t ra structure of the funct ional uni t s of the myometrium. Myome t r i al c e l l s l i ke o ther smooth mus c l e c e l l s a r e s p indl e s haped c e l l s 2 to 5. urn. i n d i ame t e r and 5 0 - 1 0 0 um i n l ength , w i th a s ingl e. nuc l eus s i tua t e d i n the wide s t port i on o f the c e l l body ( Be r gman ,. 1969 ) .. The c e l l ul a r c omponent s r e s pons i bl e f o r the dynamic c ontra c t i on a r e c ontrac t i l e p r o t e i n s , pl a sma membrane , gap junc t i ons ( Ve rhoeff and Garf i e l d , (a). s a r c o pl a smic re t i cul um ( SR ) and 1986 ) .. The c on t rac t il e apparatus :. The pro t e in c omponent s o f the. c e l l that r e s pond to cal c ium ( Ca ) f l uc tuat i ons and ut i l i ze the che m i c a l ene rgy o f ATP t o re sul t in e i ther sho r t ening or deve l o pment of tens i on a r e te rmed c o l l e c t i vely the c ont rac t i l e a pparatus .. I n smooth mus c l e ,. the ma jor c ontrac t i l e prote ins are myo s in , a c t i n and t r opomyo s in .. The. minor c omponents of the c ontrac t i l e apparatus include p r o t e i n s tha t a r e involved in the Ca de pendent r e gul a t ory mechani sm ( Wal l enburg , 1 9 8 3 ) . E l e c t ron mic r o s c o p i c stud i e s have ident i f i ed at l e a s t thr e e d i f f e rent typ e s of myo - f i l ament s i n uterine smooth muscl e c e l l s , name l y thi ck ( myo s i n ) , thin ( ac t in ) and int e rme d i a t e f i l aments a s we l l a s m i c r otubul e s ( Ve rhoeff and Garf i e l d , (b). P l a s ma mr:mbrane :. 198 6 ) .. The p l as ma membrane ( sarc o l emma ) of. uter ine smoot h mus c l e c e l l s i s a t r i l am i nar s t ructure thought to be c ompos ed of pho s phol i p i d s and p ro t e i n s .. Intra - membranous prot e in. part i c l e s a r e s e e n in f re e ze - frac ture repl i cates of the pl a sma membrane ( Ga r f i e l d , e t al . ,. 1978 ) .. The s e part i c l e s are more nume rous on. the protopl a s m i c than on the external face of the membrane . of a myome trial c e l l i s about ske l e t a l myocyte . to volume rat i o .. The vol ume. 140 , 00 0 t ime s l e s s than that of a. The smal l c e l l s i ze c orre l a t e s w i th a l arge surface On the surface of the smooth mus c l e c e l l s many f l a s k -.

(27) 15 shaped invaginati ons o f the plasma membrane a r e o pen t o t he e x t e r i or and are c l o s e l y a s s o c i ated interna l l y w i th m i t o chondr i a and the s a r c oplasmic r e t i culum .. They c ont r i bute subs tant i al l y to the c e l l sur f a c e a r e a .. The. r e l a t ive l y eno rmous area of pla sma membrane in c on junc t i on w i t h a sma l l intra - c e l lul a r volume t ends t o fac i l i t a t e both di f fus i on o f i on s and c onduc t i on of e xc i t at i on be twe en the c e l l s .. Thi s al s o f avour s rapid. e xchange of ma t e r i al s be tween the c e l l s and the i r exte rnal e nv i r onment ( Ri emer and Robe r t s , 1 9 8 6 ) .. The myome t r i a l p l a sma membr ane p l ays an. i mpor tant r o l e in the c ontra c t i on - rel axat i on cyc l e of the c e l l dur i ng ut e r i ne c ontra c t i ons a s (i) ( ii ). i t a c t sas the anchoring po i nt for the thi c k f i l ament s ; i t ha s a rol e in i on movement caus ing depo l a r i za t i on and r e p ol a r i z a t i on of the myome t r i um;. ( i i i ) i t c ontains r e c e p t o r s f o r hormone and neur o t r ansm i t t e r b i nd i ng ; ( i v ) i t c ontains gap junc t i ons and ( v ) i t ha s a key rol e in Ca mob i l i zat i on . (c). The s arcopl a smic r e ti culum ( SR) :. Ute rine smooth mus c l e. c e l l s have a n extens i ve sys t em o f S R c ons i s t i ng o f a network o f tubul e s and s a c s wi thin the cyt opl a s m who s e vol ume ha s been e s t i ma t e d to b e 2 - 7 % of the c e l l volume. The granul ar r e t i culum ( GR ) and. �ranul a r. r e t i c ul um (AR) are c ont inuous and the AR make s c l ose c onta c t w i th surface ve s i c l e s , pl a sma membrane and gap junc t i ons . Fun c t i onal l y the GR i s probably invol ved in synthe t i c proc e s s e s w i thin the c e l l whi l e the AR appe a r s t o be i nvol ved i n c a l c i llill s t o rage and r e l e a s e and the re fore control o f mus c l e c ontrac t i l i ty ( Ri emer and Robe rt s ,. 1 9 86) .. (d). The gap junctions :. Gap junc t i ons c ons i s t of s ymme t r i c al. port i ons of the p l a sma membrane from two oppos i ng c e l l s ( Pe ra c c h i a , 1 9 8 0) .. I nt ramembranous prote ins protrude through the membran e s s panning. the gap be twe e n .. Gap junc t i on proteins w i th i n oppos e d c e l l membrane s. are thought to a l ign them s e l ve s and c r e a t e channel s from the cytoplasm.

(28) 16 of one c e l l t o anothe r .. The s e channel s a r e supposed t o be the s i t e s o f. e l e c t r i c a l and me tabol i c coupl ing between c e l l s by provid i ng f o r the pa s sage of current and d i r e c t exchange of m e t abol i te s be tween c e l l s ( Hooper and Subau-Sharpe , 19 8 1) .. The c hannel s may not a l ways be open. and are be l i eved t o be dynamic s t ruc ture s . Degradat i on i s thought to oc cur by e i ther d i s pe r sal of gap junc t i on p a r t i c l e s f r om wi thin the pla sma membrane or internal i z at i on o f the e nt i r e gap junc t i on w i thin one of the c e l l s by endocyt o s i s and subse quent degradat i on by l y s o s ome s ( Ve rho e f f and Garf i e l d , 19 86) . Gar f i e l d. et. al.. (1979) s tud i e s of the devel opment of gap junc t i ons. in the myome t r i um dur ing partur i t i on demon s t ra t ed tha t : (i). myome t r i al gap junc t i ons a r e abs ent , or pr e s ent in l ow f r e quency throughout p r e gnancy ;. (ii). at the end of t e rm , gap junc t i on a reas i nc r e a s e ;. ( i i i ) the junc t i ons are pre s e nt in h i gh frequency and the s i z e incre a s e s during de l ive ry of t h e f o e tus and ( iv ). the gap junc t i ons begin t o di s a ppear wi thin 2 4 h a f t e r del ivery .. II. 2 . C .. Myometri al c ontract i o n. Myo s i n ,. the pr inc ipal e l ement of mus c l e c ontra c t i on ,. opt imi s e s. the inte rac t i on wi th the othe r ma j o r c ont r ac t i l e pro t e i n a c t in.. The. enzyme , myo s in ATP a s e fa c i l i ta t e s c onve r s i on of the che m i c a l ene rgy of ATP into mot i onjf o r c e during c ontrac t i on .. At the mol e cu l a r l evel the. mechani s m of c ont r ac t i on i s ident i c al in a l l mus c l e s and the c ommon l ink between t he c ontra c t i l e regul a t i on of ske l e t a l and smooth mus c l e s i s calc ium .. However, c a l c ium regul a t i on i s o rgani zed d i f f e r e nt l y i n the. two typ e s of mus c l e ( Hus zar, 19 8 6 ). II . 2 .D.. El e c tr ophysiology of myometr i al contracti l i ty. The uter ine mus c l e c e l l i s bounded by a s emipe rme able membrane and the d i s tr i buti on of i ons on e i ther s ide of the membrane dete rmine s an e l e c t r i c al charge on i t .. The membrane potential of the r e s t ing.

(29) 17 myome t r ial c e l l ( RMP ) i s norma l l y charged e l e t ro - nega t i ve l y o n the ins ide so that a potent i al d i f f e renc e of be twe en 20 - 8 1 mv exi s t s a c r o s s the membrane .. In c ommon w i t h o the r c on t ra c t i l e cel l s ,. the u t e r i ne. smooth mus c l e c e l l unde rgo e s a cyc l e o f e l e c t r i c al even t s whi c h i nvol ve s d e po l a r i za t i on of the c e l l membrane f o l l owed by repol a r i s a t i on , wh i ch pre c ede s me chani cal act ivi ty .. Th i s e l e c t r i cal ac tivi ty i s known a s the. I n ske l e ta l mus c l e and in ne rve s , the a c t i on. a c t i on potent i al ( A P ) .. pot ent ial r e sul t s from a momentary i nc r e a s e in the permeabi l i ty of the c e l l membrane to s odium i ons .. As a r e sul t pos i t ively charged i ons ent e r. the c e l l and depol a r i s e the membrane ( F inn and Porte r ,. 1975 ) .. Ac t i on potent i al s ( APs ) can be r e c o rded f rom the myome t r ium of an o e s t r ogen - t r e a t ed non- pregnant animal when a s ingl e mus c l e c e l l i s i mpa l e d w i t h a micro - e l e c t rode ( Ma r s ha l l ,. 1962 ) .. The a c t i v i ty of the. mus c l e i s c harac teri sed by al t e rna t ing pha s e s of APs and qui e s c ent pe r i ods , the AP trains c o inc id ing w i th the c ontrac t i on phas e o f the me chanical a c t ivity .. The ac t i on po t ent i a l is rec orded a s a s i gnal wh i ch. i s pos i t ive in d i r e c t i on and has an ampl i tude which var i e s de pend i ng upon the r e s t ing membrane potent i a l ( Ka o , be twe en - 3 0 and - 7 0 mv . i.e.. 1 9 6 7 ) but whi c h l i e s usual l y. The l arge APs a r e a c c ompanied by a n " ove r sho o t ". the s i gnal be come s po s i t ive f o r a pe r i od . The ove ral l dura t i on of. the AP is usua l l y of the orde r of l OOms ,. i.e.. 1 0 - 20ms pos i t i ve swe e p. ( when the s i gnal i s moving f r om t h e RMP t o the A P peak ) and 7 0 - 80ms nega t ive swe e p ( in whi ch the s i gnal r e turns t o the RMP ) .. S in c e t he APs. in uter ine mus c l e cannot be pr event e d by gangl i onic and ne rve bl oc king agent s the i r gene ration is b e l i ev e d to be myogenic .. Thus ut e r ine smooth. mus c l e i s c l a s s i f i ed as be ing of the " s i ngl e - uni t " type i . e . mus c l e s whi c h a r e charac t e r i zed by s pont an e ous a c t iv i t y whi ch i s i ni t i a t e d i n pacemake r a r e a s wi thin the t i s sue t ha t then spreads throughout the whol e mus c l e .. Thi s type of mus c l e i s abl e t o deve l op act ive tens i on a s i t. s t r e t che s ( Bo z l e r , 1 9 4 8 ) . The s pontaneous genera t i on o f a c t i on p o tential s in m o s t smooth mus c l e c e l l s r e sul ts from a t l ea s t two t ype s of fluc tuat i on s of the i r e l e c t r i c a l a c t ivi ty :. s l ow , rhythm i c o s c i l l a t i ons o f the membrane.

(30) 18 pot ent ial and more rap i d , l o c a l i z e d d e pol a r i za t i on of the me mbrane . . s l ow o s c i l l a t i ons , var i ou s l y c al l ed " ba s i c e l e c t r i cal rhythm " ,. The. " pacemake r potent i a l , " or s i mply " s l ow wave s , " are e s pe c i a l l y prominent in the l ongi tud inal mus c l e l ay e r o f the myome t r i um dur i ng p a r t ur i t i on . The i r dura t i on may be onl y s e c ond s , o r m i nut e s , de pending on the par t i cul ar t i s s ue and i t s env i r onme nt .. I n the s e muscl e s the r a p i d ,. l ocal i zed d e pol a r i za t i on appears a t the c r e s t of the s l ow wave and gene rates ac t i on pot ent i a l s that a r e c al l ed pac emaker potent i a l s o r prepotent i al s .. The p r e po t e nt i a l s d e t e rmine the a c t i on pot ent i a l. fre quency , the dur a t i o n o f the bu r s t o f a c t i on potent i a l s , and hence the force and durat i on of each c ontrac t i on .. The s l ow wave s s e t t he. int e rval s between c ont rac t i ons and henc e the c ontrac t i on f r e quency ( Mar shal l ,. 1980 ) .. I t has been sugg e sted that s l ow wav e s spread acr o s s the l ong i tudinal mus c l e l ay e r and int o the und e r l y ing c i rcul a r mus c l e l aye r and thus s e rve to synchron i z e spike d i s charge and contrac t i on s ove r a l arge area of mus c l e .. I n s om e s i tua t i ons , f o r example , the mid o r non­. pre gnant uterus prepotent i al s o f t e n a r i s e spontaneous l y i n the abs ence o f we l l - organ i z e d s l ow wave s and generate a c t i on poten t i a l s that are c onduc ted t o ne ighbour ing c e l l s .. Und e r such c i rcums tanc e s ,. s p ike. d i s charge i s f r e quent l y sync hronous i n va r i ous areas of t he mus c l e becaus e o f the mul t i pl e f o c i o f pac emaker a c t ivi ty .. The s e c ontra c t i on s. are i rregul ar in f re quency , ampl i tude and dur a t i on ( Marsha l l ,. 1980 ) .. The e l e c t r i c al a c t i v i ty l eads t o an inc r e a s e in i n t ra-c e l lul a r C a and produc e s C a r e l e a s e f ror 1 t h e ER .. When t h e amount o f C a n e e d e d f o r. maxi mum ac t iva t i on of the c on t rac t i l e p r o t e ins exceeds a thr e shol d l i mi t , the myome t r i al c e l l s ta r t s t o c ontrac t .. Thi s who l e p r oc e s s i s. t e rmed exc i ta t i on - c ontrac t i on c oupl ing ( Marshal l 1 9 8 0 ) . Aft e r c ontrac t i on , the e l e c t r o g e n i c pump a c t i v i ty i nc re a s e s and the membrane r epolar i ze s bring ing the pot ent i al below thr e s ho l d for sp ike gene ra t i on .. C a is removed from the cytopl asm by e x t ru s i on t o the. extra - c e l l ul ar fluid , and by uptake into the ER and rebind ing t o the b inding s i t e s in the pl a s ma membrane .. The myome t r i al c e l l i s then.

(31) 19 r e l axed and the cyc l e of c ont r a c t i on pha s e and qui e s c en t pe r i od i s c ompl e t ed ( Marshal l , 1 9 8 0 ) . Ac t i on potent i al s and s l ow wave s are c onducted throughout the mus c l e through l ow - re s i s t anc e pathway s formed by the gap junc t i ons . Dur ing the spread of c onduc t i on the t ens i on deve l o pment i s de pendent on the c o - ordinated spread o f exc i tat i on throughout neighbour i ng r e g i ons .. II . 3.. Effe c t s o f Hormon es on Emg Ac t ivity. I I . 3 .A.. Oes trogen. O e s t r ogen inc reas e s myome t r i a l re spons ivene s s by several known me chani sms : (a). The increased r e sp ons ivene s s of the myome t r i um t o s t re t c h. and inc re a s e d spontane ous c ontrac t i l e a c t i v i t y charac t e r i s t i c of the o e s t rogen - d ominated uterus pro babl y a r i s e s , at l ea s t in par t , f r om an o e s t rogen- i nduc ed change in me mbrane potent ial .. Thi s fac i l i ta t e s. spontane ous depo l ar i zat i on o f pac emaker c el l s ( Mar shal l , 1 9 8 0 ) . The r e s t ing membrane pot e n t ial of the myome t r i al ce l l s in immature or ova r i e c t omi zed animal s is a bout 35 mv and at this potent i a l the membrane is r e l a t ive l y inexc i tabl e , supposedly because the membrane i s i n a s t ate of a prol onged s t e ady depo l a r i z a t i on.. Th i s s t ate i s. int r ins ical ly l e s s exc i t abl e pre sumabl y b e c au s e o f the high d e g r e e o f i na c t i vat i on o f Na conduc tanc e .. A s t r onge r s t i mulus i s r e qui red t o. i nc r e a s e Na c onduc tance suf f i c i e n t l y t o produce a n a c t ion potent ial . Oe s t r ogen t r e atment br ings the membrane pot ent i al int o the r ange whe r e s pontaneous d i s charge o f ac t i on potent i al s oc curs ( about 5 0 mv ) and ·.:he mus c l e be c ome s rhythm i c a l l y a c t ive ( Mar shal l ,. 1980) .. The me chani s m by. whi ch the RMP i s el eva t e d i s not c l ear , a l though it i s po s s i b l e that o e s t r ogen s t i mul ates the enzyma t i c apparatus n e c e s s ary for a c t i ve i on t ransport ( Po r t e r , 1 9 7 5 ) . (b). O e s t rogen part i c i pa t e s in the forma t i on of gap junc t i on s. between a d j o i ning myome t r i al c el l s ( Ga r f i e l d. et. al . , 1 9 80 ) .. I n the r a t. and guinea p i g uterus ( Pu r i and Garf i e l d , 1 9 8 2 ) , the r e i s a good c o r r e l a t i on between gap junc t i on f o rma t i on and an increase i n.

(32) 20 c i rcul a t i ng o e s t r ogens .. Dur i ng pro - oe s t rus , the e l e c t r i c a l and. mechan i c al a c t i vi t i e s of the r a t uterus. i n v i vo. a r e w e l l s ynchr oni z e d ,. but t he s ynchrony dur ing d i - o e s t rus i s much l e s s ( I sh ikawa and Fuchs , 1978 ) .. Dur ing pregnanc y , i r re gular synchronous a c t i v i t y preva i l s in a l l. anima l s pe c i e s s tudi ed whe r e a s a good synchroni za t i on and rapid propagat i on of c ontrac t i on wave s a r e observed dur i ng the par tur i ent s t age ( Fuchs and Pobl e t e , (c). 1 9 70 ) .. O e s t r ogen induc e s hype r t rophy of the myom e t r i al c e l l s and. s t imul ates the i r synthe s i s of the c ontrac t i l e pro t e i n s , myo s i n ATPa s e and ATP ,. through the induc t i on o f spec ific RNA and pr o t e in synthe s i s .. Thus the infl uenc e of o e s t rogen on the myome t r ium inc l ud e s membrane , me tabo l i c and s t ructural c hange s whi ch promo t e e xc i t a t i on and c ont r ac t i on (d). ( Mcke rns , 1 9 7 7 ) . Ac c o rding t o Reyn o l d s ( 1 9 3 5 ) , prol onged t r ea tment w i th h i gh. do s e s of o e s t rogen rend e r s the ut e rus immo t i l e . Thi s i s c ontrary t o the c ontemporary be l i ef of the func t i on of o e s t r ogen .. He d emons trated that. uter ine mus c l e is qui e s cent when the bl ood l evel of o e s t rogen i s very. high. Und e r phy s i ol ogi cal c ond i t i ons , uterine qui e s c en c e i s observ e d. dur ing t he pro - oe s t rus surge of o e s trogens in cyc l i c r a t s and dur i ng the pre - parturi ent surge of o e s t rogen in pregnant rats. e ffe c t o f o e s t r ogen. The wi thdrawal. l evel s in bl o od is obs e rved in l at e o e s t rus and. me t - o e s t rus and during the e a r l y po st - partum pe r i od , when s t r ong s pont ane ous c ontra c t i ons a c c ompany the fal l in ovar i an o e s t r ogen s e c r e t i on ( Fuchs , (e). 1978 ) .. A further o e s t r og e n effe c t de s c r i bed i s the forma t i on of. membrane r e c e p t o r s for c e r t a in ut e rotoni c agent s .. The mo s t i mpor t ant of. the s e a r e oxy t o c i n r e c e p t o r s ( Fuchs et al . , 1 9 8 3 ) and a - adrene r g i c r e c e p t o r s ( Robe r t s. e t a1 .. 1981 ) . Inc reased r e c ept o r numb e r s l ow e r the 1 thr e shold for s t imul a t i on and increase the re spons e t o a given do s e of oxyt o c i n by r e cruit ing more uni t s to c ontrac t . i s s e l e c t i ve ;. The e f fe c t of o e s tr ogens. thus the r e c e p t o r s for pr o s t agl andin E 2 and F2a do not. appe a r to be increased by o e s t r ogens ( Wake l ing and Wyngarden ,. 1 9 74 ) and. the numbe r of b - adrene rgi c r e c ep t o r s i s d e c r e a s ed ( Robe r t s et al . ,.

(33) 21 1 9 8 1 ) . O e s trogens al s o appear to. s t i mul a t e pros tagland i n s ynthe s i s in a. rather comp l e x f a s h i on tha t r e qui r e s i n t e r a c t i on w i th proge s t e r one ( Ca s t ra c ane and J o rdan , 1 9 7 5 ) . O e s t r ogens increase the numbe r o f s pe c i f i c binding s i te s f o r oxyt o c in in r a t ( S o l o f f. and Swe e t ,. 1 9 8 2 ) a n d rabb i t ( Ni s senson. e t al . ,. 1 9 7 8 ) myome t r i um w i thout having any e f f e c t on the af f i ni ty of the receptor .. In the rat the increase i n r e c e p t o r numbe r oc cur s abrup t l y. s everal hours b e f o r e labour in paral l e l wi th a n inc r e a s e d s en s i t i v i ty t o oxyt oc in .. The inc r e a s e in s ens i t iv i t y t o oxy t o c i n has been a t t r i buted. t o the incre a s ed numbe r of oxytocin - r e c e p t o r s . (f). H i gh l eve l s of oes trogen c o r r e l a t e wi th inc r eased u t e r i ne. nor - ep inephr i n e c onc entration ind i c a t i ng that the sympathe t i c ne rve s a r e al s o a s pe c i f i c target t i s sue for o e s t r ogen a c t i on ( Mar shal l ,. 1981 ) .. Oes t rogen al s o ha s the potent ial to a l t e r the l ocal c oncent ra t i on of adrene r g i c agoni s t s a t s everal othe r l e v e l s .. I t exe r t s a d i r e c t a c t i on. on cate cholamine me tabol i sm in sympa t he t i c neur ons by the inh i b i t i on of extraneuronal c a t e chol amine uptake ( I ve r s on ,. 1973 ) .. Al s o , the. oxida t i on pr oduc t s o f o e s t rogen , pr ima r i l y 2 - and 3- hydroxy d e r ivat ive s ( known c ol l e c t i ve l y as cat echol - oe s t r ogens due to the i r s t ruc tural s imi l a r i ty t o c a t echol ) , have been demon s t ra t ed t o inhi b i t the enzyme s tyro s i ne hydroxyl a s e and cate chol me thyl t r ansferase ( COMT ) i n v i t ro ( Li p s e t t e t al . , c ontrac t i on .. 1982 ) .. Both enzyme s a r e i nvolved in smooth mus c l e. Howeve r the oc currenc e o f thi s phenomenon in v i vo and i t s. p o s s ibl e s i gni f i c an c e to neuronal func t i on i n the myome tr ium ha s not been demon s t r a t e d . I n s ummary the ma i n influenc e s of o e s t r ogen on myome t r i a l func t i on are : (i). they inc rease the capac i ty o f the uterus t o cont r a c t ;. (ii). they p romote the synchron i z a t i on o f the c ontrac t i l e uni t s by s upp re s s ing l oc a l l y gene r a t ed s p ontaneous a c t ivi t y whi l e i nc r e a s ing the exci tabi l i t y t o humoral agents and nerve t r ansmi t te r s ; and. ( i i i ) they r ender the c ontrol o f myome t r i al cont r a c t i on s mor e p r ec i s e ..

(34) 22 II .3.B.. P roge ste rone. P roge s t e r one appea r s to have l i t t l e i nf l uence on myome t r i al re spons e s unl e s s the ute rus has b e e n expo s e d t o o e s t r ogen .. O e s trogen. induc e s the s ynthe s i s of myome t r i al proge s t e r one r e c e p t o r s whi ch are normal l y l ow in c onc entra t i on ( S akamo t o. et. al . , 1986 ) .. The me chani sm by whi ch proge s t e rone dimini shes myome t r i al exc i tab i l i t y i s not compl e t e l y c l e a r , al though the f o l l ow ing observa t i on s have be en made : (a). Pr oge s t erone produc e s an increa s e in r e s t i ng membrane. po tent i al i n the myome t r ium from about 50 mv t o 65 rnv ( Ma r shal l ,. 1980 ) .. Thi s hype r - pol ar i z i ng e f f e c t would be expe c t ed to redu c e exc i tabi l i ty and the c onduc t i on of e l e c t r i c al i mpul s e s and impa i r the pr opaga t i on o f c ontra c t i on waves al ong the u t e rus ( Ma r sha l l , 1 9 6 2 ) .. The c ontrac t i ons. e l i c i t ed at vari ous par t s of the ut e rus the r e fore rema i n s ynchronous and l ocal i z e d ( Fuchs ,. 1978 ) .. I n the rat and rabbit myome t r i um ,. the membrane p o t ent i a l of the. mus c l e c el l s gradual l y be c om e s more negat i ve rea ching a max i mum ( about 60 mv ) a r ound mid - pregnancy and remaining at thi s l ev e l unt i l the end o f t e rm .. Dur ing thi s p e r i od the u t e ru s may show s ome spontaneous. c ont ra c t i ons but the s e are l oc al i z ed ,. i rr e gul a r , and weak . About 2 4 h. before par tur i t ion the membrane begins to d e p o l a r i z e and the ut e rus become s p r ogr e s s i ve l y more a c t i v e . At par tur i t i on the membrane poten t i a l i s about 5 0 m v and ute r ine c ontrac t i ons s p r e ad uniformly through the muscl e ( Ca s t e e l s and Kur iyama ,. 196 i ) .. T o i nve s t igate the s e o b s e rved change s , Casteel s and. Kur i yama. ( 1 9 6 5 ) mea sured the d i s tr i but i on of i ons and the i r permeabi l i ty in the myometr ium of the rat at var i ous s tage s of pregnancy .. They f ound no. s i gni f i cant d i fferenc e s in the Na, K or Cl c onc entrat i on gradi ents dur i ng p r e gnancy .. On. the othe r hand the K p e rmeabi l i ty g r adua l l y. i nc r e a s ed until m i d - p regnancy and then rema i ned high unti l n e a r the end of ge s ta t i on .. Na permeab i l i ty was r e l at i ve l y l ow throughout pregnancy. but i n c r e a sed several days before de l ivery . Carsten ( 1 9 7 9 ) demonstrated.