der Siidd. Versuchs- und Forschungsanstalt fur Milchwirtschaft Weihenstephan der Technischen Universitat Miinchen

Zbl. Vet. Med. A, 23,793-803 (1976)

@ 1976 Verlag Paul Parey, Berlin und Hamburg ISSN 0300-871 l/ASTM-Coden: ZVRAAX

Aus dem Institut f u r Physiologie

der Siidd. Versuchs- und Forschungsanstalt f u r Milchwirtschaft Weihenstephan der Technischen Universitat Miinchen

Testosterone, Luteinizing Hormone

(LH)

and Follicle Stimulating Hormone

(FSH)

in Peripheral Plasma of Bulls:

Levels from Birth through Puberty and Short Term Variations

H. KARG,

T.

G I M ~ N E Z , M. HARTL,

B.

HOFFMANN, E. SCHALLENBERGER

and D. SCHAMS

W i t h 4 figures and one table

(Received for publication Jaiznary 19, 1976)

Introduction

There is still considerable controversy concerning the hormonal control of sexual maturation in the bull, especially as far as possible interactions of

L H and testosterone are concerned (RAWLINGS et al., 1972; ODELL et al.,

1970; SWANSON et al., 1971;

THIBIER,

1975). In order to further elucidate the

hormonal changes and interrelationships occurring during puberty and sexual maturity in the bull, testosterone, L H and FSH were determined in plasma obtained by longitudinal sampling of individual animals. A preliminary report

of this study has been reported elsewhere ( G I M ~ N E Z et al., 1974). In order to

especially delineate the short term fluctuations in testosterone and LH secre-

tion (KATONGOLE et al., 1971) animals were serially sampled at a high fre-

quency for short time periods.

Material and Methods

Animals and blood sampling

All animals were males of the Brown Swiss breed kept under identical

management conditions. In general in this breed sexual maturity occurs at the

age of 8-10 months. I n experiment I (longitudinal or puberty study), jugular

vein plasma was collected from four bulls by venepuncture 3

x

weekly be-

tween 08.00 and 09.00 from birth until the 18th month of age. The 4 bulls

were born at different seasons (Nydo 22. 5 . 70, Lado 8. 7. 70, Kabine

27.10. 70, Kaliro 11. 11. 70). In experiment I1 jugular vein plasma was ob-

tained by means of an indwelling catheter at 15 minute intervals over a period

794 KARG, G I M ~ N E Z , HARTL, HOFFMANN, SCHALLENBERGER a n d SCHAMS

of 8 hours from five males at 4 different ages, two animals representing each age group. In a further study, blood was collected in the same way from bull

“Gilch” at the age of 14.5 months and a 34 month old bull “Kaliro” during a

period of 48 and 32 hours, respectively.

All catheters were inserted 1 day before the beginning of the experiment.

Blood was cooled (4 “ C ) immediately and centrifuged within one hour.

Plasma samples were kept frozen at - 20 OC until assayed.

Determination of testosterone

Testosterone was analyzed by radioimmunoassay (RIA). The extraction

(from 0.5 ml. plasma using 5

ml.

ether) as well as the R I A were performed

similarly to the method described by HOFPMANN and HAMBURGER (1973) for

the determination of progesterone. The antiserum used was obtained after im-

munization of rabbits against testosterone-3-carboxy-methoxylamine-bovine

serum albumin. With regard to specificity this antiserum showed a significant

cross reaction (75 ” 0 ) only with 5 a-dihydrotestosterone (DHT). However, no

differences were observed between the testosterone values in peripheral plasma

before and after separation of

DHT

by thin layer chromatography

(P

>

0,40,

n = 8). The accuracy of the method was determined by measurement of

added amounts of testosterone to charcoal-stripped calf plasma. Recovery

values for these plasma samples containing 0.2 to 0.4 ng. gave a regression

coefficient of 0.996, with a coefficient of variation (CV) for the individual

samples ranging between 4.5 “/o and 21.2 O / o , The reproducibility (interassay

variability) was controlled by determining testosterone in various plasma

pools during the whole experimental series, yielding a CV from 18.4 “/o

(0.24

I

0.04 ng. testosterone/ml. plasma, n = 8) t o 5.6 “ / o (2.99

k

0.16 ng.

testosterone/ml. plasma, n = 1 I ) . The lower limit of sensitivity was calculated

to be 0.050 ng.

Determination of L H and FSH

L H was measured by R I A as described earlier (SCHAMS and KARG, 1969;

SCHAMS and KARG, 1970). A significant increase in L H (LH-peak) was con-

sidered to be a rise in L H measurable in at least two consecutive plasma samples (positive o r negative slope) and exceeding the mean L H concentration plus the standard deviation, calculated for each period of uninterrupted blood collection for each individual animal.

Bovine FSH was determined by a heterologous R I A (SCHAMS and SCHAL-

LENBERGER, 1976). A highly purified sheep F S H preparation with a biological

activity 31 times NIH-FSH-S 1 was used for iodination. An antiserum against

ovine FSH was obtained after immunization of guinea pigs. This antiserum showed no cross reaction with bovine prolactin (NIH-P-B 2) or bovine growth hormone (NIH-GH-B 15) and only a slight cross reaction with bovine L H and TSH, which could be eliminated by the addition of bovine T S H and L H to each test tube during the assay. All results are expressed in terms of crude bovine pituitary extracts (Ambinon and NIH-FSH-B,). The biological activ-

ity of Ambinon is equivalent to 0.125 times NIH-FSH-S,, and that of NIH-

FSH-B, is equal t o 0.49 times NIH-FSH-S,. The radioimmunological potency

of NIH-FSH-B, was estimated to be 3.6 times higher than that of Ambinon.

Results

Experiment I

Plasma levels for testosterone, L H and F S H (mean values

I

SD for each

Testosterone, Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH) ₇₉₅ ng/ml N Y D O

1

L A D 0 9 21 33 4 5 5 7 69

4

l ' l ' l ' l ' l ' l ' l ' l ' i ' i ' l ' l ' 9 21 33 45 5 7 69 W E E K S O F A G E

Fig. 1. Concentrations of testosterone, L H and FSH (mean values ? SD for each 3 week sampling period) in peripheral plasma in 2 bulls from birth through maturation

secretion pattern of testosterone were similar in the bulls Nydo, Lado and

Kabine. With individual differences, 4 periods of testosterone secretion became

obvious in these 3 animals. As shown in Table 1 testosterone values were below

n g m l K A L I R O l o o o / 600 9 21 33 45 57 69

L

I I I ' I ' I ' I ' I ' I I I ' I ' I ' I ' I T 9 21 33 45 57 69 W E E K S O F A G E

Fig. 2. Concentration3 of testosterone, L H and FSH (mean values If: SD for each 3 week sampling period) in peripheral plasma in 2 bulls from birth through maturation

796 KARG, GIMBNEZ, HARTL, HOFFMANN, SCHALLENBERGER and SCHAMS

range of range of range of

ng / rnl (SO1 ng / rnl (SD) ng / rnl (SO)

secretory

phase

(w::9,‘ks,

testosterone conc. (weeks) age testosterone conc. (weeks] age testosterone conc.

7

1 ng./ml. plasma in period I, showed an initial increase in period I1 and re-

mained constant o r even decreased in period 111. I n the IVth period a final

increase in testosterone concentrations was observed. With p

<

0.05-0.001

the difference between the testosterone values in period I and I1 and period

111 and I V was highly significant. In the bull Kaliro testosterone coiicentra- tions were low until the 39th week of age. However, an initial increase

(period 11) to 1.1 ng./ml. plasma was also observed in

this

animal from the

28th to the 30th week and a second one (period IV) after the 39th week of

age.

Table 1

Phas-s of appearance of testosterone in peripheral plasma of three bulls from birth through puberty (mean values f SD; ng./ml.)

1 Bull

I

Nydo

I

Lado I Kabine

I

I 0

-

27 0 - 18 0

-

21

The L H concentrations were similar in all animals, with values ranging

between 0.60 and 2.75 ng./ml. plasma during the experimental period. While values were rather constant with increasing age in bulls Nydo and Lado

(regression equations y = 1.67-0.0053 x and y = 2.02-0.0026 x), a signifi-

cant gradual decrease in L H was observed in bulls Kabine and Kaliro [regres-

sion equations: y = 2.28-0.012 x (Pb

<

0.005) and y = 2.05-0.020 s

(Pb

<

0.005)]. No significant correlations between testosterone and L H in

peripheral plasma were observed. In contrast to LH, FSH-concentrations

were elevated in correlation (p

<

0.05-0.001) with the initial increase of

testosterone during periods I and IV in bulls Nydo, Kabine and Kaliro, while

they showed a wave-like trend throughout the experiment, with a tendency t o flatten with increasing age in bull Lado.

Experiment

II

The testosterone concentrations determined in the 4 and 8 week old

calves were constantly low (mean: 0.28

f

0.20 ng./ml.; n = 127), and simi-

larly in one of the 20 week old calves (mean: 0.39 zk 0.12 ng./ml.; n = 33).

In the other 20 week old animal and in both cases at the age of 40 weeks, testosterone values showed almost identical daily fluctuations with values

above 6 ng./ml. plasma occurring between 08.00

h.

and 10.00

h.

and again

between 14.00

h.

and 16.00

h.

No changes in the LH-levels in relation t o age were observed. Significant

increases in LH (LH-peaks), as defined above, occurred at

all

age-periods and

in any case preceded the observed afternoon increase in testosterone i n the 20 and 40 week old animals. Mean FSH levels in plasma were significantly

higher ( P < 0.0005) in the 20 and 40 week old bulls (346

f

64 ng./ml.;

n = 132) than in the 4 and 8 week old calves (214

F

55 ng./ml.; n = 132).

In fig. 3 an example for each age group is given.

The testosterone and L H levels determined in bull “Gilch” at the age of 14 months and in the 34 months old bull “Kaliro”, during a period of 48 and 32 hrs.: respectively, are shown in Fig. 4. While the profile in bull

Testosterone, Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH) ₇₉₇

W E E K S OF AGE 6 8 20 40

nplml

8 12 16 8 12 16 8 I 2 16 8 I 2 16

TIME OF D A Y t HOUR? )

Fig. 3. Changes in testosterone-, LH- and FSH-concentrations durin a period of 8 hrs. in peripheral plasma of bull calves at the age of 4, 9, 20 anc! 40 weeks

“Kaliro” was rather constant and almost diurnal, a more irregular pattern was observed in bull “Gilch”. The mean L H levels in plasma calculated for

“Gilch” and “Kaliro” were 1.01

k

0.21 ng./ml. (n = 193) and 0.85

k

0.37 ng./ml. (n = 126) plasma, respectively. In both animals each LH-peak

(range of peak-levels 1.3 to 2.6 ng./ml.) was followed by a rise of testosterone

within 1 hour. However, similarly distinct increases of testosterone were also

observed in 5 instances (from 1.4 to 13.2; 5.2 to 11.3; 4.0 to 10.0; 1.0 t o 3.1

and 1.2 t o 4.4 ng./ml.) where, by the definition suggested, no preceding signi-

ficant increase in LH could be detected. During the experiment FSH levels

were very constant around 276 ( * 29) ng./ml. plasma (n = 126) in

bull

“Kaliro” and showed irregular fluctuations in bull “Gilch”, especially during

n g l m l 8 L K A L I R O 1 o g c : 3 4 m o n t h s ) 18 1.a 0.2 16 ( oge:14,5monthsl 12 8 L I 0.24 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 , I I I 9 11 13 15 17 19 21 23 1 3 5 7 9 11 13 IS 17 19 21 23 1 3 5 7 9 Time o f doy ( h o u r s I

Fig. 4. Changes in testosterone- and LH-concentrations during a period of 32 and 48 hrs., respectively, in peripheral plasma in bulls “Kaliro” and “Gilch”

798 KARG, GIMENEZ, HARTL, HOFPMANN, SCHALLENBERGER and SCHAMS

the first 15 hrs. of the experimental period (mean: 195

k

180 ng./ml.;

n = 193). No significant correlations could be established between the levels

of FSH and those of testosterone or L H in the whole course of experiment 11.

Discussion

The results derived from the longitudinal study which concern basic shifts in hormone secretion have clearly shown that from birth until the end of puberty basal levels of L H remained rather constant or even decreased in peripheral plasma, while testosterone, in agreement with observations by

LINDNER (1959) and RAWLINGS et al. (1972), showed an initial increase be-

ginnung at the 20th week of age. The results suggest that this increase occurs

in a biphasic pattern in relation to age; due to the different times of birth, seasonal effects can be ruled out.

Evidence that various processes during the course of puberty in the bull

seem to occur in a biphasic pattern were first obtained b y MACMILLAN and

HAFS (1969), who described a similar phenomenon for fructose concentrations in seminal plasma. Testosterone concentrations in blood plasma and testicular

tissue obtained from the same bulls (RAWLINGS et al., 1972) also indicated a

biphasic testosterone secretion but this observation was not further discussed at that time. The occurrence of a biphasic increase of testosterone in peripheral plasma seems not to be unique for puberty in the bull, since a similar phe-

nomenon has also been observed in the roe deer (Capreolus capreolus) during

sexual maturation (puberty) as well as during the reproductive cycle in the

mature animal (GIMENEZ et al., 1975; BARTH et al., 1976), similarly in the

noctule bat (Nyctalus noctula) (RACEY, 1974). Contrary to observations in

the ram (COTTA et al., 1975) and in the bull (MACMILLAN and HAFS, 1968;

(RAWLINGS et al., 1972; GOMBE et al., 1973) where an increase of L H in

plasma with increasing age was observed, no changes (2 bulls) or a decrease

( 2 bulls) in L H concentrations was obserrved in the 4 animals examined from birth until the 18th month of age as has been already partially reported

elsewhere (SCHAMS and BUTZ, 1972). This is in agreement with earlier obser-

vations in cattle (ODELL et al., 1970) and the pig (ELSAESSER et al., 1973).

Since it was concluded from castration experiments in sheep and rats (CRIM

and GESCHWIND, 1972; GALLOWAY and PELLETIER, 1975; GAY and MIDGLEY,

1969) and from experiments substituting L H and FSH after hypophysectomy

(COUROT, 1971) that L H and not FSH is the major hormone responsible for Leydig cell function, the observation described is rather intriguing with respect

to the onset of testosterone increase at the beginning of puberty. As far as

can be deduced from peripheral plasma levels, the rather constant L H concen- trations would suggest that the testosterone increase before puberty cannot be explained by the common desensitization theory (MCCANN and RAMIKEZ,

1964), but rather by a changed sensitivity of the receptor sites in the testes to

LH. This theory is also supported by our findings in experiment TI, where

episodic variations were investigated. In the 4, 8 and one of the 20 week old animals, plasma testosterone showed no response to the observed changes in plasma L H , while in the other animals examined plasma testosterone respond- ed with an increase to similar rises in L H (see fig. 3).

Even though there seems to be a statistically valid relationship during sexual maturation between testosterone and F S H in 3 of the 4 bulls examined

in Expt. I, a more direct biologic role of F S H may occur in other processes,

like the synthesis of androgen-binding protein which is produced in the Sertoli

cells under the specific stimulation of FSH (HANSSON et al., 1973 a; HANSSON

Testosterone, Luteinizing Hormone ( L H ) a n d Follicle Stimulating H o r m o n e (FSH) ₇₉₉

tion concerning the role of FSH a t the time of puberty was presented by

ODELL et a]. (1973) from experiments in rats where they concluded that FSH induces the sensitivity to L H in the testes which would explain the occurrence of puberty without a necessary increase of L H o r an alteration in feedback

sensitivity. Our data in the longitudinal study, as well as in experiment 11,

where significantly higher FSH-levels were found in the 20 and 40 week old

animals, would support this theory. WUTTKE and DOHLER (1975) have pre-

sented evidence for a functional role of prolactin in the onset of puberty in the rat. Similar conclusions cannot be derived for the bovine species since sub- stantial variations of plasma prolaction levels occur in relation to the season

of year (KARG and SCHAMS, 1970; SCHAMS and REINHARDT, 1974) and would

tend to mask any such relationship. The prolactin data evaluated in the identical plasma samples of the present experiment were published earlier

(SCHAMS and REINHARDT, 1974).

The existence of short term fluctuations in testosterone is well known and

has also been shown to exist in the bovine species (KATONGOLE et al., 1971;

MONGKONPUNYA et al., 1973; SANWAL, 1974; HAYNES et al., 1975). O u r in-

vestigations have confirmed these observations and further demonstrated that these fluctuations, which seem to occur rather regularly (with the exception

of bull “Gilch” a t the age of 14 months), can be measured as early as at the

onset of puberty. Similarly, but less distinctly expressed than was reported by

KATONGOLE et al. (1971), also in these experiments a positive action of L H

with respect to the stimulation of short term testosterone fluctuations was ob-

served. No correlations of biological significance could be established for the

short term variations in FSH concentrations.

Acknowledgements

We are most grateful to the following for their kind gifts: National In-

stitutes of Health, Bethesda, USA for NIH preparation of bovine G H , pro-

lactin, LH, FSH and TSH, and sheep FSH.

This work was supported by the Deutsche Forschungsgemeinschaft, Bonn Bad Godesberg.

Summary

Peripheral plasma levels of testosterone, L H and FSH were determined

three times weekly by RIA in 4 bulls from birth through maturation and a t

15 min. intervals in 6 males during short periods (8-48 hrs) at different ages

(4 weeks-34 months). After an initial period of values below 1 ng./ml.

plasma, the subsequent rise in plasma testosterone was characterized by a

biphasic pattern. In 3 animals a first increase occurred after the 2Oth, 22nd

or 28th week of age (mean values 2.2-8.4 ng./ml.), followed b y a plateau o r

decrease. A second increase, occurred after the 39th, 51st and 54th week of

age, respectively (mean values: 1.9-1 1.9 ng./ml.). I n the 4th bull testosterone

values exhibited a similar but delayed pattern and were generally lower dur- ing the whole trial. LH-levels remained constant in all animals between

0.6-2.7 ng./ml. during the experiment without any tendency t o increase with

age. FSH increased coincidentally with testosterone in 3 of the bulls, but

showed a wave-like trend in the other bull. No changes in L H - and FSH-

short term variations were found in relation to age. Testosterone values re- mained constantly below 1 ng./ml. in the 4 and 8 week old animals and started to exhibit short term variations after 20 weeks of age with a rather constant

KARG, GIM~NEZ, HARTL, HOFFMANN, SCHALLENBERGER and SCHAMS

800

tendency of high values around 09.00, 16.00 and 22.00

h.

An LH-peak pre-

ceded the observed increases in testosterone in 16 out of 21 observations.

Zusammenfassung

Testosteron, Luteinisierungshormon

(LH)

und Follikelstimulierendes Hormon (FSH) im peripheren Plasma von Bullen:

Werte von der Geburt

bis

nach der Pubertat und Kurzzeitvariationen

Testosteron, L H und FSH wurden mit Hilfe radioimmunologischer Me- thoden im peripheren Plasma von 4 Bullen vom Zeitpunkt der Geburt bis zur vollendeten Geschlechtsreife gemessen (Experiment I) und in 15minutigem Abstand bei weiteren 6 Tieren im Alter von 4 Wochen bis 34 Monaten uber

einen Zeitraum von 8-48 Stunden (Experiment 11).

Experiment I: Nach einer ersten Periode von Testosteronkonzentrationen

unter 1 ng./ml. Plasma (Periode I) verlief der darauf folgende Anstieg in

2 Phasen. Bei 3 Tieren wurde ein erster Anstieg (Periode 11) nach der 20., 22., bzw. 28. Lebenswoche (Durchschnittswerte 2,2-8,4 ng/ml) und danach ein

Plateau oder Abfall (Periode 111) beobachtet. Dem folgte ein 2. Anstieg

(Periode IV) nach der 39., 51. bzw. 54. Lebetiswoche (Durchschnittswerte 1,9-11,9 ng/ml). Beim 4. Bullen zeigte sich ein ahnliches jedoch verzogertes Sekretionsmuster mit durchschnittlich niedrigeren Testosteronkonzentrationen. Die LH-Werte lagen bei allen Tieren konstant zwischen 0,6-2,7 ng/ml und zeigten keine Tendenzen, mit zunehmendem Alter anzusteigen. F S H stieg parallel zum Testosteronanstieg bei 3 der untersuchten Tiere an und zeigte einen nicht korrelierbaren wellenformigen Verlauf bei dem 4. Bullen.

Experiment 11: Die episodischen LH- und FSH-Schwankungen wiesen

keine Beziehungen zum Alter der Tiere auf. Testosteron lag konstant unter 1 ng/ml Plasma bei den 4 und 8 Wochen alten Tieren; mit dem Alter von 20 Wochen begannen die Konzentrationen im Verlauf eines Tages im peri-

pheren Plasma zu schwanken, wobei

-

mit der Ausnahme einer Unter-

suchungsperiode

-

die Tendenz zu hohen Werten um 0900, 1600 und 2200

erkennbar war. Ein LH-Peak ging in 16 aus 21 Beobachtungen dem Testo- steronanstieg voraus.

Resume

Testostirone, hormone lutiinisante

(LH)

et hormone folliculostimulante FSH dans le plasma piriphbrique chez des taureaux:

taux de

la

naissance

A

la puberte et variations pulsatiles

O n a mesurk la testostkrone, L H et FSH avec des mkthodes radioimmuno-

logiques dans le plasma pkriphkrique de 4 taureaux depuis la naissance

B

la

maturitk sexuelle (experience I) et chez 6 animaux hgks de

4

semaines

A

34

mois

B

des intervalles de 15 minutes durant une pkriode de 8-48 heures

(expkrience 11).

Expkrience I: Aprks une pkriode de concentration en testostkrone in-

fkrieure

A

1 ng/ml plasma (pkriode I), on a constatk une augmentation en

2 phases. Une premiere augmentation a

ktk

constatke chez 3 animaux aprks

20, 22 et 28 semaines (valeurs moyennes 2,2-8,4 ng/ml) (pkriode 11). Un

plateau ou une chute s’en suivit (pkriode 111). Une seconde augmentation se manifesta apr& 39, 51 et 54 semaines (valeurs moyennes 1,9-11,9 ng/ml) (pkriode IV). O n a obtenu un kchantillonnage semblable mais plus rapide avec des valeurs moyennes de testostkrone plus basses chez le quatrieme taureau.

Testosterone, Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH) 801

animaux et n'ont pas augment6 avec 1'9ge. FSH augmenta parallklement

2i

la

testostkrone chez 3 animaux alors qu'il n'y a pas eu de corrklation chez le quatrikme taureau.

Expkrience 11: Les variations kpisodiques de L H et FSH n'ont pas eu de

rapport avec 1'9ge des animaux. La testostkrone demeura constamment en-

dessous de 1 ng/ml plasma chez les animaux de 4-8 semaines. Les concentra-

tions commenckrent

A

varier dks la vingtikme semaine au cours d'un jour dans

le plasma pkriphkrique et,

A

l'exception d'une pkriode d'analyse, la tendance

2i

des valeurs klevkes fut remarquke 0900, 1600 et 2200. Une pointe L H

prkckda l'augmentation de la testostkrone dans 16 des 21 observations.

Resumen

Testosterona, hormona luteinizante

(HL)

y hormona estimulante del foliculo

(FSH) en plama sanguineo perifbrico de toros: niveles desde el nacimiento hasta el final de la pubertad y variaciones a plazo breve

Se midieron la testosterona, H L y FSH con ayuda de mktodos radioinmu- nol6gicos en el plasma sanguineo perifkrico de 4 toros desde el instante del

nacimiento hasta consumada la pubertad (experimento I) y en distancias de

15 minutos en otros 6 animales, de edadas comprendidas entre 4 semanas y 34

meses, por un espacio de tiempo de 8-48 horas (experimento 11).

Experimento I: Tras un primer periodo de concentraciones de testos-

terona inferiores a 1 ng/ml plasma (periodo I), el aumento subsiguiente dis-

curri6 en 2 fases. En 3 animales se observ6 un aumento primer0 (periodo 11)

tras la semana 20", 22" resp. 28" (valores medios 2,2-8,4 ng/ml) y despuks

una meseta o descenso (periodo 111). Siguib a esto un aumento 2" (periodo IV)

tras la semana 39", 51" resp. 54" (valores medios 1,9-11,9 ng/ml). Se apreci6 en el tor0 4" un modelo secretor semejante, aunque retardado con concentra- ciones medias inferiores de testosterona. Los valores de H L se hallaban cons- tantes en todos 10s animals entre 0,6-2,7 ng/ml, no mostrando tendencia alguna a aumentar con la edad. FSH aument6 paralela a1 increment0 de testosterona en 3 de 10s animales examinados, evidenciando un curso ondu- lante no correlacionable en el tor0 4".

Experimento 11: Las fluctuaciones epis6dicas de H L y F S H no evidencia-

ron ninguna relaci6n para con la edad de

10s

animales. La testosterona se

hallaba constante, siempre inferior a 1 ng/ml de plasma en 10s animales de 4 y

8 semanas de edad; con la edad de 20 semanas comenzaron a oscilar 10s valo-

res en el curso de un dia en el plasma perifkrico, reconocikndose

-

con la excepcibn de un periodo experimental

-

la tendencia a elevados

alrededor de 0900, 1600 y 2200. Una chspide de HL precedi6 en 16 de 21

observaciones a1 aumento de testosterona.

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Address of authors: Siidd. Versuchs- u. Forschungsanstalt fur Milchwirtschaft, Institut WUTTKE, W., K. D. DOHLER and M. GELATO, 1976: Oestrogens and prolactin as possible