Analysis of regional hemodynamic regulation in response to scald injury

Analysis of regional hemodynamic regulation in

response to scald injury.

P A Taheri, … , L M Flint, J J Ferrara

J Clin Invest.

1994;

93(1)

:147-154.

https://doi.org/10.1172/JCI116938

.

Ultrasonic probes were placed around dog femoral arteries to record blood flow. Hind paw

scalding with boiling water (5 s) caused a marked increase in ipsilateral femoral blood flow

that persisted for the 2-h observation period. Contralateral femoral blood flow and systemic

and pulmonary vascular resistances were unchanged. Compared to scald only animals,

methysergide pretreatment diminished and shortened the femoral vasodilator response to

scald (109 +/- 14 vs 243 +/- 27 ml/min at 5 min; 59 +/- 14 vs 191 +/- 31 ml/min at 2 h).

Pretreatment with ritanserin, BW A1433U83, atropine, ICI 118551, diphenhydramine,

ranitidine, meclofenamate, L-nitro-arginine methyl ester, 3-amino-1,2,4-triazine, and U

37883A had no effect on the increased femoral blood flow response to scald, suggesting

this vasodilator response is not dependent upon activation of serotonergic2, adenosineA1,

muscarinic, beta 2-adrenergic, histaminergic1 or histaminergic2 receptors, on

cyclooxygenase products, endothelium-derived relaxing factor derived from nitric oxide

(NO) synthase III, NO derived from NO synthase II, or KATP channels, respectively.

Methysergide given after burn immediately reduced the augmented femoral blood flow to

preburn levels, suggesting the vasodilator response to scald is mediated through continual

activation of local serotonergic1-like receptors, which may be target site(s) for therapeutic

interventions to influence burn-induced hemodynamic alterations.

Research Article

Analysis

of Regional

Hemodynamic

Regulation

in Response to Scald Injury

Paul A.Taheri,* HowardL. Lippton,**Seth D. Force,* Ernest W. Franklin,* Albert L. Hyman, *S Lewis M. Flint,*and John J. Ferrara*

*DepartmentofSurgery, Tulane University School ofMedicine,

tDepartments

ofInternal

Medicine

and Pharmacology, Louisiana State UniversitySchool ofMedicine, and

ODepartments

ofPharmacologyand InternalMedicine, TulaneUniversity School ofMedicine, NewOrleans,Louisiana 70112

Abstract

Ultrasonicprobes wereplaced arounddogfemoralarteriesto

record bloodflow.Hind paw scalding with boiling water (5 s) causedamarkedincrease inipsilateralfemoral bloodflow that persisted forthe 2-hobservation period. Contralateralfemoral blood flow and systemic and pulmonary vascularresistances

were unchanged.Compared to scald only animals,

methyser-gidepretreatmentdiminishedand shortened thefemoral

vaso-dilatorresponsetoscald(109±14vs243±27 ml/minat5min;

59±14 vs 191±31 ml/min at 2 h). Pretreatment with

ritan-serin, BW A1433U83, atropine, ICI 118551,

diphenhydra-mine,ranitidine, meclofenamate,L-nitro-arginine methyl ester,

3-amino-1,2,4-triazine, and U37883Ahad noeffectonthe

in-creased femoral bloodflowresponse toscald, suggesting this vasodilator response is not dependent upon activation of

sero-tonergic2,

adenosineAl,

muscarinic,l2-adrenergic,

histaminer-gic1 orhistaminergic2receptors, on cyclooxygenase products,

endothelium-derivedrelaxing factor derivedfrom nitric oxide

(NO)synthase III,NOderived from NO synthase II,or

KATp

channels,respectively. Methysergide

given

after burn

immedi-ately reduced the augmented femoral blood flow to preburn

levels,suggesting the vasodilator responsetoscaldis mediated throughcontinual activation oflocal

serotonergicl-like

recep-tors, which may be targetsite(s)fortherapeuticinterventions

toinfluence burn-induced

hemodynamic

alterations. (J. Clin.

Invest. 1994.93:147-154.) Key words: burns *vasodilation -serotoninreceptors * vascular resistance * ultrasonic bloodflow probes

Introduction

In patients with large body surface area (BSA)' burns, both

cardiacoutput andblood flowtotheinjuredarea areincreased for severaldays (1, 2).Animalstudies have also documenteda

Address correspondencetoJohnJ.Ferrara,M.D., Department of

Sur-gery, TulaneUniversity School ofMedicine, 1430 Tulane Avenue, NewOrleans,LA70112.

Receivedfor publication 15 March 1993 and in revisedform 16 August 1993.

1. Abbreviationsusedinthis paper:3-ATINE,

3-amino-l1,2,4-triazine;

BSA, body surfacearea;CATM,5-carboxamidotryptamine; CI,

car-diacindex; CNS, centralnervoussystem;CO,cardiacoutput;EDRF, endothelium-derived relaxing factor; L-NAME, L-nitro-arginine methylester;MAP,meanarterialpressure;MET,methysergide; NOS, nitric oxide synthase; PAP, pulmonaryartery pressure;PCWP,

pulmo-narycapillarywedgepressure;RIT, ritanserin.

prolongedincrease in blood flow to a large wound (3). How-ever, acute alterations in blood flow to a burn site are poorly delineated. Inguinea pigs, a large BSA burn produces an acute decreaseinblood flow to thewound, likely caused by dimin-ished cardiac output (4). A smaller BSA burn in rats causes only an increase in blood flow to the injured site, a response influenced by surface temperature and injury size (5). Media-tion of this regional vasodilatorresponse by potassium, prosta-glandins, lactate, and activation of

_{f3-adrenoceptors}

(3, 6-9) has been suggested. Others consider heat-induced vasodilation

a prime component of this response (5). The role of these

vasodilatory mechanisms is unclear.

Theseexperiments were designed to characterize the effect

ofa small BSA scald on systemic, pulmonary, and regional

(burned and unburned sites) hemodynamics. The effects of blocking agents for known vasoactive receptors and potassium channelsonburn-inducedhemodynamic alterations were also

investigated. These data indicate that in the absence of

sys-temicorpulmonary hemodynamic effects, blood flow to the

injuredareaacutelyincreased,andregionalvascularresistance decreased. These responses were selectively inhibited by the

serotoninreceptor blockingagent, methysergide. Since

ritan-serin, a serotonin2 receptorblocking agent, had no effect on

thesealterations,the data suggest thatcontinuousactivationof serotonin1-like receptorsmediates, in large measure, these re-sponses.

Methods

Surgicalprotocol.Adultmongrel dogs weighing 20-35 kg were anesthe-tized withintravenous sodiumpentobarbital (25 mg/kgperh) and placed on room air mechanical ventilation. Systemicmean arterial

pressure(MAP,mmHg)wasmeasured throughacannulatedbrachial

artery.Pulmonaryartery pressure(PAP, mmHg) and pulmonary capil-larywedgepressure(PCWP, mmHg)weremonitored by insertion ofa

balloon-tippedpulmonaryarterycathetervia internaljugular vein

cut-down.Ringer'slactatesolution(2-3ml/ kgperh)wasinfusedto main-tainbaselineMAPand PCWP.

An ultrasonic flow probe (Transonic Systems, Inc., Ithaca, NY)

wasplaced around theascendingaortavialeft thoracotomy in certain

groupsofdogs(designated later),torecordcardiacoutputminus

coro-nary artery flow (CO, liter/min); systemic vascular resistance (mmHg/literpermin) wascalculated.Cardiac index(CI, liter/min

per

M2)

wascalculated from caninenomograms.Isolationofacarotid

arterywascarriedoutinfour animalstoprovideaccessfor intracarotid injections.

Ultrasonic flow probeswereplacedaroundbothfemoral arteriesto

record femoralbloodflow(ml/min), and thesevalueswereusedto

calculatefemoral vascular resistance (mmHg/mlpermin). In some

dogs,asidebranch of the femoralarteryonthesideto undergoan

experimentalmanipulationwascannulatedtoprovideaccessfor intra-femoral injections. Dogswererandomlyassigned toaprotocolonly after monitoredhemodynamicparameterswerestable for 30min.

Experimentalgroups. A sham treatment group (n=4) underwent

thesurgical preparationasdescribed above,andwasthenmonitored

Regional Hemodynamic Regulation Burn 147

J.Clin.Invest.

© The AmericanSocietyforClinicalInvestigation,Inc. 0021-9738/94/01/0147/08 $2.00

*

_

120

C

* *

P=-NSvs pro burn

U zu 4U bU (iuWt 1ZU

Timepostbum(minutes)

D

- 2.5 Unbumed limb

t

E 2

Is5E 5

0*- z 1 Bumed limb

EU

E 05

0 50 100

Time post burn(minutes)

150

Figure1.Effects ofhind paw scaldonregional and systemic hemo-dynamics.Thethreefold increase in femoral blood flow (A) and

de-creaseinfemoral vascular resistance (D)tothesite ofinjury occurs without blood flow alterations to unburned tissues, systemic mean arterial pressure (B), or systemic vascular resistance (C).

for 2hwithnofurther intervention.Remaininganimalswereexposed

toscaldinjury,immersion ofonehind paw (< 3% BSA) into 100°C waterfor 5 s, and hemodynamic parameters were monitored for 2 h thereafter. Since in scald only animals (controls,n=9), identical

in-creasesinhindlimb blood flow and decreases in hind limb vascular resistance occurred regardless of which paw (right [n= 5] orleft [n =_{4])wasinjured, they were combined into one group. In subsequent}

2

-groups ofdogs,oneof thefollowingagentswasintravenouslyinfused 20minbeforescalding, inadoseshowntoadequately block the respec-tiveagonist agent response: methysergide (0.1 mg/kg, n = 7), ritan-serin (0.1 mg/kg,n=5),atropine (1 mg/kg,n =4),ICI 118551 (1 mg/kg, n=4),BWA1433U83(7.5 mg/kg,n =6), sodium meclofen-amate(2.5mg/kg,n =4), diphenhydramine ( 1 mg/kg,n =5), raniti-dine (1 mg/kg,n =4);L-nitro-arginine methylester(L-NAME, 100 mg/kg, n=7),3-amino-1,2,4-triazine (3-ATINE,75mg/kg,n =3), or U37883A (2.5 mg/kg,n =4).

Tofurtherelucidate whatwasfoundtobeamethysergide-sensitive femoral vasoactive response in animalspretreatedwith that agent, ad-ditional protocols were carried out. In separate groups of animals, methysergidewasgivenno soonerthan30 min after scald: (a) by pe-ripheral intravenousinjection(0.1 mg/kg, n =4; 1.0mg/kg,n =3) and(b)by bolusinjection directlyinto the femoral arteryonthe side of injury (20

_gg/kg,

n=4).Inanother group (n=4)ofdogs, methyser-gide (20,g/kg)wasinfused into thecranial circulationvia one com-moncarotid arterybefore scalding. Finally,todetermine thespecificity of thefemoral vasoactive responsetomethysergide,random sequence intrafemoral arteryinjectionsof thefollowingvasoconstrictor and

va-sodilator agentswereperformedinagroup(n=5) of unburned dogs before and afterperipheral intravenous administration ofmethysergide (0.1 mg/kg): methoxamine(0.1 g/kg),nitroglycerin (0.003ag/kg), verapamil(0.001 tg/kg), serotonin (0.001 ,ug/kg), 5-carboxamido-tryptamine (CATM, 0.0001 ug/kg).

Statisticalanalysis.Data arepresentedas means(±1 SE). Compar-isons bothwithinagiven group and between groupsweremadeusing ANOVA. WheneverasignificantFratio was reached, Fisher's PSLD testwasappliedtodetectspecificdifferences.Significancewasaccepted when P<0.05.

Results

Immediately after thescalding,there was asignificantthreefold

increaseinfemoralartery blood flow to theinjuredhind limb

(Fig. IA),reaching peaklevels within 5min. Over the next 25

min,aslight decline in blood flowto aplateau phasewas

ob-served, though it remained significantly elevated throughout

the2-hobservation period. Since neither systemicMAP(Fig. 1

B) norsystemic vascular resistance(Fig. 1 C) weresignificantly alteredby thescald,the increaseinfemoral blood flow ipsilat-eral to the injury reflected a decrease in hind limb vascular resistance(Fig.1D).Finally, CI increased slightly but

insignifi-cantly upon scald injury (Fig. 2). Mean PAP, PCWP, and

pulmonary vascular resistance were unaltered by scalding (TableI).

Insomeanimals (datanotshown),anadditional ultrasonic

flowprobewasplacedaround theipsilateraldorsalispedis

ar-* P=NSvsprobum

0 20 40 60

Timepostbum(minutes)

Figure

2. Timecourse

depiction

of cardiac indexafter

80 10 120 scaldingdemonstratingnosignificant changeoverthe

periodofobservation. la-350

E 250

2 E 150

f% _

A _{+P< 0.005 Burn}^P< o.ooo1 p.burn lim v.unburnd limb

* _{+ Bumedlimb* +}

50n

50 20 40 60 80 100 120

Time post bum(minutes)

B *P-NvSvprobum

tE100

50

iLO

0 20 40

Time

a E80

uc 60

:3 40

E

20

co EE

n in Ail

60 80 100

post burn(minutes)

2.5

s... 1.5

c02

10.SI

1

0.5

---a

A an an Inn 12n

E ite

,1h

TableI. Characterization of PulmonaryHemodynamic ParameterAlterationsinResponseto Scalding

Afterburn After burn Time Beforeburn (5min) (60min)

CI(liter/minperm2) 2.2±0.3 2.5±0.2 2.3±0.2

PAP(mmHg) 13±0.5 14±0.6 14±0.6

PVR(mmHg/literpermin) 6.0±0.3 5.6±0.3 6.1±0.2

PCWP(mmHg) 10±0.3 11±0.5 11±0.5

Whencompared torespectivepreburn values, there were no signifi-cantchanges inmeanPAP,PCWP,orpulmonary vascular resistance

(PVR= PAP/CO).P= NSvspreburn.

tery,immediately proximaltotheproposedsite of scald. Base-line dorsalis pedis blood flows were approximately one fourth those of femoral blood flows. After scalding, dorsalis pedis blood flows increaseddramatically when compared to baseline levels, and remained elevated throughout the observation

pe-riod. In contrast to the injured side, the unburned hind limb

showed no significant changes in blood flow or in vascular resistance.

Femoral artery blood flow, systemic MAP, and CI were

monitored before scaldindogspretreated with methysergide.

Thisdose of methysergide was foundto block the increased

regional bloodflowinduced byintrafemoral arterial bolus in-jections of serotonin (10-100 ,ig/kg), which itselfproduced no

systemic hemodynamic effects.After femoral artery blood flow

returnedtobaseline, methysergide(0.1 mg/kg) was

adminis-tered by the peripheral intravenous route; no significant re-gional orsystemic hemodynamic alterationsoccurred (Table II). However, the subsequentintrafemoral bolus injection of serotonin resulted in significant (P < 0.002) blunting of the

hyperemicresponse to serotoninbefore methysergide(65±10

ml/min increasein bloodflow before methysergide; 10±3 ml/

min bloodflow increaseafter methysergide).

In these same methysergide-treated dogs, scalding still caused an immediate, significant increase in femoral blood

flow (Fig. 3 A) and a decrease inregional vascularresistance

(Fig. 3 B). However, when compared to burn alone dogs, the

regional hemodynamic alterationsweresignificantly blunted.

A .- 300

E

250 243 ±27

t _ 204 ± 28

i 200 191

X 150

0 ~~~~~09±14

3 100 70±9 66±9 56±9

50

Baseline 5 60 Time post burn(minutes)

2 1.5

iS_i.. =E a

05

Baseline 5 60 Timepostbum (minutes)

It31

59 14

L1

Figure

3.

_Comparison

120 of femoral artery blood flow(A) and resistance

(B) alterationsbetween

burn aloneanimals and

animalstreated with in-travenousmethysergide

(MET) before injury. Notethe blunting of the vasodilatory response

in MET-treated ani-mals, with a return to preburnlevels within - 60min of scald injury.

*P<0.0005vs MET

burn;#P<0.02vs MET

burn; +P

<0.04vs

120 MET burn. ,Burn only;o, MET/burn.

Moreover, within 30 min, femoral blood flow and vascular

resistancehad begun to return toward preinjury levels,

reach-ing baseline levels by 60 min. At all observation points, the valuesforeach represent significant differences from burn only dogs.

Todeterminewhether this agent could reverse the

vasodila-tor response toscald, dogs weregiven methysergide intrave-nously (0.1 mg/kg)30 minafter injury. Immediately thereaf-ter, femoral blood flow decreased (Fig.4A) and vascular resis-tanceincreased(Fig.4B),eachreaching preburnlevels within 30 min. Tenfoldhigherdoses ofmethysergide hadsimilar ef-fects(data not shown).

Todeterminetheselectivity of methysergidetoinhibit fem-oral vasodilatorresponsesmediatedby serotonergic receptors,

anadditional group ofexperimentswasperformed, and data

fromthesestudiesarepresentedin Table III. Femoral arterial bolusinjectionsof serotonin(0.001 tg/kg),CATM(a

seroto-Table I. Scald-induced

Hemodynamic

AlterationsinAnimals Pretreated with_{Methysergide (MET)}and Ritanserin(RIT)

Before Bum AfterBurn

Before MET After MET 5min 60min 120min

Burned hind limb flow(ml/min) 64±7 61±8 109±14* 66±9 59±14

Unburned hind limb flow(ml/min) 58±11 60±14 59±14 46±8 45±14

MAP(mmHg) 125±4 122±6 128±5 122±4 114±4

CI (liter/minper

M2)

1.5±0.2 1.5±0.2 1.65±0.2 1.66±0.2 1.43±0.6

Before RIT After RIT 5 min 60 min 120min

Burned hind limb flow(ml/min) 55±6.8 57±7.3 226±27* 199±16* 182±14*

Burned hind limb resistance(mmHg/mlpermin) 2.55 2.50 0.63 0.70 0.74

MAP(mmHg) 140±14 142±14 142±14 139±15 135±13

Exceptasnotedby*, scaldingproducedminimal alterations in

regional

bloodflow when animalswerepretreatedwithmethysergide. On the

contrary,pretreatmentwithritanserinproducednochangesinregional vasodilatoryresponsestoscalding. * P<0.0005vspreburn.

A c 250

.E E 200 ° 150

g100-m t- 50

E 2 O

P<0.015 vs post burn

+P=NSvs pre burn Methysergide

24 113+26

87+24

r

Preburn 30 31 35 60 Time postburn (minutes)

B 2.5

2 mcc- .51

0

E

1.5 0.5

Methysergide

Preburn 30 31 35 Time post burn(minutes)

60

Figure 4. Effects of intravenousMET,given30 min after theburn,on

femoral blood flow(A)and vascularresistance(B)contrasted with theburn alone group. Within 1 min of METinjection,therewasa

significantdecrease in the femoralvasodilatoryresponse(andan

in-creaseinregionalresistance),witha return topreburnvalues30 min later.

ninlA-likereceptoragonist,0.0001 ,ug/kg),nitroglycerin (a

di-rect activator of guanylate cyclase, 0.003

,ug/kg),

and

vera-pamil (a calcium channel

blocking

agent,0.001

,ug/kg)

all sig-nificantly increased femoral blood flow while methoxamine

(0.1 ,ug/kg)

significantly

reduced femoral blood flow. Since

none of theseagentsaltered

systemic

meanarterial pressure,

the increasesinfemoral blood flow

produced

by

theseagents

directly

reflect decreasesin hind limb vascular resistance. 5

minafterperipheral intravenous administration of

methyser-gide (0.1 mg/kg), the hind limb vasodilatorresponses to seroto-nin and CATM weresignificantlydecreased, whereas thehind

limb vasodilatorresponses tonitroglycerinandverapamilwere

notsignificantlyaltered, nor was thehind limb vasoconstrictor response to methoxamine. These data suggest that

methyser-gide selectively inhibited thehind limbvasodilator responses

mediatedby

_{serotonergic,}

receptors.

As methysergide readily crosses the blood brain barrier

(10),

serotoninergicreceptorswithinthecentral nervous sys-tem

(CNS)

could havemediated the scald-induced alterations

in regional hemodynamics. Therefore, the contribution of

CNSreceptors tothisresponse wasinvestigatedin dogsgiven

methysergide(20

_,ug/kg)

into one common carotid artery

be-fore

scalding.

This dosewasfoundto bethelargestintracarotid

TableIII. MeanChangesinFemoral Blood Flow afterIntravenousArterial BolusInfusion ofKnown Vasodilator andVasoconstrictorSubstances

before and after PeripheralIntravenousInfusion ofMET

Percent(± 1 SE) increase Percent(± 1 SE) increase Agent in femoral blood flow in MAP

Serotonin (n = 5)

Before MET 96±27 -1.0±1.0

After MET 7±1* 1.0±1.0

CATM (n =5)

Before MET 220±68 1.4±1.0

After MET 5±1* 0.0±0.0

Nitroglycerin (n = 5)

Before MET 252±81 -0.2±0.2

After MET 189±74 -0.8±1.3

Verapamil (n = 4)

Before MET 197±92 -1.1±0.8

After MET 139±45 -2.1±1.2

Methoxamine (n=4)

Before MET -37±9 -0.2±0.2

After MET -35±7 0.6±0.6

In theabsenceof alterations in systemic mean arterial pressure, methysergideselectively blocked the vasodilator response to serotonin andCATM, but had noeffecton thevasodilator response to nitro-glycerin orverapamil, or on the vasoconstrictor response to methox-amine. * P < 0.01 vs pre-MET.

dosethat did notalter the hind limb vasodilator response to femoral artery injectionof serotonin( 10-100

l

g/kg). Before scald, bolusintracarotidinjectionofmethysergidedid not sig-nificantly alter baseline systemic or regional hemodynamic measurements. Inthese samedogs,the characteristic femoral blood flow and vascular resistance responses to scald were not

altered bythecentrallyadministeredmethysergide (Table IV).

Incontrast, the same dose ofmethysergide given preburninto the femoral artery of other dogs inhibited the femoral vasodila-torresponsetoscald(Fig. 5).

To further characterize theserotoninergicreceptor subtype mediatingtheseregional vasodilatorresponses,ritanserin (0.1 mg/kg),aserotonin2receptor

antagonist

(11),wasgiven

intra-venouslyto dogsbefore scald. This dose blocked the

intrafe-moraladministration of the

serotonin2

receptor

agonist

(+)-

1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane

hydrochlo-ride (10

,tg/kg)

after intravenous ritanserin produced no

TableIV. Regional BloodFlowResponsetoPreburn Bolus InfusionofMETDirectlyintoOneCarotidArtery

Burnedhind limb

bloodflow MAP

ml/min mmHg

Baseline 100±18 155±9

Baseline/MET (central) 110±10 155±11

AfterBurn(5 min) 357+57* 175±18

AfterBurn(60 min) 260±21* 165±13

243±27

150

-100

50

-0

73±13 70±9

T Baseline 20,g/kgi.a.methysergide

227±24

I.

204±28

5 30

TimepostbumIminutes)

60

Figure 5. Alterations in femoral blood flow in animals pretreated with MET, injected into the femoralartery

ipsilateral

tothe hindpaw

scalding.

Comparedto

burn aloneanimals, MET administration resulted in

significant modulation of the femoral vasodilatory

response. .,MET/burn; u,burnonly.

effects on femoral blood flowor femoral vascular resistance.

Preburn ritanserin injection had no effecton systemic or

re-gionalhemodynamicmeasurementsatanyobservation point

(Table II).

Thecontribution of other vasodilatormechanismswas

in-vestigated by administering one of the following blocking

agents to groups of animals before scalding: atropine (muscarinic receptors), ICI 118551 ( 32-adrenoceptors), BW A 1433U83

(adenosineAl

receptors),meclofenamate

(cycloox-ygenase enzyme system), diphenhydramine

(histaminergic,

receptors), and ranitidine (histaminergic2 receptors). These

agentsweregiven in doses that blocked the femoral vasodilator responsestointrafemoralbolusinjections ofacetylcholine, iso-proterenol, adenosine, arachidonic acid, and histamine,

respec-tively (Table V). The antagonists did not alterbaseline

sys-temicMAP,CI,orhind limb blood flow,nordidthey alter the hemodynamicresponsetoscald (TableVI).

The contribution of endothelium-derived relaxing factor (EDRF)tothis vasodilatorresponse wasassessedby giving

L-NAME(100 mg/kg),aninhibitor of nitric oxidesynthaseIII

(12). In unburned animals, administrationofL-NAME before

TableV Mean Increases inRegionalBlood Flow afterIntrafemoral Infusion ofAgonistAgentsAlone, andIntrafemoral Infusion ofAgonistAgents

afterPeripheralIntravenousInjectionofBlockingAgents

Mean (±ISE) increase in

femoral blood Mean (±ISE)increase in flowafter femoral bloodflow after

Blocking agent/agonist agonist antagonist/agonist

BWA1433U83/adenosine 60±12 15.5±4*

Meclofenamate/arachidonic

Acid 115±18 23±6*

ICI118551/isoproterenol 49.7±6 11.8±3*

Atropine/acetylcholine 66±6 21±4*

Diphenhydramine/histamine 47±8 14.3±3*

Ranitidine/histamine 99±4 17±2*

Ineachinstance, effectivereceptor blockadedosagewasconfirmedby

theinabilityof eachagonisttoincrease bloodflow in thepresence

ofarespectivereceptorblockingagent. *P<0.05vsagonist.

the burn increased systemic arterial pressure and hind limb vascular resistance, and decreased hind limb blood flow to

steady state values during a 45-75 min observation period.

However, the femoral vasodilatorresponsetoscaldingwasnot

altered by L-NAME (Table VII). The inducible form of nitric oxidesynthase II(NOS II)wasevaluated by preburn

adminis-tration of 3-ATINE. The dose of 3-ATINE (75 mg/kg) has

beenshown inratmodelstoblock the release oftumornecrosis factorandN2 intermediates, andtoabolish the endotoxin-in-duceddecrease inmeanarterialpressure (13). 3-ATINE had noeffectonbaseline systemicorregional hemodynamicsor on regional blood flow after scald injury.

The contribution of

KATP

channels in mediating the

re-gional vasodilatory response to scald was assessed with U

37883A,aselectiveinhibitor of

KATP

channels ( 14). In doses thatselectively blocked the hind limb vasodilatorresponseto

cromakalim,an activator of

KATP

channels, this dose didnot

affectthevasodilatorresponsetoisoproterenolornitroglycerin

(data not shown). Given before the burn, U 37883A had

no effect on the hind limb vasodilator response to scald

(Table VII).

Discussion

Data from this study demonstrate that inthe absence of

sys-temicorpulmonary hemodynamic changes,asmall BSA burn

indogs results inamarked increaseinblood flowtothe site of injury concomitant with a decrease in vascular resistance. These resultsareconsistentwith studiesthatsuggest the vasodi-latorresponsetoasurfacewound isprimarily directedtothat wound,nottouninjured tissuesoradjacent "watershed"areas

(1,2, 15).

Thisstudywasdesignedtolimitthesize andmagnitudeof the burntotheextentthat therewere noappreciablealterations

in (a) systemic and pulmonary hemodynamicparameters and

(b) blood flow and vascular resistance toskin/soft tissue

re-motefrom the burnsite. Each of thesegoalswasmet

through-outtheexperiments reportedhereinbystandardizingthe scald:

(a) thepercent BSAinjurywasuniformly< 3%and(b)a

sec-onddegreeburn wasconsistentlyproduced, characterizedby

cutaneous hyperemia, skin blisters, and subcutaneous tissue

swelling. Thus,inlargemeasure,thedirectimpactofscaldon

regional hemodynamics was monitored. As such, data from

this studyare consistent with others that show a small BSA

RegionalHemodynamicRegulation afterBurn 151

250

-200

t

To 3: D

0

Table VI. Alterations in Regional and SystemicHemodynamic ResponsestoScaldInjuryin Animals Pretreated with Known Vasocative BlockingAgents

Agent Burned hind limb flow Unburned hind limb flow MAP CI

Atropine Baseline

Baseline+blocker After burn (5 min) After burn (60 min) ICI 118551

Baseline

Baseline+blocker After burn (5 min) After burn (60 min)

BWA1433U83 Baseline

Baseline+blocker After burn (5 min) After burn (60 min) Meclofenamate

Baseline

Baseline+blocker After burn (5 min) After burn (60 min) Diphenhydramine

Baseline

Baseline+blocker After burn (5 min) After burn (60 min) Ranitidine

Baseline

Baseline+blocker After burn (5 min) After burn (60 min) Controlburn

Baseline

After burn (5 min) After burn (60 min)

The burn alonegroupis shown for comparativepurposes. In eachgroup,the injected blockingagenthadnoeffectonthescald-induced regional vasodilatoryresponse. P=NSvscontrol burngroupateach time interval.

scald increases blood flow for tissues involved in the burn, but doesnotalter pulmonary, systemic, orregional hemody-namics(5).

Themarkedhind limb vasodilatorresponsetoscaldinjury

was significantly reduced by administering methysergide but

notritanserin before the burn, suggesting that serotonin1-like

receptorsplaya majorrole in mediating thisresponse. Since methysergide inhibited the hind limb vasodilatorresponseto

serotonin and CATM, butnot to nitroglycerin orverapamil, thepresentdatasuggestthat methysergide acted inaselective

manner to antagonize serotonergic,-like receptors. Although prostaglandins (7, 8) and 2-adrenoceptors (9) have been im-plicatedasmediators ofthe increaseinlocal blood flow, neither ICI 11855 1normeclofenamate altered the hind limb

vasodila-torresponsetoburn, suggesting that neither

_{#2-adrenoceptors}

norcyclooxygenase productsappeartomediatethis effect. Sim-ilarly, atropine, BW 1433U83, diphenhydramine, and raniti-dine had no effect on the scald-induced increase in femoral blood flow, suggesting that thisresponse is not mediated by muscarinic,

adenosineAl,

histaminergic,,

or

histaminergic2-re-ceptors.

Thevasorelaxantresponsetoserotonin inisolated conduit blood vesselshas beenshown torequireanintactendothelial

cell layerand todepend on formation of EDRF(16). Since

pretreatment with L-NAMEand 3-ATINE, respective

inhibi-torsof NOS III-formingEDRF(12, 13, 16-19)and NOS II

(20),didnotalter thevasodilatorresponsetoscald, these data suggest that NO formed from theconstitutive andinducible forms of NO synthasedoesnot mediate thiseffecttoa large

degree. ml/min 45±11 48± 12 178±12 146±19 44±11 46±10 200±17 151±23 59±4 54±9 192±33 160±22 36±9.6 37.5±11 153±16 121±14 81±26 85±35 242±68 205±30 75±2 86±3 279± 14 266±15 70±9 243±27 217±28 mil/min 44±12 45±12 41±6 36±6 43±8 41±8 39±3 37±7 N/A N/A N/A N/A 39±7 38±6 48±9 28±6 88±31 81±28 114±58 61±7 N/A N/A N/A N/A 65±9 77±17 53±12 mmHg 115±6 116±7 113±8 117±5 115±7 114±5 111±7 117±5 115±1 116±2 123±4 122±3 124±7 120±7 129±8 126±8 150±14 157±12 180±10 165±11 123±11 114±9 119±5 117±6 114±6 114±6 117±6

liter/minperm2

TableVII. RoleofEDRFand KATPChannels, Respectively, inMediating AlterationsintheRegional Vasodilatory Response toScalding

Burned hind limb

Agent blood flow MAP

ml/min mmHg

L-NAME

Baseline 95±8 117±7

Baseline+L-NAME(before burn) 38±5* 154±12

After burn (5min) 179±19* 159±12

Afterburn(60 min) 116±18* 152±10

3-ATINE

Baseline 94±30 145±16

Baseline +3-ATINE(beforeburn) 100±37 150±14

Afterburn(5min) 321±59t 165±13

After burn (60 min) 298±43* 145±10

U37883A

Baseline 69±8 122±10

Baseline+cromakalim 213±16*$ 130±11

Baseline+cromakalim+

U37883A(beforeburn) 93±5 115±5

Afterburn(5min) 192±15t 137±7

Afterburn(60 min) 176±16t 112±9

Of the blocking agents tested,nonealteredscald-inducedregional

va-sodilatory responsetoinjury. * P<0.02vsbaseline. *P<0.02vs

pre-burn.

Recently,

KATP

channels have been identified in skeletal muscle andarterialsmooth muscle ( 14). The possibility that

this vasodilator response may be mediated by activation of

these channels is unlikely, since U 37883A, an inhibitor of

KATP

channels, hadnoeffectonthehind limb vasodilator

re-sponse toburninjury.

Since methysergidecrossesthe bloodbrain barrier( I I ), the

hypothesis that serotonin receptors within the CNS mediate

thefemoral vasodilatorresponse toscaldwastested. Intracaro-tid arterial

injection

of

methysergide

didnotalter thehind limb vasodilatorresponse to scald or tofemoralartery injection of

serotonin. Incontrast, the samemethysergide dosegiven

di-rectly into the femoral vascular bed inhibited the hind limb

vasodilatorresponse to scald and tofemoralarteryinjection of serotonin.These data suggest that

serotonin1-like

receptors ac-tivated locally,notcentrally, mediatethehind limb vasodilator response toscald.

Since pretreatmentwith methysergide prevented the hind

limb vasodilator response to scald, serotoninergic receptors

contribute in large measure tothis effect. Moreover, this

re-sponse toscaldwas

rapidly

reversedby administration of meth-ysergide aftertheburn. These data suggest thatpersistent

acti-vationof

serotonin,-like

receptorsmediatestheprolonged

in-creasein hind limbbloodflow afterscald.Although mediation of thisresponse may be

species

dependent,the presentstudy is unique by

providing

evidencethata

specific

vasodilator mecha-nism,

serotonin,-like

receptors, isdirectly responsible forthe

sustained vasodilator response to localthermal

injury.

Since

methysergide given eitherinto thefemoralartery(20

,ug/kg)

or intravenously ( 100

_igg/kg)

produced

rapid

inhibition of

other-wise augmented femoral blood

flow,

the local

hemodynamic

response to asmall scaldappearsreversible.

However,

an

early

(5 min after

burn)

component of the response is

methysergide

insensitive, and the mediation of this effect remains unknown.

Amarkedcontinuous increaseinserotoninrelease into the

systemic

circulationdoesnotappeartomediatethecontinuous activation of

_{serotoninl-like}

receptors,sinceinfusionsof

seroto-nin

directly

intothefemoral vascular

bed,

in doses necessaryto

produce femoral blood flow increases similar to those after

scald,caused marked

changes

in

systemic

hemodynamics.

This

effectwas notobservedwith the small BSA scald used herein.

Furthermore,plateletcountsremained

unchanged throughout

the

experiments,

suggesting

thatserotonin releasefrom

platelet

destruction or

aggregation

cannot accountfor the

persistent

activation of serotonin1-likereceptorsin the hind limb vascular bed after scald.

Locally released

serotonin,

viaanalterationinits local

re-movalorvia increased

sensitivity

of

serotonin1-like

receptors, may be

responsible

forthehindlimbvasodilatorresponse to

scald. Others have demonstrated that in a

septic

hind limb

model, effluent fromtheinfected leg dilated other

regional

vas-cular beds

(21). However,

Aulick et al. have

suggested

that

noninfectious forms of limited tissue

injury

donotrelease

sig-nificant

quantities

ofvasodilator substances

(

3

). Thus,

the pres-ent data are in agreement with the conceptthat the type of

pathological

insult

inducing

local vasodilationmaydetermine theextent towhichothervascular bedsare

subject

to

hemody-namic alterations. In this

regard,

the small BSA burn

injury

used in this

study

could have

explained

the

inability

ofthe

injury

toinducea

humorally

mediatedresponse inother vascu-larbeds.

In

conclusion,

a small BSA burn to the hind

leg

in

dogs

produces

marked,

selective,

and

prolonged

hindlimb

vasodila-tion. Thisvasodilatorresponseis

predominantly

mediated

by

continuous activation oflocal

_{serotoninl-like}

receptors, and

doesnot

depend

in

_large

measure on a

variety

ofotherdiverse

vasodilatormechanisms.

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