Is There a Serotonin-Induced Hypertensive Coronary Chemoreflex in the Nonhuman Primate?

Transcription

1 312 Is There a Sertnin-Induced Hypertensive Crnary Chemreflex in the Nnhuman Primate? Kurtis G. Crnish and Irving H. Zucker Frm (he Department f Physilgy and Biphysics, University f Nebraska Cllege f Medicine, Omaha, Nebraska SUMMARY. The purpse f this study was t investigate the nature f the sertnin-induced crnary chemreflex in the cnscius mnkey. Ten chrnically prepared and fur acute mnkeys were used in this study. Five chrnically prepared animals had catheters in the left atrium, ascending arta, descending arta, and, bilaterally, in the cmmn cartid arteries. In additin, Silastic catheters were placed next t bth vagi t permit vagal blck with 2% lidcaine. Sertnin was injected (12- /ig/kg) int the left atrium, ascending arta, descending arta, r, bilaterally, int the cartid arteries while bld pressure, heart rate, and respiratry mvements were recrded. Injectins f sertnin were assciated with hypertensin and bradycardia fllwed by tachycardia, all f which were preceded by a cugh respnse. Atrpine blcked the bradycardia, whereas atrpine and phentlamine eliminated the cardivascular cmpnents f the reflex. Vagal blckade eliminated the bradycardia but therwise did nt alter the respnse t left atrial sertnin. Three mnkeys were prepared with artic and left atrial catheters. Subsequently, they were subjected t sinartic deafferentatin. Sertnin injected int these animals did nt alter bld pressure r respiratin. The results f this study shw that sertnin injected int the left atrium f the cnscius mnkey prduces respiratry and cardivascular alteratins by its effect n artic and cartid chemreceptrs, and that there is n crnary chemreflex in the cnscius mnkey. (Circ Res 52: , 1983) In recent years, there have been several studies prducing descriptins f a hypertensive crnary chemreflex in the dg. Eckstein et al. (1971,1977) fund that the injectin f certain chemicals int specific crnary arterial branches caused a rapid increase in bld pressure. Thrugh careful investigatin, they were able t shw that sertnin injected int a branch f the prximal left crnary artery caused the mst prfund respnse. Histlgical examinatins identified the specific tissue perfused as a "glmus" type similar t that f the cartid and artic bdies. James et al. (1976) therized that this reflex is invlved in maintaining the patency f the crnary arteries by respnding t sertnin released frm thrmbi which frm in the prximal crnary artery. Mre recently, Urthaler et al. (198) have, by injecting sertnin int the left atrium f anesthetized dgs, examined this reflex and its cmpnent parts, thereby demnstrating a differential effect n flw t the renal, iliac, mesenteric, crnary, and cartid vascular beds. In a study frm ur labratry (Zucker and Crnish, 198), we were unable t shw a cnsistent hypertensin evked by the injectin f sertnin int the left atrium f the cnscius dg. Indeed, the bserved respnse was predminantly hyptensive in nature, invlving prfund vagal bradycardia and a dynamic stimulatin f ventilatry rate and depth. In rder t determine the nature f the crnary chemreflex in the primate, we undertk the present study in the cnscius mnkey. Methds Our study invlved the use f eight chrnically prepared mnkeys and fur acutely prepared mnkeys (five Rhesus, five stumptails, and tw fascicularis). After the chrnic mnkeys had been cnditined fr 1-2 weeks t sit quietly in a primate restraint chair, they were anesthetized with sdium pentbarbital (15 mg/kg iv) and prepared fr sterile surgery. The chest was pened at the 5th intercstal space, and Silastic catheters were placed in the ascending arta, descending arta, and the left atrium. Previus studies in the dg (Zucker and Crnish, 198; James et al., 1975) had shwn that injectin f sertnin int the left atrium r the prximal segment f the left crnary artery caused the reflex, whereas injectins int the ascending arta, descending arta, r cartid arteries prduced n effect. The descending artic catheter was used primarily fr recrding artic pressure and heart rate; the ther catheters were used fr drug injectins. The chest then was clsed and evacuated, and the mnkeys were returned t their cages. Mnkey jackets (Alice King Chatam) were used t prtect the catheters while the animals were in their cages. The mnkeys were given penicillin and streptmycin fr the 7- t 1-day recvery perid. A secnd surgery then was perfrmed and Silastic catheters were placed bilaterally int the cmmn cartid arteries. Specially prepared Silastic catheters were als placed alngside the vagi. These cntained a Silastic cuff which served t enclse the vagus nerve and the Silastic catheter. This permitted the infusin f.5 ml 2% lidcaine arund the vagus nerve t prduce vagal blck. The effectiveness f the lidcaine blck was determined by injecting veratridine int the left atrium, which prduces a vagally mediated Bezld-Jarisch reflex (Krayer and Meilman, 1977). Failure t bserve the Bezld-

2 Crnish and Zucker/The Primate Crnary Chemreflex 313 Duncan's new multiple range test. Since the statistical analysis was perfrmed n the nrmalized data, i.e., percent f cntrl, there were nly minimal effects f the animal's variatin. A P value f less than.5 was cnsidered significant. The data are expressed as the mean ± SEM. Jarisch reflex after lidcaine wuld indicate the presence f afferent vagal blck. All measured parameters were recrded n an eight-channel Sanbrn recrder. Bld pressure was recrded with a Millar pressure transducer. A pneumgraph and a Millar transducer were used t recrd respiratin. Heart rate was btained by using the bld pressure pulse t trigger a Guld carditach. In three animals, the artic arch, and 1 t 2 cm f the brachicephalic and subclavian arteries were stripped f their adventitia. Extreme care was taken nt t damage the vagus, cardiac sympathetics, phrenic, r ther majr nerves in the area. In a later surgery, the cartid sinuses and assciated vessels were stripped. Sinartic deafferentatin was cnfirmed by recrding heart rate while decreasing bld pressure with hemrrhage r nitrprusside. When bld pressure was decreased frm 131 ± 2 t 55 ± 9 mm Hg, heart rate increased frm 176 ± 16 t 177 ± 15. In the initial experiments, atrpine (.1 mg/kg) and phentlamine (2 mg/kg) were given t determine the cmpnents f the reflex. Acetychline (5 pg int the left atrium) and phenylephrine (2 fig) were used t determine the effectiveness f the autnmic blckade. Sertnin was injected int the left atrium, ascending arta, bilateral cartid arteries, and the descending arta in dses f 12- /tg/ml. The dses were varied t determine whether there was a difference in the threshld t sertnin when injected int the different sites. Since thse injectins previusly used in dgs (Zucker and Crnish, 198) emplyed - fig/1-2 ml, we felt that 5- jug/1 ml wuld be mst cmparable. The injectins f sertnin were made at 5minute intervals t avid tachyphylaxis and t allw time fr all variables t return t cntrl. Injectins f nictine (.8 jug/kg) int the left atrium, ascending arta, and, bilaterally, int the cartid arteries were als used t determine the similarity f the sertnin respnse t an agent which is knwn t stimulate primarily chemreceptrs (Zimpfer et al., 1981). The data were analyzed by means f a randmized blck fr analysis f cvariance. This analysis takes int cnsideratin the variatin fr errr and the variatin amng animals. The F rati fr treatment was determined as the Fireatmem/errr where the errr term tk int cnsideratin the treatment effect, the animal effect, and the errr effect. When the F rati indicated that there was a significant effect due t treatments, multiple cmparisns were dne using Results Typical respnses t sertnin injectins f 5 jug, bserved in cnscius mnkeys, are shwn in Figure 1. Sertnin injected int the left atrium f the mnkeys caused initial cughing, which was assciated with a cncmitant shrt bradycardia, fllwed by mderate tachycardia and an increase in bld pressure. This respnse was als bserved t a lesser degree when sertnin was injected int the ascending arta, bilaterally int the cmmn cartid arteries, r int the descending arta. Reducing the amunt f sertnin injected did nt result in a respnse which culd be islated nly t the left atrium and, thus, the crnary circulatin. The mean data fr the five cnscius mnkeys are presented in Figure 2. There was a significant difference in the bld pressure respnses t ascending artic, bilateral cartid, and descending artic injectins, cmpared t left atrial injectins, with n detectable difference in the latency f respnse. Bilateral cartid injectins caused a greater bradycardia, while there was less bradycardia with descending artic injectins when cmpared t the left atrial respnse. There were n significant differences in the bserved tachycardia. Figure 3 shws the respnses t left atrial sertnin alne, with atrpine, and with atrpine and phentlamine. The bradycardia bserved with left atrial injectins was cmpletely eliminated by atrpine, whereas atrpine ptentiated the tachycardia and the increase in bld pressure. Bth the hypertensive and tachycardic respnses were significantly attenuated by the cmbined treatment f atrpine and phentlamine; hwever, the respiratry respnse was nt altered. The infusin f lidcaine bilaterally arund the vagi attenuated the bld pressure respnse t 1O battanin RESPIRATION (irnptratinj) LA Ser AA Ser SW IDA s«r FIGURE 1. Bld pressure, heart rate, and respiratry respnses in the cnscius mnkey resulting frm the injectin f sertnin int the left atrium (LA Ser), ascending arta (AA Ser), bilateral cartids (BC Ser;, and the descending arta (DA Ser).

3 Circulatin Research/Vb/. 52, N. 3, March SEROTONIN LA AA BC DA ii. IT 8 BRAOYCARDIA TACHYCARDIA ESS 6 197* 1.6 bets/min H3»2.5mmHg FIGURE 2. Data btained in cnscius mnkeys, resvlting frm the injectin f sertnin int the left atrium (LA), ascending arta (AA), bilateral cartids (BC), and the descending arta (DA) (32 experiments, 5 mnkeys). *P <.5; ** P <.1. left atrial sertnin but did nt eliminate it. Vagal blck substantially reduced and, in many instances, cmpletely eliminated the bradycardia resulting frm sertnin injectins, while, at the same time, it increased cntrl heart rate (197 ± 1.6 t 28 ± 5) and bld pressure (113 ± 2.5 t 121 ± 8). Hwever, vagal blck did nt alter the respiratry cmpnent. When sertnin was injected int the left atrium f the mnkeys whse artic arch and cartid sinus areas had been stripped f adventitia, it failed t stimulate respiratin, elicit a bradycardia, r cause the typical abrupt increase in bld pressure. Hwever, they did cntinue t shw a delayed increase in bld pressure and an increase in heart rate. The increase in pressure prbably was due t the sertnin-induced release f adrenal catechlamines as well as the direct vascnstrictr effect f sertnin. T dcument the denervatin prcedure, nitrprusside was injected t lwer bld pressure. The absence f a tachycardia (panel A, Fig. 4) indicated barreceptr denervatin. Figure 4 shws the respnse bserved in tw sinartic denervated (SAD) mnkeys t left atrial sertnin. Figure 5 shws the mean data fr these interventins. T determine the cmpetency f the vagal pathways, we first injected veratridine int the ascending arta. Withut waiting fr any tachyphylaxic effects t wear ff, we made a secnd injectin int the left atrium. Since the artic injectins did nt induce a Bezld-Jarisch reflex, we cncluded that the artic catheters were placed far enugh away frm the crnary rifice t prevent drug injectins frm reaching the crnary circulatin. The secnd veratridine injectin caused a prnunced Bezld-Jarisch reflex. If the first injectin had reached the crnary circulatin, the animal prbably wuld have been tachyphylactic t the secnd injectin (Zucker and Crnish, 1981). After we had waited fr pssible tachyphylaxis t wear ff, vagal blck was prduced, and veratridine was again injected int the left atrium. In each instance, the Bezld-Jarisch reflex was cmpletely eliminated by the vagal blck. When veratridine was injected int the left atrium f the SAD animals, they displayed a bradycardia and hyptensin typical f the Bezld-Jarisch reflex, indicating that bth the afferent and efferent vagus are intact. These data are presented in Figure 6. Figure 7 demnstrates the effect f vagal blck upn the respnses t sertnin and veratridine. After blckade, there were n differences in the respnses t left atrial r bilateral cartid injectins f sertnin. When sertnin was injected int the left atrium :;; i; 1l.:] f:: j ~ 11 T mm "ft "I RESPIRATION (inspiratin f ) 4 LA Ser ALA Ser T P At i LA Ser At* Phe FIGURE 3. Effects f atrpine and phentlamme n the hemdynamic and respiratry respnses elicited by injecting sertnin int the left atrium f the cnscius mnkey. Left atrium sertnin after atrpine (LA Ser p At); left atrium sertnin after atrpine and phentlamine (LA SerpAt + Phe).

4 Crnish and Zucker/The Primate Crnary Chemreflex 315 RESPIRATION (INSPIRATION +) IMDHQ MEAN tmqtt/min r A B C FIGURE 4. Effect f injecting nitrprusside int the left atrium f a chrnically sinartic denervated mnkey (panel A). Panel B shws the effect f sertnin injected int the left atrium f the same mnkey, whereas panel C is the respnse t sertnin in a secnd sinartic denervated mnkey. Injectins were made at the vertical bar in each panel. and ascending arta f the pentbarbital anesthetized, pen-chest animal, a significant pressr respnse was nted. The pressr respnses were nt significantly different frm each ther when left atrial injectins were cmpared t ascending artic injectins. In additin, the hypertensin evked by left atrial sertnin in the anesthetized mnkey was nt significantly LEFT ATRIA SEROTONIN AFTER AFTER AFTER AFTER ATROPINE ATROPINE VA6AL SAD AND BLOCK PHENT different frm that bserved in cnscius mnkeys (Fig. 8). Figure 9 shws a recrd f the effects f.8 jug/kg f nictine int the left atrium, ascending arta, and O ir VERATRIDINE ASCENDING LEFT AFTER AORTA ATRIUM VAGAL 16,. BLOCK s 6 AFTER SAD 197* *25 ri(- IDC C flifi /ilit-ai 27*5 112*15 226*1 79*4 28*5 121*8 187*2.6 87*17 nmic blckade with atrpine, r atrpine and phentiamine, after vagaj b/ck with lidcaine (1 experiments, 5 mnkeys; r after chrnic sinartic denervatin (6 experiments, 3 mnkeys^. The cntrf values are presented fr cmparative purpses ' P <.5; ** P <.1. 4OL 22*4 121*8 22*3 12*5 23*4 126*7 * 3 134*19 FIGURE 6. Data btained frm injecting veratridine int the left atrium f the cnscius mnkey befre and after vagal blck (2 experiments, 5 mnkeys) and in the cnscius, sinartic denervated mnkey (6 experiments, 3 mnkeysj. The data fr veratridine delivered int the ascending arta are presented fr cmparisn.

5 316 Circulatin Research/Vi. 52, N. 3, March bets/min f LA Ser A A Ser BILATERAL + BC Ser LA Vtr VAGAL BLOCK WITH LIDOCAINE ' «1 sec mmhg beats/min f LA Ver IBCS«FIGURE 7. Effect f lidcaine-induced vagal blck n the respnses t injectins f sertnin (Ser,) and veratridine (Ver), in the cnscius mnkey. cartid arteries in the cnscius mnkey. The respnses were very similar t thse btained with sertnin (Fig. 1). The animals displayed a rapid increase in respiratry rate and depth, bradycardia, and hypertensin. The respnses were similar when injectins were made in the left atrium, ascending arta, r, bilaterally, int the cartids; hwever, the respnse was mst prnunced with bilateral cartid injectins. The mean data fr the mnkeys that received nictine are shwn in Figure 1. Discussin The effect f sertnin n receptrs lcated in the prximal prtin f the crnary circulatin has been reprted t increase bld pressure in the anesthetized dg r t decrease bld pressure in the cnscius dg (Zucker and Crnish, 198). The heart rate respnse in bth cnditins is predminantly a bradycardia. This reflex is als clsely assciated with a prnunced stimulatin f respiratin. Injectins f sertnin int the ascending arta, cartid arteries, r the descending arta d nt elicit this reflex in the dg (James et al., 1975; Zucker and Crnish, 198). Hwever, Urthaler et al. (1978) have shwn that sertnin des have a direct effect n the adrenal medulla t release catechlamines, which accunts fr the delayed pressure respnse that is seen in the dg. When sertnin is injected int the left atrium f the cnscius mnkey, the respnse is nt dissimilar t that seen in the anesthetized dg. There is an initial bradycardia, fllwed by a tachycardia, bth f which are assciated with a substantial increase in bld pressure. There is als a respiratry cmpnent which is a cugh, rather than the "gasp" heard in the dg. Hwever, there the similarities between the tw species end. Sertnin injected int the ascending arta and the cartid arteries prduces essentially the same respnse as that bserved with left atrial injectins. The afferent pathway in the dg has been reprted t be predminantly in the vagus nerve (James et al., 1979); hwever, bilateral vagtmy in the anesthetized dg des nt cmpletely eliminate it (Zucker and Crnish, 198). We therefre cncluded that part f the afferent pathways was utside the vagi, perhaps in cardiac sympathetic nerves. When the vagi f the mnkey were infiltrated with lidcaine, the veratridine-induced bradycardia and hyptensin was cmpletely eliminated. Lidcaine arund the vagi als eliminated the bradycardia induced by sertnin injectins, indicating an effective efferent blck. In spite f this vagal blck, the injectin f sertnin int the left atrium f the mnkey still prduced a substantial increase in bld pressure (Fig. 5). If sertnin is stimulating specific cardiac receptrs, they either have an afferent pathway ther than the vagus nerve, r they have afferent pathways in additin t the vagus. Whereas vagal lidcaine eliminates the vagal efferent cmpnent, it has little effect n the majr cmpnents f the reflex, thus differing significantly frm

6 Crnish and Zucker/The Primate Crnary Chemreflex ^ SEROTONIN CONSCIOUS LEFT ATRIUM PENTOBARBITAL LEFT ASCENDING ATRIUM AORTA 16^ NICOTINE INJECTIONS ASCENDING LEFT BILATERAL AORTA ATRIUM CAROTIDS 14 NS O r t- 8 6 O r u_ 8? 6. 4 L 4 197* *6 147*6 113*2.5 96*4 96*4 FIGURE 8. Data btained by injecting sertnin int the (eft atrium and ascending arta f pen-chest anesthetized mnkey. The cntri data btained in the cnscius mnkey are presented fr cmparisn. that hypertensive crnary chemreflex initially reprted fr the dg (James et al., 1979). When sertnin was given int the left atrium f the anesthetized mnkey, the respnse was nt different frm that btained by injectins int the ascending arta (Fig. 8). Except fr the lack f evked bradycardia, the respnse bserved in the anesthetized mnkey was essentially the same as that seen in the cnscius mnkey. These data are als signifi- 24* *2.6 FIGURE 1. Respnses t nictine injected int the ascending arta, left atrium, and bilateral cartids. Open bars are the bradycardia; shaded bars represent the bserved change in b/d pressure (*P <.5; ** P <.1). cantly different frm thse reprted in the dg (Zucker and Crnish, 198), since the respnse bserved in the cnscius dg is characterized by prnunced bradycardia and either a hyptensin r mild hypertensin, whereas the anesthetized dg respnds t sertnin injectins with a prnunced hypertensin. beats/min LA Nic AA Nic BC Nic FIGURE 9. Respnse btained by injecting nictine int the left atrium (La Nicj, ascending arta (AA Nic), and bilateral cartids (BC Nic) f the cnscius mnkey.

7 318 Circulatin Research/Vi. 52, N. 3, March 1983 The respnse t sertnin injectins appeared t be similar t that elicited by stimulatin f chemreceptive tissue. Fr this reasn, nictine was given s that the sertnin respnse culd be cmpared t the respnse btained by chemreceptr stimulatin. Even thugh the magnitudes were different fr the varius injectin sites, the respnses t the tw substances were essentially the same. When the chemreceptrs f the artic arch and cartid bdies were denervated, left atrial sertnin failed t elicit either a stimulatin f respiratin r an increase in bld pressure (Fig. 4), even thugh vagal pathways were intact. Frm these data, we wuld cnclude that sertnin is stimulating chemreceptr tissue which is primarily assciated with respiratry cntrl. These data d nt supprt the existence in the nnhuman primate f a receptr in the crnary circulatin which is specifically stimulated by sertnin. KG. Crnish was supprted by Nebraska Heart Assciatin Crant-in-Aid. l.h. Zucker was a recipient f an Established Investigatrship award frm the American Heart Assciatin. Address fr reprints: Dr. Kurtis C. Crnish, Department f Physilgy and Biphysics, University f Nebraska Medical Center, 42nd Street and Dewey Avenue, Omaha, Nebraska Received March 12, 1982; accepted fr publicatin December 3, References Eckstein RW, Shintani F, Rwen HE Jr, Shinmura K, Ohya N (1971) Identificatin f left crnary bld supply f artic bdies in anesthetized dgs. J Appl Physil 39: Eckstein RW (1977) The artic bdies supplied by crnary arteries in the dg. Circ Res 41: 46-5 James TN, Isbe JH, Urthaler F (1975) Analysis f cmpnents in a cardigenic hyptensive chemreflex. Circulatin 52: James TN, Urthaler F, Hageman GR (1976) Chemreceptrs f the heart. Trans Am Clin Climatl Assc 88: James TN, Hageman GR, Urthaler F (1979) Anatmic and physilgic cnsideratins f a cardigenic hypertensive chemreflex. Am J Cardil 44: Krayer O, Meilman E (1977) Veratrum alkalids with antihypertensive activity. In Handbk f Experimental Pharmaclgy. New Yrk, Springer-Verlag, pp Urthaler F, Hageman GR, James TN (1978) Hemdynamic cmpnents f a cardigenic hypertensive chemreflex in dgs. Circ Res 42: Urthaler F, James TN, Hageman GR (198) Reginal flw patterns during the sertnin-induced cardigenic hypertensive chemreflex. Cardivas Res 14: Zimpfer M, Sit SP, Vatner SF (1981) Effects f anesthesia n the canine cartid chemreceptr reflex. Circ Res 48: 4-46 Zucker IH, Crnish KG (198) Reflex cardivascular and respiratry effects f sertnin in the cnscius and anesthetized dgs. Circ Res 47: INDEX TERMS: Sertnin Chemreflex Hyptensin Crnary circulatin