THE CARDIOVASCULAR ACTIONS OF MU AND KAPPA OPIOID AGONISTS IN VIVO AND IN VITRO. By Abimbola T. Omoniyi, BSc (Hons) A thesis submitted in accordance with the requirements of the University of Surrey for the Degree of Doctor of Philosophy. Department of Pharmacology, September 1998. Cornell University Medical College, New York, NY 10021, ProQuest Number: 27733163 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 27733163 Published by ProQuest LLC (2019). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106 - 1346 ACKNOWLEDGEMENTS I would like to thank God through whom all things are made possible. Many thanks to Dr. Hazel Szeto for funding this thesis. Heartfelt gratitude to Dr. Dunli Wu for his support, encouragement and for keeping me sane. I thoroughly enjoyed the funny stories, the relentless Viagra jokes and endless tales of the Chinese revolution! Thanks to Dr. Yi Soong for all her support and generous assistance and all that food! Thanks to Dr. Ian Kitchen and Dr. Susanna Hourani for making this a successful collaborative degree. Thanks to my family for all their support and belief in me. To my network of support: Misan, Guy, Hesh, Yasmin, Arti, Vicky, Akin, Hicham, Emma and the rest of the wonderful people I am so fortunate to call friends; THANK YOU. You couldh \ possibly imagine how much of a contribution you made. Dedicated €o my parents, James and Do tun Omoniyi; 'pen ÿiaùtÿ me mtf Mttqe. iii PUBLICATIONS Publications listed below arise wholly or partly from the work described in this thesis ■ Omoniyi AT, Wu DL, Soong Y, Szeto HH. Baroreflex-mediated bradycardia is blunted by intravenous mu- but not kappa-opioid agonists. J Cardiovascular Pharmacol, 31:954-959. 1998. ■ Kett A, Omoniyi AT, Kim H, et al. Baroreflex-mediated bradycardia but not tachycardia is blunted by intravenous mu-opioid agonists in chronically-instrumented pregnant sheep. Am JObstet & Gynecol, 178:950-955, 1998. ■ Clapp JF, Kett A, Olariu N, Kim H, Omoniyi AT, Wu D and Soong Y Cardiovascular and metabolic responses to two receptor-selective opioid agonists in pregnant sheep. Am J Obstet & Gynecol, 178:397-401, 1998. ■ Omoniyi AT, Kett A, Wu D, Soong Y, Clapp JF and Szeto HH. A peripheral site of action for the attenuation of baroreflex-mediated bradycardia by intravenous mu-opioid agonists. J Cardiovascular Pharmacol. 1998. Xn » ■ Szeto HH, Soong Y, Wu DL, Omoniyi AT, Olariu N, Hyungjin K, and Clapp JF. Effect of pregnancy on cardiovascular actions of intravenously administered mu, delta and kappa- opioid agonists. AnesthAnalg, under revision, 1998. ■ Omoniyi AT, Wu DL, Soong Y, Holsey Y and Szeto HH. Development of rapid tolerance to p- opioid agonists in vivo and in vitro. Submitted to Eur. J. of Pharmacology. 1998. ■ Omoniyi AT, Wu DL, Soong Y, Holsey Y, Clapp JF and Szeto HH. The inotropic effects of selective p- opioid agonists is determined by the pre-existing condition of the heart. Submitted to J Pharmacol Exp Ther.1998. ■ Holsey Y, Wu DL, Soong Y, Omoniyi AT and Szeto HH. Differential cardiovascular effects of a mu selective agonist in maternal and fetal sheep. Submitted to Amer J Obstet Gynecol. 1998. ■ Omoniyi AT, Wu DL, Soong Y, Pastuszak A, Holsey Y and Szeto HH. Pre-ischemic and post-reperiusion effects of two selective p- opioid agonists in the isolated guinea pig heart. Manuscript in progress. iv ABBREVIATIONS U50,488H trans-3,4-dichloro-N-[2-( 1 -prrrolidinyl)cyclohexyl] benzene acetamide DAMGO [D-Ala2,7V-Me-Phe4, Gly 5-ol] enkephalin DPDPE [D-Pen 2,D-Pen5]-enkephalin DALDA Tyr-D-Arg-Phe-Lys Intravenous i.v. Intracerebroventricular i.c.v. Nucleus of the Tractus Solitarius NTS Central Nervous System CNS Sodium Nitroprusside SNP Naloxone Methiodide NM v ABSTRACT The effects of two selective fi- opioid agonistsDAMGO and DALDA, and a selective k- opioid agonist U50,488H on blood pressure and heart rate have been compared in the chronically instrumented and awake sheèp. Differences in the heart rate response to p- and K-opioid agonists in vivo w^edemonstrated. The mechanism behind the heart rate response to all three opioid agonists was investigated by studying the effects of p- and K-agonists on baroreflex sensitivity and the involvement of sympathetic activity in the heart rate response to K-opioid agonists. The site and mechanism of action involved in the effects ofDAMGO and DALDA on the baroreflex were further investigated in vivo. The opioid receptor agonists involved in these studies are undergoing development as obstetrical analgesics for clinical use hence the influence of pregnancy on the effects of p- and K-opioid agonists on blood pressure, heart rate and baroreflex sensitivity were investigated. The mechanism responsible for the blood pressure effects of p-opioid agonists observed in vivo was investigated in vitro using the isolated and perfused guinea pig heart. The effects of DAMGO and DALDA on inotropy, chronotropy and coronary flow has been demonstrated in the spontaneously beating heart. Differences in the inotropic response to DAMGO and DALDA in the absence of their chronotropic influence was demonstrated in electrically paced hearts. Inotropic responses to DAMGO and DALDA have been shown to be influenced by the contractile condition of the heart. The potential therapeutic efficacy of p-opioid agonists has been investigated by studying the development of tolerance to their cardiovascular effects in vivo and in vitro. DAMGO and DALDA have been shown to induce rapid tolerance to blood pressure responses and inotropic responses in vivo and in vitro respectively. Differences in the relative potencies of DAMGO and DALDA was confirmed in all studies. SUMMARY 1. The history of the opioid receptor system is reviewed. The classification and distribution of opioid receptors, receptor subtypes, their endogenous ligands and the developm ent o f highly selective agonists and antagonists is discussed w ith reference to the cloning o f opioid receptors and then transduction mechanisms. A discussion o f the regulation o f the cardiovascular system including that o f blood pressure, heart rate and the baroreflex is presented w ith consideration o f the influence o f pregnancy on the system. The literature on the effects o f opioids on cardiovascular regulation is r e v i e w e d . 2. In order to assess the cardiovascular effects o f system ically adm inistered opioid peptides, changes m blood pressure and heart rate w ere observed after intravenous adm inistration o f U 50.488H 3,4.dichloro-N-[2-(l.prrrolidinyl)cyclohexyl]benzeneacetam ide), a selective K-opioid receptor agomst, and tw o selective p-opioid receptor agonists, D A LD A (Tyr-D-Arg-Phe-Lys) and D A M G O (D-Ala2,7V-Me-Phe4,Gly5-ol]enkephaiin in nonpregnant and pregnant sheep. Intravenous administration of all three agonists (U 50,488H (1.2 m g/kg), D A LD A (0.3m g/kg) and D A M G O (0.3 m g/kg)) to the awake sheep resulted in an immediate increase in blood pressure. The pressor response to U 50,488H w as accompanied by an increase in heart rate and both effects w ere naloxone- sensitive. In contrast, there was no accompanying change in heart rate to D A LD A or D A M G O . The pressor response to DAM GO and DALDA was significantly attenuated in pregnant animals. In contrast, there was no difference between the pressor response to U 50488H in nonpregnant and pregnant sheep, but the tachycardia was more pronounced in pregnant animals. It was hypothesized that the lack of a reflex bradycardia to the pressor responses of both the p- and K-opioid receptor agonists was due to a blunting of baroreflex-mediated bradycardia. The reflex bradycardia to norepinephrine (0.6 pg/kg/min) was significantly reduced in the presence of DAMGO but not U50,488H. In view of the lack of effect of U50,488H on the baroreflex, it was further hypothesized that the tachycardia it elicited was due to an increase in sympathetic activity. Pretreatment with propranolol (0.1 mg/kg) completely blocked the tachycardia elicited by U50,488H. These data suggest that the lack of a reflex bradycardia to the pressor response of p-receptor agonists is due to a blunting of baroreflex-mediated bradycardia. In contrast, the increase in heart rate caused by U50,488H is mediated by sympathetic activation of the heart. 3. In order to assess the site and mechanism by which p-agonists cause an attenuation of baroreflex sensitivity, further investigations were carried out using the highly polar p-agonist DALDA, which has been shown to have a limited ability to cross the blood brain barrier. Furthermore, as the long term goal of the laboratory has been to develop these peptides for clinical obstetrical use, the effects of these peptides on baroreflex sensitivity in pregnancy was also investigated. The reflex bradycardia to norepinephrine (0.4 - 0.6pg / min) was significantly blunted in the presence of both DAMGO and DALDA in pregnant and nonpregnant animals. In view of the limited ability of DALDA to get across the blood brain barrier, it was hypothesized that the blunting of baroreflex-mediated bradycardia by p-agonists occurs at a peripheral site.