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Serotonin-4 receptor antagonists reverse cocaine-induced cardiac arrhythmia
life scicnceq Vd. 63, No. 19 pi. 16731678,1998 Publirhcd by E!hevkr scknce Inc. Printed in the USA. All rights mscmd atz4-32usp $0.00 + .oo
PII SO0243205(98)00438-X
ELSEVIER
SEROTONIN-4 RECEPTOR ANTAGONISTS REVERSE COCAINE-INDUCED CARDIAC ARRHYTHMIA Donald C. Ohuohal,
Charles W. Schindler2 and Richard B. Rothman
IClinical Psychopharmaco\ogy Section and 2Behavioral Pharmacology NII-VNIDAARP, P.O. Box 5 180, Baltimore, MD 2 1224
Section
(Received in final form August 21, 1998)
The effect of the 5-HT4 antagonists GRI 13808A and GR125487D on cocaineinduced cardiac arrhythmia was examined in the rat. Cocaine alone, given IV at a rate of 2 mg/kg every 5 min. produced an initial increase in blood pressure Sustained ventricular followed by a severe drop in pressure and bradycardia. fibrillation was noted after 6- 12 mg/kg cocaine and quickly progressed to asystole. Pretreatment with both GRI 13808A and GR125487D antagonized these effects in a dose-dependent manner. When, given after the onset of arrhythmia, both drugs reversed the cocaine-induced arrhythmia’s. Thus, the 5-HT4 antagonists may be useful in the treatment of cocaine toxicity. Key Words: cocaine, S-HT4 receptors, cardiotoxicity,serotonin
Cardiovascular complications associated with cocaine abuse have received increasing attention in recent years ( 1,2). The mechanism(s) through which cocaine affects cardiovascular function has yet to be fully elucidated, due in part to the complexity of cocaine’s effect on the cardiovascular system (3,4). On one hand, cocaine inhibits neuronal uptake of norepinephrine, an action which results in the potentiation of cardiac stimulation and the vasoconstrictor effect of this catecholamine (5). On the other hand, cocaine exerts local anesthetic effects which may result in cardiac depression and vasodilation (6). Cocaine produces a pressor response that is thought to result from both potentiation of peripheral catecholamine activity (7) and a centrally mediated sympathoexcitation (8). As a result of this sympathomimetic action, cocaine raises peripheral and coronary vascular resistance and increases oxygen demand. These effects contribute to episodes of myocardial ischemia and to precipitation of acute myocardial infarction in individuals with or without prior coronary artery disease (9). In addition to inhibiting norepinephrine update, cocaine also inhibits neuronal uptake of dopamine and serotonin (7,10,11). In isolated human atrium, it has been demonstrated that 5-HT can produce arrhythmia (12-14). The 5-HT-evoked arrhythmias are blocked b 5-HT4 antagonists (13). The mechanism for this action is thought to involve myocyte Ca Y+ overload through interaction of 5-HT with 5-HT4 receptors and subsequent activation of the CAMP dependent cascade (15). The 5-HT4 receptor, which has a wide tissue distribution and mediates a number of functional responses, has also been implicated in the 5-I-IT-induced positive inotropic and chronotropic effects in porcine and human atrium, but not in human ventricles or rat atrium and ventricles (16-18). The arthythmogenic effect of 5-I-IT on isolated human atrium resembles those of catecholamines (13,19). Therefore, it is possible that some of cocaine’s arrhythmogenic effects are mediated via 5-HT4 receptors. In this study we examined the effects of the 5-HT4 antagonists Address Correspondence
to: Richard B. Rothman
1674
Reversalof Cocaine Cardiotoxlcity
Vol. 63, No. 19, 1998
GRI 13808A and GR125487D
on the cardiovascular effects of cocaine. Both of these antagonists have been shown to have high affinity and selectivity for the 5-I-IT4 receptor in both peripheral and central tissues (20,21). All animals used in this study were maintained in facilities fully accredited by the American Association for the Accreditation of Laboratory Animal Care (AAALAC), and all procedures were conducted in accordance with the guidelines of the Institutional Care and Use Committee of the NIDA/IRP and the Guide for the Care and Use of Laboratory Animals (22). Methods Male Wistar rats weighing 300-6OOg were anesthetized with 60 mg/kg sodium pentobarbital given intraperitoneally (IP) and were artificially ventilated with room air (5 ml/kg, 48 strokesimin). The left femoral vein and artery were cannulated with a PE50 polyethylene catheter. The arterial catheter was attached to a strain gauge transducer to measure blood pressure. The femoral vein was used for the infusion of cocaine and treatment drugs. A limb lead II electrocardiogram was recorded on a chart recorder. Core body temperature was maintained at 37*l°C by a heating pad. Blood pH of the animals was maintained by adjusting the ventilation rate. Preliminary experiments showed that the 5-IIT4 antagonists would not be effective when given IP. After surgery and a 15 minute stabilization period, 1 ml of saline or drug was injected intravenously (IV) for pretreatment studies. Animals were then stabilized for 30 minutes prior to cocaine infusion. In the first experiment, 9 animals were given saline, 2 mg/kg GRl13808A or 2 mg/kg GR125487D. Cocaine was then infused at 2 mg/kg every 5 min, until the occurrence of sustained ventricular fibrillation. In a second study, groups of 3 animals each were treated with 0, 0.5, 1 .O, 1.5 or 2.0 mg/kg of each of the antagonists. For this dose-effect study, testing continued until ventricular fibrillation was noted. No other data was collected for these animals. For posttreatment studies, cocaine was administered as above until the occurrence of sustained ventricular fibrillation. Cocaine was then discontinued and the animal was then infused with 1 ml of saline or one of the antagonists. Respiration was continued until the animal went into asystole or returned to sinus tachycardia. Drugs.
1-methyl- 1HGR113808A ([ l-[(2-methylsulphonyl)amino]ethyl-4-piperidinyl]methyl indole-3-carboxylate, GR125487D sulphamate salt (Glaxo Pharmaceuticals, Hertfordshire, United Kingdom), cocaine hydrochloride and sodium pentobarbital (NIDA Baltimore) were dissolved in saline. All doses are expressed as the salt forms.
L&a Analysis. Heart rate, mean arterial pressure (MAP), and ECG parameters (QRS, PR intervals) were sampled every 2 minutes after each drug infusion. Data analysis was accomplished using a repeated measures analysis of variance (drug group X time) with follow-up contrasts for individual data points. Data is expressed as mean + standard.error of the mean (SEM). A “p” value of less than 0.05 was considered significant. For the dose-effect study, the dose of cocaine at which ventricular fibrillation was observed was compared to saline control values. Results Initial baseline heart rate, mean arterial pressure and cardiovascular parameters were not significantly different in the control or treatment groups (Table 1) for the pretreatment study. Sustained ventricular fibrillation was noted after a cumulative cocaine dose of 6 to 12 mg/kg of cocaine in the control animals, with rapid progression to fatal arrhythmia. Cardiac arrhythmia due to cocaine infusion were usually the development of ventricular tachycardia progressing to ventricular fibrillation or the sudden occurrence of ventricular premature beats, then ventricular fibrillation. At times idioventricular rhythms were also seen. The control animals quickly went into asystole at a mean cumulative cocaine dose of 14 mg/kg. An increase in mean arterial pressure followed by bradycardia and widening of the QRS and PR intervals was also noted in the control animals (Figure 1). Mean arterial pressure did not increase in the pretreated animals and remained relatively unchanged up to a cocaine dose of 30 mg/kg (p c .OOl for both GRl13808A and GR125487D
Reversal of Cocaine Cardiotoxicity
Vol. 63, No. 19, 1998
1675
groups compared to controls). Heart rate remained stable throughout the cocaine treatment following pretreatment with either GR113808A or GR125487D (p’s < .OOl compared to controls). Likewise the QRS and PR intervals were unchanged in the pretreated groups (p’s < .05 compared to the controls). In no case did the two pretreatment groups differ (p values > .2). Results for the 2 mgikg pretreatment groups are shown in Figure 1. Pretreatment with GRll3808A and GR125487D also increased the dose of cocaine required to induce fatal arrhythmia in a dose-dependent manner (Table 2). The cumulative amount of cocaine required to precipitate ventricular fibrillation was increased by 168*40 and 286&l 8 percent for 2 mg/kg GRl13808A and GR125487D, respectively. Ventricular fibrillation if no further cocaine Sustained ventricular 2 mg/kg GRl13808A
was quickly reversed in the groups treated after cocaine administration, and was given the animals gradually returned to sinus tachycardia with time. fibrillation was reversed after 15a8 and 26* 12 min following treatment with and GR125487D, respectively.
TABLE Baseline
characteristics
Control GRI 13808A GR125487D
prior
1
to onset
NMAP (rnm0-I~) 9 141*3 9 135*4 9 148*5
of cocaine
Heart Rate (Beats/min) 438klO 446i28 400*6
QRS (msec) 38*3 36*2 44+3
infusion. PR (msec) lOlk6 107*3 100+4
The baseline mean arterial pressure (MAP), heart rate and the duration of the QRS complex and the PR interval are summarized above. Each value is the mean+SEM.
TABLE Percent
increase
2
in the dose of cocaine required to initiate pretreatment with 5-HTq antagonists
arrhythmia
after
As described in Methods, rats were pretreated with the indicated doses of the 5-HT4 antagonists and then administered cocaine (2 mg/kg every 5 min) until the occurrence of sustained ventricular fibrillation. Each value is the mean*SEM.
1676
Reversalof Cocaine Cardiotoxicity
Vol. 63, No. 19, 1998
Fig. 1 Effect of cocaine given alone (2 mg/kg every 5 min) and following pretreatment with 2 mg/kg of GR125487D and GR113808A on mean arterial pressure (MAP) and heart rate and on the duration of the QRS and PR intervals. The cocaine alone curve stops at 14 mg/kg because the animals died. The arrows indicates the onset of arrhythmia’s. Discussion The results of the present study show that pre- and post-treatment with both GR113808A and GR125487D prevented or reversed cocaine-induced ventricular fibrillation in the rat. This property was dose-dependent. The cardiovascular baseline values were not altered by the HIT4 antagonists, nor were these parameters altered by cumulative cocaine infusion after pretreatment with 5-HT4 antagonists. An initial increase in blood pressure followed by marked bradycardia and widening of the QRS complex observed in the control animals duplicates what others have reported in the rat (23,24). The mechanism of 5-HT4 antagonist reversal of cocaine effects in this study is unclear. Its heen shown that 5-FIT-evoked arrhythmic contractions and positive inotropic effects are mediated by 5HT4 receptors (15,19,25), and that these contractions are observed in the presence of pl and 82 adrenoceptor blockade ( 19). The potency of GR 113808A and GRl25487D observed in our study is consistent with the ratio of their binding affinities for the 5-HT4 receptor (26). Serotonininduced inotropic effects are thought to produce increases in the contractile tension of heart
Vol. 63, No. 19, 1998
Reversal of Cocaine Cardiotoxicity
1677
muscles and such action have been shown in the ventricle of guinea pig and Japanese monkeys, and in the atrium of humans (18,27). The sensitivity of rat atria1 and ventricular muscles remain to be determined. Another pertinent issue in understanding this effect in the rat include central versus peripheral sites of action of cocaine. The 5-HT4 antagonists may not have a direct effect on receptors residing on the ventricles, but may block cocaine’s contributions peripherally and centrally to the induction of arrhythmia. The cardiovascular action of cocaine is primarily dependent on an action in the CNS which increases peripheral sympathetic tone (4). In general, the central actions of cocaine are greatly reduced by anesthesia (3). However, the effect of anesthesia is observed most prominently on blood pressure and heart rate. Therefore, one may still speculate that these antagonists may interfere with cocaine’s central effects on cardiac rhythm. Both the 5-HT4 antagonists tested can have effects in the central nervous system as demonstrated by the influence of the drugs via systemic administration on behavior (28,29) The action of cocaine centrally may be at 5-I-IT receptors, which might directly influence cardiac function. Alternatively, cocaine’s action at central dopamine receptors might be modulated by serotonin. In vitro studies using rat striatal slices or in vivo microdialysis experiments have demonstrated that 5-HT4 receptors facilitate dopamine release (30,31). Therefore, the 5-HT4 antagonists may modify cocaine’s ability to increase the synaptic availability of dopamine. In conclusion, the results in this study indicate that 5-HT4 antagonists can reverse cocaineinduced arrhythmia. The clinical implication of our study is clear: 5-I-IT4 antagonists may be useful in the treatment of acute cocaine-induced cardiotoxicity. Further study is needed to understand the exact mechanism of this phenomena. Acknowledgment We wish to thank Dr. Bain of Glaxo Pharmaceuticals Hertfordshire, United Kingdom for providing us with the 5-I-IT receptor antagonists, and Dr. Hashim Erzouki for helpful discussions and help with animal surgery. References 1. 2. 3. 4. :: 7 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.
L.R. GOLDFRANK and R.S. HOFFMAN, Ann. Emer. Med. 2Q 165- 175 (1991). R.A. KLONER, S. HALE, K. ALKER and S. REZKALLA, Circulation a 407-419 (1992). C.W. SCHINDLER, Addiction Biol. I_ 31-47 (1996). R.D. WILKERSON, J. Pharmacol. Exp. Ther. 246 466-471 (1988). U. TREDELENBERG, J. Pharmacol. Exp. Ther. 125 55-65 (1959). J.M. RITCHIE and N.M. GREEN, Local Anesthetics (8th Ed), A.G. Gilman, L.S. Goodman, T.W. Rall and F. Murad (Eds), 3 1l-33 1, Mcmillan, New York (1990). C. VAN DYKE and R. BYCK, Cocaine, E.H. Ellinwood and M.M. Kilbey (Eds), Plenum Press, New York (1977). S.R. TELLA, C.W. SCHINDLER and S.R. GOLDBERG, J. Pharmacol. Exp. Ther. 252 49 l-499 (1990). A.H. GRADMAN, Yale J. Biol. Med. 42 137-147 (1988). D.K. PITTS and J. MARWAH, Pharmacol. Biochem. Behav. 26 453-461 (1987). R.A. WISE, Pharmacol. Ther. 3 227-263 (1987). L. SANDERS, J. LYNHAM and A.J. KAUMANN, Br. J. Pharmacol. 112 35P (1994). A.J. KAUMANN and L. SANDERS, Naunyn-Schmiedeberg’s Arch. Pharmacol. w 331337 (1994). A.J. KAUMANN and L. SANDERS, Br. J. Pharmacol. 108 245P (1993). A.J. KAUMANN, Br. J. Pharmacol. .I_j_Q1172-l 174 (1993). P.R. SAXENA and C.M. VILLALOL, Trends Pharmcol. Sci. 12 223 (1991). C.M. VILLALOL, M.O. DEN BOER, J.A.C. HEILIGERS and P.R. SAXENA, Br. J . Pharmacol. m 665-667 (1990). H. ZAIZEN, S. IMANISHI, M. NASU and M. ARITA, Heart Vessels 11 lo-17 (1996).
1678
19. 20.
21. 22. ;:: 25. 26. 27. 28. 29. 30. 31.
Reversal of Cocaine Cardiotoxicity
Vol. 63, No. 19, 1998
A.J. KAUMANN and L. SANDERS, Naunyn-Schmiedeberg’s Arch. Pharmacol. 348 536540 (1993). K.T. BUNCE, J.D. GALE, A.W. OXFORD, P.P.A. HUMPHREY and C.J. GROSSMAN, The pharmacology of the potent and selective 5-HT4 receptor antagonists, GR113808 and GR125487,33, Chicago (1994). J.D. GALE, C.J. GROSSMAN, J.W. WHITEHEAD, A.W. OXFORD, K.T. BUNCE and P.P. HUMPHREY, Br. J. Pharmacol. u332-338 (1994). NATIONAL RESEARCH COUNCIL, Guide for the Care and Use of Laboratory Animals, National Academy Press, Washington, DC (1996). D.K. PMTS, C.E. UDOM and J. MARWAH, Life Sci. 40 1099- 1111 (1987). H.K. ERZOUKI, I. BAUM, S.R. GOLDBERG and C.W. SCHINDLER, J. Cardiovas. Pharmacol. 22 557-563 (1993). A.J. KAUMANN, L.M. GASTER, F.D. KING and A.M. BROWN, NaunynSchmiedeberg’s Acrh. Pharmacol. B 546-548 (1994). C.J. GROSSMAN, G.J. KILPATRICK and K.T. BUNCE, Br. J. Pharmacol. 109 618624 (1993). L. SANDERS, J.A. LYNHAM, B. BOND, F. DEL MONTE, S.E. HARDING and A. J. KAUMANN, Circulation 92 2526-2539 (1995). S. LE’ITY, R. CHILD, A. DUMUIS, A. PANTALONI, J. BOCKAERT and G. RONDOUIN, Neuropharmacology 36 68 l-687 ( 1997). I. PANOCKA, R. CICCOCIOPPO, C. POLIDORI, P. POMPEI and M. MASSI, Pharmacol. B&hem. Behav. 52 255-259 (1995). L.J. STEWARD, J. GE and N.M. BARNES, Br. J. Pharmacol. _&j 38 1P (1994). N. BONHOMME, P. DE DEURWAERDER, M. LE MOAL and U. SPAMPINATO, Neurophatmacology 34 269-279 ( 1995).
PII SO0243205(98)00438-X
ELSEVIER
SEROTONIN-4 RECEPTOR ANTAGONISTS REVERSE COCAINE-INDUCED CARDIAC ARRHYTHMIA Donald C. Ohuohal,
Charles W. Schindler2 and Richard B. Rothman
IClinical Psychopharmaco\ogy Section and 2Behavioral Pharmacology NII-VNIDAARP, P.O. Box 5 180, Baltimore, MD 2 1224
Section
(Received in final form August 21, 1998)
The effect of the 5-HT4 antagonists GRI 13808A and GR125487D on cocaineinduced cardiac arrhythmia was examined in the rat. Cocaine alone, given IV at a rate of 2 mg/kg every 5 min. produced an initial increase in blood pressure Sustained ventricular followed by a severe drop in pressure and bradycardia. fibrillation was noted after 6- 12 mg/kg cocaine and quickly progressed to asystole. Pretreatment with both GRI 13808A and GR125487D antagonized these effects in a dose-dependent manner. When, given after the onset of arrhythmia, both drugs reversed the cocaine-induced arrhythmia’s. Thus, the 5-HT4 antagonists may be useful in the treatment of cocaine toxicity. Key Words: cocaine, S-HT4 receptors, cardiotoxicity,serotonin
Cardiovascular complications associated with cocaine abuse have received increasing attention in recent years ( 1,2). The mechanism(s) through which cocaine affects cardiovascular function has yet to be fully elucidated, due in part to the complexity of cocaine’s effect on the cardiovascular system (3,4). On one hand, cocaine inhibits neuronal uptake of norepinephrine, an action which results in the potentiation of cardiac stimulation and the vasoconstrictor effect of this catecholamine (5). On the other hand, cocaine exerts local anesthetic effects which may result in cardiac depression and vasodilation (6). Cocaine produces a pressor response that is thought to result from both potentiation of peripheral catecholamine activity (7) and a centrally mediated sympathoexcitation (8). As a result of this sympathomimetic action, cocaine raises peripheral and coronary vascular resistance and increases oxygen demand. These effects contribute to episodes of myocardial ischemia and to precipitation of acute myocardial infarction in individuals with or without prior coronary artery disease (9). In addition to inhibiting norepinephrine update, cocaine also inhibits neuronal uptake of dopamine and serotonin (7,10,11). In isolated human atrium, it has been demonstrated that 5-HT can produce arrhythmia (12-14). The 5-HT-evoked arrhythmias are blocked b 5-HT4 antagonists (13). The mechanism for this action is thought to involve myocyte Ca Y+ overload through interaction of 5-HT with 5-HT4 receptors and subsequent activation of the CAMP dependent cascade (15). The 5-HT4 receptor, which has a wide tissue distribution and mediates a number of functional responses, has also been implicated in the 5-I-IT-induced positive inotropic and chronotropic effects in porcine and human atrium, but not in human ventricles or rat atrium and ventricles (16-18). The arthythmogenic effect of 5-I-IT on isolated human atrium resembles those of catecholamines (13,19). Therefore, it is possible that some of cocaine’s arrhythmogenic effects are mediated via 5-HT4 receptors. In this study we examined the effects of the 5-HT4 antagonists Address Correspondence
to: Richard B. Rothman
1674
Reversalof Cocaine Cardiotoxlcity
Vol. 63, No. 19, 1998
GRI 13808A and GR125487D
on the cardiovascular effects of cocaine. Both of these antagonists have been shown to have high affinity and selectivity for the 5-I-IT4 receptor in both peripheral and central tissues (20,21). All animals used in this study were maintained in facilities fully accredited by the American Association for the Accreditation of Laboratory Animal Care (AAALAC), and all procedures were conducted in accordance with the guidelines of the Institutional Care and Use Committee of the NIDA/IRP and the Guide for the Care and Use of Laboratory Animals (22). Methods Male Wistar rats weighing 300-6OOg were anesthetized with 60 mg/kg sodium pentobarbital given intraperitoneally (IP) and were artificially ventilated with room air (5 ml/kg, 48 strokesimin). The left femoral vein and artery were cannulated with a PE50 polyethylene catheter. The arterial catheter was attached to a strain gauge transducer to measure blood pressure. The femoral vein was used for the infusion of cocaine and treatment drugs. A limb lead II electrocardiogram was recorded on a chart recorder. Core body temperature was maintained at 37*l°C by a heating pad. Blood pH of the animals was maintained by adjusting the ventilation rate. Preliminary experiments showed that the 5-IIT4 antagonists would not be effective when given IP. After surgery and a 15 minute stabilization period, 1 ml of saline or drug was injected intravenously (IV) for pretreatment studies. Animals were then stabilized for 30 minutes prior to cocaine infusion. In the first experiment, 9 animals were given saline, 2 mg/kg GRl13808A or 2 mg/kg GR125487D. Cocaine was then infused at 2 mg/kg every 5 min, until the occurrence of sustained ventricular fibrillation. In a second study, groups of 3 animals each were treated with 0, 0.5, 1 .O, 1.5 or 2.0 mg/kg of each of the antagonists. For this dose-effect study, testing continued until ventricular fibrillation was noted. No other data was collected for these animals. For posttreatment studies, cocaine was administered as above until the occurrence of sustained ventricular fibrillation. Cocaine was then discontinued and the animal was then infused with 1 ml of saline or one of the antagonists. Respiration was continued until the animal went into asystole or returned to sinus tachycardia. Drugs.
1-methyl- 1HGR113808A ([ l-[(2-methylsulphonyl)amino]ethyl-4-piperidinyl]methyl indole-3-carboxylate, GR125487D sulphamate salt (Glaxo Pharmaceuticals, Hertfordshire, United Kingdom), cocaine hydrochloride and sodium pentobarbital (NIDA Baltimore) were dissolved in saline. All doses are expressed as the salt forms.
L&a Analysis. Heart rate, mean arterial pressure (MAP), and ECG parameters (QRS, PR intervals) were sampled every 2 minutes after each drug infusion. Data analysis was accomplished using a repeated measures analysis of variance (drug group X time) with follow-up contrasts for individual data points. Data is expressed as mean + standard.error of the mean (SEM). A “p” value of less than 0.05 was considered significant. For the dose-effect study, the dose of cocaine at which ventricular fibrillation was observed was compared to saline control values. Results Initial baseline heart rate, mean arterial pressure and cardiovascular parameters were not significantly different in the control or treatment groups (Table 1) for the pretreatment study. Sustained ventricular fibrillation was noted after a cumulative cocaine dose of 6 to 12 mg/kg of cocaine in the control animals, with rapid progression to fatal arrhythmia. Cardiac arrhythmia due to cocaine infusion were usually the development of ventricular tachycardia progressing to ventricular fibrillation or the sudden occurrence of ventricular premature beats, then ventricular fibrillation. At times idioventricular rhythms were also seen. The control animals quickly went into asystole at a mean cumulative cocaine dose of 14 mg/kg. An increase in mean arterial pressure followed by bradycardia and widening of the QRS and PR intervals was also noted in the control animals (Figure 1). Mean arterial pressure did not increase in the pretreated animals and remained relatively unchanged up to a cocaine dose of 30 mg/kg (p c .OOl for both GRl13808A and GR125487D
Reversal of Cocaine Cardiotoxicity
Vol. 63, No. 19, 1998
1675
groups compared to controls). Heart rate remained stable throughout the cocaine treatment following pretreatment with either GR113808A or GR125487D (p’s < .OOl compared to controls). Likewise the QRS and PR intervals were unchanged in the pretreated groups (p’s < .05 compared to the controls). In no case did the two pretreatment groups differ (p values > .2). Results for the 2 mgikg pretreatment groups are shown in Figure 1. Pretreatment with GRll3808A and GR125487D also increased the dose of cocaine required to induce fatal arrhythmia in a dose-dependent manner (Table 2). The cumulative amount of cocaine required to precipitate ventricular fibrillation was increased by 168*40 and 286&l 8 percent for 2 mg/kg GRl13808A and GR125487D, respectively. Ventricular fibrillation if no further cocaine Sustained ventricular 2 mg/kg GRl13808A
was quickly reversed in the groups treated after cocaine administration, and was given the animals gradually returned to sinus tachycardia with time. fibrillation was reversed after 15a8 and 26* 12 min following treatment with and GR125487D, respectively.
TABLE Baseline
characteristics
Control GRI 13808A GR125487D
prior
1
to onset
NMAP (rnm0-I~) 9 141*3 9 135*4 9 148*5
of cocaine
Heart Rate (Beats/min) 438klO 446i28 400*6
QRS (msec) 38*3 36*2 44+3
infusion. PR (msec) lOlk6 107*3 100+4
The baseline mean arterial pressure (MAP), heart rate and the duration of the QRS complex and the PR interval are summarized above. Each value is the mean+SEM.
TABLE Percent
increase
2
in the dose of cocaine required to initiate pretreatment with 5-HTq antagonists
arrhythmia
after
As described in Methods, rats were pretreated with the indicated doses of the 5-HT4 antagonists and then administered cocaine (2 mg/kg every 5 min) until the occurrence of sustained ventricular fibrillation. Each value is the mean*SEM.
1676
Reversalof Cocaine Cardiotoxicity
Vol. 63, No. 19, 1998
Fig. 1 Effect of cocaine given alone (2 mg/kg every 5 min) and following pretreatment with 2 mg/kg of GR125487D and GR113808A on mean arterial pressure (MAP) and heart rate and on the duration of the QRS and PR intervals. The cocaine alone curve stops at 14 mg/kg because the animals died. The arrows indicates the onset of arrhythmia’s. Discussion The results of the present study show that pre- and post-treatment with both GR113808A and GR125487D prevented or reversed cocaine-induced ventricular fibrillation in the rat. This property was dose-dependent. The cardiovascular baseline values were not altered by the HIT4 antagonists, nor were these parameters altered by cumulative cocaine infusion after pretreatment with 5-HT4 antagonists. An initial increase in blood pressure followed by marked bradycardia and widening of the QRS complex observed in the control animals duplicates what others have reported in the rat (23,24). The mechanism of 5-HT4 antagonist reversal of cocaine effects in this study is unclear. Its heen shown that 5-FIT-evoked arrhythmic contractions and positive inotropic effects are mediated by 5HT4 receptors (15,19,25), and that these contractions are observed in the presence of pl and 82 adrenoceptor blockade ( 19). The potency of GR 113808A and GRl25487D observed in our study is consistent with the ratio of their binding affinities for the 5-HT4 receptor (26). Serotonininduced inotropic effects are thought to produce increases in the contractile tension of heart
Vol. 63, No. 19, 1998
Reversal of Cocaine Cardiotoxicity
1677
muscles and such action have been shown in the ventricle of guinea pig and Japanese monkeys, and in the atrium of humans (18,27). The sensitivity of rat atria1 and ventricular muscles remain to be determined. Another pertinent issue in understanding this effect in the rat include central versus peripheral sites of action of cocaine. The 5-HT4 antagonists may not have a direct effect on receptors residing on the ventricles, but may block cocaine’s contributions peripherally and centrally to the induction of arrhythmia. The cardiovascular action of cocaine is primarily dependent on an action in the CNS which increases peripheral sympathetic tone (4). In general, the central actions of cocaine are greatly reduced by anesthesia (3). However, the effect of anesthesia is observed most prominently on blood pressure and heart rate. Therefore, one may still speculate that these antagonists may interfere with cocaine’s central effects on cardiac rhythm. Both the 5-HT4 antagonists tested can have effects in the central nervous system as demonstrated by the influence of the drugs via systemic administration on behavior (28,29) The action of cocaine centrally may be at 5-I-IT receptors, which might directly influence cardiac function. Alternatively, cocaine’s action at central dopamine receptors might be modulated by serotonin. In vitro studies using rat striatal slices or in vivo microdialysis experiments have demonstrated that 5-HT4 receptors facilitate dopamine release (30,31). Therefore, the 5-HT4 antagonists may modify cocaine’s ability to increase the synaptic availability of dopamine. In conclusion, the results in this study indicate that 5-HT4 antagonists can reverse cocaineinduced arrhythmia. The clinical implication of our study is clear: 5-I-IT4 antagonists may be useful in the treatment of acute cocaine-induced cardiotoxicity. Further study is needed to understand the exact mechanism of this phenomena. Acknowledgment We wish to thank Dr. Bain of Glaxo Pharmaceuticals Hertfordshire, United Kingdom for providing us with the 5-I-IT receptor antagonists, and Dr. Hashim Erzouki for helpful discussions and help with animal surgery. References 1. 2. 3. 4. :: 7 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.
L.R. GOLDFRANK and R.S. HOFFMAN, Ann. Emer. Med. 2Q 165- 175 (1991). R.A. KLONER, S. HALE, K. ALKER and S. REZKALLA, Circulation a 407-419 (1992). C.W. SCHINDLER, Addiction Biol. I_ 31-47 (1996). R.D. WILKERSON, J. Pharmacol. Exp. Ther. 246 466-471 (1988). U. TREDELENBERG, J. Pharmacol. Exp. Ther. 125 55-65 (1959). J.M. RITCHIE and N.M. GREEN, Local Anesthetics (8th Ed), A.G. Gilman, L.S. Goodman, T.W. Rall and F. Murad (Eds), 3 1l-33 1, Mcmillan, New York (1990). C. VAN DYKE and R. BYCK, Cocaine, E.H. Ellinwood and M.M. Kilbey (Eds), Plenum Press, New York (1977). S.R. TELLA, C.W. SCHINDLER and S.R. GOLDBERG, J. Pharmacol. Exp. Ther. 252 49 l-499 (1990). A.H. GRADMAN, Yale J. Biol. Med. 42 137-147 (1988). D.K. PITTS and J. MARWAH, Pharmacol. Biochem. Behav. 26 453-461 (1987). R.A. WISE, Pharmacol. Ther. 3 227-263 (1987). L. SANDERS, J. LYNHAM and A.J. KAUMANN, Br. J. Pharmacol. 112 35P (1994). A.J. KAUMANN and L. SANDERS, Naunyn-Schmiedeberg’s Arch. Pharmacol. w 331337 (1994). A.J. KAUMANN and L. SANDERS, Br. J. Pharmacol. 108 245P (1993). A.J. KAUMANN, Br. J. Pharmacol. .I_j_Q1172-l 174 (1993). P.R. SAXENA and C.M. VILLALOL, Trends Pharmcol. Sci. 12 223 (1991). C.M. VILLALOL, M.O. DEN BOER, J.A.C. HEILIGERS and P.R. SAXENA, Br. J . Pharmacol. m 665-667 (1990). H. ZAIZEN, S. IMANISHI, M. NASU and M. ARITA, Heart Vessels 11 lo-17 (1996).
1678
19. 20.
21. 22. ;:: 25. 26. 27. 28. 29. 30. 31.
Reversal of Cocaine Cardiotoxicity
Vol. 63, No. 19, 1998
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