Indian J Physiol Pharmacol 2002;46 (4);

Involvement of 5-HT_1a and 5-HT₂ Receptor in Cisplatin Induced Emesis in Dogs
Y. K. GUPTA* AND S. S. SHARMA
Department of Pharmacology,
All Institute of Medical Science
New Delhi – 110 029
*Corresponding Author : Email : ykgupta@hotmail.com and Fax : 91-011-6864789.
 (Received on May 1, 2002)

Abstract: The effect of drug acting on 5-HT_1A, 5-HT₂ and 5-HT₃ receptors were studied against cisplatin and apomorphine induced emesis in dogs. Buspirene, 5-HT_1A receptor partial agonist significantly reduced the emetic episode thought it had no significant effect on emetic latency. Mianserin, 5-HT₂ receptor antagonist exhibits significant reduction in emetic episodes and in latency. Buspirone prevented the apomorphine induced emesis while Mianserin had no effect. The antiemetic activity of Buspirone may be attributable to its agonistic activity at 5-HT_1A receptor and antagonistic activity at dopamine receptors. These findings further confirm the involvement of 5-HT_1A and 5-HT₂ receptor in cytotoxic drug induced emesis, though the speices difference in their antimetic action can not be ruled out.

Key Words:    buspirone                     mianserin                      ondansetron

                                                Cisplatin                       apomorphine                emesis

Introduction
Results
Discussion
References

INTRODUCTION

Nausea and vomiting are the major side effect associated with the use of highly efficacious chemotherapy in cancer patients (1, 2). Cisplatin, decarbazine and mechlorethamine produced vomiting in 90% of the patients. Serotonergic 5-HT₃ receptor antagonists have been shown to prevent cancer chemotherapeutic drug induced emesis in dog, ferret, cat and Suncus murinus (3, 4, 5). Clinical studies have also confirmed the high efficacy of 5-HT₃ receptor antagonists (6).

Evidence also suggest that other 5-HT receptor subtypes are also involved in the emetic reflex (7, 8, 9). It has been reported that 5-HT_1A receptor agonsit such as buspirone, flesinoxan and 8-OH DPAT suppresses emesis induced by cisplatin, motion sickness and several emetic agents in cat (9) and Suncus murinus (10). 5-HT₂ receptor antagonist ketanserin prevented cisplatin induced emesis in Suncus murinus (5). In the present study the effect of buspirone, 5-HT_1A receptor partial agonist and mianserin, a 5-HT₂ receptor antagonist was investigated against cisplatin and apomorphine induced emesis in dogs, which is the most sensitive animal species to all emetic stimuli.

Animals

Healthy Mongrel dogs of either sex (8-12 Kg) were housed individually and quarantined for 14 days. They were maintained on wheat bread, beef and water ad libitum. In all the animals used in this study the presence of emetic reflex was confirmed by injecting 25  mg/kg apomorphine intravenously.

Emetic status

The 100% emetic dose of cisplatin (3mg/Kg, i.v.) was used as an emetic challenge as established in our laboratory (11). This dose induced consistent vomiting in 100% of the animals and is within the calculated cytotoxic dose (2.66 – 5.32 mg/Kg, i.v.) of cisplatin for dogs (12). The drugs were also tested against emetic challenge of apomorphine 25 mg/kg subcutaneously.

Prior to the experiment the animals were fasted overnight with water available ad libitum. Thirty minutes before the administration of cisplatin challenges the dog were fed bread and milk. Actual expulsion of food from the mouth was taken as an emetic episode and if occurring after a gap of one minute or more they were considered as separate emetic episodes. The dogs were observed for latency of the first emetic episodes and the number of emetic episodes for a period of 6 h. In any dog only 2 emetic test were done. First with apomorphine challenge and after a gap of atleast 7 days this animal was tested against cisplatin challenge.

Drug and their solution

Drugs used were cisplatin (courtesy Dabur India Limited); buspirone  (courtesy Intas Laboratories Ahmedabad); Mianserin (courtesy Torrent Pharmaceuticals, Ahmedabad); ondansetron) courtesy Glaxo, UK) and apomorphine (Sigma USA). All the drugs were dissolved in normal saline. Cisplatin was dissolved at 50°C in normal saline and cooled to 37°C before administration.

Drugs treatment

Buspirone and mianserin were administered 4 mg/kg, s.c. and 1 mg/kg, s.c. respectively 30 min after cisplatin challenge. The effect of these drugs was also studied against 100% emetic dose of apomorphine. These drugs were administered 10 min prior to apomorphine challenge. Antiemetic effectiveness of buspirone and mianserin was compared with 5- HT₃ receptor antagonist-ondansetron.
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RESULTS

Effect of buspirone, mianserin and ondansetron on cisplatin induced emesis

Busiprone administered at the dose of 4 mg/kg, s.c. significantly reduced cisplatin induced emesis. The mean number of emetic episodes were reduced to 3.4 ±1.52 as compared to cisplatin controlled (13.67 ± 2.2). In 3 out of 5 (60%), there was a complete protection. The mean emetic latency was increased to 217  ± 60 as compared to cisplatin control 102.5 ± 7.45 (Table I). Mianserin 1 mg/kg pre-treatment also significantly reduced cisplatin induced emesis. In mianserin pretreated group 4 out of 5 dogs vomited. The mean number of emetic episodes were 0.8 ± 0.49 and mean latency was increased to 207 ± 35.67 (Table II). Ondansetron 0.1 mg/kg, i.v. when administered 30 min post cisplatin emetic challenge afforded complete protection in 80% of the dogs. At the higher doses of 0.5 and 1 mg/kg, i.v.; it afforded complete protection against cisplatin emesis.

Effect of buspirone, mianserin and ondansetron on apomorphine induced emesis

Buspirone (4 mg/kg, s.c.) when administered 10 min prior to emetic challenge of apomorphine (25 µg/kg, i.v.) afforded complete protection. However mianserin and ondansetron treatment upto the dose of 1 mg/kg did not show any protection.

No behavioral changes were seen with any of the 5-HT modulating drugs except mild salivation with buspirone.
TABLE I: Effect of buspirone, mianserin and ketanserin on cisplatin induced emesis in dogs.

*P<0.05 as compared to saline treated group
#Complete protection

TABLE II: Effect of drugs acting on different 5-Ht receptor subtypes on apomorphine induced emesis in dogs.

#Complete protection
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DISCUSSION

In the present study buspirone produced significant antiemetic activity against cisplatin induced emesis in dogs. The findings is in consistent with that of Lucot and Crampton, 1987 (13) and Okada et al., 1994 (10). Lucot and Crampton observed near complete protection with buspirone in cat, while in ferret it showed only 32% protection (13). In our study it afforded complete protection in 40% of the dogs tested. The difference in antiemetic efficacy of buspirone in cat, ferret and dog suggest the species variation in antiemetic action. However the fact buspirone, 5-HT_1A receptor partial agonist has antiemetic effect though of variable efficiency in different species suggest 5-HT_1A receptor involvement. This is further supported by the fact that high concentration of 5-HT_1A binding sites and of receptor tractus solitarius (nTS), an important area in the control of emesis (14).

In the present study buspirone also blocked vomiting of apomorphine, a potent emetic agent known to act by stimulating dopamine D₂ receptor in chemoreceptor trigger zone. That 5-T_1A agonistic action is involved in prevention of cisplatin induced emesis as evidenced as specific dopamine antagonist such as domperidone does not afford complete protection against cisplatin emesis.

Recently acute dosing with oral buspirone did not protect against acute emesis induced by cisplatin. The lack of buspirone antiemetic effect can be due to the difference in the degree of involvement of 5-HT_1A receptor in emesis within species. For example buspirone was less effective in ferrets than in the cat against cisplatin emesis. Recent reports indicate that 5-HT_1A receptor agonist have a much broader range of antiemetic activity in contrast to 5-HT₃ receptor antagonists. These agents are also effective in cyclophosphamide (15), apomorphine (16), xylazine (13), nicotine and veratrine (10) induced emesis. It has been proposed that 5-HT_1A receptor agonist produced antiemetic effect by interfering with the integrated emetic reflex. It was also assumed that 5-HT_1A receptor agonist possess an inhibitory action for 5-HT release at serotonergic nerve endings. There is also evidence that enterochrommaffin cells possess 5-HT_1A and 5-HT₂ receptors that regulate 5-HT release (8).

Interestingly, 5-HT₂ receptor antagonist mianserin also afforded significant protection to cisplatin induced emesis in dogs. This indicate involvement of 5-H_T2 receptors in the mediation of cytotoxic drug induced emesis. The results are consistent with that of Torii et al. 1991 who showed that the administration of ketanserin, 5-HT₂ receptors antagonist alone prevented receptor antagonist alone prevented cisplatin induced emesis (5). Ketanserin in the higher doses caused marked sedation in Suncus murinus but in our study mianserin did not produce any behavioural changes. In a recent study, (±) -1-(2, 5 dimethoxy-4-iodophenyl)-2-aminopropane (DOI), 5-HT₂ receptor agonist prevented motion as well as 5-HT_2A completely inhibited the motion and cisplatin induced emesis in Suncus murinus (17). The antiemetic effect of DOI is mediated by the 5-HT₂ receptor in the central nervous system. DOI may act on the 5-HT₂ receptors of inhibitory neurons in these regions and indirectly inhibits the brain stem which mediate the emetic reflex. Mianserin which showed significant antiemetic efficacy against cisplatin induced emesis, failed to prevent apomorphine induced emesis. These findings thereby suggest the involvement of 5-HT₂ receptors in the cisplatin induced emesis.

In conclusion, buspirone and mianserin exerted antiemetic effect against cisplatin induced emesis in dogs. Buspirone also possess dopamine receptor blocking activity as evidenced by inhibition of apomorphine induced emesis. These findings further confirm the involvement of 5-HT_1A and 5-HT₂ receptor in cytotoxic drug induced emesis, though the species in their antiemetic action cannot be ruled out.

ACKNOWLEDGMENT

We are thankful to Council of Scientific and Industrial Research. New Delhi for financial assistance to YKG.
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REFERENCES

1. Laszlo J. Nausea and vomiting as a major complications of cancer chemotherapy. Drugs 1983; 25: 1
2. Sanger GJ. New antiemetic drugs. Can J Physiol Pharmacol 1990; 68: 314-324.
3. Miner W, Sanger GJ, Inhibition of cisplatin induced vomiting by 5-hydroxytryptamine-M receptor antagonism. Br J Pharmacol 1986; 88: 497-499.
4. Bhadari P, Gupta YK, Seth SD. BRL 43694, a new 5-HT₃ antagonist prevent cisplatin induced emesis in dogs. Meth Findings Exp Clin Pharmacol 1989; 11: 361-363.
5. Torii Y, Saito H, Matsuki N. Selective blockade of cytotoxic drug induced emesis by 5-HT₃ receptor antagonists in Suncus murinus. Jpn J Pharmacol 1991; 55: 107-113.
6.  Cubeddu LX, Hoffman IS, Fuenmayor NT. Efficacy of ondansetron (GR38032F) and the role of serotonin in cisplatin induced nausea and emesis. N Eng J Med 1990; 322: 810-816.
7. Hasler WL. Serotonin receptor physiology: relation to emesis. Digestive Disease Sci 1999; 44: 108S-113S.
8. Endo T, Minami M, Hirafuji M, Ogawa T, Akita K, Nemoto M, Saito H, Yoshioka M, Parvez SH. Neurochemistry and neuropharmacology of  vomiting-the role of serotonin. Toxicology 2000; 153: 19-201.
9. Lucot JB, Crampton GH. 8-OH DPAT suppresses vomiting in the cat elicited by motion, cisplatin or xylazine. Pharmacol Biochem Behav 1989; 33: 627.
10. Okade F, Saito H, Matsuki N. Antiemetic effect of serotonergic 5-HT_1A receptor agonists in Suncus murinus. Jpn J Pharmacol 1994; 64: 109-114.
11. Bhandari P, Gupta YK, Seth SD. Emetic profile of Cisplatin in dogs. Asia Pacific J Pharmacol 1988; 3: 131-134.
12. Devita VT Jr. Principles of Chemotherapy. In: Cancer, Principle and Practice of Oncology, VT Devitta Jr. S. Hallman and SA Rosenberg eds. Phillidelphia, PA, Lippincott 1985; 274.
13. Lucot JB, Crampton GH. Buspirone blocked cisplatin induced emesis in cats. J Clin Pharmacol 1987; 27: 817-818.
14. Lucot JB. Prevention of motion sickness by 5-HT_1A agonists in cats, in, Mechanism and control of emesis, vol. 223, eds. A. L. Bianchi, L. Grelot, A. D. Miller and G. L. King.): 1992; 195.
15. Wolf MC, Leander JD. Effect of 5-HT_1A receptor agonist on acute and delayed cyclophosphamide induced vomiting: Eur J Pharmacol 1997; 340: 217-220.
16. Rudd JR, Bunce KT, Naylor RJ. The effect of 8-OH DPAT on drug induced emesis in the ferret. Br J Pharmacol 1992; 101-104.
17. Okade F, Saito H, Matsuki N. Blockade of motion and cisplatin induced emesis by a 5-HT₂ receptor agonist in Suncus murinus. Br J Pharmacol 1995; 114: 931-934.
    
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