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Title: Effects of serotonin 5-HT3 receptor antagonists on stress-induced colonic hyperalgesia and diarrhoea in rats: a comparative study with opioid receptor agonists, a muscarinic receptor antagonist and a synthetic polymer. Author: Hirata T, Keto Y, Nakata M, Takeuchi A, Funatsu T, Akuzawa S, Sasamata M, Miyata K. Journal: Neurogastroenterol Motil; 2008 May; 20(5):557-65. PubMed ID: 18221252. Abstract: In this study, we examined the effects of serotonin (5-HT)3 receptor antagonists (5-HT3RAs) including ramosetron, alosetron, and cilansetron on colonic nociceptive threshold in rats. Furthermore, we established a restraint stress-induced colonic hyperalgesia model in rats, and compared the inhibitory effects of 5-HT3RAs on restraint stress-induced colonic hyperalgesia and diarrhoea with those of loperamide, trimebutine, tiquizium and polycarbophil. The colonic nociceptive threshold was measured as the balloon pressure at the time the rat showed a nociceptive response during colonic distension by an intrarectally inserted balloon. Oral administration of ramosetron (3-30 microg kg(-1)), alosetron (30-300 microg kg(-1)), or cilansetron (30-300 microg kg(-1)) increased the colonic nociceptive threshold in a dose-dependent manner in non-stressed rats. Restraint stress for 1 h significantly decreased the colonic nociceptive threshold, but ramosetron (0.3-3 microg kg(-1)), alosetron (3-30 microg kg(-1)), cilansetron (3-30 microg kg(-1)) and trimebutine (100-1000 mg kg(-1)) significantly inhibited the decrease in the threshold. Loperamide (3-30 mg kg(-1)), tiquizium (100-1000 mg kg(-1)) and polycarbophil (1000 mg kg(-1)) did not affect the restraint stress-induced decrease in the colonic nociceptive threshold. All drugs tested in this study showed dose-dependent inhibition of restraint stress-induced diarrhoea in rats. These results indicate that, unlike existing antidiarrhoeal and spasmolytic agents, 5-HT3RAs have inhibitory effects on colonic nociception, and prevented restraint stress-induced both diarrhoea and hyperalgesia at almost the same doses in rats. This suggests that the 5-HT3RAs may be useful in ameliorating both colonic hyperalgesia and diarrhoea in patients with irritable bowel syndrome.[Abstract] [Full Text] [Related] [New Search]