INHIBITORY EFFECT OF ETHANOL ON THE 5-HYDROXYTRYPTAMINE-INDUCED BEZOLD-JARISCH REFLEX - INVOLVEMENT OF PERIPHERAL 5-HT3 RECEPTORS

The influence of ethanol (0.5, 1.0 and 2.0 g/kg i.p.) on the Bezold-Ja risch reflex in urethane-anaesthetized rats was studied. 5-Hydroxytryp tamine (serotonin; 5-HT; 1, 3, 10 and 30 mu g/kg i.v.) and capsaicin ( 1, 3 and 10 mu g/kg i.v.) reflexly decreased heart rate in a dose-depe ndent manner. The 5-HT3 receptor antagonist ondansetron 10 mu g/kg i.v . abolished the 5-HT- but not the capsaicin-stimulated bradycardia, in dicating that 5-HT and capsaicin acted via different trigger mechanism s (5-HT3 receptor-dependent and -independent, respectively). Ethanol a t 1.0 and 2.0 g/kg i.p. inhibited in a dose-dependent manner (by 20-45 %) the 5-HT- but not the capsaicin-stimulated decrease in heart rate. Our results demonstrate that the inhibitory effect of ethanol on the 5 -HT3 receptor-mediated Bezold-Jarisch reflex may be related to the dir ect effect of ethanol on 5-HT3 receptors on sensory vagal nerves in th e heart.