Scorpion (Buthus tamulus) venom toxicity on cardiopulmonary reflexes involves kinins via 5-HT3 receptor subtypes

the mechanisms underlying the action of indian red scorpion buthus tamulus (bt) venom-induced augmentation of cardiopulmonary reflexes elicited by intravenous injection of 5-ht were examined in urethane anaesthetized rats. the 5-ht produced a concentration-dependent increase in time-response area of bradycardiac response, with the responses at submaximal concentrations shifted to the left after exposure to bt venom (20 μg/kg, iv). aprotinin (6000 kallikrein inactivating unit, iv) as such had no effect on 5-ht reflex responses (bradycardia, hypotension, and apnea), but blocked the venom-induced reflex augmentation. while ondansetron (10 μg/kg, iv) completely blocked the 5-ht reflex responses, these reappeared partially after venom exposure (20 μg/kg). exposure to bradykinin (50 μg/kg, iv) for 30 min also augmented the 5-ht-induced reflex responses similar to venom. the bradykinin-induced augmentation was also blocked by ondansetron. results indicate that the venom-induced augmentation of cardiopulmonary reflexes is mediated through kinins sensitizing 5-ht3 receptor subtypes.