SCORPION (Buthus tamulus) VENOM TOXICITY ON CARDIOPULMONARY REFLEXES INVOLVES KININS VIA 5-HT3 RECEPTOR SUBTYPES

S. BAGCHI(1), S. B. DESHPANDE(1)

(1)Department of Physiology, Institute of Medical Sciences, Banaras Hindu University, Varanasi-221005, India.

ABSTRACT: 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.

KEY WORDS: Bezold-Jarisch reflex, aprotinin, bradykinin, indian red scorpion, ondansetron, Buthus tamulus, kinins, 5-HT3 receptors, cardiopulmonary reflexes.

CORRESPONDENCE TO:

S. B. DESHPANDE - Department of Physiology, Institute of Medical Sciences, Banaras Hindu University, Varanasi-221005, India. Phone: 91-542-317629 - Fax: 91-542-316068 or 91-542-317074  Email desh@banaras.ernet.in