EFFECTS OF ANDROCTONUS-CRASSICAUDA SCORPION-VENOM ON ENDOTHELIUM-DEPENDENT AND ENDOTHELIUM-INDEPENDENT VASCULAR-RESPONSES OF RABBIT AORTA

The effects of Androctonus crassicauda scorpion venom on acetycholine (ACh) induced relaxations and contractions of rabbit thoracic aorta we re studied. Endothelium dependent relaxations induced by ACh in phenyl ephrine precontracted arteries were enhanced by the scorpion venom, AC h-induced contractions in endothelium intact open aortic rings were le ss than those obtained in denuded preparations (n = 6, P < 0.05, ANOVA ), Venom (5, 10 and 30 mu g/ml) potentiated ACh induced contractions i n intact and denuded segments. In the denuded segments, this potentiat ion was inhibited by indomethacin (10 mu M). Thromboxane synthase inhi bitor, BW; 149H (100 mu M) and thromboxane A(2) (TXA(2)) receptor anta gonist, R 68070 (10 mu M) partly inhibited venom induced potentiation, N-G-nitro-L-arginine (100 mu M) increased venom potentiated ACh respo nses in intact arterial segments, Venom increased the basal tone by 25 -35% at 30 mu g/ml, These results suggest that A. crassicauda venom ma y release a relaxing factor from endothelium and contracting factor fr om the smooth muscle of rabbit isolated thoracic aorta. The contractin g factor may be a cyclooxygenase like product, most likely TXA(2). The increase in basal tone by 30 mu g/ml venom was inhibited by phentolam ine(10 mu M) and guanethidine (10 mu M), indicating a venom induced re lease of a neurotransmitter from adrenergic nerve endings.