The role of nitric oxide on the relaxations of rabbit corpus cavernosum induced by Androctonus australis and Buthotus judaicus scorpion venoms

In this study, we have investigated the relaxing effects of both Androctonu s australis venom (AAV) and Buthotus judaicus venom (BJV) on the rabbit cor pus cavernosum (RbCC) smooth muscle strips. The RbCC strips were mounted in a cascade system and superfused with warmed and gassed Krebs solution. The nitric oxide (NO) synthesis inhibitor N-omega-nitro-L-arginine methyl este r (L-NAME, 10 muM), but not D-NAME (10 muM), significantly inhibited the Rb CC relaxations induced by acetylcholine (ACh, 0.6 nmol), AAV (30 mug) and B JV (30 mug). Subsequent infusion of L-arginine (300 muM), but not of D-argi nine (300 muM), partially restored the relaxations evoked by these agents. The brain NO synthase inhibitor 7-nitroinciazole (7-NI, 10 muM) also inhibi ted the relaxant responses elicited by the scorpion venoms. The guanylyl cy clase inhibitors methylene blue (MB, 30 muM) and 1H-[1.2,4] oxadiazolo [4,3 ,-alquinoxalin-1-one] (ODQ, 10 muM) virtually abolished the relaxations ind uced by either AAV or BJV. The infusion of muscarinic receptor antagonists such as scopolamine and atropine (1 muM, each) completely abolished the ACh -induced relaxations but had no effect on those evoked by the scorpion veno ms. The Na+ channel blocker tetrodotoxin (1 muM) prevented the relaxations evoked by both AAV and BJV, Thus, NO released from nitrergic nerve fibres m ediates the relaxations elicited hy AAV and BJV in the rabbit cavernosal ti ssue. (C) 2000 Elsevier Science Ltd. All rights reserved.