Effects of hydroxocobalamin and carboxy-PTIO on nitrergic transmission in porcine anococcygeus and retractor penis muscles

1 The effects of carboxy-PTIO and hydroxocobalamin were studied on nitrergi c transmission in anococcygeus and retractor penis muscles taken during pos t mortem examination from young male pigs. 2 In both muscles under resting conditions, electrical field stimulation (E FS) caused contractions that were sensitive to tetrodotoxin (1 mu M) and we re greatly inhibited by prazosin (1 mu m) and guanethidine (10-30 mu M), bu t were not significantly affected by atropine (l mu M). In the anococcygeus muscle, but not in the retractor penis muscle, guanethidine produced a pro longed contraction. 3 After tone was raised by guanethidine in the anococcygeus or by phenyleph rine (1 mu M) in the presence of guanethidine in the retractor penis, EFS c aused tetrodotoxin-sensitive relaxations. The EFS-induced relaxations were abolished by the NO synthase inhibitor N-G-L-nitro-arginine methyl ester (L -NAME; 100 mu M) and its effect was partly overcome by L-arginine (1 mM), i ndicating it was mediated by nitrergic nerves. 4 Carboxy-PTIO (0.1-1 mM) had no significant effect in reducing stimulation -induced nitrergic relaxations in either muscle. However, hydroxocobalamin (0.1-1 mM) caused concentration-dependent reductions of nitrergic relaxatio ns in both muscles. Relaxations to exogenous nitric oxide (1 mu M) in both muscles were abolished by carboxy-PTIO (0.3 mM) and hydroxocobalamin (0.1 m M). 5 There were no differences in reactivity to carboxy-PTIO or hydroxocobalam in between anococcygeus and retractor penis muscles from the same species ( pig) The finding also confirms earlier observations that the nitrergic tran smitter is generally resistant to the NO-scavenger carboxy-PTIO.