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

The effects of carboxy‐PTIO and hydroxocobalamin were studied on nitrergic transmission in anococcygeus and retractor penis muscles taken during post mortem examination from young male pigs. In both muscles under resting conditions, electrical field stimulation (EFS) caused contractions that were sensitive to tetrodotoxin (1 μM) and were greatly inhibited by prazosin (1 μM) and guanethidine (10–30 μM), but were not significantly affected by atropine (1 μM). In the anococcygeus muscle, but not in the retractor penis muscle, guanethidine produced a prolonged contraction. After tone was raised by guanethidine in the anococcygeus or by phenylephrine (1 μM) in the presence of guanethidine in the retractor penis, EFS caused tetrodotoxin‐sensitive relaxations. The EFS‐induced relaxations were abolished by the NO synthase inhibitor NG‐L‐nitro‐arginine methyl ester (L‐NAME; 100 μM) and its effect was partly overcome by L‐arginine (1 mM), indicating it was mediated by nitrergic nerves. 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 relaxations in both muscles. Relaxations to exogenous nitric oxide (1 μM) in both muscles were abolished by carboxy‐PTIO (0.3 mM) and hydroxocobalamin (0.1 mM). There were no differences in reactivity to carboxy‐PTIO or hydroxocobalamin between anococcygeus and retractor penis muscles from the same species (pig). The finding also confirms earlier observations that the nitrergic transmitter is generally resistant to the NO‐scavenger carboxy‐PTIO. British Journal of Pharmacology (1999) 127, 172–176; doi:10.1038/sj.bjp.0702496