RESUMO
PURPOSE: Vaginal engorgement depends, in part, on the relaxation of vaginal smooth muscle. The aim of this study was to evaluate the role of nitric oxide(NO) in the relaxation of the vaginal smooth muscle. MATERIALS AND METHODS: New Zealand White female rabbits(n=8) were sacrificed and distal 1/3 of the vagina was dissected. Strips of vaginal tissues were immediately processed for isometric tension measurement in the organ bath. The vaginal strips were precontracted with phenylephrine and the responses to electrical field stimulation(EFS) or sodium nitroprusside were examined. Each preparations was also processed immunohistochemically to determine the presence of neuronal NO synthase(n-NOS) in the tissue. RESULTS: EFS caused a frequency-dependent relaxation, which was significantly inhibited in the presence of Nw-nitro-L-arginine methyl ester(L-NAME), a competitive inhibitor of NOS. Sodium nitroprusside, a NO donor, caused concentration-dependent relaxations in the vaginal tissue and the relaxation was not affected by L-NAME(10-4M). n-NOS immunoreactivity was detected in perivascular space and vicinity of vaginal smooth muscle. CONCLUSIONS: These results suggest that the relaxation of the rabbit vaginal smooth muscle is partly mediated by the NO pathway.