Effects of sildenafil citrate, acetylcholine, and sodium nitroprusside on the relaxation of rabbit cavernosal tissue in vitro

Abstract Objectives. To investigate the effect of sildenafil together with the influence of sodium nitroprusside and acetylcholine and further discuss its mechanism of action in vitro. Methods. Isolated strips of rabbit corpus cavernosum were stimulated isometrically with phenylephrine. Graded relaxations were induced using increasing concentrations of acetylcholine, sodium nitroprusside, and sildenafil alone and in combination. Results. The agents all relaxed the rabbit corpus cavernosal strips in a dose-dependent manner. The inhibitory potentials of the test agents were ranked (from least inhibitory to most inhibitory) as follows: sildenafil, acetylcholine plus sildenafil, sodium nitroprusside, sodium nitroprusside plus sildenafil, acetylcholine. The presence of sodium nitroprusside in the medium reduced the median effective dose for the sildenafil-induced relaxation of the cavernosal tissue from 3.65 × 10 −5 M to 2.73 × 10 −7 M, and the presence of acetylcholine reduced it to 9.79 × 10 −6 M. Conclusions. Sildenafil enhances the relaxing effect of both sodium nitroprusside and acetylcholine on the phenylephrine-induced contraction of rabbit cavernosal tissue.