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

Objectives. To investigate the effect of sildenafil together with the influ ence of sodium nitroprusside and acetylcholine and further discuss its mech anism of action in vitro. Methods, Isolated strips of rabbit corpus cavernosum were stimulated isomet rically with phenylephrine. Graded relaxations were induced using increasin g concentrations of acetylcholine, sodium nitroprusside, and sildenafil alo ne and in combination. Results, The agents all relaxed the rabbit corpus cavernosal strips in a do se-dependent manner. The inhibitory potentials of the test agents were rank ed (from least inhibitory to most inhibitory) as follows: sildenafil, acety lcholine plus sildenafil, sodium nitroprusside, sodium nitroprusside plus s ildenafil, acetylcholine. The presence of sodium nitroprusside in the mediu m reduced the median effective dose for the sildenafil-induced relaxation o f the cavernosal tissue from 3.65 x 10(-5) M to 2.73 x 10(-7) M, and the pr esence of acetylcholine reduced it to 9.79 x 10(-6) M. Conclusions. Sildenafil enhances the relaxing effect of both sodium nitropr usside and acetylcholine on the phenylephrine-induced contraction of rabbit cavernosal tissue. UROLOGY 58: 119-124, 2001. (C) 2001, Elsevier Science I nc.