This study was designed to investigate the effects of sildenafil and zaprinast, two inhibitors of type 5 cyclic guanosine monophosphate phosphodiesterase (PDE5), on human penile dorsal and cavernous arteries (approved by Ethics Committee of our Institution). Artery rings obtained from eighteen multiorgan donors were suspended in organ bath chambers for isometric recording of tension at 37°C. Sildenafil (10^-9-3 X 10^-5 M) caused concentration-dependent relaxation in precontracted arteries that was of greater magnitude in dorsal (median effective concentration, EC₅₀ = 4.7 X 10^-8 M) than in cavernous artery (EC₅₀ = 2.3 X 10^-7 M). Compared with sildenafil, zaprinast was 12 times less potent (EC₅₀ = 3.8 X 10^-7 M) in the dorsal artery and seven times (EC₅₀ = 3.5 X 10^-6 M) in the cavernous artery. Sildenafil (10^-7 M) and zaprinast (10^-6 M) potentiated the relaxation induced by sodium nitroprusside (10^-10-10^-5 M) in the dorsal artery. In the cavernous artery the potentiating effect was small. However, the response to sodium nitroprusside was greater in the cavernous artery (EC₅₀ = 6.1 X 10^-9 M) than in the dorsal artery (EC₅₀ = 6.0 X 10^-8 M). The results demonstrate that PDE5 inhibitors sildenafil and zaprinast have a modest relaxant effect on human cavernous artery, probably due to a low PDE5 activity in this artery.

This work was supported by the Ministerio de Sanidad and Generalitat Valenciana.