Comparative effects of dilator drugs on human penile dorsal artery and deep dorsal vein

The present study was designed to characterize the response of human penile dorsal artery and deep dorsal vein to dilator drugs used in the diagnosis and treatment of erectile dysfunction with special emphasis on the effects on sympathetic neurotransmission. Ring segments of penile dorsal artery and deep dorsal vein were obtained from 20 multi-organ donors during procureme nt of organs for transplantation. The rings (3 mm long) were suspended in o rgan bath chambers for isometric recording of tension. We then studied the relaxant responses to prostaglandin E-1 (PGE(1)), vasoactive intestinal pep tide (VIP), papaverine (PV), sodium nitroprusside (SNP) and linsidomine chl orhydrate (SIN-1), and analysed the effects of these drugs on contractions induced by stimulation of perivascular sympathetic nerves. In artery and ve in rings contracted by noradrenaline, all the drugs tested caused concentra tion-dependent relaxation. The order of potencies in terms of IC50 values ( concentration of agonist causing 50% of the maximal relaxation) was PGE(1) = VIP > SNP > SIN-1 = PV. Both arteries and veins contracted to electrical field stimulation (15 V, 0.5-2 Hz, 0.2 ms duration for 15 s) in a frequency -dependent manner. All relaxant drugs caused concentration-dependent inhibi tion of neurogenic contractions; the relative order of potencies was PGE(1) > VIP > SNP > SIN-1 = PV. It is concluded that inhibition of sympathetic a ctivity constitutes an effective relaxing mechanism in penile dorsal artery and vein. Modulation of sympathetic activity together with the direct effe cts on smooth muscle should be considered to evaluate adequately the effica cy of relaxant drugs to increase human penile blood supply.