Endothelin-1-induced vasoconstriction is inhibited during erection in rats

Recent evidence indicates that endothelin-1 (ET-1) might be a principal vas oconstrictor in the penis. We report that ET-1 injection into the cavernous sinuses before erection sharply reduced the magnitude of subsequent erecti ons. Corpus cavernosum pressure-to-mean arterial pressure ratios (CCP/MAP), with maximal ganglionic stimulation, were 0.62 +/- 0.05 before ET-1 inject ion and 0.31 +/- 0.05 after, indicating that ET-1 acted as a vasoconstricto r. When ET-1 was injected during a maximal neurally induced erection, the a bility of ET-1 to attenuate subsequent erections was diminished (CCP/MAP 0. 75 +/- 0.02 before ET-1, 0.61 +/- 0.03 after). At submaximal stimulation vo ltages, injection of ET-1 during erection also attenuated its vasoconstrict ive effect. Similarly, when ET-1 was injected during erection induced by in tracavernosal injection of the nitric oxide (NO) donor NOR-1, subsequent er ections were not significantly suppressed (CCP/MAP 0.53 +/- 0.04 before ET- 1, 0.45 +/- 0.04 after). These findings that ET-1-induced vasoconstriction is attenuated during erection are consistent with the hypothesis that NO me diates erection both by initiating pathways that cause smooth muscle relaxa tion and by inhibiting the vasoconstrictive actions of ET-1.