ANDROGENS MODULATE THE ALPHA-ADRENERGIC RESPONSIVENESS OF VASCULAR SMOOTH-MUSCLE IN THE CORPUS CAVERNOSUM

Rat penile erection is an androgen-dependent process with castration l eading to a loss of potency. The present study was designed to determi ne if one of the mechanisms by which androgens maintain the erectile r esponse is the regulation of the alpha-adrenergic responsiveness of ca vernosal smooth muscle. Electrical stimulation of the major pelvic gan glion (MPG) was used to elicit erection in untreated, castrated rats ( CASTRATE) or castrated rats given testosterone replacement (TESTO). Th e effects of phenylephrine (an alpha(1)-adrenergic agonist) and prazos in (an alpha(1)-adrenergic antagonist) on the erectile response were i nvestigated. Phenylephrine, when administered to both TESTO and CASTRA TE animals during erection, resulted in a dose-dependent decrease in t he intracavernosal pressure (CCP) with an ED(50) value of 1.8 +/- 0.48 mu g/kg BW for TESTO rats; in the CASTRATE animals, the ED(50) was si gnificantly reduced to 0.29 +/- 0.08 mu g/kg BW. The increases in mean arterial pressure (MAP) resulting from phenylephrine injection in TES TO and CASTRATE animals were of similar magnitude and were not signifi cantly different. Prazosin administration resulted in an enhancement o f the erectile response in CASTRATE but not in TESTO animals. Taken to gether these results demonstrate that the cavernosal vasculature in CA STRATE animals possesses increased reactivity to alpha-adrenergic stim ulation as compared to the sensitivity in TESTO rats. Based on these f indings, we conclude that one of the mechanisms by which androgens mai ntain erectile function is by regulating the alpha(1)-adrenergic respo nsiveness of the cavernosal smooth muscle.