Effects of Androgen on Expression of Androgen Receptor mRNA and Penile Erection in the Rat

Seo, Seongil; Paick, Jae Seung

Abstract

PURPOSE: Although it is well known that androgens have beneficial effects on erectile dysfunction, their precise roles have been contentious. Recently it has been shown in the rat that castration induces loss of penile reflexes and considerable reduction in the erectile response to electrical stimulation(ES) of the cavernosal nerve. Both of these effects can be reversed by testosterone replacement. In this study, we have investigated the effects of androgen on the expressions of androgen receptor(AR), penile reflex(glans engorgement, cup, flip), erectile response to electrical stimulation, and penile NOS activity.
MATERIALS AND METHODS
Male Sprague-Dawly rats(300-35Og) were castrated and implanted with silastic brand silicone tube containing dihydrotestosterone (DHT) or testosterone with or without daily injections of the 5a-reductase inhibitor(MK434). Animals of control groups were either sham operated or castrated with no androgen supplementation. All animals were maintained for 7 days under normal animal house conditions. Penile tissues were removed and processed either for Northern hybridization using [a-32P]UTP-labelled cKNAs and for measurement of NOS activities. In penile reflex, number of glans engorgement. flip and cup were measured in each group and compared with control. And, ES-induced intracarvenosal pressure(ICP)/systolic blood pressure(SBP) ratio and penile NOS activities of each groups were compared with control.
RESULTS
Penile AR mRNA expressions were down-regulated by androgen Penile reflex erection was significantly reduced in castrated group and restored to the control level by androgen supplementation. However, the reflex erection was decreased in MK434-treated group. Erectile response to ES and penile NOS activity of each group showed similar patterns.
CONCLUSIONS
These results showed that androgen might play a important role in regulation of penile erection and its actions were mediated by AR. Androgens, especially DHT, were essential modulators of the normal penile function including erectile relaxation of the cavernous smooth muscle, their effects being mediated, at least partially, by changes in nitric oxide synthase levels.