Aim: To investigate the effects of androgen on penile erection through the reflex arc and penile corpus cavernosum, and study the respective roles of testosterone (T) and dihydrotestosterone (DHT) in penile erection in rats. Methods: Male Sprague-Dawley rats were castrated and implanted with silastic brand silicone tube containing T or DHT, with or without daily injections of a 5-reductase inhibitor, MK-434. The penile reflex, erectile response to electrical stimulation (ES) of the cavernous nerves and penile nitric-oxide synthase (NOS) activity were observed under varying androgenic status. Results: Penile reflex erection in the rat was, on the whole, related to serum T levels though the number of glans engorgements was not. The number of cups and flips was significantly decreased by castration, and restored to the control level by T supplementation. Erectile response to ES and NOS activity in penile tissue was also related to serum T level. T administered together with a 5-reductase inhibitor nolonger restored the number of reflex erection, erectile responses to ES and NOS activity in the corpus cavernosum. Conclusion: Androgen influenced the penile reflex arc, corpus cavernosum, and the perineal striated muscles. In reflex erection, erectile response to ES and penile NOS activity in the rat, T seems to be first converted to DHT, the more active androgen modality.

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