Effects of androgens on the expression of nitric oxide synthase mRNAs in rat corpus cavernosum

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Abstract
To examine the effects of androgens on erectile response and the expression of nitric oxide synthase (NOS) isoform mRNAs in the penile corpus cavernosum of castrated rats. The study comprised 50 adult male Sprague-Dawley rats in five groups: sham controls; castrated; castrated and receiving testosterone; castrated and receiving dihydrotestosterone (DHT); castrated and receiving testosterone and 5α-reductase inhibitor (finasteride). Androgen replacements were administered via implants of silicone tubing. After 7 days, some animals underwent electrical stimulation of the cavernosal nerves and the remainder were used for further analysis. NOS activity was measured in the soluble fraction of the corpus cavernosum, using the Griess reaction. Total RNA was isolated and nNOS and eNOS mRNA expression examined using semiquantitative reverse-transcriptase polymerase chain reaction. Castration caused a marked decrease in erectile response and the ratio of maximal intracavernosal pressure (ICPmax) to systemic blood pressure (SBP), although both testosterone and DHT effectively restored the response to normal. NOS activity and the amount of nNOS mRNA were reduced in castrated rats but restored by androgen replacement. Although there was no significant difference in NOS activity between the androgens, nNOS mRNA expression was higher in rats treated with DHT. There were no effects of androgen in rats treated with finasteride, as the ICPmax/SBP ratio, NOS activity and amount of nNOS mRNA decreased. eNOS mRNA expression was independent of androgen. Androgens enhance nNOS gene expression in the penile corpus cavernosum of rats, suggesting that they play an important role in maintaining NOS activity. Of the two androgens, DHT was more potent.