The Effect of Testosterone on Nitric Oxide Synthase in the Penis of the Rabbit

Purpose: Androgen was thought to be linked to sexual activity in man but its peripheral action have not been identified precisely. Recently, androgens dependent nature of nitric oxide synthase(NOS), the enzyme system producing nitric oxide(NO) as the principal mediator in penile erection, has been studied. The present study was designed to determine if NO within the penis is regulated by androgen. Materials and Methods: Effect of testosterone on the penile NO was investigated from three groups of rabbit; control(a sham operation), castration group(four sub-groups: 1, 2, 3 and 4 weeks after castration) and testosterone replacement group(four sub-groups: testosterone propionate(10㎎/day) was given subcutaneously from 1, 2, 3 and 4 weeks after castration for 7 days respectively). Strips of rabbit corpus cavernosum were isolated and mounted in organ chambers. The relaxation effects were assessed with electrical field stimulation(EFS) in the precontracted cavernosal muscle strips with phenylephrine. Penile NOS activity was measured by the rate of 14C-L-arginine-citrulline conversion. Penile tissue was subsequently stained for the presence of NOS, using a nicotinamide adenine dinucleotide phosphate diaphorase(NADPH-d) histochemistry. Results: EFS evoked a relaxation of rabbit corpus cavernosum. A gradual decrease in the EFS evoked relaxation was recorded, proportional to the duration of being castrated, which was restored to the level of control by testosterone replacement. After castration, penile NOS activity was significantly reduced to 51.3%, 43.7%, 37.5%, and 32.7% of the level of control at 1, 2, 3, 4 weeks. This decrease in penile NOS activity after castration was also restored by testosterone replacement. Diffusely scattered delicate nerve fibers showing blue color reaction after NADPH-d histochemical staining were reduced in castrated cavernosum in comparison with control. Conclusions: Based on presented data we conclude that testosterone plays a direct role in penile erection by regulating the activity of NOS within the penis.prohibitio