Effect of testosterone on the number of NADPH diaphorase-stained nerve fibers in the rat corpus cavernosum and dorsal nerve

Objectives. To elucidate the effect of testosterone on penile nerve supply. Methods. Three groups of 10 rats each were assessed; two groups were castra ted and the third underwent a sham operation (control). After castration, o ne group received subcutaneous injection of testosterone while the others r eceived sesame oil. At 8 weeks, the rats underwent a functional analysis. T he evaluation included a subcutaneous injection with apomorphine to study c entrally mediated erection, and cavernous nerve electrostimulation and papa verine injection to study peripherally mediated erection. At death, a penil e midshaft specimen was taken for nicotinamide adenine dinucleotide phospha te (NADPH) diaphorase staining. Results. In the apomorphine study, castrated rats had no erections, but the erectile function of those receiving testosterone was restored to the leve l of the controls. The mean numbers of NADPH-diaphorase-stained nerve fiber s in the copora cavernosa and both dorsal nerves of castrated rats, at 165. 8 +/- 20.0 and 271.3 +/- 21.1, respectively, were significantly lower than those of the controls, at 271.7 +/- 14.6 and 471.2 +/- 27.6, respectively. Those of the testosterone replacement group, at 290.7 +/- 10.1 and 500.7 +/ - 23.9, respectively, recovered to the control level. The intracavernosal p ressure decreased significantly in the absence of testosterone, both after electrostimulation and intracavernosal papaverine injection, and recovered to the control level after testosterone replacement. Conclusions. Our results indicate that testosterone acts on the nervous sys tem to mediate erection. When it is absent, there may be downregulation of both the production and activity of nitric oxide (NO), thereby decreasing t he response to peripheral stimulation via the NO pathway. Testosterone repl acement may upregulate NO activity to the control level. UROLOGY 56: 533-53 8, 2000. (C) 2000, Elsevier Science inc.