Elsevier

Urology

Volume 56, Issue 3, September 2000, Pages 533-538
Urology

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

https://doi.org/10.1016/S0090-4295(00)00667-1Get rights and content

Abstract

Objectives. To elucidate the effect of testosterone on penile nerve supply.

Methods. Three groups of 10 rats each were assessed; two groups were castrated and the third underwent a sham operation (control). After castration, one group received subcutaneous injection of testosterone while the others received sesame oil. At 8 weeks, the rats underwent a functional analysis. The evaluation included a subcutaneous injection with apomorphine to study centrally mediated erection, and cavernous nerve electrostimulation and papaverine injection to study peripherally mediated erection. At death, a penile midshaft specimen was taken for nicotinamide adenine dinucleotide phosphate (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 level of the controls. The mean numbers of NADPH-diaphorase-stained nerve fibers 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 pressure 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 system to mediate erection. When it is absent, there may be downregulation of both the production and activity of nitric oxide (NO), thereby decreasing the response to peripheral stimulation via the NO pathway. Testosterone replacement may upregulate NO activity to the control level.

Section snippets

Animal preparation

Two-month-old male Sprague-Dawley rats were divided into three groups of 10 each: castrated, control, and castrated + testosterone groups. All animals were ear-tagged for identification and housed 3 per cage. Light was maintained on a 12-hour light/dark cycle, with the dark cycle starting at 6 pm.

On day 1, the control rats underwent a sham operation (consisting mainly of scrotal exploration) and the other two groups underwent castration. At 1 and 5 weeks after surgery, the control and castrated

Apomorphine study

Castration inhibited the sexual behavior induced by apomorphine. The number of erections in 30 minutes for the castrated, control, and castrated + testosterone groups were 0, 4.8 ± 0.9, and 8.0 ± 1.6, respectively. A difference in the number of times of yawns in 30 minutes for the castrated, control, and castrated + testosterone groups were observed to be 0.5 ± 0.3, 18.8 ± 3.8, and 48.5 ± 4.5 (Fig. 1).

Electrostimulation study

The intracavernosal pressure in the castrated group, in response to electrostimulation of the

Comment

Several studies have established that NO is the principal mediator of arterial dilation and smooth muscle relaxation within the sinusoids, which bring about tumescence of penile erectile tissue.15 In vitro study has shown that electrical field stimulation of cavernosal tissue leads to an increase in NO and cyclic guanine monophosphate, and the relaxation of cavernosal smooth muscle.16 Furthermore, this response can be completely blocked by a low dose of N-nitroarginine and N-methyl-arginine,

Conclusions

The present study indicated that testosterone acts on the nervous system to mediate erection. The removal of testosterone by castration may incur downregulation of both the production and activity of NO, thereby decreasing the response to peripheral stimulation via the NO pathway.

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    Dr. Serge Carrier was supported by a grant from the Fonds de Recherche en Santé du Québec.

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