Is ß-endorphin significant in the control of the male sexual response?

ABSTRACT

It has been assumed that ß-endorphin, belonging to the family of opiodergic neuropeptides, might facilitate the inhibition of the male sexual response; however, its role in the control of the penile erectile tissue remains to be elucidated. This study aimed to evaluate in healthy men the course of ß-endorphin in the systemic and cavernous blood through different stages of sexual arousal. Thirty-four (34) men were exposed to erotic stimuli to induce penile tumescence and rigidity. Blood was aspirated from the corpus cavernosum and a cubital vein during the penile conditions flaccidity, tumescence, rigidity and detumescence. Plasma levels of ß-endorphin were determined by means of radioimmunometric methods. The effects of ß-endorphin on isolated human penile erectile tissue were investigated in vitro. ß-endorphin did not induce a contractile response of the cavernous tissue or reverse the contraction induced by noradrenaline. ß-endorphin decreased in the systemic blood when the penis became tumescent and rigid and increased during detumescence. In the cavernous blood, no alterations in ß-endorphin concentrations were observed. The drop in ß-endorphin observed during tumescence and rigidity seems likely to reflect the inhibition of the opioidergic input with the beginning of sexual arousal.