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

It has been assumed that β-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 β-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 β-endorphin were determined by means of radioimmunometric methods. The effects of β-endorphin on isolated human penile erectile tissue were investigated in vitro. β-endorphin did not induce a contractile response of the cavernous tissue or reverse the contraction induced by noradrenaline. β-endorphin decreased in the systemic blood when the penis became tumescent and rigid and increased during detumescence. In the cavernous blood, no alterations in β-endorphin concentrations were observed. The drop in β-endorphin observed during tumescence and rigidity seems likely to reflect the inhibition of the opioidergic input with the beginning of sexual arousal.