The role and regulation of testicular opioids.
Endogenous opioids are present in the male gonad and may be involved in the local control of testicular function. Testicular opioids are mainly produced in Leydig cells and exert direct paracrine inhibitory actions on the tubule, which in turn may have indirect Sertoli-cell-mediated effects on Leydig cell steroidogenesis. Gonadotropins and CRF stimulate production of gonadal opioids, and the presence of a gonadotropin milieu appears to be a requisite for the inhibitory paracrine actions of opioids on steroidogenesis. The recognition of such multiple intratesticular hormonal interactions should provide insights into the mechanisms involved in idiopathic infertility in men.
Fabbri
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Molecular Endocrinology Section, Endocrinology and Reproduction Research Branch, National Institutes of Health, Bethesda, MD 20814, USA.