In vitro-perifused rat testes secrete beta-endorphin and dynorphin: their effect on testosterone secretion

Leydig cells of many species synthesize and secrete opioid peptides, but the Sertoli and possibly the peritubular cells are the only intratesticular cells having opiate receptors. It is known that Sertoli and peritubular cells can modify the secretion of testosterone from Leydig cells. To test the hypothesis that testicular opioid peptides participate in a Leydig-Sertoli-peritubular-Leydig cell feedback loop that can regulate the intratesticular concentration of testosterone, we have developed a method for the in vitro perifusion of rat testicular fragments in which the intratesticular structure and thus the paracrine feedback loop remains intact. Our data show that both immunoreactive (IR)-beta-endorphin and IR-dynorphin were present in the testicular perifusion effluent; gel chromatography of pooled perifusion effluent show that the bulk of the secreted IR-beta-endorphin had the apparent mol. wt. of synthetic rat beta-endorphin whereas most of the secreted IR-dynorphin was composed of smaller than 4000 mol. wt. forms. On the other hand, the bulk of IR-dynorphin present in rat testicular tissue homogenates eluted in two higher mol. wt. peaks. The effect of mu and kappa opioid agonists and naloxone (a universal opioid antagonist) on both basal and gonadotropin-stimulated testosterone secretion from perifused testicular fragments was then examined; no stimulatory or inhibitory effect of the opioid receptor agonists or naloxone was found on basal and gonadotropin-stimulated testosterone secretion. Parallel experiments with Leydig cells in culture gave similar results.(ABSTRACT TRUNCATED AT 250 WORDS)