IN-VITRO EFFECTS OF BETA-ENDORPHIN ON TESTICULAR RELEASE OF ANDROGENSIN THE LIZARD PODARCIS-SICULA RAF

The effects of the proopiomelanocortin-derived opioid peptide, beta-en dorphin (beta-EP), and of the opioid antagonist, naloxone (NAL), on bo th basal and pituitary-stimulated androgen secretion from superfused q uiescent and active testes were assessed in the adult lizard, Podarcis sicula. In the absence of the homologous pituitary, in vitro treatmen t with beta-EP and/or NAL did not affect basal secretion of androgens from quiescent and active testes. Conversely, in the presence of the h omologous pituitary, treatment with beta-EP brought about a decrease i n androgen secretion in active testes, but no effect on quiescent ones . Naloxone counteracted the inhibitory effect of beta-EP in active tes tes, and enhanced maximal pituitary-stimulated secretion of androgens in quiescent but not in active testes. The effects produces by beta-en dorphin and naloxone were reversible. These results suggest that, in t his lizard, opioids might be involved in the control of androgen relea se. The lack of effect of beta-EP and naloxone when added directly to the testes seems to suggest that the opioid agonist and antagonist act on androgen release by modulating pituitary gonadotrophin output. (C) 1996 Wiley-Liss, Inc.