Effect of beta-endorphin and naloxone on rat testicular steroidogenesis.

With a view to examine the possibility of a direct role of opioids in the regulation of testicular steroidogenesis, the following in vivo and in vitro experiments were conducted in male rats of different age groups. Intratesticular (i.t.) injections of beta-endorphin (beta-EP) and its antagonist naloxone (nal) were given bilaterally to adult (80-100 days), peripubertal (40 days) and juvenile (20 days) rats and blood was collected at different time intervals up to 90 min and assayed for testosterone (T). beta-EP suppressed T levels in all age groups of rats while naloxone stimulated T secretion only in adult rats. In another experiment, adult rats were also injected with 60 IU of hCG (sc) after 30 min. of beta-EP/nal treatment. Naloxone induced a greater rise in T in the presence of hCG while beta-EP blocked the hCG induced rise in testosterone. In the in vitro sets of experiments, isolated interstitial cells from testes of adult, 40 and 20 days old rats were incubated for 4 hr with hCG (25 IU), beta-EP (0.5ng) and nal (5.0ng) alone or in combinations. Naloxone alone was ineffective although it significantly enhanced hCG stimulated T release. beta-EP decreased both basal and hCG stimulated T release. Based on these results we postulate that opioids may influence steroidogenesis possibly by altering the response of interstitial cells to LH.