THE EFFECT OF OPIOID ANTAGONISTS IN LOCAL-REGULATION OF TESTICULAR RESPONSE TO ACUTE STRESS IN ADULT RATS

The present study examined the effects of naloxone (N) and naltrexone- methobromide (NMB; an opioid receptor antagonist that does not cross t he blood-brain barrier) on testicular steroidogenesis during acute imm obilization stress (IMO; 2 h) in adult rats. Unstressed rats as well a s IMO mts were treated by unilateral intratesticular injection of N (2 0 mu g/testis), NMB (36 mu g/testis), or vehicle at the beginning of a nd at 1 h of the IMO period. in IMO rats serum T levels were significa ntly reduced, while serum luteinizing hormone levels were not affected , N and NMB normalized serum T levels in IMO rats and had no effects i n controls. In IMO rats the activities of 3 beta-hydroxysteroid dehydr ogenase (HSD) and P450(17 alpha,lyase) were significantly reduced, whi le the activity of 17 beta-HSD was nor affected. N and NMB antagonized the inhibitory effect of IMO on 3 beta-HSD and P450(17 alpha,lyase) b ut did not alter enzyme activity in freely moving rats. Acute IMO decr eased basal and human chorionic gonadotropin-stimulated androgen produ ction by hemitestis preparation, but N (10(-4) M) added directly to th e incubation medium blocked the decrease and had no effect on testes f rom freely moving control rats. These results support the conclusion t hat endogenous opioid are potentially important paracrine regulators o f testicular steroidogenesis under stress conditions. (C) 1997 by Else vier Science Inc.