THE EFFECT OF ACUTE STRESS AND OPIOID ANTAGONIST ON THE ACTIVITY OF NADPH-P450 REDUCTASE IN RAT LEYDIG-CELLS

Previous studies indicate that acute immobilization stress (IMO; 2 h) impaired testicular steroidogenesis primarily at the testicular level decreasing the activity of certain steroidogenic enzymes. In the prese nt study unstressed rats as well as IMO rats (2 h) were treated by int ratesticular injection of naltrexone methobromide (NMB; peripheral opi oid receptor antagonist; 36 mu g/testis) or vehicle at the beginning o f and at I h of the IMO period. In IMO rats the activity of P450c17 wa s significantly reduced as well as the activity of NADPH-P450 reductas e (which catalyzes the transfer of electrons from NADPH to cytochrome P450), while the activity of NADH-b5 reductase was not affected. Prese nt data confirmed previous results that acute IMO reduced testicular P 450c17 activity and implicate that decreased activity of NADPH-P450 re ductase could be responsible for the inhibition of P450c17 under IMO c onditions, while NADH-b5 reductase is probably not involved. NMB treat ment antagonized the inhibitory effect of IMO on P450c17 and NADPH-P45 0 reductase activities. Such results put forward the implication that endogenous opioid peptides are involved in mediating the inhibitory ef fect of IMO on testicular steroidogenesis, and allow the speculation t hat NADPH-P450 reductase could be a possible site of such an inhibitio n. (C) 1998 Elsevier Science Ltd. All rights reserved.