title: Effect of a peripheral and a central acting opioid antagonist on the testicular response to stress in rats.
abstract: The possible involvement of opioid receptors in mediating the inhibitory effects of immobilization stress on testicular steroidogenesis was determined in adult male rats. Unstressed controls and animals exposed to 3 h of immobilization stress were injected subcutaneously with either vehicle or 1 or 10 mg/kg body weight (BW) of naloxone or naltrexone methobromide (NMB; an opioid receptor antagonist that does not cross the blood-brain barrier) at the beginning of and at 1.5 h of the stress period. Animals were sacrificed at 2 h (30 min after the second injection of antagonist) or 3 h (90 min after the second injection of antagonist) of stress. Plasma LH was not affected by stress, but 30 min after naloxone (1 or 10 mg/kg BW) injection, LH was elevated in both control and stressed rats above levels in vehicle-injected animals. By 90 min after naloxone injection, plasma LH had declined to levels comparable to those in vehicle-injected animals. NMB had no effect on plasma LH concentrations in either control or stressed rats. Three hours of stress reduced plasma testosterone (T) levels by 60% in vehicle-injected animals. This effect of stress on plasma T levels was antagonized by the 10 mg/kg BW dose of naloxone and 1 or 10 mg/kg BW of NMB. The ability of naloxone to reverse the effect of stress on plasma T levels was likely related to its ability to stimulate LH secretion, but NMB normalized plasma T values in stressed animals without altering plasma LH concentrations. Only the highest dose of NMB increased plasma T levels in unstressed control animals.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Physiology, Morehouse School of Medicine, Atlanta, GA 30310-1495.
authors.forename: M A
authors.initials: MA
authors.lastname: Akinbami
authors.forename: M F
authors.initials: MF
authors.lastname: Taylor
authors.forename: D C
authors.initials: DC
authors.lastname: Collins
authors.forename: D R
authors.initials: DR
authors.lastname: Mann
mesh_terms: D000446:Aldehyde-Lyases / Q000378:metabolism; D000818:Animals; D003345:Corticosterone / Q000097:blood; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D007103:Immobilization; D007700:Kinetics; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology*; D000644:Quaternary Ammonium Compounds; D051381:Rats; D017208:Rats, Wistar; D013254:Steroid 17-alpha-Hydroxylase / Q000378:metabolism; D013315:Stress, Psychological / Q000503:physiopathology*; D013737:Testis / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D013739:Testosterone / Q000096:biosynthesis / Q000097:blood
chemical_list: D009292:Narcotic Antagonists; D000644:Quaternary Ammonium Compounds; C032257:methylnaltrexone; D009270:Naloxone; D013739:Testosterone; D009271:Naltrexone; D007986:Luteinizing Hormone; D003577:Cytochrome P-450 Enzyme System; D013254:Steroid 17-alpha-Hydroxylase; D000446:Aldehyde-Lyases; D003345:Corticosterone