title: Effects of morphine in rats treated chronically with U-50,488 H, a kappa opioid receptor agonist.
abstract: The pharmacological effects of morphine, namely analgesic, hyperthermic and cataleptic effects, were assessed in rats rendered tolerant to U-50,488H, a kappa opioid receptor agonist. Male Sprague-Dawley rats were injected intraperitoneally with U-50,488H (25 mg/kg) twice a day for four days. The rats which served as controls were injected similarly with the vehicle. Chronic administration of U-50,488H resulted in the development of tolerance to its analgesic and hypothermic effects, but not to its diuretic effect. The development of tolerance to the pharmacological effects of U-50,488H was associated with decreased binding of [3H]ethylketocyclazocine [( 3H]EKC) to brain and spinal cord membranes. The decreased binding of [3H]EKC in U-50,488H-treated rats was due to changes in the Bmax value; the Kd values remained unaltered. Intraperitoneal administration of morphine (8 mg/kg) to rats produced analgesia (as determined by the tail-flick test) and hyperthermia. A dose of 50 mg/kg of morphine produced cataleptic response. The intensity of analgesic, hyperthermic and cataleptic effects of morphine were unaltered in rats tolerant to U-50,488H. The development of tolerance to analgesic and hypothermic effects of U-50,488H were associated with down-regulation of brain and spinal cord kappa opioid receptors. Finally, U-50,488H does not confer cross-tolerance to morphine, a predominantly mu opioid receptor agonist.
authors.affiliation: Department of Pharmacodynamics, College of Pharmacy, University of Illinois, Chicago 60612.
authors.forename: H N
authors.initials: HN
authors.lastname: Bhargava
authors.forename: P
authors.initials: P
authors.lastname: Ramarao
authors.forename: A
authors.initials: A
authors.lastname: Gulati
mesh_terms: D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D001923:Brain Chemistry / Q000187:drug effects; D002375:Catalepsy / Q000139:chemically induced; D003496:Cyclazocine / Q000031:analogs & derivatives / Q000378:metabolism; D004361:Drug Tolerance; D016314:Ethylketocyclazocine; D008297:Male; D008566:Membranes / Q000378:metabolism; D009020:Morphine / Q000494:pharmacology*; D011759:Pyrrolidines / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000502:physiology*; D017473:Receptors, Opioid, kappa; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism; D013997:Time Factors
chemical_list: D000700:Analgesics; D011759:Pyrrolidines; D011957:Receptors, Opioid; D017473:Receptors, Opioid, kappa; D016314:Ethylketocyclazocine; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D009020:Morphine; D003496:Cyclazocine