title: Effect of thyrotropin releasing hormone on the development of tolerance to the analgesic and hyperthermic actions of morphine in the rat.
abstract: The effect of thyrotropin releasing hormone (TRH) on the development of tolerance to the analgesic and hyperthermic actions of morphine was determined in male Sprague-Dawley rats. The tolerance to morphine was induced by subcutaneous implantation of 6 morphine pellets, each containing 75 mg of morphine free base. Rats serving as controls were implanted with 6 placebo pellets. Subcutaneous injections of TRH (1, 3 or 10 mg/kg) twice a day for 7 days inhibited the development of tolerance to the analgesic, but not to the hyperthermic action of morphine. Doses lower than 1 mg/kg or greater than 10 mg/kg administered twice a day for 7 days did not modify tolerance development. The inability of higher doses of TRH to inhibit tolerance to morphine may be related to rapid down-regulation of TRH receptors. The results suggest that in appropriate doses, TRH can selectively inhibit the development of tolerance to the analgesic action of morphine.
authors: Department of Pharmacodynamics, University of Illinois, Chicago 60612.
authors: P
authors: P
authors: Ramarao
authors: H N
authors: HN
authors: Bhargava
mesh_terms: D000818:Animals; D004361:Drug Tolerance / Q000502:physiology; D005334:Fever / Q000139:chemically induced*; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D010146:Pain / Q000503:physiopathology*; D051381:Rats; D011919:Rats, Inbred Strains; D013973:Thyrotropin-Releasing Hormone / Q000502:physiology*
chemical_list: D013973:Thyrotropin-Releasing Hormone; D009020:Morphine