INTRACELLULAR DISPOSITION OF H³-MORPHINE IN THE BRAIN AND LIVER OF NONTOLERANT AND TOLERANT GUINEA PIGS

¹ National institute of Mental Health, Addiction Research Center, and Department of Pharmacology, University of Kentucky Medical Center, Lexington, Kentucky

This study was initiated to ascertain the intracellular localization of H3-morphine and to determine the effect of both tolerance and nalorphine on the intracellular disposition of this drug. H3-morphine was prepared by catalytic exchange and was purified, and a specific activity of 9.2 mc/mmol was obtained. A sensitive and specific method for the estimation of H3-morphine in the intracellular fractions was utilized. After differential centrifugation the chemical and enzymatic composition of the subcellular fractions were determined. One hour after the s.c. administration of 10 mg/kg (free base) of H3-morphine, the intracellular localization of the drug was determined in the brain and liver of nontolerant, tolerant and nalorphine-antagonized guinea pigs. The mean percentage values for the nontolerant guinea-pig brain fractions were: 10% crude nuclei; 14% crude mitochondria; 6% microsomes; 68% supernatant; 1% subnuclear N1; 2% purified nuclei N₂; in the submitochondrial fractions, 3% myelin fragments (A); 1 % nerve ending fragments with synaptic vesicles (B); 1% cholinergic nerve endings (C); 0.2% noncholinergic nerve endings (D); 1% free mitochondria (E); hypoosmotic shock of the crude mitochrondria, 4% swollen mitochondria (M1); 1% synaptic vesicles (M2); and 8% supernatant (M3). The mean percentage values for the nontolerant guinea-pig liver fractions were: 25% crude nuclei; 3% purified nuclei; 10% mitochrondria; 11% microsomal-1 8% microsomal-2 4% smooth mierosomes; 3% rough microsomes: and 52% supernatant. Neither the development of tolerance nor the administration of nalorphine to the nontolerant and tolerant animals altered significantly the subcellular localization of H³-morphine. It is concluded that morphine was primarily localized in the supernatant fractions of brain and liver as free drug and that neither tolerance nor nalorphine antagonism alters the intracellular disposition of morphine.