May 1, 1976

Disposition of (15,16-3H)naltrexone in the central nervous system of the rat

Drug Metabolism and Disposition : the Biological Fate of Chemicals
A L MisraK Verebely

Abstract

After injection of (15,16-3H)naltrexone (10 mg/kg s.c.) in male Wistar rats, peak concentrations of drug occurred in brain and plasma within 0.5 hr. Levels of naltrexone were sustained in brain between 2 and 24 hr and were barely detectable at 48 hr. Significant amounts of metabolities were present in brain and plasma at longer time periods. The t1/2 of naltrexone in brain and plasma were approximately 8.0 and 11.4 hr. respectively. The brain/plasma ratios of naltrexone at earlier times (0.5-1 hr) were higher than those at later times. The binding of naltrexone in vitro with rat plasma proteins in concentrations of 1-10 mug/ml ranged between 41 and 59% 6beta-Naltrexol was present in very small amounts in brain but not in plasma. In addition to 7,8-dihydro-14-hydroxynormophinone and 7,8-dihydro-14-hydroxynormophine, tentative evidence was obtained for three other metabolites of naltrexone in brain. These metabolites were also present in plasma in addition to free and conjugated naltrexone and its N-dealkylated metabolites.

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Mentioned in this Paper

Blood - Brain Barrier Anatomy
Brain
Entire Central Nervous System
Plasma Proteins
Naltrexone
Metabolite
Rats, Wistar
Naloxone, (5 beta,9 alpha,13 alpha,14 alpha)-Isomer
In Vitro [Publication Type]
Thin Layer Chromatography

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