Distribution and Excretion of Radioactivity after Administration of Morphine-N-methyl C14 to Rats.

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Abstract
After the admini-stration of morphine-N-methyl-C14 to rats, radioactivity concen-trated chiefly in the urinary and intestinal tracts with only minimal amounts in the central nervous system. Urinary excretion pre-dominated but there is evidence for an entero-hepatic circulation of morphine or its metabolites following initial excretion by the liver in the bile. Male rats excreted significantly more radio-activity via the pulmonary route than did females. Treatment of females with cyclopentyl testosterone propionate increased their pulmonary excretion to the male level. Liberation of C1402 by liver slices from male and female rats to which morphine-N-methyl-Cl4 was added in vitro followed the same pattern. Liver homogenates did not liberate C14O2.