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

Summary After the administration of morphine-N-methyl-C14 to rats, radioactivity concentrated chiefly in the urinary and intestinal tracts with only minimal amounts in the central nervous system. Urinary excretion predominated but there is evidence for an enterohepatic circulation of morphine or its metabolites following initial excretion by the liver in the bile. Male rats excreted significantly more radioactivity via the pulmonary route than did females. Treatment of females with cyclopentyl testosterone increased their pulmonary excretion to the male level. Liberation of C14O2 by liver slices from male and female rats to which morphine-N-methyl-C14 was added in vitro followed the same pattern.