Distribution and metabolism in vivo of 14C-tetrahydrocannabinol in the rat

14 C-Tetrahydrocannabinol (THC) was injected i.v. into a total of 92 adult Wistar rats. At 14 times ranging from 2 min to 48 hr afterwards, groups of animals were examined for total 14 C activity and thin-layer chromatographic (TLC) pattern of 14 C distribution in blood, brain, heart, kidney, liver, lung, muscle, spleen and perirenal fat. The time course of rise and fall of radioactivity in the various organs and tissues closely resembled that of thiopental and other strongly lipophilic substances. Relatively high levels persisted in fat 48 hr, but levels in brain were quite low. TLC analysis showed the early appearance of 7-hydroxy-THC in all tissues, followed by increasing amounts of more polar compounds and disappearance of THC, except in fat. Levels were much lower after i.p. injection, and whole body autoradiography showed most of the activity remaining in the peritoneal cavity.