Effects of phenobarbital, phorone and carbon tetrachloride pretreatment on the biliary excretion of acetaminophen in rats.

Rats with cannulated bile ducts excreted 24.6% of an i.v. dose of 100 mg/kg acetaminophen (AA) into bile within 8 hr, 0.9% as unchanged drug, 5.5% as sulfate, 15.1% as glucuronide and 3.1% as the glutathione conjugate. Pretreatment with phenobarbital (0.1% solution for 7 days instead of drinking water) significantly decreased the amount of total AA recovered in bile, to 12.8% mainly as a consequence of reduced glucuronide excretion (3.5%), whereas the GSH-conjugate was augmented to 6.3%. Pretreatment with the GSH-depletor phorone (250 mg/kg i.p. 1 hr prior to AA) slightly reduced the total recovery of AA to 19.2%, due to a diminished excretion of the glucuronide (10.3%). Liver damage due to carbon tetrachloride administration (0.5 ml/kg p.o. 24 hr prior to AA) markedly decreased the total recovery of AA to 8.9% as a consequence of the reduction of the glucuronic acid (5.0%) and the GSH-conjugates (0.2%). These observations are discussed with respect to the effects of phenobarbital, phorone and CCl4 on microsomal and cytosolic GSH-dependent enzymes involved in the metabolism of AA.