Metabolism of caffeine to 6-amino-5-[N-methylformylamino]-1,3-dimethyluracil in the isolated, perfused liver from control or phenobarbital-, beta-naphthoflavone- and 3-methylcholanthrene-pretreated rats.

Caffeine metabolism to 6-amino-5-[N-methylformylamino]-1,3-dimethyluracil was studied in the isolated, perfused rat liver. The [2-14C]-labelled drug and metabolites were separated by thin-layer chromatography or high-pressure liquid chromatography. The chemical structure of 6-amino-5-[N-methylformylamino]-1,3-dimethyluracil was confirmed by mass spectrometry and it was quantitatively determined by liquid scintillation counting. 6-Amino-5-[N-methylformylamino]-1,3-dimethyluracil is one of the major metabolites of caffeine found in the perfusion medium. The kinetics of caffeine elimination and of the uracil metabolite formation were studied up to 2 h perfusion time using livers from control rats and rats pretreated with phenobarbital, beta-naphthoflavone or 3-methylcholanthrene. Phenobarbital pretreatment did not modify the rate of caffeine elimination or the extent of 6-amino-5-[N-methylformylamino]-1,3-dimethyluracil formation. In contrast, there was a highly significant inducing effect on both drug elimination and formation of the uracil metabolite in perfusions of livers from beta-naphthoflavone- and 3-methylcholanthrene-pretreated animals.