The effect of daily ingestion of caffeine on the microsomal enzymes of rat liver.

The effect of repeated ingestion of caffeine on rat-liver microsoma Jenzymes was studied. In the rat, ingestion of 20-24 mg caffeine/kg/day in the drinking water for more than 2 wk inhibited aminopyrine N-demethylase activity. This loss of activity approached 60 ~o at the end of an 8-wk dosing schedule. Acetanilide-hydroxylating activity of rat-liver microsomal enzyme was initially stimulated, with a peak (145 + 11 ~ of control) at 2 wk, and returned to normal levels at the end of 8 wk. Caffeine-treated rats did not respond to the phenobarbitone stimulation of microsomal enzymes to the same extent as did rats treated with phenobarbitone alone.