Effects of phenobarbital upon bile acid synthesis in two strains of rats

Rats of the Wistar and Sprague‐Dawley strains were injected with sodium phenobarbital (100 mg/kg body wt/day) for 8 days. Fecal bile acid excretion was measured on days 6 and 8 of the experiment, and biliary bile acid composition, hepatic microsomal cholesterol, 7α‐hydroxylase, and 7α‐hydroxy‐4‐cholesten‐3‐one 12α‐hydroxylase were determined at the end of the study. In the Wistar rat, injection of phenobarbital produced a doubling of fecal bile acid output (controls, 5.3 mg/rat/day; treated rats, 10.6 mg/rat/day) and a two‐three fold increase in cholesterol 7α‐hydroxylase. The fecal bile acid output of Sprague‐Dawley rats increased 20% in response to phenobarbital (controls, 9.5 mg/rat/day; treated rats, 11.6 mg/rat/day). The activity of cholesterol 7α‐hydroxylase remained unchanged. In both strains, phenobarbital treatment produced a decrease in the proportion of cholic acid in total biliary bile acids (controls, 85%; treated groups, 65%). This was associated with a decrease of 7α‐hydroxy‐4‐cholesten‐3‐one 12α‐hydroxylase activity by ca. 50%. Biliary cholesterol concentrations were reduced in phenobarbital treated rats of both strains, but liver cholesterol concentrations remained unchanged. The drug produced a 25% increase in liver wt, on the average.