The effects of phenobarbitone on urinary 6 beta-hydroxycortisol excretion and hepatic enzyme activity in the guinea-pig.

Urinary 6 beta-hydroxycortisol is a useful, non-invasive index of microsomal mixed-function oxidase activity in man (review: [1]). Administration of phenobarbitone (40 mg/kg/day) for 4 days to male guinea-pigs, produced significant increases in hepatic microsomal cytochrome P-450 content and cytochrome P-450 reductase activity but did not increase 6 beta-hydroxycortisol excretion. The lack of relationship between urinary 5 beta-OHC excretion and microsomal mixed-function oxidase activity in the guinea-pig may be accounted for by the finding that 6 beta-hydroxycortisol itself undergoes extensive and variable metabolism in the guinea-pig.