Activation of hepatic microsomal biphenyl 2-hydroxylation by corticosteroids.

1. 4-Hydroxylation was a major route of biphenyl metabolism in liver microsomes from control and phenobarbitone-pretreated rats, with 2- and 3-hydroxybiphenyl as lesser metabolites. 2. Many corticosteroids, when added to the microsomal incubation mixture, selectively increased 2-hydroxylation with little or no effect on 3- and 4-hydroxylation. Betamethasone caused the greatest activation (400%). 3. In liver microsomes from controls hamsters and 3-methylcholanthrene-pretreated rats, the basal hydroxylase activity, especially 2-hydroxylation, was much higher, but the quantitative increase following betamethasone addition was similar to that in liver microsomes from control and phenobarbitone-pretreated rats. 4. Pretreatment of rats with betamethasone also resulted in a small increase in biphenyl 2-hydroxylation activity after 4 h, returning to control values after 6 h. 5. In vitro addition of estradiol or testosterone had no effect on either basal or betamethasone-activated biphenyl 2-hydroxylation.