Characterization of the activation of hepatic microsomal hydroxylation by betamethasone and α naphthoflavone

Biphenyl 2-hydroxylation is selectively activated in vitro by incubation of betamethasone or α naphthoflavone with control male rat liver microsomes. Biphenyl 3- and 4-hydroxylation activities are unchanged or marginally inhibited. The nature of the enzymes involved in the activation has been investigated. Metyrapone (1 mM) completely inhibited the expression of the activation but had a lesser effect on the basal 2-, 3- and 4-hydroxylation activities. SKF525A (1 mM) 2 inhibited both basal and betamethasone-activated enzyme activities by 25–35 per cent. Of other drug metabolizing enzymes investigated, only benzoa]pyrene hydroxylation activity was increased by betamethasone and α naphthoflavone. Acetone (0.6M) caused a small activation (40 per cent) of biphenyl 2-hydroxylation but inhibited 4-hydroxylation. The non-ionic detergent Brij 35 inhibited biphenyl 2-, 3- and 4-hydroxylation. It was concluded that activation of biphenyl 2-hydroxylation differs from activation of aromatic amine hydroxylation and glucuronyl transferase but may be related to activation of benzoa]pyrene hydroxylation by naphthoflavones.