Effects of phenobarbital, dexamethasone, and 3-methylcholanthrene administration on the metabolism of 17 beta-estradiol by liver microsomes from female rats

Abstract

Female rats were treated with phenobarbital, dexamethasone, 3-methylcholanthrene, clofibrate, or isoniazid to induce different hepatic cytochromes P-450. The profile of hydroxylated metabolites of estradiol (E2) formed by liver microsomes was then determined using a new HPLC method for the separation of hydroxylated estrogen metabolites. Inhibition of liver microsomal E2 metabolism by monoclonal antibodies raised against specific cytochrome P-450 isozymes was also evaluated. Treatment of immature or adult female rats with phenobarbital caused a 3-fold increase in the 2-hydroxylation of E2 and a more than 5-fold increase in liver microsomal hydroxylation of E2 at the 4-, 6 alpha, 6 beta-, and 14 alpha-positions. Monoclonal antibody directed toward CYP2B1/2B2 completely inhibited the 6 alpha- and 6 beta-hydroxylation of E2 and partially inhibited the 2-hydroxylation of E2 by liver microsomes from phenobarbital-treated adult female rats. Antibodies directed toward CYP3A1/3A2 completely inhibited the 4- and 14 alpha-hydroxylation of E2 by these liver microsomes. Treatment of immature or adult female rats with dexamethasone resulted in a 2- to 3-fold increase in the microsomal 2-hydroxylation of E2 and a several-fold increase in the hydroxylation of E2 at the 4-, 6 beta-, 7 alpha-, and 14 alpha-positions. A substantial increase in the formation of two unidentified nonpolar metabolite peaks (UK1 and UK2) was also observed. A monoclonal antibody directed against CYP3A1/3A2 markedly inhibited the 2-, 4-, and 14 alpha-hydroxylation of E2 by liver microsomes from adult female rats treated with dexamethasone. Antibody directed against CYP2B1/2B2 inhibited only the 6 beta-hydroxylation of E2 by these microsomes. Treatment of immature or adult female rats with 3-methylcholanthrene resulted in a several-fold increase in the metabolism of E2 to 7 alpha-hydroxyestradiol (7 alpha-OH E2) and 15 alpha-OH E2, but there was a substantial decrease in the formation of 16 alpha-OH E2. Treatment with 3-methylcholanthrene caused a small increase in 2-hydroxylation (< or = 50%) in liver microsomes from immature or adult female rats, whereas a substantial increase in 6 alpha-hydroxylation was seen in liver microsomes from adult female rats. A monoclonal antibody directed toward CYP1A1 partially inhibited the 6 alpha-hydroxylation of E2 and the formation of the 7 alpha-OH E2/15 alpha-OH E2 peak by microsomes from adult female rats treated with 3-methylcholanthrene, but the 2-hydroxylation of E2 was not inhibited. Treatment of adult female rats with clofibrate increased the 2- and 4-hydroxylation of E2 by about 2-fold and by more than 6-fold, respectively. Isoniazid treatment had little or no effect on the metabolism of E2. The data demonstrate that prototype inducers of cytochrome P-450 can substantially alter the profile of hepatic E2 metabolism in female rats. Our results suggest that inducers of environmental relevance may also have an impact on E2 metabolism and homeostasis in humans.