EFFECTS OF PHENOBARBITAL, DEXAMETHASONE, AND 3-METHYLCHOLANTHRENE ADMINISTRATION ON THE METABOLISM OF 17-BETA-ESTRADIOL BY LIVER-MICROSOMESFROM FEMALE RATS

Female rats were treated with phenobarbital, dexamethasone, 3-methylch olanthrene, clofibrate, or isoniazid to induce different hepatic cytoc hromes P-450. The profile of hydroxylated metabolites of estradiol (E( 2)) formed by liver microsomes was then determined using a new HPLC me thod for the separation of hydroxylated estrogen metabolites. Inhibiti on of liver microsomal E(2) metabolism by monoclonal antibodies raised against specific cytochrome P-450 isozymes was also evaluated. Treatm ent of immature or adult female rats with phenobarbital caused a 3-fol d increase in the 2-hydroxylation of E(2) and a more than 5-fold incre ase in the liver microsomal hydroxylation E(2) at the 4-, 6 alpha-, 6 beta-, and 14 alpha-positions. Monoclonal antibody directed toward CYP 2B1/2B2 completely inhibited the 60 alpha- and 6 beta-hydroxylation E( 2) and partially inhibited the 2-hydroxylation of E(2) by liver micros omes from phenobarbital-treated adult female rats. Antibodies directed toward CYP3A1/3A2 completely inhibited the 4- and 14 alpha-hydroxylat ion of E(2) 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 E(2) and a several-fold increase in the hydroxylation of E(2) at the 4-, 6 beta-, 7 alpha-, and 14 alpha-p ositions. A substantial increase in the formation of two unidentified nonpolar metabolite peaks (UK1 and UK2) was also observed. A monoclona l antibody directed against CYP3A1/3A2 markedly inhibited the 2-, 4-, and 14 alpha-hydroxylation of E(2) by liver microsomes from adult fema le rats treated with dexamethasone. Antibody directed against CYP2B1/2 B2 inhibited only the 6 beta-hydroxylation of E(2) by these microsomes . Treatment of immature or adult female rats with 3-methylcholanthrene resulted in a several-fold increase in the metabolism of E(2) to 7 al pha-hydroxyestradiol (7 alpha-OH E(2)) and 15 alpha-OH E(2), but there was a substantial decrease in the formation of 16 alpha-OH E(2). Trea tment with 3-methylcholanthrene caused a small increase in 2-hydroxyla tion (less than or equal to 50%) in liver microsomes from immature or adult female rats, whereas a substantial increase in 6 alpha-hydroxyla tion was seen in liver microsomes from adult female rats. A monoclonal antibody directed toward CYP1A1 partially inhibited the 6 alpha-hydro xylation of E(2) and the formation of the 7 alpha-OH E(2)/15 alpha-OH E(2) peak by microsomes from adult female rats treated with 3-methylch olanthrene, but the 2-hydroxylation of E(2) was not inhibited. Treatme nt of adult female rats with clofibrate increased the 2- and 4-hydroxy lation of E(2) by about 2-fold and by more than 6-fold, respectively. Isoniazid treatment had little or no effect on the metabolism of E(2). The data demonstrate that prototype inducers of cytochrome P-450 can substantially alter the profile of hepatic E(2) metabolism in female r ats. Our results suggest that inducers of environmental relevance may also have an impact on E(2) metabolism and homeostasis in humans.