Mestranol-induced hypertension: Characterization of cytochrome P-450 dependent catechol estrogen formation in brain microsomes

Abstract

An animal model of estrogen-induced hypertension was used to study the effects of chronic administration of the synthetic estrogen mestranol on cytochrome P-450 content and catechol estrogen formation in brain microsomes. Cytochrome P-450 content of brain microsomes from untreated female rats in estrus was 0.034 nmole/mg protein and the dithionite-reduced carbon monoxide absorbance peak (γ max) was 452 nm. Catechol estrogen formation in brain microsomes was optimal in the presence of both NADPH and NADH cofactors with an apparent K m value of 71 μM for 17β-estradiol substrate. Brain microsomes from animals in estrus and diestrus were compared, and no significant differences were observed in cytochrome P-450 content, or in the apparent K m and V max values of catechol estrogen formation. Administration of mestranol, 15 μg biweekly, for 3–4 weeks resulted in a significant increase in systolic blood pressure in unanesthetized female rats. Mestranol treatment was not associated with a change in microsomal cytochrome P-450 content or the spectral γ max. At 10 μM substrate concentration, catechol estrogen formation in microsomes from mestranol-treated animals was increased 2- to 3-fold, with enzyme activity being expressed either per mg protein or per nmole cytochrome P-450. In contrast, no difference was observed between groups when enzyme activity was measured at 100 μM substrate concentration. These data suggest that chronic administration of a synthetic estrogen can regulate the enzyme system involved in formation of brain catechol estrogen metabolites, a mechanism which may alter the biological impact of the parent steroid.