Regulation of testosterone hydroxylation by rat liver microsomal cytochrome P-450

Abstract

The pathways of testosterone oxidation catalyzed by purified and membrane-bound forms of rat liver microsomal cytochrome P-450 were examined with an HPLC system capable of resolving 14 potential hydroxylated metabolites of testosterone and androstenedione. Seven pathways of testosterone oxidation, namely the 2α-, 2β-, 6β-, 15β-, 16α-, and 18-hydroxylation of testosterone and 17-oxidation to androstenedione, were sexually differentiated in mature rats (male/female = 7–200 fold) but not in immature rats. Developmental changes in two cytochrome P-450 isozymes largely accounted for this sexual differentiation. The selective expression of cytochrome P-450h in mature male rats largely accounted for the male-specific, postpubertal increase in the rate of testosterone 2α-, 16α-, and 17-oxidation, whereas the selective repression of cytochrome P-450p in female rats accounted for the female-specific, postpubertal decline in testosterone 2β-, 6β-, 15β-, and 18-hydroxylase activity. A variety of cytochrome P-450p inducers, when administered to mature female rats, markedly increased (up to 130-fold) the rate of testosterone 2β-, 6β-, 15β-, and 18-hydroxylation. These four pathways of testosterone hydroxylation were catalyzed by partially purified cytochrome P-450p, and were selectively stimulated when liver microsomes from troleandomycin- or erythromycin estolate-induced rats were treated with potassium ferricyanide, which dissociates the complex between cytochrome P-450p and these macrolide antibiotics. Just as the testosterone 2β-, 6β-, 15β-, and 18-hydroxylase activity reflected the levels of cytochrome P-450p in rat liver microsomes, so testosterone 7α-hydroxylase activity reflected the levels of cytochrome P-450a; 16β-hydroxylase activity the levels of cytochrome P-450b; and 2α-hydroxylase activity the levels of cytochrome P-450h. It is concluded that the regio- and stereoselective hydroxylation of testosterone provides a functional basis to study simultaneously the regulation of several distinct isozymes of rat liver microsomal cytochrome P-450.