Of 11 structurally related steroids, 5α-androstane-3β,17β-diol was the one most efficiently hydroxylated to polar metabolites by microsomes isolated from the rat ventral prostate. The metabolites were identified by gas chromatography-mass spectrometry as 6α-, 7α-, and presumably 6β-hydroxylated 5α-androstane-3β,17β-diol. The hydroxylated metabolites were separated and quantitated by high performance liquid chromatography using an aminopropylsilane hypersil column. Maximum velocity (V(max)) values of 0.36, 0.12, and 0.044 nmol/min.mg of microsomal protein were determined for the 6α-, 7α-, and 6β-hydroxylase activities, respectively, with an apparent Michaelis-Menten constant (K(m)) of 30 μM for all hydroxylases. Hydroxylation of 5α-androstane-3β,17β-diol in prostatic microsomes was NADPH dependent and was inhibited by several cytochrome P-450 inhibitors in vitro and by antibodies against rat liver NADPH-cytochrome P-450 reductase. The enzyme activities were stimulated by treatment of the rats with phenobarbital, β-naphthoflavone, 5α-androstane-3β,17β-diol, 5α-dihydrotestosterone, and methyltrienolone, whereas the activities were suppressed by ovine PRL, human GH, estradiol benzoate, cholesterol, adrenalectomy, hypophysectomy, and castration. It is concluded that the prostatic 5α-androstane-3β,17β-diol hydroxylase activities represent a constitutive cytochrome P-450 form in the rat ventral prostate with a high steroid substrate specificity. Endocrine factors are involved in the regulation of the activity of the enzyme. The ratio between the 3 hydroxylated metabolites was constant in almost all experiments suggesting that only one cytochrome P-450 species was involved in the hydroxylation.
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