Regulation of Hydroxylation of 5α-Androstane-3α, 17β-diol in Liver Microsomes from Male and Female Rats

Abstract

Abstract The metabolism of 5α-[4-14C]androstane-3α, 17β-diol was studied in the microsomal fraction of livers from adult male and female rats after castration and treatment with various steroid hormones and drugs. In intact male control rats 5α-[4-14C]androstane-3α, 17β-diol was hydroxylated in positions 2α, 2β, 7α, 7β, and 18, whereas female control rats only hydroxylated in positions 2α and 7α. Castration had no effect on the activities of the 2α- and 7α-hydroxylase systems in female rats but led to decreased activities of the 2α-, 2β-, 7β-, and 18-hydroxylase systems in male rats. The activities of these four enzyme systems were restored by treatment with testosterone propionate, 5α-dihydrotestosterone and 5α-androstane-3α, 17β-diol but similar treatment of castrated female rats had a very small effect on the hydroxylase activities and demonstrated a relative androgen unresponsiveness in postpubertal female rats. The 7α-hydroxylase system active on 5α-[4-14C]androstane-3α, 17β-diol was more active in female rats; this enzyme system was found to be primarily regulated by nongonadal factors and only slightly affected by androgens. Treatment of castrated male rats with estradiol benzoate led to a complete feminization of the activities of the liver microsomal hydroxylase systems. The activities of all hydroxylase systems active on 5α-[4-14C]androstane-3α, 17β-diol in both male and female rats decreased in incubations carried out in the presence of carbon monoxide indicating that carbon monoxide binding pigments were involved in all hydroxylations studied. Administration of phenobarbital and 16α-cyanopregnenolone to castrated male and female rats led to increased activities of all hydroxylase systems in both sexes even if quantitative sexual differences in responses were observed. Methylcholanthrene treatment specifically stimulated 7αhydroxylation, especially in female rats. It is speculated that 7α-hydroxylation of 5α-[4-14C]androstane-3α, 17β-diol is mainly carried out with cytochrome P-448 as the hemoprotein component and that the 2α-, 2β-, 7β-, and 18-hydroxylase systems mainly use cytochrome P-450 as hemoprotein. The hydroxylation of 5α-[4-14C]androstane-3α, 17β-diol was also studied in male and female rats 0, 7, 18, 28, 35, 42, and 56 days of age. No sexual differences were found in prepubertal rats and in these animals 2α-, 2β-, 7α-, and 18-hydroxylations were of the same order of magnitude as in adult male rats and regulated by nongonadal factors. At the time of puberty, sexual differences were found to develop and the control of the activities of the 2α-, 2β-, 7α-, and 18-hydroxylase systems changed from nongonadal to androgenic regulation.