Intraadrenal steroid metabolism in the guinea pig: Guinea pig adrenal microsomes metabolize androstenedione in a manner distinct from liver microsomes

Abstract

Several immunochemical homologs of hepatic cytochromes P450 (CYPs) capable of steroid catabolism have been identified in the guinea pig adrenal cortex. Their predominance in males suggests a role in sex-differentiated metabolism of androgens. Therefore, we examined the ability of microsomes from male guinea pig adrenals and liver to metabolize androstenedione. Microsomes were incubated in the presence of radiolabeled steroids, the products of the reaction extracted, separated by TLC, and visualized by autoradiography. Metabolites were identified by comigration with commercially available standards in several solvent systems, in one and two dimensional TLC. Microsomes from both tissues metabolized androstenedione. However, the products formed differed markedly in the two tissues. Liver microsomes formed one major metabolite, testosterone. It represented 85% of the metabolized androstenedione. 6β-Hydroxylated androstenedione and testosterone each comprised 3-4% of the liver metabolites. In addition, at least 10 other products were formed, but taken together they constituted less than 8% of the metabolized androdostenedione. Adrenal microsomes, on the other hand, produced several major metabolites: 16α-, 16β-, and 6β-hydroxy-androstenedione, plus one unidentified product constituted 93% of the metabolized androstenedione. 16α-Hydroxylation of androstenedione was 60 fold, 16β-hydroxylation 12 fold, and 6β-hydroxylation 2.5 fold greater in adrenal than in liver microsomes. The unidentified product, which was the least polar, was formed exclusively by adrenal microsomes. The hydroxyiation reactions periomed by adrenal tissue are consistent with the presence in adrenal microsomes of immunochemical homologues of members of the CYP1A, 2B, 2C and 3A families which have known steroid hydroxyiation functions in liver. The Kms of the formation of 16α-, 16β- and 6β-hydroxyandrostenedione by adrenal microsomes are in the range reported for steroid hydroxyiation reactions in rat liver tissue. Their distinct values suggest that these hydroxylation steps are performed by different CYPs. However, assignment of site-specific steroid hydroylation reactions to individual hepatic CYP homologs in the adrenal requires further investigation and is being pursued using combined techniques of biochemistry and molecular biology.