3 - Catabolism of the Adrenocortical Hormones

Abstract

Publisher Summary The biosynthesis of the active adrenocortical steroids is predominantly an oxidative process, progressing from the simple cholesterol molecule via a series of hydroxylating steps to the polyhydroxylated 3-oxo-4-ene structure characteristic of the corticosteroids. The deactivation, or catabolism, of these steroids on the other hand is mainly a reductive process, leading predominantly to tetrahydro derivatives of the 3β-hydroxy-5β type. Oxidative processes do, however, take place to some extent during catabolism, leading to the products of hydroxylation and side-chain cleavage. This chapter discusses the catabolic transformation of the steroids of adrenal origin—the corticosteroids, including aldosterone, and dehydroepiandrosterone (DHA) and its sulfate. It also discusses the catabolism of the androgens and estrogens as these can themselves be considered as catabolites of the corticosteroids. The endocrine glands that secrete the steroids contribute very little to their metabolism although many of the steroid oxidases, reductases, hydroxylases, and sulfotransferases are also present in the gonads and adrenals. With the exception of the feto-placental unit, extrahepatic tissues are not of great importance in the catabolism of steroids. The chapter discusses the most catabolic transformations of the adrenal steroids—reduction at C-20 and ring A, hydroxylation, side-chain cleavage, and conjugation.