Steroid hormones: Synthesis, secretion, and transport

Abstract

In mammalian systems, there are six families of steroid hormones that can be classified on both a chemical and a biological basis. They are the estrogens, progesterone, androgens, mineralocorticoids, glucocorticoids, and vitamin D. These steroid hormones play a critical role in numerous physiological and pathophysiological processes and consequently garnered substantial research interest over the last century. The vast majority of circulating steroids in mammals come from the endocrine activity of the gonads and adrenal glands, which metabolize the lipid cholesterol to generate the steroid repertoire. Numerous investigations spanning decades have painstakingly elucidated the molecular enzymes and reactions of steroidogenesis distributed throughout the mitochondrial and microsomal compartments of steroidogenic cells. This chapter deals with the biosynthetic pathways, release, and transport of the major classes of steroid hormones in mammals. In particular, steroidogenesis is discussed as a single process that is repeated in each gland with cell type-specific variations on a single theme. Moreover, the homeostatic mechanisms that regulate the secretion or release of the steroid hormones and precursor hormone by feedback loops or by biological rhythms have been also discussed. Finally, the role of steroid-specific plasma transport proteins and the local inactivation of the excess of active steroids inside the cells are reported in order to obtain a clear picture on how the concentrations of active steroid hormones are regulated.