Human Biochemistry, Volume 2 - Murray R. 1993

Biochemistry of Intracellular and Intercellular Communications
Adrenal Cortex Hormones
Hormones

About 50 Steroids have been isolated from the adrenal cortex tissue and obtained in crystalline form. Most of them are intermediates; only a few are secreted in significant quantities, and very few possess substantial hormonal activity. The adrenal cortex produces three Major Classes of Steroid Hormones, which are grouped according to their predominant action. Overall, their biological activities overlap; thus, all natural glucocorticoids exhibit mineralocorticoid effects and, conversely, mineralocorticoids possess glucocorticoid activity. Glucocorticoids are 21-carbon steroids that exert a variety of effects, the most important of which is The stimulation of Gluconeogenesis. The primary human glucocorticoid is cortisol, produced in the zona fasciculata. Corticosterone, produced in the zona fasciculata and zona glomerulosa, is present in smaller amounts in humans, but is the principal glucocorticoid in rodents. Mineralocorticoids also belong to the 21-carbon steroids. The primary action of these hormones is to promote Na⁺ retention and K⁺ and H⁺ excretion, mainly via the Kidneys. The most potent hormone in this Class is aldosterone, produced exclusively in the zona glomerulosa. The zona fasciculata and zona reticularis produce significant amounts of the androgen precursor dehydroepiandrosterone and the weak androgen androstenedione. These steroids are converted into more potent androgens in extra-adrenal Tissues and, in cases of steroidogenic enzyme deficiencies, serve as a pathological source of androgens. As for estrogens, they are not normally produced by the Adrenal Glands in notable amounts; however, they can be secreted in certain adrenal tumors. Adrenal androgens serve as the primary precursors of estrogens (via peripheral aromatization) in postmenopausal women.

Fig. 48.1. Characteristic elements of steroid Structure.