While the adrenal cortex also produces aldosterone (in the zona glomerulosa) and some sex hormones (in the zona reticularis), cortisol is its main secretion in humans and several other species. (However, in cattle, corticosterone levels may approach or exceed cortisol levels.). The medulla of the adrenal gland lies under the cortex, mainly secreting the catecholamines adrenaline (epinephrine) and noradrenaline (norepinephrine) under sympathetic stimulation. The synthesis of cortisol in the adrenal gland is stimulated by the anterior lobe of the pituitary gland with ACTH; ACTH production is, in turn, stimulated by CRH, which is released by the hypothalamus. ACTH increases the concentration of cholesterol in the inner mitochondrial membrane, via regulation of the steroidogenic acute regulatory protein. It also stimulates the main rate-limiting step in cortisol synthesis, in which cholesterol is converted to pregnenolone and catalyzed by Cytochrome P450SCC (side-chain cleavage enzyme). Metabolism
11beta-hydroxysteroid dehydrogenases
Cortisol is metabolized reversibly to cortisone by the 11-beta hydroxysteroid dehydrogenase system (11-beta HSD), which consists of two enzymes: 11-beta HSD1 and 11-beta HSD2. 11-beta HSD1 uses the cofactor NADPH to convert biologically inert cortisone to biologically active cortisol
11-beta HSD2 uses the cofactor NAD+ to convert cortisol to cortisoneOverall, the net effect is that 11-beta HSD1 serves to increase the local concentrations of biologically active cortisol in a given tissue; 11-beta HSD2 serves to decrease local concentrations of biologically active cortisol.
Cortisol is thus better thought of as stimulating glucose/glycogen turnover in the liver. This is in contrast to cortisols effect in the skeletal muscle where glycogenolysis is promoted indirectly through catecholamines. Metabolism of proteins and lipids
Elevated levels of cortisol, if prolonged, can lead to proteolysis (breakdown of proteins) and muscle wasting. The reason for proteolysis is to provide the relevant tissue with a feedstock for gluconeogenesis; see glucogenic amino acids. The effects of cortisol on lipid metabolism are more complicated since lipogenesis is observed in patients with chronic, raised circulating glucocorticoid (i.e. cortisol) levels, although an acute increase in circulating cortisol promotes lipolysis. The usual explanation to account for this apparent discrepancy is that the raised blood glucose concentration (through the action of cortisol) will stimulate insulin release. Insulin stimulates lipogenesis, so this is an indirect consequence of the raised cortisol concentration in the blood but it will only occur over a longer time scale. Immune response
Cortisol prevents the release of substances in the body that cause inflammation. It is used to treat conditions resulting from overactivity of the B-cell-mediated antibody response. Examples include inflammatory and rheumatoid diseases, as well as allergies. Low-dose topical hydrocortisone, available as a nonprescription medicine in some countries, is used to treat skin problems such as rashes and eczema. Cortisol inhibits production of interleukin 12 (IL-12), interferon gamma (IFN-gamma), IFN-alpha, and tumor necrosis factor alpha (TNF-alpha) by antigen-presenting cells (APCs) and T helper cells (Th1 cells), but upregulates interleukin 4, interleukin 10, and interleukin 13 by Th2 cells.