Adrenocorticotrophic hormone ACTH

Adrenocorticotrophic hormone is a 39 amino acid peptide which is secreted by corticotroph cells of the anterior pituitary, being cleaved from a precursor molecule, pro-opiomelanocortin (POMC). It is secreted in a pulsatile fashion, with a diurnal rhythmicity. Peak secretion is in early morning, with a trough in late evening. Secretion of ACTH is controlled by closed loop feedback responsive to changes in serum cortisol, and by an open-loop component related to neurally mediated stimuli such as stress.

5 Corticotrophin releasing hormone, a 41 amino acid hypothalamic peptide, g stimulates secretion and release of pro-opiomelanocortin and its derivatives g from the anterior pituitary. Pro-opiomelanocortin is the precursor for ACTH, y a-, ,0-, and 7-MSH, ^-lipoprotein and endorphins. ACTH binds to cell membrane

§• receptors in the adrenal cortex, activating adenyl cyclase. Steroidogenesis is y initiated in the mitochondria by the binding of cholesterol to a C27 side chain cleavage enzyme, thereby starting its step-wise conversion to pregnenolone.

Secretagogues for ACTH include CRH, vasopressin, catecholamines, angioten-sin II, atrial natriuretic peptide and serotonin.

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