The adrenocorticotropic hormone (ACTH), or corticotropin, is a small proteinaceous hormone secreted by the anterior lobe of the pituitary gland. It controls the secretion of other hormones of the cortex of the adrenal gland. It stimulates the adrenal gland to produce the coricosteroid hormones.
Pituitary secretion of ACTH (adrenocorticotropic hormone) regulates adrenal steroidogenesis by stimulating the synthesis and release of cortisol, the major glucocorticoid; the adrenal androgens; and aldosterone, the most potent mineralocorticoid. Of these, only cortisol exerts a negative feedback effect on ACTH release.
ACTH is a 39 amino acid polypeptide derived from pro-opiomelanocortin (POMC). This large protein, synthesized in the pituitary, also contains the amino acid sequence for beta-endorphins, the endogenous opioids, and beta-melanocyte stimulating hormone. The first 13 amino acids of ACTH also have melanocyte stimulating activity. Thus, clinical states of ACTH excess are associated with hyperpigmentation proportional to the chronicity and severity of the ACTH elevation.
ACTH secretion is characterized by acute secretory bursts conforming to a circadian rhythm. Frequent secretory bursts that occur during REM sleep (rapid extraocular muscle movements) prior to awakening in the early morning produce the highest ACTH and cortisol levels. Normal circadian periodicity involved in ACTH release is readily altered by stressful stimuli such as trauma, exercise, fever, vaso-active substances, hypoglycemia, and emotional distress. Stress may produce direct CNS stimulation of the hypothalamus, resulting in the release of corticotropin releasing hormone (CRH) into the hypothalamic–pituitary portal system that mediates ACTH synthesis and release. Overstimulation of the ACTH-secreting cells of the pituitary by CRH may result in a micro or macroadenoma demonstrable by pituitary CT. CRH is currently under clinical investigation to determine its usefulness in the diagnosis of pituitary ACTH pathology and other functional disorders of CNS, such as endogenous depression.
Sources:
1. National Library of Medicine - Medical Subject Headings, 2008 MeSH
2. Louis F. Amorosa. Clinical Methods X. The Endocrine System. Abbreviated Tests of Endocrine Function