Adrenocorticotropic hormone (ACTH), also known as corticotropin, is a polypeptide tropic hormone produced and secreted by the anterior pituitary gland. It is an important component of the hypothalamic-pituitary-adrenal axis and is often produced in response to biological stress (along with corticotropin-releasing hormone from the hypothalamus). Its principal effects are increased production and release of corticosteroids and, as its name suggests, cortisol from the adrenal cortex.
ACTH is synthesized from pre-pro-opiomelanocortin (pre-POMC). The removal of the signal peptide during translation produces the 241-amino acid polypeptide POMC, which undergoes a series of post-translational modifications such as phosphorylation and glycosylation before it is proteolytically cleaved by endopeptidases to yield various polypeptide fragments with varying physiological activity. These fragments include NPP, Melanotropin Gamma (γ-MSH), Potential Peptide, Corticotropin (Adrenocorticotropic Hormone, or ACTH), Melanotropin Alpha (Melanocyte-Stimulating Hormone, or α-MSH), Corticotropin-like Intermediate Peptide (CLIP), Lipotropin Beta (β-LPH), Lipotropin Gamma (γ-LPH), Melanotropin Beta (β-MSH), Beta-Endorphin, and Met-Enkephalin. POMC, ACTH and β-lipotropin are secreted from corticotropes in the anterior lobe (or adenohypophysis) of the pituitary gland in response to the hormone corticotropin-releasing hormone (CRH) released by the hypothalamus.
In order to regulate the secretion of ACTH, many substances secreted within this axis exhibit slow/intermediate and fast feedback-loop activity. Glucocorticoids secreted from the adrenal cortex work to inhibit CRH secretion by the hypothalamus, which in turn decreases anterior pituitary secretion of ACTH. Glucocorticoids may also inhibit the rates of POMC gene transcription and peptide synthesis. The latter is an example of a slow feedback loop, which works on the order of hours to days, whereas the former works on the order of minutes.
ACTH is also related to the circadian rhythm in many organisms. The half-life of ACTH in human blood is about ten minutes.