Adenocorticotropic hormone

Adrenocorticotropic hormone (ACTH, also known as corticotropin) is a tropic hormone and an important player in the HPA axis. It is produced and released by the anterior pituitary gland. ACTH acts on its target organ, the adrenal glands, by stimulating the release of cortisol.

Structure and Function
There is a two-step process for the release of ACTH. First, the hypothalamus releases corticotropin-releasing hormone (CRH) through the hypophyseal portal system to stimulate the anterior pituitary gland. Corticotropin-releasing hormone is normally released in response to biological stress, and is a part of the general stress response. The anterior pituitary gland responds by releasing ACTH, targeting the adrenal glands (specifically the adrenal cortex). ACTH stimulates the production and secretion of glucocorticoid steroid hormones from the adrenal cortex. Cortisol is one of the principal hormones secreted, and is released into the bloodstream where it helps convert fats and proteins into glucose, and has an anti-inflammatory effect. ACTH also affects the production of aldosterone in the adrenal cortex. Aldosterone facilitates sodium reabsorption and potassium secretion in the kidneys. Thus, ACTH is important in glucose, fat, and protein metabolism, the immune system’s response, and maintenance of blood pressure.

Dysfunction
Pathophysiology of ACTH arises from dysfunction of the pituitary, the adrenal glands, or ectopic secretion. If the pituitary is hypo- or hyper-functioning, there will be a respective decrease or increase in ACTH secretion. If the adrenal glands are hypo- or hyper-functioning, the response to ACTH may be muted or exaggerated. Ectopic secretion describes the secretion of ACTH from an abnormal source, such as a tumor, such that normal regulatory pathways do not control such levels.

Pathophysiologies associated with ACTH dysregulation include :
 * Hypopituitarism
 * Pituitary adenoma
 * Sheehan syndrome
 * Cushing’s disease and syndrome


 * Addison’s disease


 * Hypercortisolism
 * Small cell carcinoma

ME
As ACTH is a major hormone in the HPA axis, ACTH may be related to myalgic encephalomyelitis (ME) because HPA axis dysregulation has been associated with ME. However, studies in this area have found a wide range in results; a 2007 review of HPA function in ME found that about half of all studies indicated HPA hypofunction in ME, whereas the other half of the studies did not find differences in ACTH within HPA function between ME and controls. This could be partly explained by how some patients report higher levels of ACTH and cortisol early in the disease, with depleted/lower levels as the disease progresses.

Learn more

 * Anatomy and Physiology | ACTH