Adrenocorticotropic hormone

Adrenocorticotropic hormone (ACTH), also known as corticotropin, is a polypeptide tropic hormone produced and secreted by the anterior pituitary gland. It is an important player in the body's stress response and has a role in maintaining body homeostasis.

Function

ACTH stimulates the adrenal cortex, the outer part of the adrenal gland, to produce and release cortisol, a steroid hormone. This is done by binding to the ACTH receptor (or melanocortin 2 receptor) located on the cells of the adrenal cortex.

Cortisol, the primary stress hormone, increases sugars (glucose) in the bloodstream, enhances the brain's use of glucose and the availability of substances that repair tissues. It also curbs functions that would be nonessential in a fight or flight situation.

Production and Regulation

The production of ACTH is regulated by the hypothalamic-pituitary-adrenal (HPA) axis. The hypothalamus releases corticotropin-releasing hormone (CRH), which directs the pituitary gland to produce ACTH. In turn, ACTH directs the adrenal glands to produce and release cortisol. Cortisol then feeds back to both the pituitary and hypothalamus to decrease the production of ACTH and CRH.

Clinical Significance

Abnormal levels of ACTH can lead to serious conditions. Overproduction of ACTH can lead to Cushing's syndrome, characterized by a buildup of cortisol in the blood. Symptoms may include high blood pressure, abdominal obesity but with thin arms and legs, reddish stretch marks, a round red face, and a fat lump between the shoulders.

On the other hand, underproduction of ACTH can lead to secondary adrenal insufficiency. This is characterized by fatigue, nausea, loss of appetite, and skin darkening.

Measurement and Interpretation

Measurement of ACTH in the blood can be used to diagnose diseases related to the pituitary or adrenal glands. It is usually measured in the morning when ACTH levels are at their highest.