Adrenocorticotropic hormone

Hormone produced by the anterior pituitary gland

Adrenocorticotropic hormone (ACTH), also known as corticotropin, is a polypeptide hormone produced and secreted by the anterior pituitary gland. It is an important component of the hypothalamic-pituitary-adrenal axis and plays a crucial role in stimulating the production and release of cortisol from the adrenal cortex.

Structure and Synthesis

ACTH is derived from the precursor molecule pro-opiomelanocortin (POMC). The synthesis of ACTH occurs in the corticotrophs of the anterior pituitary gland. POMC is cleaved by specific enzymes to produce ACTH and other peptides, including melanocyte-stimulating hormone (MSH).

Diagram showing the cleavage of pro-opiomelanocortin (POMC) into ACTH and other peptides.

Function

The primary function of ACTH is to stimulate the adrenal cortex to secrete glucocorticoids, primarily cortisol. ACTH binds to specific receptors on the adrenal cortex, activating the adenylate cyclase pathway, which increases the production of cAMP. This cascade ultimately leads to the synthesis and release of cortisol.

Regulation

The secretion of ACTH is regulated by the hypothalamus through the release of corticotropin-releasing hormone (CRH). The release of CRH is influenced by various factors, including stress, circadian rhythm, and negative feedback from circulating cortisol levels.

Clinical Significance

Abnormal levels of ACTH can lead to various disorders. Excessive production of ACTH can result in Cushing's disease, characterized by high levels of cortisol. Conversely, insufficient ACTH production can lead to adrenal insufficiency, such as Addison's disease.

Measurement

ACTH levels can be measured in the blood to assess the function of the hypothalamic-pituitary-adrenal axis. Normal blood levels of ACTH vary depending on the time of day due to its circadian rhythm.

Chart showing blood values sorted by mass and molar concentration, including ACTH.

Related pages

• Cortisol
• Adrenal gland
• Hypothalamus
• Pituitary gland