Adrenocorticotropic Hormone (ACTH, Corticotropin)
Adrenocorticotropic hormone, as its name implies, stimulates the adrenal cortex. More specifically, it stimulates secretion of glucocorticoids such as cortisol, and has little control over secretion of aldosterone, the other major steroid hormone from the adrenal cortex.
ACTH is secreted from the anterior pituitary in response to corticotropin-releasing hormone from the hypothalamus. corticotropin-releasing hormone is secreted in response to many types of stress, which makes sense in view of the "stress management" functions of glucocorticoids. Corticotropin-releasing hormone itself is inhibited by glucocorticoids, making it part of a classical negative feedback loop.
Within the pituitary gland, ACTH is produced in a process that also generates several other hormones. A large precursor protein named proopiomelanocortin (POMC, "Big Mama") is synthesized and proteolytically chopped into several fragments as depicted below. Not all of the cleavages occur in all species and some occur only in the intermediate lobe of the pituitary.
The major attributes of the hormones other than ACTH that are produced in this process are summarized as follows:
- Lipotropin: Originally described as having weak lipolytic effects, its major importance is as the precursor to beta-endorphin.
- Beta-endorphin and Met-enkephalin: Opioid peptides with pain-alleviation and euphoric effects.
- Melanocyte-stimulating hormone (MSH): Known to control melanin pigmentation in the skin of most vertebrates.
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