ACTH is a single-chain polypeptide originate from proopiomelanocortin (POMC) in the pituitary, its half-life in the circulation in humans is about 10 min. In humans, maximum production of cortisol occurs between 4:00 AM and 10:00 AM.A second smaller peak occurs in evening time. It stimulates the secretion of Cortisol (and adrenal androgens) of adrenal cortex. Cortisol supÂpresses the release of ACTH by acting on the hypothalamus and anterior pituitary.
Corticotropin-Releasing Hormone (CRH): Secretion of CRH increases in response to stress & in the early morning. It then increase ACTH level.
Note : POMC is the precursor of ACTH as well as several other peptides, including melanocyte stimulating hormone (MSH), b-lipotropin, b-endorphin etc.