Adrenocorticotropic Hormone (ACTH), also known as corticotropin, hormone secreted by the anterior part of the pituitary gland. The specific function of ACTH is to stimulate the growth and secretions of the cortex (outer layer) of the adrenal gland. One of these secretions is cortisone, a hormone involved in carbohydrate and protein metabolism. ACTH is used medically for its anti-inflammatory action to alleviate symptoms of allergies and arthritis. ACTH is a complex protein molecule containing 39 amino acids. Its molecular weight is approximately 5000. The biological activity of the ACTH of various animal species is similar to that of humans, but the sequence of amino acids has been found to vary somewhat among species. ACTH production is controlled in part by the hypothalamus and in part by the existing levels of adrenal gland hormones. ACTH levels increase in response to stress, disease, and decreased blood pressure.