Adrenocorticotropin (ACTH) occurs in cells of the anterior pituitary and in neurons in brain. It regulates the corticosteroid production in the adrenal cortex. Beta endorphin and Met enkephalin are endogenous opiates. MSH (melanocyte stimulating hormone) increases the pigmentation of skin by increasing melanin production in melanocytes. ACTH can alter pain sensitivity. The effect of corticosteroids like ACTH on the sensitivity to pain is an indirect one by virtue of their negative feedback action on the hypothalamic-pituitary system.