Adrenocorticotropic hormone (ACTH), also known as corticotropin, is a polypeptide hormone produced by the anterior pituitary gland. It stimulates the adrenal cortex to release corticosteroids like cortisol in response to biological stress. ACTH acts through cell surface receptors on adrenocortical cells in the adrenal cortex, causing the synthesis and secretion of corticosteroids and androgens. Primary hyperparathyroidism, caused by excess parathyroid hormone (PTH) release from enlarged or abnormal parathyroid glands, is the most common cause of hypercalcemia, or too much calcium in the blood.