A polypeptide hormone secreted by the alpha cells of the islets of Langerhans in response to hypoglycemia or to stimulation by growth hormone. It increases blood glucose concentration by stimulating glycogenolysis in the liver and can be administered parenterally to relieve severe hypoglycemia from any cause, especially hyperinsulinism. Because it slows motility of the gastrointestinal tract, it is also used as an aid in gastrointestinal radiography.
