The stimulating ligands binding to G protein–coupled receptors are various: glucose-dependent insulinotropic peptide receptor (GIPR) responsible for food-dependent Cushing syndrome [51, 52], luteinizing hormone/human chorionic gonadotropin receptor responsible for Cushing syndrome during pregnancy and after menopause [53], and vasopressin, catecholamine, serotonin (5-hydroxytryptamine), angiotensin II, and glucagon receptors [54-60]. Here, GCGR is linked to Cushing syndrome.