Gastric inhibitory polypeptide-dependent cortisol hypersecretion - a new cause of Cushing's syndrome

Cushing's syndrome may be caused by an increased cortisol response to gastric inhibitory polypeptide (GIP) in patients with nodular adrenal hyperplasia, or enlargement of the adrenal glands. Cushing's syndrome is a disorder characterized by excess secretion of the steroid hormone cortisol by the adrenal glands. Pituitary-adrenal gland function in a 48-year-old woman with Cushing's syndrome and nodular adrenal hyperplasia was compared to that of five other patients with Cushing's syndrome and four healthy individuals. The patient's blood levels of cortisol were low-to-normal between meals and higher than normal after meals. Her blood levels of cortisol increased after ingestion of oral glucose (sugar) or after lipid-rich or protein-rich meals, but not after receiving intravenous (IV) glucose. Blood levels of cortisol increased after IV administration of GIP for one hour in the patient, but not in the four healthy individuals.