Diurnal variation in oral glucose tolerance: Insulin and growth hormone changes with special reference to women taking oral contraceptives

Summary Plasma glucose, immunoreactive insulin, and growth hormone (GH) have been estimated during morning (AM) and afternoon (PM) oral glucose tolerance tests (GTT) in a group of 22 subjects, 13 of whom were young women receiving combined oestrogen-progestogen oral contraceptives. Impaired PM glucose tolerance with associated delay and impairment of insulin secretion has been confirmed, as has the inverse correlation between obesity and diurnal GTT variation. Diurnal changes in GH are unlikely to be responsible for this circadian GTT rhythm. Patients on oral contraceptives continue to show a normal GTT rhythm, so that a mildly abnormal AM test is likely to be associated with a more severely diabetic PM test. These observations indicate that while obesity and oral contraceptive use may have metabolic features in common, they differ in this respect; they support the view that, if possible, carbohydrate tolerance should be monitored in women taking oral contraceptives in whom a tendency to diabetes is suspected.