Failure of cortisol blockade to inhibit early morning increases in basal insulin requirements in fasting insulin-dependent diabetics

SUMMARY Overnight basal insulin requirements to maintain euglycemia were determined in five insulin-dependent diabetic subjects using a closed-loop insulin infusion system. A significant increase in hourly insulin requirements occurred between 0600 h and 0900 h as compared with 0100 h–0600 h. Although the increased insulin requirement was coincident with only the physiologic diurnal increase in plasma cortisol, the oral administration of the 11-beta hydroxylase inhibitor, metyrapone, decreased only the total overnight (0100 h–0900 h) basal insulin requirement, but not the early morning (0600 h-0900 h) rise in insulin required to maintain euglycemia. It would appear that although cortisol is an important counterregulatory factor, its diurnal elevation cannot account for the increase in early morning basal insulin requirements to maintain euglycemia in insulin-dependent diabetics.