Nocturnal spikes of growth hormone secretion cause the dawn phenomenon in type 1 (insulin-dependent) diabetes mellitus by decreasing hepatic (and extrahepatic) sensitivity to insulin in the absence of insulin waning.

The aim of the present studies was to test the hypothesis that the dawn phenomenon in Type 1 (insulin-dependent) diabetes mellitus is due to a decrease in insulin sensitivity caused by nocturnal spikes of growth hormone. Twelve subjects with Type 1 diabetes were studied on two different occasions, from 24.00 to 02.00 hours, and from 06.00 to 08.00 hours with the euglycaemic clamp technique at two plasma free insulin levels (approximately 25 mU/l, n = 7; approximately 80 mU/l, n = 5). To eliminate the confounding factor of insulin waning of previous Biostator studies, prior to clamp experiments the diabetic subjects were infused with i.v. insulin by means of a syringe pump according to their minute-to-minute insulin requirements. Insulin sensitivity decreased at dawn as compared to the early night hours (approximately 30% increase in the rate of hepatic glucose production, approximately 25% decrease in the rate of peripheral glucose utilisation). Plasma insulin clearance did not change overnight. In seven Type 1 diabetic subjects, suppression of nocturnal spikes of growth hormone secretion by somatostatin during basal glucagon and growth hormone replacement resulted in complete abolition of the increased rate of hepatic glucose production at dawn. Replacement of nocturnal spikes of growth hormone faithfully reproduced the increase in hepatic glucose production at dawn of the control study.(ABSTRACT TRUNCATED AT 250 WORDS)