FAILURE OF NOCTURNAL CHANGES IN GROWTH-HORMONE TO ALTER CARBOHYDRATE-TOLERANCE THE FOLLOWING MORNING

To determine whether the increases in growth hormone that occur during sleep alter carbohydrate tolerance the following morning, two groups of volunteers were studied on two occasions. In one group saline alone was injected and infused (i.e. no octreotide) on one occasion and on the other octreotide was injected at 23.00 hours to inhibit endogenous growth hormone secretion followed by saline infusion to create a stat e of relative nocturnal growth hormone deficiency. In the other group the octreotide injection was followed on one occasion by a constant gr owth hormone infusion designed to maintain growth hormone concentratio ns at ''basal'' levels throughout the night whereas on the other it wa s followed by a constant infusion plus two supplemental growth hormone infusions given at midnight and 02.30 hours to mimic the normal noctu rnal rise in growth hormone. The next morning, subjects were fed a rad iolabelled mixed meal. The differences in the nocturnal growth hormone concentrations had no effect on the glucose, insulin, C-peptide and g lucagon concentrations following breakfast ingestion nor did they alte r postprandial rates of glucose production, disappearance or substrate oxidation. Thus, the normal nocturnal rise in growth hormone does not appear to be an important regulator of carbohydrate tolerance the fol lowing morning.