Influence of growth hormone on glucose-induced glucose uptake in normal men as assessed by the hyperglycemic clamp technique

To determine whether physiological increments in circulating GH concentrations influence glucose-induced glucose uptake (GIGU), two-step sequential hyperglycemic clamp (plasma glucose, 6 and 14 mmol/L) studies were performed in six normal subjects with and without GH infusion (40 ng/kg.min). The latter resulted in serum GH levels of 15 +/- 1 (+/- SE) microgram/L. Infusion of somatostatin (250 micrograms/h during step 1 and 750 micrograms/h during step 2) together with a replacement dose of insulin (1.1 pmol/kg.min) resulted in serum insulin levels comparable to basal levels in both studies. The GIGU ([3-3H]glucose), assessed as the difference between steps 2 and 1 glucose utilization during the final 60 min of each step (150 min) was markedly impaired during GH infusion (with GH, 1.1 +/- 0.2 mg/kg.min; without GH, 3.1 +/- 0.3 mg/kg.min; P less than 0.001). Moreover, the percent increase in glucose uptake was considerably reduced during hypersomatotropinemia (with GH, 44 +/- 9%; without GH, 97 +/- 11%; P less than 0.01). In the GH infusion as well as control studies, endogenous glucose production (EGP) was similar at the two levels of glycemia, whereas GH infusion approximately doubled EGP [2.3 +/- 0.2 vs. 1.1 +/- 0.3 mg/kg.min and 2.0 +/- 0.4 vs. 1.1 +/- 0.4 mg/kg.min (step 1 and 2, respectively)]. We conclude that moderate hypersomatotropinemia for several hours is characterized by impaired GIGU as well as augmented EGP.