The aim of this present investigation was to study the relationship between the reduction in insulin sensitivity accompanying 5 days of treatment with growth hormone (GH; 0.05mgċ24h-1ċkg-1) and intracellular substrate oxidation rates in six healthy subjects, while maintaining glucose flux by a constant glucose infusion and adjusting insulin infusion rates to achieve normoglycaemia (feedback clamp). Protein synthesis rates in skeletal muscle (flooding dose of L-[2H5]phenylalanine) were determined under these conditions. We also compared changes in insulin sensitivity after GH treatment with simultaneous changes in energy requirements, protein synthesis rates, nitrogen balance, 3-methylhistidine excretion in urine, body composition and the hormonal milieu. After GH treatment, 70% more insulin was required to maintain normoglycaemia (P < 0.01). The ratio between glucose infusion rate and serum insulin levels decreased by 34% at the two levels of glucose infusion tested (P < 0.05). Basal levels of C-peptide, insulin-like growth factor (IGF)-I and IGF-binding protein-3 increased almost 2-fold, while levels of glucose, insulin, glucagon, GH and IGF-binding protein-1 remained unchanged. Non-esterified fatty acid levels decreased (P < 0.05). In addition, 24h urinary nitrogen excretion decreased by 26% (P < 0.01) after GH treatment, while skeletal muscle protein synthesis and 3-methylhistidine excretion in urine remained unchanged. Energy expenditure increased by 5% (P < 0.05) after treatment, whereas fat and carbohydrate oxidation were unaltered. In conclusion, when glucose flux was normalized by compensatory hyperinsulinaemia under conditions of GH-induced insulin resistance, intracellular rates of oxidation of glucose and fat remained unchanged. The nitrogen retention accompanying GH treatment seems to be due largely to improved nitrogen balance in non-muscle tissue.

This content is only available as a PDF.
You do not currently have access to this content.