Metabolic and thermogenic effects of amino acid infusion in man

Amino acid solutions are an obligatory constituent of paternal nutrition regimens. Their metabolic interactions with glucose utilization and their thermogenic effect are not well characterized. To study these aspects, we infused an amino acid solution (Freamine III, 0.7 g/kg) or saline during a euglycemic insulin (1 mU/min. kg) clamp combined with continuous computerized indirect calorimetry in paired fashion in a group of seven healthy subjects. Amino acids stimulated insulin secretion (100 ± 8 vs 60 ± 5 μU/ml, p < 0.001) and inhibited whole-body glucose disposal (24.6 ± 2.0 vs 32.7 ± 2.2 μmol/min. kg, p < 0.01). Net carbohydrate oxidation (indirect calorimetry) rose from 6.1 ± 1.7 to 19.5 ± 1.7 μmol/min.kg (p < 0.005) under control conditions, but only from 9.1 ± 1.6 to 15.5 ± 1.2 μmol/min.kg (p < 0.05) with amino acids. In contrast, the ability of insulin to suppress net lipid oxidation and to enhance nonoxidative glucose diposal was not altered by amino acid infusion. Energy production increased significantly with time during amino acid infusion (from 1.11 to 1.35 kcal/min during the 2nd hour of the study, p < 0.001); over two hours, some 13% of the caloric content of amino acid solution was dissipated in this way. We conclude that Freamine administration, under the experimental circumstances of the present study, stimulates insulin secretion, inhibits glucose oxidation and strongly enhances energy production.