The role of glucose, long-chain triglycerides and amino acids for promotion of amino acid balance across peripheral tissues in man

The role of amino adds, glucose and lipids in improving amino acid balance in peripheral tissues was evaluated. Primed constant infusion of L- [ring-H -2(5)]phenylalanine in combination with flux measurements of glucose, free fatty acids (FFA) and amino acids across arm and leg tissues were applied i n male volunteers after an overnight fast with subsequent primed Constant i nfusions of amino acids (0.2 g N kg(-1) body weight day(-1)), long-chain ni glycerides (0.98-1.079 g kg(-1) day(-1)) and glucose (3.13-3.62 g kg(-1) da y(-1)). Amino acids and phenylalanine tracer infusion continued for 6 h; th e lipid infusion was presided during 2-6 h: from the start, and glucose inf usion was provided between 4 and 6 h. Flux measurements were performed at s teady state before the next infusion started. Arterial concentrations of in fused substrates increased during provision, but remained constant thereaft er. Plasma insulin increased when glucose was provided, whereas insulin-lik e growth factor (IGF)I was unchanged during all infusions. Blood flow was u nchanged in arm tissue during all infusions, while leg blood flow increased during fat and glucose infusion. FFA arid glucose balance were unchanged d uring amino acid infusion but improved during lipid and glucose infusions, Amino acid balance was negative across arm and leg tissues in the fasted st ate, but reached balance during amino acid infusion. This effect was equall y dependent on protein synthesis and protein degradation without any contri bution from lipids and glucose.. 3-Methylhistidine release from tissues was not influenced by any substrate. Our results suggest that extracellular am ino acid concentrations determine amino acid balance across peripheral tiss ues independently of non-protein calories, insulin and IGF-I.