Insulin reduces leucine oxidation and improves net leucine retention in parenterally fed humans

Protein metabolism during parenteral feeding was measured with and without euglycemic hyperinsulinemic clamping in five healthy human subjects using t he primed Continuous infusion of [C-13]leucine(LEU) tracer methodology. All subjects underwent two periods of protein measurement. Subjects were rando mized to have the clamp first or second. Two subjects had the clamp first, and they participated in another study in which the measurement period afte r the clamp was increased by another 2 h. Insulin reduced LEU oxidation (fr om 26 to 22 mu M . kg(-1) . h(-1); P < 0.05) and improved net LEU balance ( from 3 to 7 mu M . kg(-1) . h(-1); P < 0.05). The order of the clamp influe nced the effects of insulin. With clamping performed second, insulin reduce d LEU flux (from 152 to 134 mu M . kg(-1) . h(-1); P < 0.01), endogenous LE U rate of appearance (Ra; from 125 to 107 mu M . kg(-1) . h(-1); P < 0.01), and non-oxidative LEU disappearance (NOLD; from 128 to 113 mu M . kg(-1) . h(-1); P < 0.01) With clamping performed first, NOLD decreased after insul in was slopped (from 129 to 121 mu M . kg(-1) . h(-1); P < 0.05), but no ch ange was seen in the Aux and LEU Ra, despite the return of plasma insulin a nd amino acid concentrations to basal levels. The reduction in NOLD was acc entuated with time and did not reach plateau even after 6 h and indicated a prolonged carry-over effect for NOLD and Pa. This effect was not seen for leucine oxidation. (C) Elsevier Science Inc. 2000.