Traditional methods to calculate amino acid kinetic parameters in specific tissues require steady state in plasma and intramuscular amino acid enrichments. Determination of glutamine (GLN) kinetics may be problematic because it has been shown that, despite priming, in some circumstances it takes many hours to reach an isotopic equilibrium in the intracellular pool. We have developed a novel method that allows the determination of the rate of GLN transport across the muscle cell and de novo synthesis by measuring arterial (EA) and intramuscular (EM) GLN enrichments at two different time points prior to reaching an isotopic equilibrium during a constant infusion of tracer infusion. This new method relies on the fact that the intramuscular GLN enrichment at two different time points will be unique for any given value of intracellular FAR (fractional appearance rate) of GLN from muscle protein breakdown and de novo synthesis. GLN de novo synthesis is calculated by subtracting GLN appearance via protein breakdown from FAR. Breakdown is determined simulatneously with a phenylalanine tracer. The rate of GLN transport into the cell is derived from the arterial and intracellular GLN enrichment. We tested this method by infusing 15N-GLN and ring-2H3-PhC into six volunteers. GLN de novo synthesis was 3.88±0.75 μmol 100ml leg-1 min-1 and GLN inward transport was 1.42±0.22 μmol 100ml leg-1 min- 1 (mean±SEM). In conclusion this method provides a feasible approach for measurement of intramusclular GLN kinetics.
|State||Published - Mar 20 1998|