GLUTAMINE-METABOLISM IN HEALTHY ADULT MEN - RESPONSE TO ENTERAL AND INTRAVENOUS-FEEDING

To assess the effect of feeding on glutamine kinetics, six healthy men received 4-h intravenous infusions of L-[2-N-15]glutamine and L-[1-C-13]leucine on 3 separate days: 1) in the postabsorptive state, 2) over the course of an 8-h nasogastric infusion of a small peptide-based nutrient mixture, and 3) during an 8-h isonitrogenous, isoenergetic intravenous infusion (1.5 g amino acid.kg(-1).d(-1); 130 kJ.kg(-1).d(-1), or 31 kcal.kg(-1).d(-1); 58% carbohydrate and 42% fat). Regardless of the route, nutrition increased leucine appearance rate (Ra) and oxidation, stimulated protein synthesis, and improved leucine balance; apparent rates of protein breakdown decreased during enteral nutrition only. Glutamine Ra increased 16.8% (NS) and 26.2% (P < 0.01) with parenteral and enteral feeding, respectively, over postabsorptive values. The present findings are consistent with a major role of glutamine in interorgan nitrogen transport in the fed state and further suggest that increased availability of precursors may stimulate glutamine synthesis de novo, and enteral infusion of peptide-bound amino acids may be an effective route to provide free glutamine to the rest of the body.