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-'5Nlglutamine and L-(1-'3C)leucine on 3 separate days: 1) in the postabsorptive state, 2) over the course of an 8-h nasogas- tric infusion of a small peptide-based nutrient mixture, and 3) during an 8-h isonitrogenous, isoenergetic intravenous infusion (1.5 g amino acidkg'd'; 130 kJkgd�, or 31 kcal . kg ' . d �� 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, respec- lively, over postabsorptive values. The present findings are con- sistent with a major role of glutamine in interorgan nitrogen transport in the fed state and further suggest that increased avail- ability 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. Am J ClinNutr l994;59:l395-1402.