Amino acid metabolism in muscle and in the whole body of man before and after ingestion of a single mixed meal.

Whole-body energy expenditure, protein oxidation, and exchange of amino acids, glutathione, and other metabolites across forearm muscle were assessed before and for 4 h after ingestion of a single meal containing 3274 kJ (783 kcal) and 25.5 g protein (4.08 g nitrogen). The study 1) demonstrates the dominance of glutamine over all other amino acids in carrying N out of skeletal muscle (1.33 mumol.L muscle-1.min-1 between 0 and 4 h--equivalent to 71% of the amino acid release or 82% of the amino acid N release); 2) suggests that glucose-alanine recycling between muscle and liver is not increased in the postprandial period despite the large uptake of glucose by muscle; 3) provides no support for the hypothesis that a substantial amount of N is exchanged between blood and muscle in the form of glutathione; and 4) considers the overall quantitative importance of amino acid oxidation in the whole body and the accompanying exchange of amino acids in skeletal muscle.