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Departments of 1 Surgery, 2 Internal Medicine, and 3 Anesthesiology, University of Texas Medical Branch at Galveston, and 4 Metabolism Unit, Shriners' Burns Hospital, Galveston, Texas 77550
We measured glutamine kinetics using
L-[5-15N]glutamine and
L-[ring-2H5]phenylalanine
infusions in healthy subjects in the postabsorptive state and during
ingestion of an amino acid mixture that included glutamine, alone or
with additional glucose. Ingestion of the amino acid mixture increased
arterial glutamine concentrations by ~20% (not by 30%;
P < 0.05), irrespective of the presence or absence of
glucose. Muscle free glutamine concentrations remained unchanged during
ingestion of amino acids alone but decreased from 21.0 ± 1.0 to
16.4 ± 1.6 mmol/l (P < 0.05) during simultaneous ingestion of glucose due to a decrease in intramuscular release from
protein breakdown and glutamine synthesis (0.82 ± 0.10 vs. 0.59 ± 0.06 µmol · 100 ml
leg
1 · min
1; P < 0.05). In both protocols, muscle glutamine inward and outward transport
and muscle glutamine utilization for protein synthesis increased during
amino acid ingestion; leg glutamine net balance remained unchanged. In
summary, ingestion of an amino acid mixture that includes glutamine
increases glutamine availability and uptake by skeletal muscle in
healthy subjects without causing an increase in the intramuscular free
glutamine pool. Simultaneous ingestion of glucose diminishes the
intramuscular glutamine concentration despite increased glutamine
availability in the blood due to decreased glutamine production.
transport; synthesis; stable isotopes; protein; amino acid; glucose
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