Whole body and skeletal muscle glutamine metabolism in healthy subjects

Am J Physiol Endocrinol Metab. 2001 Feb;280(2):E323-33. doi: 10.1152/ajpendo.2001.280.2.E323.


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 approximately 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 micromol x 100 ml leg(-1) x 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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Biological Availability
  • Blood Glucose / analysis
  • Female
  • Glutamine / blood
  • Glutamine / metabolism*
  • Humans
  • Kinetics
  • Leg / blood supply
  • Male
  • Muscle, Skeletal / metabolism*
  • Osmolar Concentration
  • Phenylalanine / blood
  • Phenylalanine / metabolism
  • Reference Values
  • Regional Blood Flow
  • Viscera / metabolism


  • Blood Glucose
  • Glutamine
  • Phenylalanine