Alanine and glutamine kinetics at rest and during exercise in humans. Med. Sci. Sports Exerc., Vol. 30, No. 7, pp. 1053-1058, 1998.
Purpose: The purpose of this study was to quantify both alanine and glutamine kinetics during exercise of moderate intensity to determine the sum total of alanine and glutamine flux.
Methods: Tracer methods were used to quantify alanine and glutamine rates of appearance (Ra) in plasma at rest and during 180 min of ∼45% V˙O2max treadmill exercise in six normal volunteers (25 ± 2 yr, 68 ± 2.5 kg, V˙O2max 43 ± 2.4 mL·min−1·kg−1; means ± SE). Bolus injections (N = 3) or primed-constant infusions (N = 3) of 2H5-glutamine and 3-13C-alanine were given at rest on 1 d and 10-15 min after the onset of exercise on a separate day less than 2 wk later. Plasma enrichment decay curves and plateau enrichments were used to estimate alanine and glutamine kinetics.
Results: Whereas alanine Ra increased significantly from rest to exercise (5.72 ± 0.31 vs 13.5 ± 1.9 μmol·min−1·kg−1, respectively; P < 0.01), glutamine Ra was not significantly altered by exercise (6.11 ± 0.44 and 6.40 ± 0.69 μmol·min−1·kg−1 at rest and during exercise, respectively). The total of alanine and glutamine flux increased from 17.93 ± 0.88 to 25.98 ± 3.04 (P < 0.05).
Conclusions: Since most muscle amino-N is released as alanine and glutamine, these findings provide strong evidence that amino-N delivery from muscle to the liver is increased during exercise. In addition, it appears that alanine, rather than glutamine, is the predominant N carrier involved in the transfer of N from muscle to the liver during moderate intensity exercise.
The Metabolism Unit, Shriners Burns Institute, and the Departments of Surgery and Anesthesiology, The University of Texas Medical Branch, Galveston, TX 77550-2725
Submitted for publication December 1996.
Accepted for publication January 1998.
This work was supported by grants R01-DK-47344 and R01-DK-38010, also Shriners Hospital grant 15849. B. D. Williams received a National Aeronautics and Space Administration Texas Space Grant Consortium Fellowship during the project. This manuscript reflects work for the partial fulfillment of B. D. Williams' doctoral degree from the University of Texas Medical Branch, Galveston, Texas.
Address for correspondence: Robert R. Wolfe, Shriners Burns Institute, Metabolism Unit, 815 Market Street, Galveston, TX 77550.