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.