ALANINE AND GLUTAMINE KINETICS AT REST AND DURING EXERCISE IN HUMANS

Purpose: The purpose of this study was to quantify both alanine and gl utamine kinetics during exercise of moderate intensity to determine th e sum total of alanine and glutamine flux. Methods: Tracer methods wer e used to quantify alanine and glutamine rates of appearance (Ra) in p lasma at rest and during 180 min of similar to 45% (V) over dot O-2max treadmill exercise in six normal volunteers (25 +/- 2 yr, 68 +/- 2.5 kg, (V) over dot O-2max 43 +/- 2.4 ml min(-1) k(-1); means +/- SE). Bo lus injections (N = 3) or primed-constant infusions (N = 3) of H-2(5)- glutamine and 3-C-13-alanine were given at rest on 1 d and 10-15 min a fter the onset of exercise on a separate day less than 2 wk later. Pla sma enrichment decay curves and plateau enrichments were used to estim ate alanine and glutamine kinetics. Results: Whereas alanine Pa increa sed significantly from rest to exercise (5.72 +/- 0.31 vs 13.5 +/- 1.9 mu mol min(-1) kg-L, respectively; P < 0.01), glutamine Ra was not si gnificantly altered by exercise (6.11 +/- 0.44 and 6.40 +/- 0.69 mu mo l min-l kg(-1) at rest and during exercise, respectively). The total o f 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.