Bd. Williams et al., ALANINE AND GLUTAMINE KINETICS AT REST AND DURING EXERCISE IN HUMANS, Medicine and science in sports and exercise, 30(7), 1998, pp. 1053-1058
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.