Abstract

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 ca. 45% VO2max treadmill exercise in six normal volunteers (25+/-2 yr, 68+/-2.5 kg, VO2max 43+/-2.4 mL/min/kg; means+/-SE). Bolus injections (N=3) or primed-constant infusions (N=3) of 2H5-glutamine and 3-13C-alanine were given at rest in 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 micro-mol/min/kg, respectively; P<0.01), glutamine Ra was not significantly altered by exercise (6.11+/-0.44 and 6.40+/-0.69 micro-mol/min/kg 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. Verf.-Referat