Effects of exercise and pacing loads on myocardial amino acid balance in patients with normal and stenotic coronary arteries, with special reference to branched chain amino acids.

Arterial and coronary sinus differences (A-S) of alanine, glutamate, isoleucine, leucine, valine and phenylalanine were measured in 7 control subjects and 12 patients with coronary artery disease (CAD) at rest and during exercise, and in 8 controls and 21 CAD patients at rest and during pacing. Lactate, great cardiac vein flow and oxygen were also measured. However, none of these parameters distinguished CAD from controls. Changes in alanine and glutamate during each load were, for the most part, consistent with previous studies, i.e., a greater release of alanine and uptake of glutamate was observed in the ischemic group. A-S of isoleucine, leucine and valine showed significant positive correlation to that of alanine (r = 0.59, r = 0.89, r = 0.77, respectively, during exercise, and r = 0.57, r = 0.65, r = 0.72, respectively, during pacing). A-S of isoleucine, leucine and valine showed significant positive correlations to each arterial concentration during exercise (r = 0.54, r = 0.62, r = 0.63, respectively), but not during pacing. Although none of the uptakes of the branched chain amino acids (BCAA) were significant, the mean A-S of each BCAA was positive at rest in both controls and CAD, and declined during each load. A-S of leucine was significantly smaller in CAD than in controls during exercise (0.7 +/- 7.0 vs 6.8 +/- 4.1 mumol/l, p < 0.05) and those of leucine and valine were significantly smaller in CAD patients with ischemic electrocardiographic change than in those without electrocardiographic change during pacing (0.1 +/- 5.9 vs 6.1 +/- 5.5, p < 0.05; -3.1 +/- 10.1 vs 9.9 +/- 6.8 mumol/l, p < 0.01, respectively). These results suggest that BCAA, especially leucine and valine, tend to be taken up by human myocardium physiologically and show characteristic changes under myocardial stress similar to those seen with alanine and glutamate.