Alanine, glutamate, and ammonia exchanges in acutely ischemic swine myocardium

Coronary artery disease causes an increase in glutamate uptake and alanine output by the heart. We assessed the effects of acute myocardial ischemia on alanine and glutamate exchange and ammonia production in 10 anesthetized open-chest domestic swine (46.9±0.7 kg). Coronary blood flow was controlled through an extracorporal perfusion circuit. After a nonischemic control period (aerobic) the blood flow in the left anterior descending coronary artery was reduced by 60%. Arterial and anterior interventricular venous samples where drawn before and during 35 min of ischemia. Subendocardial blood flow, measured using radiolabeled microspheres, decreased from 1.27±0.16 to 0.25±0.09 (ml/g)/min, and left-ventricular wall-thickening fell to 47% of aerobic values. Ischemia resulted in a significant increase in the rate of glucose uptake (p<0.05) and a switch to net lactate production (p<0.01). Ischemia did not affect the rates of alanine output (-0.9±1.0 vs. -0.3±0.3 μmol/min) or glutamate uptake (-0.4±1.1 vs. 0.3±0.6 μmol/min), but did increase the venous-arterial difference for ammonia (-4.1±4.1 to 52.7±5.5 μM, p<0.0001) and the ammonia output (-0.33±0.24 to 1.34±0.14 μmol/min, p<0.0001). In conclusion, acute ischemia did not stimulate greater alanine output or glutamate uptake. However, acute ischemia did cause an increase in anaerobic glycolysis rate and ammonia output, which reflects a profound disruption in myocardial energy metabolism.