Amino acid substrate preloading and postischemic myocardial recovery.

During induced myocardial ischemia for cardiac surgery, myocardial stunning occurs and aerobic metabolism of glucose, fatty acids, and lactate is inhibited as anaerobic pathways predominate. Even following reperfusion, stunned myocardium uses oxygen and substrate inefficiently leading to poor functional recovery as less mechanical work is developed per oxygen utilized. Amino acids potentially can act as cardiac metabolic substrates during and after ischemia, utilizing the transamination of amino acids by the malate-aspartate shuttle to form high energy phosphates via the tricarboxylic acid cycle. We investigated if "preloading" hearts with a physiologic spectrum of amino acids could increase postischemic myocardial recovery. Isolated perfused rabbit hearts were subjected to 120 min of 34 degrees C cardioplegic ischemia. Hearts received cardioplegia alone as controls or were "preloaded" with a 0.05% amino acid perfusion for 30 min prior to cardioplegic ischemia. Following reperfusion, analysis of functional recovery revealed that contractility and cardiac efficiency were improved with amino acids substrate preloading. The mechanism of this may be due to uptake of amino acids prior to ischemia, which are later utilized for internal reparative work during ischemia and external contractile work after ischemia.