THE MECHANISM OF AMINO-ACID LOADING IN IMPROVING POSTISCHEMIC MYOCARDIAL RECOVERY

During induced ischemia for cardiac surgery, myocardial stunning occur s and aerobic metabolism of glucose, fatty acids, and lactate is alter ed. Following reperfusion, stunned myocardium uses oxygen and substrat e inefficiently, leading to poor functional recovery. However, amino a cids may be used as anaplerotic metabolic substrates during and after ischemia, utilizing transamination of amino acids to form high-energy phosphates via the tricarboxylic acid cycle. We investigated if loadin g hearts with a physiologic spectrum of amino acids prior to ischemia could increase postischemic myocardial recovery. Isolated perfused rab bit hearts were subjected to 120 min of 34 degrees C cardioplegic isch emia. Hearts received cardioplegia alone as controls or were loaded wi th a 0.05, 0.1, 0.5, 1, 2, or 5% amino acid perfusion prior to cardiop legic ischemia, Following reperfusion, functional recovery revealed th at hearts perfused with 0.05 and 0.1% amino acids had improved contrac tility and compliance vs untreated controls. To determine if the mecha nism of amino acid loading in improving postischemic function was enha ncement of high-energy phosphate resynthesis, nucleotides and nucleosi des were measured. While all preischemic values were equivalent, amino -acid-loaded hearts had significantly greater high energy nucleotides at end ischemia and after reperfusion. These data demonstrate that met abolism, as well as function, is improved with amino acid loading prio r to ischemia, which allowed for better internal reparative work durin g ischemia and external contractile work after ischemia. This strategy may have application in cardiac surgery. (C) 1995 Academic Press, Inc .