Aspartate/glutamate-enriched blood does not improve myocardial energy metabolism during ischemia-reperfusion: A ³¹P magnetic resonance spectroscopic study in isolated pig hearts

Objective: Our objective was to test the effects of exogenous L- aspartate and L-glutamate on myocardial energy metabolism during ischemia- reperfusion. Methods: Phosphorus 31-magnetic resonance spectroscopy was used to observe cellular energetics and intracellular pH in isolated pig hearts perfused with blood (group A, n = 8) or blood enriched with 13 mmol/L each of L-aspartate and L-glutamate (group B, n = 6). The hearts were subjected to 30 minutes of total normothermic ischemia and then reperfused for 40 minutes. Two hearts from each group were inotropically stimulated by titration with calcium after normokalemic reperfusion. Left ventricular function was measured with the use of a compliant balloon and oxygen consumption was calculated. Results: Magnetic resonance spectroscopy showed no decrease. In the rate of energy decline during ischemia for group B versus group A. No significant differences were observed between the two groups in terms of myocardial function, oxygen consumption, or the rate or extent of high- energy phosphate recovery after normokalemic reperfusion or inotropic stimulation. Inotropic stimulation of postischemic hearts, however, led to dramatic improvement in myocardial function in both groups (p < 0.05 for all parameters) and significant improvement in oxygen consumption (p = 0.01). Conclusions: In a normal, isolated, blood-perfused pig heart subjected to 30 minutes of total normothermic ischemia, (1) enrichment of the perfusate with aspartate/glutamate before and after ischemia affects neither myocardial energy metabolism during ischemia-reperfusion nor postischemic recovery of myocardial function or oxygen consumption and (2) inotropic stimulation can recruit significant postischemic function and sufficient aerobic respiration to support it, irrespective of aspartate/glutamate enrichment.