Predicting functional recovery from ischemia in the rat myocardium

Depletion of high-energy phosphates, accumulation of inorganic phosphate and intracellular acidosis have each been proposed as important events in the transition from reversible to irreversible ischemic injury. To assess whether each variable is predictive of functional recovery on reperfusion, these were measured in the isolated isovolumic rat heart using³¹P NMR. Perfused hearts were subjected to either 10, 12 or 40 min of normothermic ischemia followed by 40 min of reperfusion. Hearts were then freeze-clamped for further analysis of phosphate metabolites by NMR and ion chromatography. High-energy phosphates, P_i, phosphomonoesters and pH were measured by³¹P NMR spectroscopy at 2 minute intervals. Heart rate and developed pressure were monitored simultaneously. All hearts undergoing 10 min of ischemia and 40% of hearts subjected to 12 min of ischemia demonstrated good functional recovery. The remainder of hearts ischemic for 12 min went into contracture on reperfusion with little return of function. Hearts subject to 40 min of ischemia went into ischemic contracture and showed no recovery on reperfusion. Intracellular pH, [ATP], and [P_i] measured prior to reperfusion did not predict the extent of recovery. However, phosphomonoesters were detected prior to reperfusion in all hearts that did not recover well, but were not observed in hearts that showed good mechanical recovery. Analysis of tissue extracts by³¹P NMR and ion chromatography indicated that the most prominent components of the phosphomonoesters were glucose 6-phosphate, α-glycerol phosphate and AMP. In conclusion, of the various phosphorus metabolites that can be measured by³¹P NMR, only one group, the phosphomonoesters, was predictive of functional recovery.