pH heterogeneity in aged hypertensive rat hearts distinguishes reperfused from persistently ischemic myocardium

Myocardium reperfused following ischemia may contain regions that are adequately perfused but temporarily dysfunctional or metabolically abnormal, and regions that are persistently ischemic. By examining heterogeneity in the inorganic phosphate (Pi) resonance in 31P NMR spectra obtained for isolated perfused young v old hypertensive rat hearts made globally ischemic and then reperfused, areas of persistent intracellular acidosis (pHi about 6) were distinguished from recovering tissue (pHi about 7). The extent of persistent regional acidosis reported by Pi heterogeneity in the 31P NMR spectrum of the reperfused heart correlates well with (1) whole heart flow deficit measured as coronary flow, (2) the decrease in extracellular (primarily vascular) 23Na NMR resonance area measured using 23Na NMR and shift reagent, and (3) regional flow deficits identified using perfusate-borne dye markers. Persistent intracellular acidosis during reperfusion was observed only in the hearts of aged hypertensive rats, confirming that the vasculature of these animals is more susceptible to ischemic injury than both younger hypertensive rats and age-matched controls. The portion of the heart that is reperfused following only 16 min of global ischemia is metabolically abnormal, showing incomplete recovery of ATP and pH.