Are age-related differences in response to myocardial ischemia and cardioplegia pH dependent?

Phosphorus-31 nuclear magnetic resonance and left ventricular pressure development (dP/dt) were used to test the hypothesis that age-related differences in myocardial functional recovery after ischemia and cold crystalloid cardioplegia (CCC) are the result of an inverse relationship between recovery and the decrease in intracellular pH (pHi) during ischemia. Neonatal (3-8 days) and adult rabbit hearts were Langendorff perfused using two protocols: (1) control--30 min perfusion, 30 min global ischemia, 2 h reperfusion; (2) CCC--the same except ischemia was initiated after a 4-min infusion of cold hyperkalemic solution. Analysis of variance and the Tukey test showed the following significant differences between the protocols (p < 0.05). CCC decreased inorganic phosphate (Pi) during ischemia in both age groups, but more in adult hearts, and decreased Pi during reperfusion in adult hearts. CCC increased pHi during ischemia and ATP during ischemia and reperfusion in both age groups but more in adult hearts. CCC increased dP/dt during reperfusion only in adult hearts. The results are consistent with the hypothesis.