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 relations hip between recovery and the decrease in intracellular pH (pH(i)) duri ng ischemia. Neonatal (3-8 days) and adult rabbit hearts were Langendo rff perfused using two protocols: (1) control - 30 min perfusion, 30 m in global ischemia, 2 h reperfusion; (2) CCC - the same except ischemi a was initiated after a 4-min infusion of cold hyperkalemic solution. Analysis of variance and the Tukey test showed the following significa nt differences between the protocols (p < 0.05). CCC decreased inorgan ic phosphate (Pi) during ischemia in both age groups, but more in adul t hearts, and decreased Pi during reperfusion in adult hearts. CCC inc reased pH(i) during ischemia and ATP during ischemia and reperfusion i n 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.