The reciprocal protective effects of magnesium and calcium in hyperkalemic cardioplegic solutions on ischemic myocardium.

The cardioprotective effects of magnesium and calcium in hyperkalemic cardioplegic solutions were investigated in isolated rat hearts. Isolated rat hearts were arrested for 30 min at 37 degrees C in cardioplegic solutions containing magnesium and calcium in varying concentrations. In St. Thomas' Hospital cardioplegic solution, the magnesium and calcium concentrations were varied as follows: Mg 0; Ca 0.1, 0.3, 0.6, 1.2 mmol/l (mM)./ Mg 4; Ca 0.1, 0.3, 0.6, 1.2 mM./ Mg 8; Ca 0.1, 0.3, 0.6, 0.9, 1.2 mM./ Mg 12; Ca 0.1, 0.6, 0.9, 1.2 mM./ Mg 16; Ca 0.1, 0.6, 1.2, 1.5 mM. For each magnesium concentration, the percentage recovery of aortic flow generated dose-response curves depending on calcium concentration. The maximum percentage recovery of aortic flow was 76.0% +/- 2.7% (mean +/- SEM) in the Mg0-Ca0.1 mM group, 77.1% +/- 2.0% in the Mg4-Ca0.3 mM group, 78.5% +/- 2.3% in the Mg8-Ca0.6 mM group, 79.8% +/- 2.4% in the Mg12-Ca0.9 mM group and 80.0% +/- 3.4% in the Mg16-Ca1.2 mM (ST solution) group. Significant difference in the recovery of aortic flow has not been observed among these groups, and furthermore, significant differences in the recovery of other parameters of cardiac function and Ck leakage have not been observed among these groups. These results suggest that the cardioprotective effects depend on the relative combination of magnesium and calcium concentrations, and that it is important to maintain an appropriate balance of magnesium and calcium in hyperkalemic cardioplegic solutions.