MAGNESIUM IN ST-THOMAS CARDIOPLEGIC SOLUTION - A P-31-NMR AND FUNCTIONAL-STUDY IN ISOLATED RAT AND PIG HEARTS

Using isolated rat and pig heart preparations in conjunction with P-31 NMR spectroscopy, the myocardial protective effect of adding 16 mmol/ L magnesium to St Thomas' cardioplegic solution has been evaluated. Ra t hearts were arrested with St Thomas' solution containing either 0 (n = 7) or 16 (n = 7) mmol/L magnesium and then kept ischemic for 30 min at 37-degrees-C, followed by 30 min of reperfusion with Krebs-Hensele it solution. The two groups of hearts showed a similar degree of recov ery during reperfusion with respect to cardiac output (75 vs. 79% of t he pre-arrest value), myocardial oxygen consumption (90 vs. 94%) and e xternal working efficiency (82 vs. 86%). When 0 and 16 mmol/L magnesiu m St Thomas' solutions were used to preserve pig hearts for 4 h at 12- degrees-C, the changes in high energy phosphates in both groups were v ery similar throughout the protocol. Expressed as a % of the pre-arres t ATP value, inorganic phosphate increased to 230 and 251% from a cont rol value of 41 % and phosphocreatine decreased to 29 and 30% from a c ontrol value of 211%, respectively. Futhermore, the hearts showed a si milar recovery of contractile function (heart rate, 96 vs. 103%; left ventricular developed pressure, 102 vs.102%; maximum rates of pressure increase and decrease, 86 vs. 90.; and 82 vs. 88%, respectively). The results showed that a high concentration of magnesium in St Thomas' s olution provides no demonstable benefit to isolated ischemic hearts un der the conditions used in our experiments.