MYOCARDIAL RECOVERY DURING POSTISCHEMIC REPERFUSION - OPTIMAL CONCENTRATIONS OF NA+ AND CA2+ IN THE REPERFUSATE AND PROTECTIVE EFFECTS OF AMILORIDE ADDED TO CARDIOPLEGIC SOLUTION

The effects of Na+ and Ca2+ concentrations in the reperfusate on post- ischemic myocardial recovery were examined. Also, the myocardial prote ctive effects of amiloride, an inhibitor of the Na+/Ca2+ and Na+/H+ ex change systems, added to cardioplegic solutions were assessed, using a n isolated working rat heart perfusion system. Global myocardial ische mia was induced by 30-min normothermic cardioplegic arrest, using St. Thomas' solution. The concentration of Na+ in the reperfusate varied, stepwise, from 75 to 145 mM/l, and that of Ca2+, from 0.1 to 2.5 mM/l. In this study post-ischemic functional recovery was best at 110 mM/l Na+ and 1.2-1.8 mM/l Ca2+ in the reperfusate. A significantly greater postischemic functional recovery and a lower creatine kinase release w ere observed when amiloride was added to the cardioplegic solution. Ca 2+ overload via Na+/Ca2+ and Na+/H+ exchange systems would, thus, appe ar to be due, at least in part, to post-ischemic reperfusion injury.