Steroids and Cardioplegia: Effects of Glucocorticoids upon Vascular Resistance During Cardioplegic Perfusion

Abstract

The effects are assessed of methyl prednisolone sodium succinate (MPSS) upon coronary flow rate (CFR) during a 20 minute anoxic, cold (20 degrees C) cardioplegic perfusion with a potassium-enriched (K+ 20 mmol/l) commercially obtained Ringer solution and 15 min of subsequent normothermic aerobic reperfusion without steroid, based on measurements made on the isolated rat heart. Myocardial release of creatine kinase (CK) was obtained during reperfusion and at the end of the experiments the hearts were freezeclamped and analyzed for high energy phosphate compounds and tissue calcium. In the absence of filtering and MPSS the coronary flow rate gradually declined to 32% +/- 4 after 20 min. MPSS presented a bell-shaped concentration response curve with respect to improvement of CFR. An optimal effect (only reduction to 64% +/- 11) was obtained with MPSS 100 mg/l, while no improvement was obtained with 1000 mg/l (reduction to 28% +/- 3). After 15 min of reperfusion with normal medium at 37 degrees the hearts perfused with MPSS 100 mg/l presented with higher values for energy charge and ATP and lower tissue calcium content than the hearts perfused with MPSS 1000 mg/l. Using filtration (0.8 micron) of the cardioplegic solution the CFR was reduced to 45% +/- 4. We therefore conclude that MPSS in an optimal concentration (100 mg/l) may afford effective coronary vasodilation and overcome particle induced vasospasm, and that in higher concentrations (1000 mg/l) the improvement in CFR is lost. This high concentration may also have unfavorable effects upon the myocardium.