HYPERCAPNIC ACIDOSIS AND DIMETHYL AMILORIDE REDUCE REPERFUSION-INDUCED CELL-DEATH IN ISCHEMIC VENTRICULAR MYOCARDIUM

Objective: The aim was to investigate the effects of slowing the recovery of ischaemia induced intracellular acidosis with hypercapnic acidosis or dimethyl amiloride (DMA) on the extent of reperfusion induced cell death. Methods: Isolated arterially perfused rabbit papillary muscles and septa were suspended in a controlled atmosphere and perfused with a modified Tyrode solution containing erythrocytes and trypan blue (500 mu M). Ischaemia was produced by arrest of perfusion and withdrawl of atmospheric O-2. Extracellular pH of the muscle during reperfusion was controlled by adjusting the pH of the perfusate (pH 6.6 or pH 7.6 with and without DMA 20 mu M) and changing the PCO2 Of the chamber atmosphere. After 30 min of reperfusion following 30 min (group A) or 60 min (group B) of ischaemia, papillary muscles were fixed with paraformaldehyde. Cell death was assessed by trypan blue staining of nuclei in histological sections of the papillary muscles. Results: The magnitude of cell death was greatest after reperfusion with pH 7.6 as measured by the percentage of nuclei staining with trypan blue (15.1% in group A; 41.8% in group B). By contrast, reperfusion at pH 6.6 reduced cell killing (group A, 3.6%; group B, 7.2%). Reperfusion at pH 7.6 with DMA (20 mu M) also reduced trypan blue uptake (group A, 2.8%; group B, 3.8%). Despite the attenuation of cell death afforded by acidosis or Na+/H+ exchange inhibition, significant swelling of the extracellular space and microvascular injury was noted. Conclusions: Hypercapnic acidosis and Na+/H+ exchange inhibition during reperfusion attenuate lethal reperfusion injury to ventricular myocardium and extend to the intact myocardium the concept of the ''pH paradox'' in which recovery of intracellular pH after reperfusion is a precipitating factor in lethal cell injury.