Stunned myocardium has increased mitochondrial NADH oxidase and ATPase activities.

Ten anesthetized, open-chest dogs were subjected to occlusion of the left anterior descending coronary artery for 15 minutes, followed by reperfusion for 150 minutes. Hemodynamics were recorded and regional myocardial contraction was measured sonometrically. The hearts were then fixed in situ using glutaraldehyde for cytochemical studies. Systolic wall thickening remained unchanged in the non-ischemic myocardium, but was significantly depressed (stunned) in the area of the left anterior descending coronary artery during reperfusion. NADH oxidase and ATPase activities were very weakly present in mitochondria from non-ischemic myocardium. In the ischemic endocardium, irreversibly injured cells had mitochondria which were severely altered and contained no reaction products to the two enzymes. In contrast, high NADH oxidase and ATPase activities were present in mitochondria from the less severely injured cells of the endocardial zone of stunned areas. Since this zone is particularly susceptible to ischemia in dogs, the high mitochondrial NADH oxidase and ATPase activities may be early signs of ischemic damage, reflecting a disturbance in mitochondrial respiratory activity in stunned myocardium.