Abstract
Reperfusion after reversible regional ischemia has been shown to result in delayed recovery of myocardial function, but the mechanism responsible for this phenomenon remains unknown. We explored the potential role of oxygen-free radicals as mediators of postischemic dysfunction in open-chest dogs undergoing a 15 min occlusion of the left anterior descending coronary artery (LAD) followed by 2 hr of reperfusion. Treated animals (n = 19) received an infusion of the oxygen free-radical scavengers superoxide dismutase (SOD; 15,000 U/kg) and catalase (CAT; 55,000 U/kg) for 1 hr starting 15 min before LAD occlusion, while control animals (n = 20) received an equal volume of saline. SOD and CAT produced no discernible effect on heart rate, aortic pressure, or left atrial pressure. Collateral flow to the ischemic zone (radioactive microspheres) was 0.07 ± 0.01 ml/min/g in both groups. The size of the occluded bed as determined by postmortem perfusion was 26.1 ± 1.2% of the left ventricle in the control group and 26.5 ± 0.9% in the treated group. Systolic wall thickening (an index of regional function) was assessed with an epicardial pulsed-Doppler probe. The two groups exhibited comparable systolic thickening under baseline conditions and similar degrees of dyskinesia during ischemia. Nevertheless, recovery of function (expressed as percent of baseline) was considerably greater in the treated dogs, both at 1 hr (43.8 ± 14.3 vs 12.8 ± 11.6) and 2 hr of reperfusion (74.2 ± 8.4 vs 31.6 ± 9.8, p < .005). This improved recovery of function obtained with SOD and CAT suggests that oxygen-free radicals play an important role in the genesis of myocardial dysfunction after a brief episode of regional ischemia.