Inhibitory Effect of Free Radical Scavengers on Cyclic Flow Variations in Unsedated Dogs with Coronary Stenosis and Endothelial Injury

Abstract

Severe coronary artery stenosis with endothelial injury in the canine model induces cyclic coronary flow variations (CFVs), which are partially due to spontaneous platelet aggregation and dislodgement at the stenotic site. In the present study, we used anesthetized open-chest and unsedated closed-chest dogs with CFVs to investigate whether oxidative metabolic burst (hydrogen peroxide generation) occurred in neutrophils during CFVs and whether CFVs were attenuated by superoxide dismutase (SOD) and catalase. CFVs were produced by placing a cylindrical constrictor on the left anterior descending coronary artery (LAD). LAD blood flow was monitored by means of a Doppler flow probe placed proximally to the constrictor, and the severity of CFVs was expressed by both the frequency of CFVs and mean LAD blood flow. Hydrogen peroxide generation in neutrophils was measured by flow cytometry, using single cell analysis, and was expressed as the mean fluorescence intensity of 2’, 7’-dichlorofluorescein. Dogs received an intravenous infusion of saline (n = 8), SOD (5 mg/kg, n = 7), catalase (5mg/kg, n = 7), or a combination of SOD and catalase (same doses, n = 7). Although the mean fluorescence intensity did not change in sham-operated dogs without CFVs (61.7 ± 15.8 to 60.4 ± 11.8; NS), the intensity in the dogs with CFVs was significantly increased during CFVs (62.2 ± 13.7 to 79.8 ± 9.8; P < 0.005). These results indicate that hydrogen peroxide is generated in neutrophils.