Background—Oxygen free radicals have been shown to cause endothelial vasomotor dysfunction. This study examined the effect of reduced glutathione (GSH), an antioxidant, on human coronary circulation.
Methods and Results—Responses of epicardial diameter and blood flow of the left anterior descending coronary artery to intracoronary infusion of acetylcholine (ACh, 50 µg/min) were measured by quantitative coronary angiography and Doppler flow-wire technique, respectively, before and during combined intracoronary infusion of GSH (50 mg/min) or saline in 26 subjects with no significant coronary stenosis. GSH infusion suppressed the constrictor response of epicardial diameter to ACh and enhanced the increase in blood flow response to ACh. Furthermore, GSH potentiated the coronary dilator effect of nitroglycerin. A beneficial effect of GSH on the epicardial diameter response to ACh was observed in a subgroup of subjects with 
1 coronary risk factors but not in a subgroup without risk factors. Saline infusion did not have any effects.
Conclusions—The results indicate that GSH improved coronary endothelial vasomotor function, particularly in subjects with coronary risk factors, and it potentiated the vasodilator effect of nitroglycerin in human coronary arteries.