High-Dose Allopurinol Improves Endothelial Function by Profoundly Reducing Vascular Oxidative Stress and Not by Lowering Uric Acid

Background— Allopurinol has been shown to improve endothelial function in chronic heart failure. This study aimed to establish its mechanism of action and to construct a dose–response curve for the effect of allopurinol. Methods and Results— Two randomized, placebo-controlled, double-blind, crossover studies were performed for 1 month on patients with New York Heart Association Class II–III chronic heart failure, comparing 300 mg allopurinol, 600 mg allopurinol, and placebo for the first study and 1000 mg probenecid versus placebo in the second study. Endothelial function was assessed by standard forearm venous occlusion plethysmography. Allopurinol 600 mg/d significantly increased forearm blood flow response to acetylcholine compared with both allopurinol 300 mg/d and placebo (% change in forearm blood flow [mean±SEM]: 240.31±38.19% versus 152.10±18.21% versus 73.96±10.29%, P<0.001). For similar levels of urate lowering, the uricosuric agent probenecid had no effect on endothelial function. Sodium nitrop...