XDH and hypertensive disorder: ,52, 53, 54, 55, 56 Biomarkers of oxidative stress, including plasma and urinary thiobarbituric acid–reactive substances (TBARS) and F2α-isoprostanes, tissue concentrations of O2− and H2O2, and activation of Noxs and xanthine oxidase, are increased, whereas levels of NO and antioxidant enzymes are reduced in experimental hypertension.52, 53, 54, 55, 56, 57 Further supporting a role for oxidative stress in the pathophysiology of hypertension are studies demonstrating blood pressure–lowering effects of antioxidants, ROS scavengers, and Nox inhibitors.