XDH and endothelial dysfunction: We hypothesized that, due to a cross-talk between cytoplasmic O2−-sources and intraluminally expressed xanthine oxidase (XO), intraluminal O2− is instrumental in mediating intraluminal (endothelial dysfunction) and cytosolic (p38 and ERK1/2 MAPKs phosphorylation) manifestations of vascular oxidative stress induced by endothelin-1 (ET-1) and angiotensin II (AT-II).