Background and Purpose--Cerebral vascular injury occurs in response to hypoxia/reoxygenation (H/R). However, the cellular signaling pathways that regulate this event remain unclear. The present study was designed to determine whether reactive oxygen species (ROS) mediate endothelial dysfunction after hypoxia/reoxygenation in cerebral resistance arteries and, if so, the relative contribution of ROS, NADPH oxidase, and a nuclear factor-B (NF-B) pathway.

Methods--Arterial diameter and intraluminal pressure were simultaneously measured on rat posterior cerebral arteries (PCA). Superoxide was measured by 5-µmol/L lucigenin-enhanced chemiluminescence.

Results--Hypoxia/reoxygenation selectively inhibited cerebral vasodilation to the endothelium-dependent agonist acetylcholine (Ach) (0.01 to 10 µmol/L) by 50%. Impaired vasodilation after H/R was reversed by 2,2,6,6-tetramethylpiperidine-N-oxyl (Tempo) (100 µmol/L), a cell-permeable superoxide dismutase mimetic, and partially by ebselen (10 µmol/L), a peroxynitrite scavenger. H/R-impaired vasodilation to Ach was also preserved by apocynin (1 mmol/L), a specific inhibitor for NADPH oxidase. Correspondingly, H/R significantly increased lucigenin-detectable superoxide, which was reduced by either Tempo or apocynin, but not by allopurinol (10 µmol/L), an inhibitor of xanthine oxidase. Finally, the NF-B inhibitors helenalin (10 µmol/L) and MG-132 (1 µmol/L) independently antagonized H/R-impaired Ach-induced vasodilation without affecting dilator response to sodium nitroprusside, an endothelium-independent vasodilator.

Conclusions--These results indicate that superoxide mediates cerebral endothelial dysfunction after hypoxia/reoxygenation largely via activation of NADPH oxidase and possibly activation of NF-B pathway.