Hypoxia-reoxygenation impairs endothelium-dependent relaxation in isolated rat aorta

The effects of hypoxia followed by reoxygenation on endothelium-dependent relaxation in isolated rat aorta were investigated. Acetylcholine (ACh, 3 nM-10 mu M) and calcium ionophore A-23187 (3 nM-300 nM)-induced endothelium-dependent vasorelaxation of isolated rat aortic vessel rings was impaired after 15 min of hypoxia followed by 30 min of reoxygenation. Impairment of ACh-induced relaxation was prevented by pretreatment with the combination of superoxide dismutase (200 U/ml) and catalase (1,000 U/ml). Hypoxia-reoxygenation did not affect sodium nitroprusside (0.1 nM-1 mu M)-induced endothelium-independent relaxation nor the dissociation constant of ACh to endothelial M(3) muscarinic receptors. Propidium iodide staining of the vascular endothelium revealed a significant increase in the number of dead endothelial cells on the aortic vessel rings following hypoxia-reoxygenation, but not on those pretreated with superoxide dismutase and catalase. These results suggest that hypoxia-reoxygenation impairs endothelium-dependent relaxation of rat aorta by a mechanism that involves oxidant-mediated endothelial cell death.