Background--We hypothesized that atherosclerosis inhibits NO-mediated endothelium-dependent dilation of coronary arterioles through interaction of ox-LDL with its receptor, LOX-1, through the production of O₂ÿ^- in endothelial cells.

Methods and Results--We assessed the role of ox-LDL in endothelial dysfunction in a murine model of atherosclerosis (ApoE KO mice). Coronary arterioles from WT control and ApoE KO mice were isolated and pressurized without flow. Although dilation of vessels to endothelium-independent vasodilator SNP was not altered between ApoE KO and WT mice, dilation to the endothelium-dependent agonist, ACh was reduced in ApoE KO versus WT mice. Impaired vasodilation to ACh in ApoE KO mice is partially restored by NAD(P)H oxidase inhibitor, apocynin or DPI. Messenger RNA expression for NAD(P)H oxidases was higher in ApoE KO mice than that in WT and anti-LOX-1 treated ApoE KO mice. Anti-LOX-1, given in vivo, restored NO-mediated coronary arteriolar dilation in ApoE KO mice, but did not affect the endothelium-dependent vasodilation in controls.

Conclusions--These results suggest that ox-LDL impairs endothelium-dependent NO-mediated dilation of coronary arterioles by activation of a signaling cascade involving LOX-1 and NAD(P)H oxidase expression.