Flow Dilation in Rat Small Mesenteric Arteries is Mediated by H ydrogen Peroxide Generated from CYP Epoxygenases and Xanthine Oxidase

We have previously demonstrated that hydrogen peroxide (H2O2) mediates flow-induced vascular dilation in rat small mesenteric arteries. In the present study, the source of this flow-induced H2O2 was explored. The arteries were pressurized to 50 mm Hg and preconstricted with phenylephrine. Intraluminal flow reversed the effect of phenylephrine, resulting in vascular dilation. Cytochrome P450 (CYP) inhibitors N-methylsulfonyl-6-(2-proparglyoxyphenyl) hexanoic acid (MS-PPOH, 10 M) and miconazole (30 M) reduced the magnitude of peak flow dilation by ~20%-30%, and reduced the duration of dilatory response by ~70-80%. Nevertheless, sulphaphenazole (10 M), a selective inhibitor of CYP 2C9, had no effect neither on the peak flow dilation nor the duration of dilatory response. Oxypurinol (100 M), an inhibitor of xanthine oxidase, attenuated the duration of dilatory response by ~60% but exerted no effect on the magnitude of peak flow dilation. Cyclosporin A (2 M), an inhibitor for mitochondrial permeability transition pore, MitoQ (300 nM), a mitochondria-targeted antioxidant, and apocynin (1 mM), a NADPH oxidase inhibitor, had no effect neither on the magnitude of peak flow dilation nor the duration of dilatory response. To further confirm the role of CYP in flow-induced H2O2 production, a fluorescent probe CM-H2DCFDA was used to monitor the production of H2O2 in the primary endothelial cells isolated from rat small mesenteric arteries. The results showed that flow-induced H2O2 production was markedly reduced in MS-PPOH and miconazole pretreated endothelial cells. Taken together, our results suggest that, during flow dilation, H2O2 is generated from CYP epoxygenases and xanthine oxidase.