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

ABSTRACT

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 µM) and miconazole (30 µM) reduced the magnitude of peak flow dilation by ~20%-30%, and reduced the duration of dilatory response by ~70-80%. Nevertheless, sulphaphenazole (10 µM), a selective inhibitor of CYP 2C9, had no effect neither on the peak flow dilation nor the duration of dilatory response. Oxypurinol (100 µM), 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 µM), 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.