High glucose impairs EDHF-mediated dilation of coronary arterioles via reduced cytochrome P450 activity

Endothelium-derived hyperpolarizing factor (EDHF) is an important vasodilator that regulates the vasomotor function. However, it remains unclear whether diabetes/hyperglycemia-induced vascular impairments extend to the EDHF. The present study aims to determine the effect of high glucose (HG) on EDHF-mediated arteriolar dilation and the underlying mechanism. Porcine coronary arterioles were isolated and pressurized for vasomotor study. Cultured porcine coronary artery endothelial cells (ECs) were used for molecular and biochemical analysis. Our results demonstrate that bradykinin (BK)-simulated arteriolar dilation is mediated by nitric oxide (NO) and EDHF pathways. Direct incubation of HG impaired vasodilation to BK but not to sodium nitroprusside (endothelium-independent vasodilator). In the presence of inhibitors of endothelial NO synthase (eNOS) and cyclooxygenase, the EDHF-mediated dilation was reduced by HG incubation. The inhibitory effect of HG was prevented by treating the vessels with superoxide scavenger Tempol. In cultured coronary endothelial cells, HG reduced endothelial epoxyeicosatrienoic acid (EET) production as well as cytochrome P450 epoxygenase (CYP) activity. Furthermore, the superoxide production was elevated in ECs after HG incubation. Pretreatment with Tempol before HG incubation prevented the increase of cellular superoxide and abolished the decrease of CYP activity. Collectively, our results suggest that, in addition to NO-mediated pathway, HG impairs the EET/EDHF-mediated vasodilation in coronary arterioles via the elevated level of superoxide leading to inhibition of CYP activity in coronary ECs.