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Z. Yuan, L. Kuo, T. W. Hein; High Glucose Impairs Endothelium-Dependent Nitric Oxide-Mediated Dilation of Retinal Arterioles via Oxidative Stress and Protein Kinase C Activation. Invest. Ophthalmol. Vis. Sci. 2009;50(13):400.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal blood flow is regulated by the vasomotor activity of retinal arterioles. Although hyperglycemia is associated with reduction in retinal blood flow in early stages of diabetic retinopathy, the direct effect of elevated glucose on retinal arteriolar reactivity and its underlying signaling events remain unknown. Herein, we examined whether high glucose can directly affect endothelium-dependent nitric oxide (NO)-mediated dilation of retinal arterioles by increasing oxidative stress and activating protein kinase C (PKC).
Pig retinal arterioles (<100 µm) were isolated, cannulated, and pressurized without flow for in vitro study. Vascular diameter changes and superoxide production were monitored using videomicroscopic and dihydroethidium (DHE) staining techniques, respectively.
Retinal arterioles exposed to normal level of glucose (5 mM, intraluminal) dilated dose-dependently to endothelium-dependent NO-mediated agent bradykinin and to endothelium-independent NO donor sodium nitroprusside (SNP). However, elevation of intraluminal glucose (25 and 50 mM, 90 min) produced a graded inhibition of vasodilation to bradykinin, but not to SNP. This inhibitory effect was prevented by intraluminal administration of superoxide scavenger TEMPOL (0.1 mM) or PKC inhibitors (chelerythrine, 1 µM or Go 6976, 1 µM). Intraluminal exposure of vessels to superoxide generator pyrogallol (0.1 mM) caused a similar inhibition of bradykinin-induced dilation as that by high glucose. DHE staining showed that high glucose elicited TEMPOL- and chelerythrine-sensitive superoxide production in endothelium of arterioles.
These data show that acute exposure of retinal arterioles to high glucose specifically impairs endothelium-dependent NO-mediated dilation. It appears that activation of PKC and subsequent increase in superoxide production contributes to the high glucose-induced endothelial dysfunction. Such alterations in arteriolar function may contribute to decreased retinal blood flow in early diabetes.
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