. Microvascular dysfunction after transient high glucose is caused by superoxide-dependent reduction in the bioavailability of NO and BH4. Am J Physiol Heart Circ Physiol 287: H626 -H633, 2004. First published March 25, 2004 10.1152/ajpheart.00074.2004.-We hypothesized that transient high-glucose concentration interferes with mediation by nitric oxide (NO) of flow-induced dilation (FID) of arterioles due to enhanced production of superoxide. In isolated, pressurized (80 mmHg) rat gracilis muscle arterioles (ϳ130 m) after transient high-glucose treatment (tHG; incubation with 30 mM glucose for 1 h), FID was reduced (maximum: control, 38 Ϯ 4%; after tHG, 17 Ϯ 3%), which was not further diminished by the NO synthase (NOS) inhibitor N -nitro-L-arginine methyl ester (L-NAME; 18 Ϯ 2%). Correspondingly, an enhanced polyethylene-glycol-SOD (PEG-SOD)-sensitive superoxide production was detected after tHG in carotid arteries by dihydroethydine (DHE) staining. Presence of PEG-SOD during tHG prevented the reduction of FID (41 Ϯ 3%), which could be inhibited by L-NAME (20 Ϯ 4%). Administration of PEG-SOD after tHG did not prevent the reduction of FID (22 Ϯ 3%). Sepiapterin, a precursor of the NO synthase cofactor tetrahydrobiopterin (BH4), administered during tHG did not prevent the reduction of FID (maximum, 15 Ϯ 5%); however, it restored FID when administered after tHG (32 Ϯ 4%). Furthermore, inhibition of either glycolysis by 2-deoxyglucose or mitochondrial complex II by 2-thenoyltrifluoroacetone reduced the tHG-induced DHE-detectable enhanced superoxide production in carotid arteries and prevented FID reduction in arterioles (39 Ϯ 5 and 35 Ϯ 2%). Collectively, these findings suggest that in skeletal muscle arterioles, a transient elevation of glucose via its increased metabolism, elicits enhanced production of superoxide, which decreases the bioavailability of NO and the level of the NOS cofactor BH4, resulting in a reduction of FID mediated by NO.arteriole; glycolysis; mitochondrial complex II; 2-deoxyglucose EPIDEMIOLOGIC STUDIES (45, 45a) have shown that strict glycemic control delays the development of microangiopathy and related cardiovascular risks in patients with diabetes mellitus. These studies (45, 45a) suggest that even transient increases in plasma glucose concentrations play an important role in the development of microvascular dysfunction in diabetes. However, the underlying mechanisms leading to functional impairment of microvessels in response to transient hyperglycemia are still not fully elucidated.One of the important physiological roles of microvessels is the local regulation of blood flow, hence tissue perfusion (26, 32), which is known to be affected in the early phase of diabetes (37). Previous studies (13,14) in small arteries and arterioles of diabetic subjects have demonstrated that before the appearance of morphological changes, a vasomotor dysfunction of microvessels develops, affecting both smooth muscle-and endothelium-mediated regulatory mechanisms. In line with these findings, we and othe...

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Bagi, Zsolt, Csongor Csekő , Erika Tó th, and Akos Koller. Oxidative stress-induced dysregulation of arteriolar wall shear stress and blood pressure in hyperhomocysteinemia is prevented by chronic vitamin C treatment. Am J Physiol Heart Circ Physiol 285: H2277-H2283, 2003. First published July 17, 2003 10.1152/ajpheart.00448.2003.-We aimed to test the hypothesis that an enhanced level of reactive oxygen species (ROS) is primarily responsible for the impairment of nitric oxide (NO)-mediated regulation of arteriolar wall shear stress (WSS) in hyperhomocysteinemia (HHcy). Thus flow/WSS-induced dilations of pressurized gracilis muscle arterioles (basal diameter: ϳ170 m) isolated from control (serum Hcy: 6 Ϯ 1 M), methionine diet-induced HHcy rats (4 wk, serum Hcy: 30 Ϯ 6 M), and HHcy rats treated with vitamin C, a known antioxidant (4 wk, 150 mg ⅐ kg body wt Ϫ1 ⅐ day Ϫ1 ; serum Hcy: 32 Ϯ 10 M), were investigated. In vessels of HHcy rats, increases in intraluminal flow/WSS-induced dilations were converted to constrictions. Constrictions were unaffected by inhibition of NO synthesis by N -nitro-L-arginine methyl ester (L-NAME). Vitamin C treatment of HHcy rats reversed the WSS-induced arteriolar constrictions to L-NAME-sensitive dilations but did not affect control responses. Similar changes in responses were obtained for the calcium ionophore A-23187. In addition, diastolic and mean arterial blood pressure and serum 8-isoprostane levels (a marker of in vivo oxidative stress) were significantly elevated in rats with HHcy, changes that were normalized by vitamin C treatment. Taken together, our data show that in chronic HHcy long-term vitamin C treatment, by decreasing oxidative stress in vivo, enhanced NO bioavailability, restored the regulation of shear stress in arterioles, and normalized systemic blood pressure. Thus our study provides evidence that oxidative stress is an important in vivo mechanism that is primarily responsible for the development of endothelial dysregulation of WSS in HHcy.homocysteine; nitric oxide; thromboxane A2 power dissipation SEVERAL EPIDEMIOLOGICAL STUDIES have shown that hyperhomocysteinemia (HHcy) increases the risk for cardiovascular diseases, such as ischemic heart diseases; cerebrovascular, peripheral vascular diseases; and hypertension (1,6,7,9,29,32). Homocysteine is formed during the metabolism of the essential amino acid methionine, and its normal plasma concentration is between 5 and 15 M, but it can be increased due to genetic (e.g., cystathione-␤-synthase and methyltetrahydrofolate reductase) and nutritional alterations (deficiency of vitamins, e.g., folic acid, vitamin B 6 , and B 12 ), factors that participate in the metabolism of homocysteine and methionine (8).Although the underlying mechanisms responsible for the elevated risks have not yet been fully elucidated, there is increasing evidence to suggest that endothelial dysfunction of vessels contributes to the development of vascular diseases observed in both humans and animals with HHcy (19,34). Several studies have doc...

Hyperglycemia increases glucose metabolism via the polyol pathway, which results in elevations of intracellular sorbitol concentration. Thus we hypothesized that elevated level of sorbitol contributes to the development of hyperglycemia-induced dysfunction of microvessels. In isolated, pressurized (80 mmHg) rat gracilis muscle arterioles (approximately 150 microm), high glucose treatment (25 mM) induced reduction in flow-dependent dilation (from maximum of 39 +/- 2% to 15 +/- 1%), which was significantly mitigated by an aldose reductase inhibitor, zopolrestat (maximum 27 +/- 2%). Increasing doses of sorbitol (10(-10)-10(-4) M) elicited dose-dependent constrictions (maximum 22 +/- 3%), which were abolished by endothelium removal, a prostaglandin H(2)/thromboxane A(2) (PGH(2)/TXA(2)) receptor (TP) antagonist SQ-29548, or superoxide dismutase (SOD) plus catalase (CAT). Incubation of arterioles with sorbitol (10(-7) M) reduced flow-dependent dilations (from maximum of 39 +/- 2% to 20 +/- 1.5%), which was not further affected by inhibition of nitric oxide synthase by N(omega)-nitro-l-arginine methyl ester but was prevented by SOD plus CAT and mitigated by SQ-29548. Nitric oxide donor sodium nitroprusside-induced (10(-9)-10(-6) M) dilations were also decreased in a SQ-29548 and SOD plus CAT-reversible manner, whereas adenosine dilations were not affected by sorbitol exposure. Sorbitol significantly increased arterial superoxide production detected by lucigenin-enhanced chemiluminescence, which was inhibited by SOD plus CAT. Sorbitol treatment also increased arterial formation of 3-nitrotyrosine. We suggest that hyperglycemia by elevating intracellular sorbitol induces oxidative stress, which interferes with nitric oxide bioavailability and promotes PGH(2)/TXA(2) release, both of which affect regulation of vasomotor responses of arterioles. Thus increased activity of the polyol pathway may contribute to the development of microvascular dysfunction in diabetes mellitus.