Background-Isoforms of the NADPH oxidase contribute to vascular superoxide anion ( · O 2 Ϫ ) formation and limit NO bioavailability. We hypothesized that the endothelial gp91phox-containing NADPH oxidase is predominant in generating the O 2 Ϫ to scavenge endothelial NO and thus is responsible for the development of endothelial dysfunction. Methods and Results-Endothelial dysfunction was studied in aortic rings from wild-type (WT) and gp91phox-knockout (gp91phox Ϫ/Ϫ ) mice with and without renovascular hypertension induced by renal artery clipping (2K1C). Hypertension induced by 2K1C was more severe in WT than in gp91phox Ϫ/Ϫ mice (158Ϯ2 versus 149Ϯ2 mm Hg; PϽ0.05). Endothelium-dependent relaxation to acetylcholine (ACh) was attenuated in rings from clipped WT but not from clipped gp91phox Ϫ/Ϫ mice. The reactive oxygen species (ROS) scavenger Tiron, PEG-superoxide dismutase, and the NADPH oxidase inhibitory peptide gp91ds-tat enhanced ACh-induced relaxation in aortae of clipped WT mice. Inhibition of protein kinase C, Rac, and the epidermal growth factor receptor kinase, elements involved in the activation of the NADPH oxidase, restored normal endothelium-dependent relaxation in vessels from clipped WT mice but had no effect on relaxations in those from gp91phox Ϫ/Ϫ mice. Relaxations to exogenous NO were attenuated in vessels from clipped WT but not clipped gp91phox Ϫ/Ϫ mice. After removal of the endothelium or treatment with PEG-superoxide dismutase, NO-induced relaxations were identical in vessels from clipped and sham-operated WT and gp91phox mice. Conclusions-These data indicate that the formation of O 2Ϫ by the endothelial gp91phox-containing NADPH oxidase accounts for the reduced NO bioavailability in the 2K1C model and contributes to the development of renovascular hypertension and endothelial dysfunction.
Proline-rich tyrosine kinase 2 (PYK2) can be activated by angiotensin II (Ang II) and reactive oxygen species. We report that in endothelial cells, Ang II enhances the tyrosine phosphorylation of endothelial NO synthase (eNOS) in an AT1-, H2O2-, and PYK2-dependent manner. Low concentrations (1–100 µmol/liter) of H2O2 stimulated the phosphorylation of eNOS Tyr657 without affecting that of Ser1177, and attenuated basal and agonist-induced NO production. In isolated mouse aortae, 30 µmol/liter H2O2 induced phosphorylation of eNOS on Tyr657 and impaired acetylcholine-induced relaxation. Endothelial overexpression of a dominant-negative PYK2 mutant protected against H2O2-induced endothelial dysfunction. Correspondingly, carotid arteries from eNOS−/− mice overexpressing the nonphosphorylatable eNOS Y657F mutant were also protected against H2O2. In vivo, 3 wk of treatment with Ang II considerably increased levels of Tyr657-phosphorylated eNOS in the aortae of wild-type but not Nox2y/− mice, and this was again associated with a clear impairment in endothelium-dependent vasodilatation in the wild-type but not in the Nox2y/− mice. Collectively, endothelial PYK2 activation by Ang II and H2O2 causes the phosphorylation of eNOS on Tyr657, attenuating NO production and endothelium-dependent vasodilatation. This mechanism may contribute to the endothelial dysfunction observed in cardiovascular diseases associated with increased activity of the renin–angiotensin system and elevated redox stress.
Hyperlipidemia enhances xanthine oxidase (XO) activity. XO is an important source of reactive oxygen species (ROS). Since ROS are thought to promote atherosclerosis, we hypothesized that XO is involved in the development of atherosclerosis. ApoE(-/-) mice were fed a Western-type (WD) or control diet. In subgroups, tungsten (700 mg/L) was administered to inhibit XO. XO is a secreted enzyme which is formed in the liver as xanthine dehydrogenase (XDH) and binds to the vascular endothelium. High expression of XDH was found in the liver and WD increased liver XDH mRNA and XDH protein expression. WD induced the conversion of XDH to the radical-forming XO. Moreover, WD increased the hepatic expression of CD40, demonstrating activation of hepatic cells. Aortic tissue of ApoE(-/-) mice fed a WD for 6 months exhibited marked atherosclerosis, attenuated endothelium-dependent relaxation to acetylcholine, increased vascular oxidative stress, and mRNA expression of the chemokine KC. Tungsten treatment had no effect on plasma lipids but lowered the plasma XO activity. In animals fed a control diet, tungsten had no effect on radical formation, endothelial function, or atherosclerosis development. In mice fed a WD, however tungsten attenuated the vascular superoxide anion formation, prevented endothelial dysfunction, and attenuated KC mRNA expression. Most importantly, tungsten treatment largely prevented the development of atherosclerosis in the aorta of ApoE(-/-) mice on WD. Therefore, tungsten, potentially via the inhibition of XO, prevents the development of endothelial dysfunction and atherosclerosis in ApoE(-/-) mice on WD.
The neurochemical specificity of physiological, biochemical, and psychological responses to dextroamphetamine was tested by pretreating volunteers with haloperidol (0.014 mg/kg IM), propranolol (0.1 mg/kg IV), thymoxamine (0.1 mg/kg IV), or placebo prior to 0.3 mg/kg IV amphetamine. Healthy volunteers (N = 12) participated in the studies, but not all volunteers received each drug combination. Haloperidol prevented dextroamphetamine-induced behavioral excitation, but did not significantly affect plasma norepinephrine or pressor responses, whereas propranolol inhibited norepinephrine and pressor responses without influencing excitation or other behavioral responses. Thymoxamine did not affect any of the responses measured. None of the agents significantly affected plasma cortisol or growth hormone responses. The prolactin rise following dextroamphetamine was potentiated by haloperidol. The results are consistent with the hypothesis that behavioral excitation after dextroamphetamine occurs through a dopaminergic mechanism, and pressor responses through a noradrenergic mechanism.
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