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      Effect of L-Carnitine and Propionyl- L-Carnitine on Endothelial Function of Small Mesenteric Arteries from SHR

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          Background:The effect of treatment with either 200 mg·kg<sup>–1</sup> of L-carnitine (LC) or propionyl- L-carnitine (PLC) was studied on endothelial dysfunction of small mesenteric arteries (SMA) from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Methods: Systolic blood pressure (SBP) was measured and endothelial and vascular functions were assessed by the effect of carbachol (CCh) and phenylephrine (Phe). O<sub>2</sub><sup>–</sup> produced by SMA and eNOS expression were evaluated by chemiluminescence and Western blot, respectively. Results: Although SBP was not affected, endothelial relaxation increased in both LC- and PLC-treated SHR. Nevertheless, the CCh-induced contraction remained sensitive to indomethacin in these rats. On the contrary, NO participation was increased in all the groups except for LC-treated WKY. Furthermore, high concentrations of Phe produced NO-dependent relaxation of SMA from PLC-treated rats. Both compounds decreased basal and NADPH-stimulated O<sub>2</sub><sup>–</sup> in SHR toward values observed in WKY. Only PLC increased eNOS protein expression in SHR. Neither LC nor PLC affected endothelium-derived hyperpolarizing factor-induced relaxation. Conclusions: LC and its propionate improved endothelial responses of SMA from SHR by decreasing O<sub>2</sub><sup>–</sup> production and thus increasing NO availability. PLC also increased NO synthesis by enhancing eNOS expression.

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          Most cited references 27

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          EDHF: bringing the concepts together

          Endothelial cells synthesize and release vasoactive mediators in response to various neurohumoural substances (e.g. bradykinin or acetylcholine) and physical stimuli (e.g. cyclic stretch or fluid shear stress). The best-characterized endothelium-derived relaxing factors are nitric oxide and prostacyclin. However, an additional relaxant pathway associated with smooth muscle hyperpolarization also exists. This hyperpolarization was originally attributed to the release of an endothelium-derived hyperpolarizing factor (EDHF) that diffuses to and activates smooth muscle K(+) channels. More recent evidence suggests that endothelial cell receptor activation by these neurohumoural substances opens endothelial cell K(+) channels. Several mechanisms have been proposed to link this pivotal step to the subsequent smooth muscle hyperpolarization. The main concepts are considered in detail in this review.
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            Endothelial dysfunction: from physiology to therapy.

            The endothelium controls the tone of the underlying vascular smooth muscle mainly through the production of vasodilator mediators. In some cases, this function is hampered by the release of constrictor substances. The endothelial mediators are also involved in the regulation by the endothelium of vascular architecture and the blood cell-vascular wall interactions. The endothelium-derived factors comprise nitric oxide (NO), prostacyclin, and a still unknown endothelium-derived hyperpolarizing factor(s) (EDHF). In most vascular diseases, the vasodilator function of the endothelium is attenuated. In advanced atherosclerotic lesions, endothelium-dependent vasodilatation may even be abolished. Various degrees and forms of endothelial dysfunction exist, including (1) the impairment of Galphai proteins, (2) less release of NO, prostacyclin and/or EDHF, (3) increased release of endoperoxides, (4) increased production of reactive oxygen species, (5) increased generation of endothelin-1, and (6) decreased sensitivity of the vascular smooth muscle to NO, prostacyclin and/or EDHF. The levels of bradykinin and angiotensin II within the vascular wall are controlled by angiotensin-converting enzyme (ACE). ACE degrades bradykinin and generates angiotensin II. Bradykinin stimulates endothelial cells to release vasodilators. The actions of the kinin are maintained despite endothelial dysfunction, except in very severe arterial lesions. Angiotensin II may be in part responsible for endothelial dysfunction because it induces resistance to the vasodilator action of NO. Thus, impairment of the generation of angiotensin II blocks the direct and indirect vasoconstrictor effect of the peptide. By potentiating bradykinin, ACE inhibitors promote the release of relaxing vasodilator mediators to restore vasodilator function, and to prevent platelet aggregation as well as the recruitment of leukocytes to the vascular wall.
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              Reversal of endothelial nitric oxide synthase uncoupling and up-regulation of endothelial nitric oxide synthase expression lowers blood pressure in hypertensive rats.

              We sought to examine the hypothesis that a pharmacologic up-regulation of endothelial nitric oxide synthase (eNOS) combined with a reversal of eNOS uncoupling provides a protective effect against cardiovascular disease. Many cardiovascular diseases are associated with oxidant stress involving protein kinase C (PKC) and uncoupling of eNOS. Messenger ribonucleic acid (mRNA) expression was analyzed with RNase protection assay or quantitative real-time polymerase chain reaction, vascular nitric oxide (NO) with spin trapping, and reactive oxygen species (ROS) with dihydroethidium fluorescence. Aortas of spontaneously hypertensive rats (SHR) showed an elevated production of ROS when compared with aortas of Wistar-Kyoto rats (WKY). The aortic expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits (Nox1, Nox2, Nox4, and p22phox) was higher in SHR compared with WKY. In SHR, aortic production of ROS was reduced by the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME), indicating eNOS "uncoupling" in hypertension. Oral treatment with the PKC inhibitor midostaurin reduced aortic Nox1 expression, diminished ROS production, and reversed eNOS uncoupling in SHR. Aortic levels of (6R)-5,6,7,8-tetrahydro-L-biopterin (BH4) were significantly reduced in SHR compared with WKY. Midostaurin normalized BH4 levels in SHR. In both WKY and SHR, midostaurin increased aortic expression of eNOS mRNA and protein, stimulated bioactive NO production, and enhanced relaxation of the aorta to acetylcholine. Midostaurin lowered blood pressure in SHR and, to a lesser extent, in WKY; the compound did not change blood pressure in WKY made hypertensive with L-NAME. Pharmacologic interventions that combine eNOS up-regulation and reversal of eNOS uncoupling can markedly increase bioactive NO in the vasculature and produce beneficial hemodynamic effects such as a reduction of blood pressure.

                Author and article information

                J Vasc Res
                Journal of Vascular Research
                S. Karger AG
                August 2007
                04 May 2007
                : 44
                : 5
                : 354-364
                Department of Pharmacology, Faculty of Pharmacy, University of Seville, Seville, Spain
                102303 J Vasc Res 2007;44:354–364
                © 2007 S. Karger AG, Basel

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                Page count
                Figures: 8, Tables: 1, References: 40, Pages: 11
                Research Paper


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