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      Role of the Adventitia in the Cyclic GMP-Mediated Relaxant Effect of N ω -Hydroxy- L-Arginine in Rat Aorta

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          Abstract

          N<sup>ω</sup>-hydroxy- L-arginine ( L-NOHA), the stable intermediate of the nitric oxide synthase (NOS)-catalyzed reaction, can induce NO/cyclic GMP-dependent relaxation in the rat aorta, in an endothelium- and NOS-independent manner. In this study, the role of the adventitia in the endothelium-independent effect of L-NOHA was investigated. Despite a decrease in norepinephrine (NE)-induced precontraction, adventitia removal in the rat aorta did not markedly alter the relaxant effect of forskolin, S-nitroso-N-acetylpenicillamine or glyceryl trinitrate. In contrast, both inhibition of NE-induced contraction and relaxation of NE-precontracted rings produced by L-NOHA were diminished in the absence of adventitia. Moreover, exposure to L-NOHA significantly enhanced the cyclic GMP level in the media of the aorta with, but not without adventitia. These findings demonstrate the role of the adventitia in the L-NOHA-induced decrease in tone and increase in cyclic GMP in the endothelium-denuded rat aorta. They suggest that NO or an NO-related compound formed from L-NOHA in the adventitia may produce paracrine effects.

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          Most cited references 14

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          Structure-function aspects in the nitric oxide synthases.

           D Stuehr (1996)
          Research on the biological roles of nitric oxide has revealed that it functions as an important signal and effector molecule in a variety of physiologic and pathologic settings. In animals, nitric oxide is synthesized enzymatically from L-arginine through the actions of the nitric oxide synthases (NOSs). The three known NOS isoforms are all dimeric, bi-domain enzymes that contain iron protoporphyrin IX, flavin adenine dinucleotide, flavin mononucleotide, and tetrahydrobiopterin as bound prosthetic groups. This chapter summarizes information regarding the structure-function aspects of the NOSs, which includes composition of the domains, the protein residues and regions involved in prosthetic group binding, catalytic properties of the domains, the relationship between dimeric structure and prosthetic group binding and function, and factors that control assembly of NOS in cells. A general model for NOS structure and assembly is presented.
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            Phagocytosis and macrophage activation associated with hemorrhagic microvessels in human atherosclerosis.

            Previously, we demonstrated that activated inducible NO synthase (iNOS)-expressing foam cells in human carotid plaques often produce autofluorescent (per)oxidized lipids (ceroid). Here, we investigate whether intraplaque microvessels can provide foam cells with lipids and trigger macrophage activation. Microvessels (von Willebrand factor [vWf] immunoreactivity), activated macrophages (iNOS immunoreactivity), and ceroid were systematically mapped in longitudinal sections of 15 human carotid endarterectomy specimens. An unbiased hierarchical cluster analysis classified vascular regions into 2 categories. One type with normal vWf expression and without inflammatory cells was seen, and another type with cuboidal endothelial cells, perivascular vWf deposits, and iNOS and ceroid-containing foam cells was seen in 4 (27%) of 15 plaques. The perivascular foam cells frequently contained platelets (glycoprotein Ibalpha) and erythrocytes (hemoglobin, iron), pointing to microhemorrhage/thrombosis and subsequent phagocytosis. Similar lipid-containing cells, expressing both ceroid and iNOS, were generated in atherosclerosis-free settings by incubating murine J774 macrophages with platelets or oxidized erythrocytes and also in vivo in organizing thrombi in normocholesterolemic rabbits. Focal intraplaque microhemorrhages initiate platelet and erythrocyte phagocytosis, leading to iron deposition, macrophage activation, ceroid production, and foam cell formation. Neovascularization, besides supplying plaques with leukocytes and lipoproteins, can thus promote focal plaque expansion when microvessels become thrombotic or rupture prone.
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              Does nitric oxide mediate the vasodilator activity of nitroglycerin?

              Nitroglycerin (glyceryl trinitrate, GTN) relaxes blood vessels primarily via activation of the soluble guanylyl cyclase (sGC)/cGMP/cGMP-dependent protein kinase (cGK-I) pathway. Although the precise mechanism of sGC activation by GTN in the vascular wall is unknown, the mediatory role of nitric oxide (NO) has been postulated. We tested the GTN/NO hypothesis in different types of isolated rat and rabbit blood vessels using two novel approaches: (1) EPR spin trapping using colloid Fe(DETC)2 and (2) analysis of cGK-I-dependent phosphorylation of the vasodilator-stimulated phosphoprotein at Ser239 (P-VASP). For comparison, another organic nitrate, isosorbide dinitrate (ISDN), and endothelium-dependent vasodilator, calcium ionophore A23187, were tested. We found a marked discrepancy between GTN's strong vasoactivity (vasodilation and augmentation of P-VASP) and its poor NO donor properties. In aortas precontracted with phenylephrine, GTN, ISDN, and A23187 induced nearly full relaxations (>80%) and doubling of vascular P-VASP content at concentrations of 100 nmol/L, 100 micromol/L, and 1 micromol/L, respectively. GTN applied in vasorelaxant concentrations (10 to 1000 nmol/L) did not significantly increase the basal vascular NO production, in contrast to ISDN and A23187. The absence of GTN-derived NO was confirmed in rabbit vena cava and renal artery. A significant increase in vascular NO formation was observed only at suprapharmacological GTN concentrations (>10 micromol/L). The concentration dependency of NO formation from GTN was comparable to that of ISDN, although the latter exhibits 100-folds lower vasorelaxant potency. We conclude that GTN activates the sGC/cGMP/cGK-I pathway and induces vasorelaxation without intermediacy of the free radical NO. The full text of this article is available online at http://www.circresaha.org.
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                Author and article information

                Journal
                JVR
                J Vasc Res
                10.1159/issn.1018-1172
                Journal of Vascular Research
                S. Karger AG
                1018-1172
                1423-0135
                2005
                August 2005
                29 July 2005
                : 42
                : 4
                : 331-336
                Affiliations
                Pharmacologie et Physico-Chimie, UMR CNRS 7034, Université Louis Pasteur de Strasbourg, Strasbourg, France
                Article
                86489 J Vasc Res 2005;42:331–336
                10.1159/000086489
                15976507
                © 2005 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Figures: 3, References: 23, Pages: 6
                Categories
                Research Paper

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