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      Magnesium and Vascular Tone and Reactivity

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          Abstract

          It has been reported that the concentration of extracellular magnesium ions ([Mg<sup>++</sup>]<sub>o</sub>) can affect blood flow, blood pressure and vascular reactivity in intact mammals. The present studies, using a variety of rat and rabbit blood vessels, were undertaken to shed further light on the relationship between [Mg<sup>++</sup>]<sub>o</sub>, Ca<sup>++</sup>, tone and vascular responsiveness. [Mg<sup>++</sup>]<sub>o</sub> was found to differentially affect a variety of hormone and drug-induced contractions in isolated rat and rabbit arteries as well as isolated perfused rat mesenteric arterioles (15–20 µm i.d.). Progressive elevations in [Mg<sup>++</sup>]<sub>o</sub> above physiologic levels will dose-dependently produce progressive, increased inhibition of most contractile substances. These results are not reflections of osmolarity. Withdrawal of [Mg<sup>++</sup>]<sub>o</sub> can induce contractions of rat arteries as well as of isolated perfused rat mesenteric arterioles. Using isolated rat portal veins, withdrawal of [Mg<sup>++</sup>] results in rapid enhancement of the spontaneously evoked mechanical responses and increases in rhythmic contractility; these spontaneously evoked responses are abolished in hypermagnesemic solutions (e.g., 10 mM). The contractile responses observed upon withdrawal of [Mg<sup>++</sup>]<sub>o</sub> are dependent upon the [Ca<sup>++</sup>] and the polarity of the membrane but are not related to inhibition of Na<sup>+</sup>, K<sup>+</sup> ATPase. With rat aortic strips, addition of CaEDTA potentiates contractions induced by Mg<sup>++</sup> withdrawal, while EGTA promotes rapid relaxations. Rapid relaxations of contractions induced by Mg<sup>++</sup> withdrawal in rat aorta could also be induced by Mn<sup>++</sup>, Ni<sup>++</sup>, Co<sup>++</sup> and Cd<sup>++</sup> but not Sr<sup>++</sup>. Addition of [Ni<sup>++</sup>] to portal veins exposed either to a Mg<sup>++</sup>-free solution, or to a solution containing Mg<sup>++</sup>, results in dose-dependent, and eventual complete, inhibition of all spontaneous mechanical events. These data suggest that [Mg<sup>++</sup>]<sub>o</sub>: (a) plays an important role in regulating membrane permeability to [Ca<sup>++</sup>]<sub>o</sub>; (b) probably occupies sites which are exchangeable with membrane-bound Ca in arterial, venous and arteriolar smooth muscle; (c) acts intracellularly as well to compete with Ca for certain divalent cation sites; and (d) may play an important role in regulating arteriolar tone and blood pressure.

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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
          978-3-8055-2857-3
          978-3-318-02028-1
          1018-1172
          1423-0135
          1978
          1978
          18 September 2008
          : 15
          : 1-3
          : 5-16
          Affiliations
          Department of Physiology, State University of New York, Downstate Medical Center, Brooklyn, N.Y.
          Article
          158148 Blood Vessels 1978;15:5–16
          10.1159/000158148
          © 1978 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
          Pages: 12
          Categories
          Molecular and Cellular Aspects of Vascular Smooth Muscle in Health and Disease

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