Elsevier

Life Sciences

Volume 71, Issue 6, 28 June 2002, Pages 679-692
Life Sciences

Effects of spontaneous or induced brain ischemia on vessel reactivity: The role of inducible nitric oxide synthase

https://doi.org/10.1016/S0024-3205(02)01711-3Get rights and content

Abstract

Short episodes of ischemia and reperfusion in various organs may protect the organ itself, and the heart both as an immediate and a delayed effect. The present study investigates whether a systemic protection of vascular function occurs during adaption to ischemia. Brain ischemia was induced by bilateral ligation of the internal carotid arteries in C57BL6 mice, and 24–36 hours later rings of the thoracic aorta were mounted to study in vitro relaxation and contraction, or proteins were extracted for immunoblotting for endothelial nitric oxide synthase (eNOS) or inducible NOS (iNOS). eNOS decreased, while iNOS increased in the aortic wall after carotid artery ligation. In vitro contraction to increasing concentrations of prostaglandin F (PGF) was attenuated, while relaxation to acetylcholine (ACh) was enhanced. The latter was abolished by the iNOS-inhibitor aminoguanidine. When brain ischemia was induced in iNOS deficient mice, an increase of aortic eNOS was found 24 hours later. The ischemia-induced attenuated relaxation to PGF and enhanced relaxation to ACh were abolished. Aortic rings from mice with severe atherosclerosis (apolipoprotein E and low density lipoprotein receptor double knockout (ApoE/LDLr KO) mice) and spontaneous ischemic events in the heart or brain in vivo were also studied. Spontanous ischemic events in ApoE/LDLr KO animals did not influence iNOS and eNOS in the vessel wall. A reduced contraction to PGF was observed, but relaxation to ACh was unchanged. These findings suggest that induced brain ischemia as a model of delayed, remote preconditioning protects vessel reactivity, and this protection is mediated by iNOS.

Introduction

Ischemic preconditioning of the heart is a powerful mode of myocardial protection which results in improved contractile function, increased coronary flow, and reduced infarct size when performed immediately (classic) or 24–72 hours (delayed) before sustained ischemia. The preconditioning process involves trigger substance(s), signal transduction pathways, and probably synthesis of organ effector(s) of protection. Nitric oxide (NO) has been suggested as a trigger and a mediator of the preconditioning response [1]. Delayed preconditioning of the heart may be mediated by inducible nitric oxide synthase (iNOS), as preconditioning is inhibited by iNOS blockers such as aminoguanidine and S-methylisothiourea [2]. In addition, it was recently shown that mice with targeted disruption of the iNOS gene could not be preconditioned [3]. Pharmacological preconditioning by lipopolysaccharide or monophosphoryl lipid A not only protects the heart against ischemic injury [5], [6], but also results in systemic vasodilatory effects [4], [5], [6]. The beneficial effects of these agents appear to be mediated by iNOS, as the effects are abolished by pharmacological or genetical iNOS inhibition [5], [7], [8], [9].

During the last few years remote preconditioning, which can be both classic and delayed, has been discovered. Thus, short episodes of ischemia and reperfusion of the limb [10], colon [11], and kidney [12] protects not only the organ itself, but also the heart. The mechanisms of remote preconditioning are not clarified. We have demonstrated that spontaneous ischemic events in hearts or brains of mice with severe atherosclerosis protects their isolated hearts against induced ischemia 24–36 hours later [13]. Preconditioning of other organs to evoke myocardial protection indicates that a general as well as an organ specific protection is induced. The possible involvement of NO and iNOS as mediators of remote protection indicates that preconditioning may affect vascular function; however, to the author’s knowledge there are no publications on this.

The aim of the present study was therefore to investigate if delayed, remote preconditioning induced by brain ischemia influences vessel reactivity in vitro, and whether iNOS is involved as a mediator of this effect.

Section snippets

Animals

The study was performed in accordance with the Guide for the Care and Use of Laboratory Animals published by the US NIH, and was approved by the Ethics Committee for Animal Research at the Karolinska Institute. Apolipoprotein E and low density lipoprotein receptor double knockout mice (ApoE/LDLr KO) of either sex on C57BL6 background were purchased from Bomholtgård (Bomholt, Denmark), and fed an atherogenic diet containing 21% fat and 0.15% cholesterol (R683, AnalyCen, Lidköping, Sweden) for

Response to ACh and PGF in mice with induced brain ischemia

ACh evoked a concentration-dependent relaxation of aortic rings from both C57BL6 and iNOS KO mice. In C57BL6 mice, the relaxations induced by ACh were enhanced in mice with induced brain ischemia. The highest concentration of ACh (10 μmol/L) relaxed the vessels by 79 ± 4% in mice without brain ischemia, and by 92 ± 3% in mice with induced brain ischemia (Fig. 1A, p < 0.05). The enhanced response to ACh was abolished by pre-incubation with aminoguanidine (Fig. 1B). In iNOS KO mice, the response

Discussion

In the present study in vitro reactivity of thoracic aortic rings from animals with spontaneous or induced brain ischemia was investigated. These animals had a preconditioning-like protection of heart function and infarct size when their hearts were Langendorff-perfused and subjected to global ischemia and reperfusion [13]. The present study investigated whether this was associated with changes of vessel reactivity and expression of iNOS/eNOS protein. The main findings were that induced brain

Acknowledgements

The work has been supported by grants from the Swedish Medical Research Council (10857 and 12665), the Swedish Heart–Lung Foundation, Jeanssonska Stiftelserna, Fredrik and Ingrid Thuring Foundation, King Gustav V:s and Queen Victorias Foundation, and the Karolinska Institute. Shinichi Tokuno was supported by a grant from the Japanese Self Defense Force.

References (24)

  • A. Takaoka et al.

    Renal ischemia/reperfusion remotely improves myocardial energy metabolism during myocardial ischemia via adenosine receptors in rabbits: effects of “remote preconditioning”

    J. Am. Coll. Cardiol.

    (1999)
  • S. Shimizu et al.

    Presence of excess tetrahydrobiopterin during nitric oxide production from inducible nitric oxide synthase in LPS-treated rat aorta

    Life Sci.

    (1999)
  • R. Bolli et al.

    The nitric oxide hypothesis of late preconditioning

    Basic Res. Cardiol.

    (1998)
  • J. Imagawa et al.

    Pharmacological evidence that inducible nitric oxide synthase is a mediator of delayed preconditioning

    Br. J. Pharmacol.

    (1999)
  • Y. Guo et al.

    The late phase of ischemic preconditioning is abrogated by targeted disruption of the inducible NO synthase gene

    Proc. Natl. Acad. Sci. U.S.A.

    (1999)
  • L. Xi et al.

    Essential role of inducible nitric oxide synthase in monophosphoryl lipid A-induced late cardioprotection: evidence from pharmacological inhibition and gene knockout mice

    Circulation

    (1999)
  • K. Zacharowski et al.

    Endotoxin induces a second window of protection in the rat heart as determined by using p-nitro-blue tetrazolium staining, cardiac troponin T release, and histology

    Arterioscler., Thromb., Vasc. Biol.

    (1999)
  • C.A. Gunnett et al.

    Vascular effects of LPS in mice deficient in expression of the gene for inducible nitric oxide synthase

    Am. J. Physiol.

    (1998)
  • A.L. Weigert et al.

    Expression and preferential inhibition of inducible nitric oxide synthase in aortas of endotoxemic rats

    J. Am. Soc. Nephrol.

    (1995)
  • M.H. Yen et al.

    Comparison of responses to aminoguanidine and N omega-nitro-L-arginine methyl ester in the rat aorta

    Clin. Exp. Pharmacol. Physiol.

    (1995)
  • L. Xi et al.

    Glycolipid RC-552 induces delayed preconditioning-like effect via iNOS-dependent pathway in mice

    Am. J. Physiol.

    (1999)
  • T. Oxman et al.

    Limb ischemia preconditions the heart against reperfusion tachyarrhythmia

    Am. J. Physiol.

    (1997)
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    Present address: Section of Military and Emergency Medicine, Medical Service School of Japanese Ground Self Defence Force, Tokyo, Japan.

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