Alterations of the vascular and the myocardial guanylate cyclase/cGMP-system induced by long-term hypertension in rats

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Abstract

NO as produced by NO-synthases (NOS) contributes to the regulation of cardiovascular functions. In hypertension, there is a reduced production and/or activity of endogenous NO in the vasculature. We investigated if hypertension alters the NO-sensitivity of soluble guanylate cyclase (sGC) in blood vessels and heart muscle isolated from 15 month old spontaneously hypertensive rats (SHR15) and normal Wistar rats (WIS). Inhibition of NOS by 1 mM -nitro-l-arginine decreased dP/dtmax in WIS (−27.6±3.4%) and SHR15 (−26.0±4.4%), while stimulation of NOS with 1 mM l-arginine increased dP/dtmax in WIS (9.9±0.7%) and SHR15 (8.9±2.3%). The positive inotropic response to 0.1 μM glyceryl trinitrate (GTN) was comparable in WIS (dP/dtmax: 4.5±1.7%) and SHR15 (dP/dtmax: 3.75±0.7%) as was the positive inotropic response to the NO-donor sodium (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolat (DEA/NO, 1 μM) in WIS (dP/dtmax: 10.7±2.9%) and SHR15 (dP/dtmax: 5.1±1.5%, P=0.1873). In aortas of SHR15 we found an increased superoxide production of 19.4±1.7 nM/mg/min (WIS: 6.1±0.6 nM/mg/min) in the smooth muscle and the endothelial layer. Endothelium-dependent relaxation by acetylcholine was markedly impaired in SHR15 as was the vasorelaxant activity of S-nitroso-N-acetyl-d,l-penicillamine (SNAP), pentaerythritol tetranitrate and GTN. Maximal cGMP-production by sGC isolated from the lung and stimulated with SNAP (0.5 mM) was much lower in SHR15 (115±14 pmol/mg/min) than in WIS (348±36 pmol/mg/min). We suggest that hypertension is associated with a reduced activity of the sGC/cGMP-system in the vasculature but not in the heart muscle. Our results provide the first evidence that excess superoxide production in hypertension may trigger a desensitization of vascular sGC.

Introduction

Activation of soluble guanylate cyclase is a major vasorelaxant principle in the body. Recent investigations have shown that activation of soluble guanylate cyclase also has an effect on myocardial contractility (Brady et al., 1993; Kojda et al., 1996; Mohan et al., 1996). Physiologically, soluble guanylate cyclase is activated by endogenous NO, which is produced by specific NO-synthases (Nathan and Xie, 1994). Pharmacologically, activation of soluble guanylate cyclase occurs through the release of NO from nitrovasodilators such as glyceryl trinitrate (GTN) (Ahlner et al., 1991). Previous data from animal and clinical studies suggest that hypertension is associated with a reduced endothelium dependent vasorelaxation, which itself is mediated by endogenous NO-production (Mayhan et al., 1987; Moncada and Higgs, 1993, Moncada and Higgs, 1995; Panza et al., 1993). By contrast, it is not known whether the production and/or the effects of endogenous NO in the myocardium are altered by hypertension. Furthermore, the mechanism of the impairment of endothelium-dependent vasorelaxation in hypertension is not fully understood. Previous studies provided evidence for a reduced endogenous NO-production, an inactivation of endogenous NO initiated by superoxide radicals and the existence of a counteracting vasocontractile factor (Konishi and Su, 1983; Lüscher et al., 1987; Mayhan et al., 1987, Mayhan et al., 1988; Linder et al., 1990; Panza et al., 1990; Nakazono et al., 1991; Malinski et al., 1993; Taddei et al., 1993; Grunfeld et al., 1995; Küng and Lüscher, 1995; Tschudi et al., 1996; Crabos et al., 1997; Forte et al., 1997). By contrast, it is not known if hypertension alters the sensitivity of the soluble guanylate cyclase/cGMP-system, which is extremely important for the initiation of the effects of NO in both, blood vessels and heart muscle. The aim of the present study was to investigate if long-term hypertension is associated with alterations of the sensitivity of the myocardial and the vascular soluble guanylate cyclase/cGMP-system. To accomplish this we investigated the responses of the heart and the aorta isolated from 15 months old spontaneously hypertensive rats (SHR15). These animals have substantial vascular and myocardial hypertrophic changes due to long-term hypertension with systolic blood pressure >220 mm Hg (Stasch et al., 1987).

Section snippets

Preparation of isolated hearts, experimental protocols

We investigated isolated hearts, lungs and thoracic aortic rings of 11 normal male Wistar rats (WIS) at an age of 3–4 months and of 9 `stroke-prone' spontaneously hypertensive rats at an age of 15 months (SHR15). The average body weight of WIS and SHR15 was similar, while the average wet weight of the WIS-hearts was 1.11±0.05 g and that of SHR15-hearts was 2.1±0.11 g indicating substantial myocardial hypertrophy in SHR15. The hearts were rapidly excised and perfusion was done according to the

Effects of hypertension on myocardial contractility

Changes of the contractile activity of the myocardial muscle were investigated after infusion of NA to stimulate adrenergic receptors, l-NA to inhibit endogenous NO-production, l-arginine to stimulate endogenous NO-production and NO-donors such as DEA/NO and GTN. Infusion of NA increased dP/dtmax significantly stronger (P=0.0007) in WIS as compared to SHR15 indicating an impairment of the myocardial adrenergic response in SHR15 (Fig. 2A).

Activation of soluble guanylate cyclase by infusion of

Discussion

In this investigation the effects of long-term hypertension on the positive inotropic and the vasorelaxing actions of endogenous and exogenous NO were studied. The new finding is that long-term hypertension decreases the activity of the soluble guanylate cyclase/cGMP-system in the vasculature but not in the myocardial muscle. In hypertensive rats stimulation of endogenous NO-production and the response to exogenous NO was impaired only in the vasculature. In parallel, vascular production of

Acknowledgements

This study was supported by the Deutsche Forschungsgemeinschaft SFB 242; Projekt A11.

References (59)

  • M Kitakaze et al.

    Evidence for nitric oxide generation in the cardiomyocytes: Its augmentation by hypoxia

    J. Mol. Cell. Cardiol.

    (1995)
  • R.E Klabunde et al.

    Cardiovascular actions of inhibitors of endothelium-derived relaxing factor (nitric oxide) formation/release in anesthetized dogs

    Eur. J. Pharmacol.

    (1991)
  • R.E Klabunde et al.

    NG-Methyl-l-arginine decreases contractility, cGMP and cAMP in isoproterenol-stimulated rat hearts in vitro

    Eur. J. Pharmacol.

    (1992)
  • G Kojda et al.

    The new NO donor SPM3672 increases cGMP and improves contraction in rat cardiomyocytes and isolated heart

    Eur. J. Pharmacol.

    (1995)
  • H Luss et al.

    Characterization of inducible nitric oxide synthase expression in endotoxemic rat cardiac myocytes in vivo and following cytokine exposure in vitro

    J. Mol. Cell. Cardiol.

    (1995)
  • T Malinski et al.

    Nitric oxide synthase activity in genetic hypertension

    Biochem. Biophys. Res. Commun.

    (1993)
  • C Nathan et al.

    Nitric oxide synthases: Roles, tolls and controls

    Cell

    (1994)
  • B.E Strauer

    Evidence for a positive inotropic effect of nitroglycerol on isolated human ventricular myocardium

    Pharmacol. Res. Commun.

    (1971)
  • J Ahlner et al.

    Organic nitrate esters: Clinical use and mechanisms of actions

    Pharmacol. Rev.

    (1991)
  • Allen, R.C., 1986. Phagocytic leucocyte oxigenation activities and chemiluminescence: A kinetic approach to analysis....
  • A.J.B Brady et al.

    Nitric oxide attenuates cardiac myocyte contraction

    Am. J. Physiol.

    (1993)
  • S.J Chung et al.

    Identification of the subcellular site for nitroglycerin metabolism to nitric oxide in bovine coronary smooth muscle cells

    J. Pharmacol. Exp. Ther.

    (1990)
  • L Field et al.

    An unusual stable thionitrite from N-acetyl-d,l-penicillamine; X-ray crystal and molecular structure of 2-(acetylamino)-2-carboxy-1,1-dimethyl thionitrite

    J. Chem. Soc. Chem. Commun.

    (1978)
  • R.F Furchgott

    Role of endothelium in response of vascular smooth muscle

    Circ. Res.

    (1983)
  • S Grunfeld et al.

    Role of superoxide in the depressed nitric oxide production by the endothelium of genetically hypertensive rats

    Hypertension

    (1995)
  • W.P Hood et al.

    The effects of intracoronary nitroglycerin on left ventricular systolic and diastolic function in man

    Circulation

    (1980)
  • L.J Ignarro et al.

    Mechanism of vascular smooth muscle relaxation by organic nitrates, nitrites, nitroprusside and nitric oxide: Evidence for the involvement of S-nitrosothiols as active intermediates

    J. Pharmacol. Exp. Ther.

    (1981)
  • G Kojda et al.

    Nitric oxide liberating, soluble guanylate cyclase stimulating and vasorelaxing properties of SPM 3672

    J. Cardiovasc. Pharmacol.

    (1993)
  • G Kojda et al.

    The influence of 3-ester side chain variation on the cardiovascular profile of nitrendipine in procine isolated trabeculae and coronary arteries

    Naunyn Schmiedebergs Arch. Pharmacol.

    (1991)
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