Myocardial β-adrenergic reactivity in volume overload-induced cardiac hypertrophy in the rat |
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Authors: | C Communal C Ribuot A Durand and P Demenge |
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Affiliation: | Laboratoire de Pharmacologie Cardiovasculaire Expérimentale —Biomolécules (PCEBM), Facultéde Pharmacie, UniversitéJoseph Fourier —Grenoble I, 38706 La Tronche, France |
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Abstract: | Summary— The purpose of this study was to evaluate the changes in myocardial β-adrenergic reactivity in animals undergoing a 4 week cardiac volume overload. Aortocaval shunt (ACS) or sham operation (sham) were performed in male Wistar rats, and 4 weeks later, isoproterenol dose-effects (chronotropic, inotropic and lusitropic properties) were studied after pithing. Noradrenaline (NA) and adrenaline (A) concentrations and NA turn-over index were evaluated in plasma and heart ventricles, while β-adrenoceptor characteristics in ventricle homogenates and slices with [125I]iodocyanopindolol, and the β(1)/β(2)-adrenoceptor ratio were estimated. Four weeks of cardiac volume overload resulted in a 55% increase in ventricle weight/body weight ratio (from 2.5 ± 0.1 to 3.9 ± 0.1 mg/g in sham and ACS rats, respectively) and a 20% increase in protein contents (from 11.3 ± 0.7 to 13.8 ± 1.1 mg/100 mg ventricles in sham and ACS rats, respectively). Furthermore, NA and A concentrations and NA turn-over index were increased in ACS rats (14, 40 and 80% versus sham, respectively). A shift to the right of the responses in heart rate, left ventricular systolic pressure, +d P /d t max and -d/ P /d t max responses following increasing doses of isoproterenol was observed, without change in the dose inducing maximum effect. Total β-adrenoceptor characteristics and β(1)/β(2) ratio were unchanged. However, β(1)-adrenoceptor density increased in epicardium while decreasing in endocardium of left ventricle from ACS rats. Rightward shift at lower doses of isoproterenol-induced cardiac responses in volume-overloaded rats are not likely due to overall β-adrenoceptor density changes. |
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Keywords: | aortocaval shunt Wistar rat β-adrenoceptors isoproterenol-induced effects catecholamines |
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