Myocardial beta-adrenergic reactivity in volume overload-induced cardiac hypertrophy in the rat.
The purpose of this study was to evaluate the changes in myocardial beta-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 beta-adrenoceptor characteristics in ventricle homogenates and slices with [125I]iodocyanopindolol, and the beta(1)/beta(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, +dP/dtmax and -dP/dtmax responses following increasing doses of isoproterenol was observed, without change in the dose inducing maximum effect. Total beta-adrenoceptor characteristics and beta(1)/beta(2) ratio were unchanged. However, beta(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 beta-adrenoceptor density changes.
Laboratoire de Pharmacologie Cardiovasculaire Expérimentale-Biomolécules (PCEBM), Faculté de Pharmacie, Université Joseph Fourier-Grenoble I, La Tronche, France.
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Communal
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Ribuot
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A
Durand
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Demenge
D000318:Adrenergic beta-Agonists / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D002306:Cardiac Volume / Q000502:physiology*; D006332:Cardiomegaly / Q000378:metabolism*; D002395:Catecholamines / Q000097:blood; D004305:Dose-Response Relationship, Drug; D006352:Heart Ventricles / Q000187:drug effects / Q000378:metabolism; D020120:Iodocyanopindolol / Q000494:pharmacology; D007545:Isoproterenol / Q000008:administration & dosage / Q000494:pharmacology; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism*
D000318:Adrenergic beta-Agonists; D002395:Catecholamines; D011943:Receptors, Adrenergic, beta; D020120:Iodocyanopindolol; D007545:Isoproterenol