Search

Altered sensitivity to the chronotropic effect of catecholamines and a reduction in the [[beta].sub.1]/[[beta].sub.2]-adrenoceptor ratio have previously been reported in right atria of stressed rats, human failing heart, and aging. In this report, we investigated whether left atrial inotropism was affected by foot-shock stress. Male rats were submitted to 3 foot-shock sessions and the left atrial inotropic response, adenylyl cyclase activity, and [beta]-adrenoceptor expression were investigated. Left atria of stressed rats were supersensitive to isoprenaline when compared with control rats and this effect was abolished by ICI118,551, a selective [[beta].sub.2]-receptor antagonist. Schild plot slopes for the antagonism between CGP20712A (a selective [[beta].sub.1]-receptor antagonist) and isoprenaline differed from unity in atria of stressed but not control rats. Atrial sensitivity to norepinephrine, as well as basal and forskolin-or isoprenaline-stimulated adenylyl cyclase activities were not altered by stress. The effect of isoprenaline on adenylyl cyclase stimulation was partially blocked by ICI118,551 in atrial membranes of stressed rats. These findings indicate that foot-shock stress equally affects inotropism and chronotropism and that [[beta].sub.2]-adrenoceptor upregulation contributes to the enhanced inotropic response to isoprenaline. Key words: adenylate cyclase, CGP20712A, foot-shock stress, forskolin, inotropic response, isoprenaline, left atria, ICI118,551. La diminution de la sensibilite aux effets chronotropes des catecholamines et la reduction du ratio entre les recepteurs [[beta].sub.1] et [[beta].sub.2] adrenergiques ont deja ete rapportees pour l'oreillette droite de rats soumis a un stress, dans le creur insuffisant chez l'homme et avec le vieillissement. Dans cet article, nous avons tente de savoir si les proprietes inotropes de l'oreillette gauche sont affectees par le stress provoque par le choc au pied (<>). Nous avons soumis des rats males a trois seances de choc au pied et etudie la reaction inotrope de l'oreillette gauche, ainsi que l'activite de l'adenylate cyclase et l'expression des recepteurs [beta] adrenergiques. L'oreillette gauche des rats soumis a un stress etait plus sensible a l'isoprenaline que dans le groupe temoin, et cet effet etait aboli par le ICI118,551, un antagoniste selectif des recepteurs [[beta].sub.2] adrenergiques. Contrairement a chez les rats temoins, les pentes du diagramme de Schild de l'antagonisme entre le CGP20712A (un antagoniste selectif des recepteurs [[beta].sub.1] adrenergiques) et l'isoprenaline n'etaient pas egales a un chez les rats soumis a un stress. Le stress ne modifiait ni la sensibilite des oreillettes a la norepinephrine ni l'activite de l'adenylate cyclase de base ou stimulee par la forskoline ou l'isoprenaline. Dans les membranes auriculaires de rats soumis a un stress, le ICI118,551 permettait d'inhiber partiellement les effets de l'isoprenaline sur la stimulation de l'adenylate cyclase. Ces resultats montrent que le stress provoque par le choc au pied entraine des modifications inotropes et chronotropes equivalentes et que la regulation a la hausse des recepteurs [[beta].sub.2] adrenergiques contribue a l'accentuation des proprietes inotropes en reaction a l'isoprenaline. [Traduit par la Redaction] Mots-cles : adenylate cyclase, CGP20712A, stress provoque par le choc au pied, forskoline, reaction inotrope, isoprenaline, oreillette gauche, ICI118,551., Introduction [Beta.sub.1]-and [beta.sub.2]-adrenoceptors ([[beta].sub.1]-and [[beta].sub.2]-ARs) are expressed in rat and human heart, with [[beta].sub.1]-AR predominating over [[beta].sub.2]-AR in a ratio of about 4:1 (Juberg et al. 1985; Kaumann and Molenaar [...]

Alfred Sully was not born to conquer, but as a young marl seeking distinction in an era of relentless American expansion, he found that path laid out for him. The [...]

Abstract: Bothrops snake venoms cause renal damage, with renal failure being the main cause of death in humans bitten by these snakes. In this work, we investigated the cytoskeletal rearrangement [...]

When fabled bison hunter William 'Buffalo Bill' Cody first staged his Wild West show in 1883, he needed more than heroic cowboys, villainous Indians, teeming horses and roaming buffalo to [...]

When American explorer Zebulon Pike stayed into the Spanish territory of New Mexico in 1807, the Spaniards accused him of spying. And some Americans wondered if Pike was part of [...]