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Dual effects of alpha-adrenoceptor agonist on contractility of mice isolated atria
1Centro de Estudios Farmacológicos y de Principios Naturales (CEFAPRIN), Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentia (CONICET), Buenos Aires, Argentina.
Abstract:
Contractility responses of mice atria to alpha-adrenergic agonists (methoxamine and clonidine) were studied. The alpha-adrenergic agonists increased the rate of force development (dF/dt) and decreased contractile frequency. The positive inotropic effect was mediated through cardiac alpha-adrenoceptors, while the negative chronotropic effect involved parasympathetic activation. Blockers of phospholipase C inhibited both the positive inotropic and the negative chronotropic effects of the alpha-adrenergic agonists. Inhibitors of phospholipase A2 and cyclooxygenase activity attenuated the positive inotropic effect of the agonists without modifying the negative chronotropic effect.