Influences of Age on the Positive Inotropic Effect Mediated by α- and β-Adrenoceptors in Rat Ventricular Strips

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Abstract
The positive inotropic effect of phenylephrine (in the presence of atenolol) and isoprenaline was studied in isolated right ventricular strips obtained from Wistar rats aged 2 weeks, 3 months, and 26 months. The positive inotropic effects induced by phenylephrine and isoprénaline were higher in the 2-week-old than in the 3- or 26-month-old rats. The typical ‘α-type’ or ‘ß-type’ responses were induced by phenylephrine (plus atenolol) or isoprcnaline, in all the age groups. The ECSo values for the α-mediated positive inotropic effect decreased with age, while the EC50 value for the positive inotropic effect of isoprcnaline increased in the senescent heart. These results suggest an enhanced α-adrenergic sensitivity in the senescent heart.