Increased incidence of isoproterenol-induced ventricular fibrillation in aging rats

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Abstract
Prolonged β-adrenergic stimulation obtained by subcutaneous injection of isoproterenol in unanesthetized, unrestrained rats elicited ventricular fibrillation in approximately 80% of animals at 10–12 months of age. Ventricular fibrillation failed to occur in 1-month-old rats and involved only 12% of rats at 2 months. Senescence appeared not to increase the frequency of ventricular fibrillation since a similar incidence was seen in rats at 10–12 and 19–21 months. In all instances, ventricular fibrillation was preceded by ECG changes consistent with acute subendocardial ischemia. To evaluate whether acute β-adrenergic stimulation elicits comparable cardiovascular effects in animals of different age, a dose–response curve to intravenous injection of isoproterenol was performed in anesthetized rats. Changes in heart rate, systemic arterial pressure, left ventricular pressure, and dP/dt were not different among animal groups. It was concluded that the arrhythmogenic potential of isoproterenol may not be related to differences in cardiac β-receptor sensitivity with age as suggested by the comparable changes in the inotropic and chronotropic actions of isoproterenol in the animal groups studied.