Age-dependent variations in the intensity of isoprenaline-induced myocardial lesions in rats

Isoprenaline dosed 50 mg/kg was injected intraperitoneally into rats aged 42 days, 3 months, and 18 months. At intervals of 12, 18, 24, 48 hours and 5 days the degree of myocardial lesion was checked by the technetium-labeled oxytetracycline [99mTc-Sn-oxytetracycline] method. Three hours after its i. v. injection the myocardial radioactivity was measured in a control group and in the group treated with isoprenaline. Markedly higher radioactivity was found in animals given isoprenaline than in the controls. Besides, the degree of myocardial lesion considerably varied in dependence on the animals' age, being lowest in the 42-days-old and highest in the 18-months-old rats. In all age groups a biphasic alteration was observed, consisting of a phase of rapid decrease in radioactivity up to 24 hours, and a phase of slow decrease from the 24th hour till the 5th day after injection of isoprenaline. The authors consider the method using technetium-labeled oxytetracycline convenient for assessing the degree of myocardial lesion.