The Effects of Isoproterenol Stress on the Hearts of Old and Young Rats

Abstract

In pharmacological doses isoproterenol, a typical beta agonist, produces a positive inotropic and chronotropic cardiac effect. On the other hand in even large doses isoproterenol has a negative inotropic effect, may produce various cardiac arrhythmias and, also, necrosis in the cardiac tissue. Rona et al. (1) discovered that isoproterenol inflicted serious damage on the hearts of old rats, whereas, younger animals were relatively more resistant to the toxic effects of this drug. The results of our own experiments are summarized in Table 1. After a single intraperitoneal injection of isoproterenol (70 mg/kg) approximately 80% of the older rats became very sick and after the second injection (1 injection/day), 50% of the rats died within two hours. On the other hand, only 10% of the younger animals became sick and died under otherwise similar experimental conditions. Propranolol (4 mg/kg) decreased and aminophylline (50 mg/kg) increased the effects of isoproterenol. These results led us to believe that the isoproterenol stress may serve as a useful tool in uncovering biochemical differences, if any, between the hearts of old and young rats.