The influence of spontaneous motor activity on the development of isoprenaline-induced heart lesions was studied in male rats of different ages. The extent of the lesions was evaluated quantitatively from raised accumulation of 203HgCl2 in the damaged tissue. Spontaneous activity in rotation cages rose with the animals, age and attained maximum values (6 562 m/d) at 3 months. The increase in motor activity in 10 months was very low and attained only 561 m/d. In all the experimental groups in which spontaneous activity was higher than this limit, a decrease in the cardiotoxic effect of isoprenaline was found after 2--3 weeks. The extent of the heart lesions in the individual animals was not proportional to the degree of their motor activity. The smallest myocardial damage was not found in animals which ran the most metres and vice versa. A marked decrease in the extent of the heart lesions occurred when the motor regimen was prolonged to 70 days. After a three days' break in the motor regimen, reduction of the cardiotoxic effect was still maintained. The extent of the heart lesions after 14 days' interruption corresponded to the values found in animals which were not allowed increased motor activity.

Heart glycogen content and isoprenaline-induced myocardial lesions

The role of myocardial glycogen content for the development of isoprenaline-induced myocardial lesions in different inbred strains of rats