Influence of physical exertion on early isoproterenol-induced heart injury.

The effect of swimming instantly following an injection of isoproterenol was studied in rats in whom the administration of the drug caused changes in the cardiac muscle. The animals were compared with those of a group kept only under normal cage activity after the administration. Oxygen inhalation in the exercised group of rats was higher than in the sedentary group and after 4 minutes of measuring, continually remained at a higher level. It was determined that swimming prevented the early death of the rats. This was more pronounced in the animals of higher body weight. The extent of myocardial damage in the exercised group was markedly smaller. The intensity of enzyme reaction, SDH, LDH and G6PDH, in the area of undamaged tissue was the same in both the exercised and sedentary groups, in areas of damage it was minimal. The intensity of alpha GP was lowered in the exercised group, but in the sedentary group it was lowered throughout the entire section. Electron optic examination of the tissue, which under the light microscope appeared normal, revealed no substantial differences between the exercised and sedentary groups. We presume that the better condition of the rats was in part due to the peripheral breakdown of the catecholamine owing to the increased blood flow created by muscular activity.