[Ultrastructural changes in the myocardial capillaries of rats following local irradiation of the heart region].

It was shown that single irradiation of the heart region in rats in doses 600, 900 and 2000 r could bring about congestion phenomena in the myocardium blood capillaries and drastic destructive alterations in the endothelial cells; these changes were noted in all time periods under study following the exposure (2 hr., 1, 5, 10 days, 1, 3, 6 and 12 months) the gravity of lesions being directly proportional to the dose rate. Irradiation led to the breakdown of the integrity of the endothelial wall due to formation of defects and delatation of the intercellular fissures, which results in a considerable rise in permeability. Due to perish of some part of capillaries diminishing of the capillary bed of the myocardium took place, particularly in remote periods. The irradiated animals showed an intensive overgrowth of the connective-tissue stroma in the intercellular and pericapillary spaces.