The dynamics of the endothelial cell population was investigated in the rat brain after local irradiation with different doses of X rays. A fluorescent-histochemical technique was used for the visualization of the cells. A decrease in endothelial cell number was observed within 1 day of irradiation with doses of 5-200 Gy. At this time the endothelial cell number had decreased by up to 15% compared with the pre-treatment values. This early dose-independent loss in cell number was maintained for up to 1 month after irradiation. This was then followed by a slow dose-independent decrease in cell density up to 6 months after exposure. Subsequently the depletion of the endothelial cell population exposed to 40 and 60 Gy continued. After a dose of 25 Gy an abortive recovery of cell numbers occurred followed by an abrupt depletion of the endothelial cell population. The possible mechanisms of such changes are discussed.

Possible causes of diminution of endothelial cells of rat brain vessels immediately after local irradiation have been investigated. It has been shown that the diminution occurs during the first 24 h following irradiation, its value (-15%) being independent of radiation dose within a wide range (from 5 to 100 Gy), and the cellularity is not restored during the subsequent two weeks of observation. Interphase death of part of cells distinguished by high radiosensitivity seems to be the most probable reason for the population heterogeneity observed.

A vascular system of several strains of brain tumors: neurinoma 46-1, gliomas: 11-9-2 and 101-8 were investigated by means of automatic analysis of microangiograms and histochemical-luminescent estimation of endothelial cells. It was shown that the mean quantity of vessels and their section-size in all strains of tumors are less than control independently of the rates of tumor development. The linear density of the endothelial cells appear less that in control vessels and is equal in different strains of tumors, though the inclination to hemorrhages in gliomas is higher than in neurinoma. The cause of this phenomenon is discussed.

Age changes in the vascular network density and transversal section of the vessels have been studied in the cerebral hemisphere cortex, corpus callosum, septum and nucleus caudatus of Wistar rats. Angiography has been performed by means of intracardiac injection of Indian ink, frontal colloidin slices of the brain 15 mcm thick have been prepared. Amount of vessels and section area of each vessel have been measured, using the automatic analysis. Each brain area studied has homogeneous vascularization density, however, they differ from each other by the amount of vessels. The vascular size in the areas does not differ. At the age of 2-20 months the average number of vessels in all the cerebral areas investigated does not change, while the vascular diameters demonstrate certain tendency to increase after 17 months of life.

Dynamics of changes in endothelium cellularity of rat brain vessels was studied during 12 months following local irradiation with a dose of 25 Gy that approximated the therapeutic one by its efficacy. A 15 per cent decrease in the endothelium cellularity was registered 24 h after irradiation followed by a slow 40 per cent depletion of the population at a constant rate up to the 6th month. By month 10 the cellularity was restored and after 12 months it dropped again drastically.

The influence of a radioprotector, gammaphos, on the development of delayed vascular changes and necrosis in rat brain following local brain irradiation with 25 Gy was investigated. The radioprotective effect was manifested by both the morphometric parameters of vessels and the survival rate and relative number of animals with gross vascular abnormalities and brain necrosis. There was a causative relationship between the development of gross vascular abnormalities and the occurrence of brain necrosis after exposure to moderate radiation doses.

The ability of a radioprotector-gammaphos to modify the development of late vascular changes in the rat brain after local irradiation with 40 and 60 Gy was investigated by means of an angiographic method. The relative number of animals with gross vascular abnormalities, the size of foci with vascular lesions, and the changes in size and number of vessels were less in the drug-treated groups. Thus, it may be possible to increase the tolerance of host tissues to curative radiation therapy by chemical radioprotectors such as gammaphos.

A study was made of the influence of prophylactic administration of gammaphos (300 mg/kg) on radiation alterations in the system of cerebral microcirculation of rats in a long-term period following local irradiation of doses of 40-60 Gy. It has been shown that the number of animals with severe vascular injuries and the degree of these injuries lessen. A computerized analysis has shown that gammaphos administration weakens a decrease in the mean number of vessels and an increase in their average size caused by irradiation.