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A change in the structure of FAF-28 Chinese hamster cell population occurred during 24 h following gamma-irradiation or hyperthermia heating, or the effect of both factors was studied by flow cytofluorometry. With radiation delivered immediately after heating the distribution of cells among cycle phases was nearly the same as with hyperthermia alone: the share of cells at the S-phase was invariable during the first 4-6 h, then it slowly diminished; at G1 it slowly decreased and at G2 increased. When irradiation preceded heating the pattern of cell redistribution during the first hours was the same as that with radiation alone: the "wave" of transition from G1 to S phase was the same, but shorter in amplitude and longer in time; then cells were accumulated at G2+M and remained there for 24 h. Thus, of the two factors applied, the first was the major one in changing the cell population structure during the first hours after treatment. In 24 h the result was the same, that is, the considerable accumulation of cells at G2+M.

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.

It was found that at the time when cystamine and mexamine exert their maximum radioprotective action DNA synthesis rate decreases in bone marrow cells, the ratio between the colony-forming units in the bone marrow and peripheral blood changes, and functional activity of neutrophils increases.

Whole-body exposure of rats to X-rays (4, 6 and 8 Gy) and neutron radiation (1, 1.5 and 2 Gy) causes a dose-dependent inhibition of endocrine function of thymus and death of its lymphoid cells. Shielding of thymus somewhat reduces the degree and duration of inhibition of thymus hormone secretion.

After large-field fractionated irradiation of dogs at a cumulative dose of 54 Gy, a stable bone marrow depletion occurs persisting for a year following irradiation. The automyelotransplantation after the end of the exposure elicits a transient recovery of the exposed bone marrow, 1.5-2 months after the beginning of irradiation, followed by a secondary depletion of the exposed haemopoietic sites. The control and the automyelotransplanted animals exhibited bone marrow recovery one year and six months after irradiation, respectively, the cellularity being maintained at a high level for 3 years of observation.

A study was made of the influence of gamma-irradiation of rats (14.4, 9.6, 7.2 and 4.8 Gy) on the number of nucleate cells, and the concentration of triacylglycerides (TG) and phospholipids (PL). Cellularity and concentration of PL decreased while that of TG increased under the effect of radiation. The degree of the changes in the above parameters was a function of dose and time after irradiation.

A study was made of adherence to plastic Petri dishes and viability (as non-pyknotic cell counts) of rat bone marrow cells cultured for 5 to 22 h in 199 medium containing 15 per cent fresh isologous serum. An overall decrease in the number of viable myelokaryocytes, including mature neutrophils, was observed in the cultures irradiated with doses of 3 to 12 Gy. In addition, gamma-irradiation increased substantially the adherence of neutrophils and, to a lesser extent, of other myelokaryocytes. A possibility of early radiation-induced disturbances in granulocytic maturation is discussed.

The combined effect of external gamma-radiation (137Cs, 103-26 mC/kg) and incorporated alpha-radiation (239Pu nitrate, 93-9.3 kBq/kg body mass) was estimated by changes in the nucleic acid metabolism and the number of cells in rat thymus, spleen and bone marrow. The data obtained were processed using a model of multiplicate action of the factors which is equivalent, in the case of low effects, to a traditional model of additive effects. The results of the combined action of the two factors may be estimated by the coefficient of the interaction and the coefficient of the enhancement of the effects.

In experiments with Wistar rats a study was made of the content of antibody-forming cells (AFC) in the spleen at remote times (3 to 12 months) after intravenous injection of 239Pu(IV) in doses of 166, 55, and 18 kBq/kg body mass. The doses absorbed in the central and peripheral immunity organs were defined. Pronounced spleen hypoplasia and profound inhibition of humoral immunity were displayed 1 year after the injection of a small amount of the radionuclide. AFC deficiency in animals was amounted to 11-32 per cent throughout the entire period of observation.

In experiments on HeLa cells a study was made of a change in the rate of DNA synthesis, proliferative activity and reproductive death of exposed cells and their descendants throughout a number of generations. The rate of DNA synthesis decreased in 4 postirradiation generations, and a maximum inhibition (by 50%) was registered 48 h following irradiation. The proliferative activity of the irradiated cell descendants markedly decreased throughout 18-20 generations resulting in an increased death rate and a loss of cells from a generation. It is suggested that even the distant descendants (18-20 generations) of expose cells exhibited some lesions which may, in time, become fatal events leading to cell death.

Effectiveness of the diffusion chamber cloning of subpopulations of cells isolated by the sedimentation method from intact and exposed (5 Gy) mouse tumors NKLy was determined. It was shown that cells at the G2-M stages were highly radiosensitive. The recovery from potentially lethal damages was maximum at the G0-G1 stages of the cell cycle.

Whole-body exposure of guinea pigs to microwaves of 60 mW/cm2 for 10 min causes quantitative changes in glial population of outer geniculate bodies and visual cortex that are manifested by the enlarged perineuronal glia, an increased glioneuronal index, and a relatively stable perivascular glia. The dynamics of the changes observed indicates higher reactivity and repair capacity of the glioneuronal complex of outer geniculate bodies.

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.