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It has been established using hemopoietic bone marrow cells or EHrlich ascites carcinoma cells that endogenous glutathione affects the realization of only those lesions which appear in response to an increase in radioresistance, for example during anoxia. The involvement of glutathione in the realization of the oxygen effect is not limited to the time of irradiation. The effect of glutathione extends to the postirradiation period i. e., it is not determined only by the competition with oxygen for target radicals.

In experiments with Ehrlich ascites tumor cells, using a specific thiol blocker, 6,6'-dithiodinicotinic acid, that does not penetrate the cell and therefore only binds SH-groups of peripheral areas of an external cell membrane, it was demonstrated that (1) the external cell membrane is the site where the radioprotective effect of anoxia (the oxygen effect) is realised (2) thiols of the external cell membrane contribute markedly to the oxygen effect, and (3) they are needed at both stages of its realization.

It was shown that the administration of adrenaline before or after X-irradiation intensified the recovery of mouse haemopoiesis. When adrenaline was administered before irradiation the survival of CFUs (endo- and exo-tests) increased and the bone marrow cellularity and the spleen weight were restored more rapidly than those of the controls. With adrenaline administered after irradiation, the survival of endo-CFUs increased, the bone marrow cellularity was restored and the spleen weight increased.

Mice were injected with serotonin (0.5 and 2.0 mg/mouse) 15 min before and immediately after irradiation (4.5 and 7.0 Gy). With the preparation administered prior to irradiation one could observe an increase in the quantity of CFUc survived (endo- and exo-test), acceleration of restoration of cellularity (in the bone marrow) and growth of the spleen weight. The acceleration of restoration of the bone-marrow cellularity was also noted when serotonin was administered after irradiation. The post-irradiation effect of serotonin was also detected in cells in vitro. It is concluded that the radiomodifying effect of serotonin on the haemopoietic system is due to a decrease in the number of damaged cells and increase in the rate of reproduction of intact cells.

A study was made of the influence of binding of endogenous nonprotein thiols (glutathione, GSH) by N-ethylmaleimide before or after irradiation (7 Gy) of Ehrlich ascites tumor cells on the radioprotective effect of anoxia (argon, 0.003% O2). It was shown that the radioprotective effect of anoxia decreased as cell glutathione was removed before or after irradiation (similarly both immediately and 1 h after irradiation). Inspite of the fact that the GSH level decreased similarly before and after irradiation the radioprotective effect of anoxia was less pronounced in the latter case. The data obtained permit to evaluate quantitatively the contribution of endogenous GSH to the processes occurring at the time of irradiation and during the post-irradiation period.

In experiments with Ehrlich ascites tumor cells with the use of a specific thiol blocker, 6,6'-dithiodinicotinic acid, it was shown that thiols of a cell plasmic membrane are necessary for the radioprotective effect of mercaptoethylamine to be realized.

Some radiobiological characteristics of CBWA mice (e. g. response to gamma r and X-radiation and the radioprotective efficiency of 2-AT and AET were shown not to differ virtually from those of F1 hybrids (CBA X C57Bl/6). No essential differences were also found in radiosensitivity of the bone marrow cells of (CBA X C57Bl/6)F1 and CBWA mice in vitro and in situ. On the basis of the data obtained, the authors recommend CBWA mice for radiobiological experiments as well as hybrids (CBA X C57Bl/6)F1.

In experiments on Ehrlich ascite tumor cells, the dependence of the radioprotective effect of beta-mercaptoethylamine and beta-mercaptopropionylglycine on the initial level of endogenous glutathione was studied. A varying degree of N-ethylmaleimide induced decrease of SH-glutathione content in the cells led to either easing or elimination of the radioprotective effect of the agents under study.

The effect of 2-amino-2-thiazoline (2-AT) on radiosensitivity of mice, their haemopoietic system status, and GFUc has been studied. 2-AT was shown to contribute to the survival of an increased number of haemopoietic stem cells, earlier recovery of bone marrow cellularity, and normalization of the spleen weight.

It was shown on Ehrlich ascites tumor cells that for realization of the radioprotective effect of anoxia and beta-mercaptoethylamine normal content of glutathione is necessary not only at the time of irradiation but in the postirradiation period as well while glutathione content should be normal only after irradiation for realization of the radiotherapeutic effect of serotonin.

5-HT applied prior to, immediately or 5 min after irradiation decreased equally the radiation damage to Ehrlich ascite tumor cells. A decrease in the endogenous glutathione content by N-ethylmaleimide (NEM) led to reduced the 5-HT radio-modifying effect. Its radio-modifying effect decreased irrespective of whether NEM was applied prior to or after irradiation.