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One of the significant changes developing in animals and humans in the space mission environments is a decreased volume of red blood mass. For the analysis of causes of this phenomenon it is reasonable to compare the data on erythrocyte resistance to hemolysis in vivo and in vitro obtained in the rat experiments on Cosmos biosatellites. After 18 to 22-day space missions, the osmotic resistance of erythrocytes in vitro in animal blood samples and the level of spontaneous hemolysis in vivo directly in the vascular bed of rat have been determined. To this end, an original method based on a quantitative determination of 14Co in the expired air following previous (prior to space mission) 2(14)C glycine labeling in vivo of erythrocyte 2 group has been utilized. In both cases there were a decreased erythrocyte resistance and an increased hemolysis level. During the studies in vivo these changes were significantly great. Inflight application of artificial gravity of 1 G prevented microgravity-induced changes in the characteristics of the erythrocyte life cycle. The changes in erythrocyte shape and membrane properties as well as the factors affecting the cells in vascular bed (altered concentration of fatty acids in blood plasma and others) are discussed as possible causes of the above alterations.

The authors' opinion that adaptation inhibition of erythron functioning under weightlessness produces an unfavourable effect on the optimal physical state of a cosmonaut and his working capacity in the post-flight period has been confirmed by the analysis of certain hematological parameters studied in cosmonauts. The data obtained have necessitated investigation of threshold values of erythron functioning under weightlessness, and creation of artificial gravitation on board the piloted space ship to normalize erythropoiesis. Investigation of these problems of space hematology would be helpful in validation of the limits of human's long-term stay under weightlessness, and in the pre- and post-flight period management.