Effect of irradiation in the space environment on the blood-forming system in rats

A special experiment was carried out on board Cosmos 690 [correction of 605] in order to study the modifying influence of weightlessness on the radiobiological effect. On the tenth flight day 35 rats were exposed to irradiation using an on-board gamma-ray source. They were irradiated for 24 hours at a dose rate of 32 rads/hr with a total dose of 220 +/- 25 rads and 800 +/- 53 rads. On the 1st and 26th post-flight days haemopoiesis in bone marrow (determined from myelograms and the total count of myelo-karyocytes) was examined and the blood composition was analysed. The total count of thymocytes and spleenocytes was measured in the thymus and spleen. Identical measurements were made in the control animals exposed to irradiation on the earth. The haematological findings indicate an enhancement of the radiobiological effect in the rats irradiated in space flight.