[en] The regulation of haemopoiesis occurs via complex interactions between the stroma and the haemopoietic cells. An attempt to further clarifying the mechanisms and the exact role of the stroma in the regulation was made in a study. Results revealed that the murine bone marrow stromal cells are highly radiosensitive after injection with 241-americium and can thus be considered as a target population after internal contamination. In addition, observations are made which may be important for risk estimation for the developing animal and during pregnancy. Contamination in utero and by lactation shows persistent damage up to 1 year after contamination at an average annual dose of 5 cGy. (author)

[en] The bone marrow stromal cells have been implicated as an integral part of the haemopoietic microenvironment, which is responsible for the in vivo regulation of adult haemopoiesis Stromal stem cells give rise to adherent colonies of fibroblast-like cells in vitro. This CFU-F assay allows the study of functional characteristics and qualitative and quantitative responses of the stromal cells. Experiments to determine CFU-F concentrations in femoral bone marrow pooled from 3 to 8 normal adult mice gave results which were not reproducible. From one experiment to another, the mean CFU-F concentrations varied from 0.5 to 4 CFU-F 10^-5 bone marrow cells even though all the experiments were performed with identical culture conditions according to a standard procedure for CFU-F assay. In this study the authors found that the variability was due to important individual variations in the concentration of CFU-F between different animals (mice). (author)

[en] Pregnant mice were given intravenous injections of ²⁴¹ Am citrate at 14 days of gestation. The fetal skeleton had a higher or similar uptake of ²⁴¹Am per gram of fresh tissue than the liver. The liver in adults concentrated 5 to 20 times more ²⁴¹ Am per gram of fresh tissue than the bones. Measurement of changes in calcium and iron content and concentration with time, showed that in developing mice intensive calcification of bones determined uptake of ²⁴¹Am. The ²⁴¹Am uptake was related to calcium concentration of the fetal bones, which was greater at 14 days of gestation in the anterior bones, mandibles and calvaria, than in ribs and femurs. Transfer of ²⁴¹Am to pups via milk resulted in further accumulation of ²⁴¹Am in skeleton and liver. The incorporation in the skeleton persisted after weaning and contributed to the lifetime body burden. The ²⁴¹Am concentration decreased rapidly with time after injection in relation to growth of the organs. Radiation dose rates and cumulative radiation doses were calculated for liver and bones of contaminated offspring. (author)