Kinetics of Cell Proliferation of Murine Bone Marrow Cells Cultured in Diffusion Chambers: Effect of Hypoxia, Bleeding, Erythropoietin Injections, Polycythemia, and Irradiation of the Host

Mouse bone marrow cells were cultured in diffusion chambers implanted in the abdominal cavity of host mice that were subjected to different kinds of treatment. Preirradiation of the chamber host enhanced the cell growth in the chambers as follows: the number of cells capable of proliferation and differentiation in the chambers (diffusion chamber progenitor cells, DCPC) as determined by a limiting dilution method increased significantly. Similarly, the spleen colony-forming units (CFU’s) in the chambers proliferated more rapidly in irradiated than in normal hosts. The total number of cells in the granulocytic series harvested after culture periods of 3-7 days was also significantly increased. The number of cells in the granulocytic series harvested per DCPC in irradiated animals was twice normal. These findings indicate that the progenitor cells probably proceed through multiplicative mitoses before differentiation in the irradiated animals. A higher cloning efficiency or a shortened generation time of stem cells are other possibilities. The increased number of differentiating granulocytes may simply be a consequence of the events taking place in the stem cell compartment, but a stimulating effect of the irradiation environment on proliferating cells in the granulocytic series cannot be excluded. Preirradiation also stimulated the growth of macrophages but less consistently. When normal mice carrying chambers with normal marrow were subjected to intermittent hypoxia during the culture period, the number of DCPC’s and of cells in the granulocytic series and macrophages were reduced approximately to the same extent. Hypoxic treatment of donor animals for 3-5 days resulted in a similar reduction in number of DCPC’s and CFU’s at both intervals. These findings may suggest competition for a common pool of stem cells for erythrocytes, granulocytes, and macrophages. However, a toxic effect cannot be excluded. Erythropoiesis, which is usually absent, was significantly increased when hypoxia and irradiation of the chamber hosts were combined. Bleeding and erythropoietin injections also enhanced erythropoiesis to some extent.