Changes in Proliferation Rate and Maturation Time of Erythroid Precursors in Response to Anaemia and Ionizing Radiation

The cell population kinetics of the erythroid system have been studied by means of 'suicide' methods with methotrexate and tritiated thymidine, and autoradiographic methods with tritiated thymidine and 55Fe. These experiments provided estimates of the proliferation rate of two distinct populations of unrecognized erythroid cells and the proliferation rate and time of maturation of cells as they pass through the recognizable erythroid stages. With these methods it has been found that in response to anaemia there is an increase in the cell proliferation rate of the recognizable erythroid cells and in unrecognized cells immediately preceding the recognizable cells, but with no change in the proliferation rate of the earlier cells that are responsible for repopulating the marrow of bone-marrow depleted hosts. In response to continuous irradiation there is a marked increase in proliferation of the repopulating bone-marrow cells, but little change in the proliferation rate of later stages. However, there is an increase in maturation time which leads to extra cell divisions as cells mature through the recognizable stages. The role of erythropoietin in producing increased proliferation and more rapid maturation is discussed. (author)