BONE MARROW CELLULARITY IN POSTIRRADIATED RATS

The specific objectives of this study were (1) to determine to what extent cell turnover (reproduction) effects the difference in radiation sensitivity of the individual cell types, and (2) to investigate the relationship which exists among the cell types during the damage and recovery period. Six hundred and seventy-two rats were exposed to either of the two radiation sources and sacrificed at periodic intervals following exposure for the purpose of determining the change in numbers of cells in the marrow. The results indicate that the difference in the response of the individual types of cells is not directly related to their turnover rate. The turnover rate for the myelocytic cells is greater than the turnover rate for the erythrocytic cells, yet the erythrocytic precursor cells are more sensitive to radiation than the myelocytic precursor cells. The results also show that erythrocytic cells recover before myelocytic or lymphocytic cells. This recovery indicates that lymphocytic cells probably could not give rise to the other two cell types (function as a stem cell) through a process of differentiation or dedifferentiation. However, it may be possible that the lymphocytic cells could function as trephocytes.