Cellularity and Deoxyribonucleic Acid Synthesis in Bone Marrow after Total- and Partial-Body Irradiation

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Abstract
Rats were exposed to 600 r, and the cellularity, cytology, and ability to synthesize DNA by using H3-thymidine and autoradiography were studied in the erythroid precursors over the first 24 hours after exposure. The loss of red cell precursors was early and profound, most marked in the younger forms. The number of cells capable of labeling during DNA synthesis in all maturation compartments decreased more rapidly than did the total number of similar cells, or the number of similar cells not in DNA synthesis. The marked effect on DNA-synthesizing ability was due to an inhibition or to a decreased rate of DNA synthesis as indicated by reduced grain counts and also to normal movement of cells out of the DNA synthetic phase, with failure of replacement due to cell death and/or delay of cells entering DNA synthesis. Effects of the exposure on the number of mitotic figures and on cytology are described. A slight and transient effect in shielded bone marrow on the number of labeled cells, the grain count, and the number of mitotic figures was observed.