Bone marrow cellularity in normal and polycythemic mice estimated by DNA incorporation of 3H-TdR

Nucleated bone marrow cell numbers in normal and polycythemic mice were determined using 3H-thymidine (3H-TdR). The cellularities were estimated by extrapolating the exponential disappearance of labeled cells after a single injection of 3H-TdR to the time of injection. Dermestid beetles (Anthrenus piceus) were used to prepare tissue-free skeletons labeled with 3H-TdR. The correlation between tritium activity in bone marrow DNA and tritium derived from the combusted skeleton was determined. The total skeletal cellularity determined by isotope dilution analysis in both normal and polycythemic mice was 2.6 x 10(8) cells/mouse or 17.6 x 10(9) cells/kg body weight. Although the red cell component of the marrow was reduced in the polycythemic mouse, the total numbers of nucleated cells in both types of animals were similar. The differential distribution of cells in the polycythemic animal showed a twofold increase in granulocytic cells, which may explain the identical nucleated cell count in normal and in polycythemic mice.