The ploidy distribution of bone marrow megakaryocytes after M-CSF administration. M-CSF was administered at the indicated doses to C57BL mice, starting on day 1, for up to 5 days. Bone marrow was harvested on the morning of the indicated days, before M-CSF administration. DNA levels (ploidy) of megakaryocytes were determined by flow cytometry. Each panel shows the DNA distribution (ploidy class) on the abscissa and the mean frequency ± 1 SE of each ploidy class as a percentage of all megakaryocytes on the ordinate. One million bone marrow cells were analyzed from each animal. The number of determinations at each time point, representing individual animals, is shown on each panel. (A) Illustrates the ploidy distribution of normal C57BL mice. (B through F) Demonstrate the ploidy distributions on the indicated days following administration of 2 mg/kg/d M-CSF. (G through H) Demonstrate the ploidy distributions on days 6 and 7 following the administration of 8 mg/kg/d M-CSF. The asterisks in panels C through H indicate that the frequencies of these ploidy classes were significantly different from control (P < .05).