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36. Effects of Fractionated Total Body Irradiation on Megakaryocyte Progenitor Cells(CFU-Meg) and Granulocyte-Macrophage Progenitor Cells(CFU-G) in Mice
Kaoru Tanaka and Eiichi Kojima
Keywords: fractionated total body irradiation, CFU-Meg, CFU-GM, mice
Hematopoietic systems are the most sensitive to radiation in the body, but effects of fractionated irradiation on hematopoietic systems have not been well established. We previously reported the effects of two equal fractionation doses (3.12Gy
2) upon mouse survival and peripheral blood cell number. The mouse survival increased on increasing intervals up to 5h, at which 90% of the mice survived. With a longer interval, the survival decreased once until about 11h and then increased again. On the other hand, 99% of the mice died around 15 days after the single irradiation of 6.24Gy. From this result, we concluded that the mice died due to bone marrow death. In the present study, we investigated the effects of two equally split doses with 5h intervals on hematopoietic progenitor cells, megakaryocyte progenitor cells (CFU-Meg) and granulocyte-macrophage progenitor cells (CFU-GM), in mice. Spleen weights was also investigated because spleen is one hematopoietic organ.
Female BALB/c mice, 10-14 weeks old, were used. The mice were exposed to total body irradiation with X-rays (200kVp, 20mA, 0.7Gy/min) delivered as a single dose or two equally split doses (0.24-3.12Gy2) with 5h intervals. After the second irradiation, they were sacrificed, and the femur and spleen were removed. Then femoral bone marrow and spleen cells were cultured.
CFU-Meg were studied by using a fibrin clot culture system for 5h intervals. After 4 days of plating, colonies of 4 or more acetylcholinesterase-positive cells were scored as CFU-Meg. There was a recovery in the survival of femoral CFU-Meg after the fractionated doses of irradiation. A smaller recovery was observed for splenic CFU-Meg than for femoral CFU-Meg. CFU-GM cultures were performed in semisolid medium containing alpha modification of Eagle's medium, WEHI-3b cell line-conditioned medium as a source of colony-stimulating factor, and 0.8% wt/vol methylcellulose. Seven days later, colonies consisting of 50 or more cells were scored as CFU-GM. As shown in Fig.16, there was a recovery in the survival of femoral CFU-GM after the fractionated doses. At high dose (6.24Gy), the difference of femoral CFU-GM survival between single and fractionated irradiations was larger than that at low doses. A small recovery was also observed for splenic CFU-GM at low doses (0.47-2.84Gy) and a large recovery was observed at the high dose.
The spleens of mice were weighed for 30 days after irradiation. Spleen weights decreased similarly in both single and split doses (3.12Gy~2) of irradiation until 13 days. Weights of split dose groups began to show an increase on 15 days, and then extended beyond a normal level until 20 days. By contrast, single dose groups did not show any increase.
