Summary. The effects of low‐dose gamma radiation to haemopoietic progenitor cell compartments of the marrow and spleen of virgin female mice and pregnant mice were studied. Microplasma clot cultures were used to assess burst‐forming uniterythroid (BFU‐E) and colony‐forming unit‐erythroid (CFU‐E) activity, and double‐layer agar cultures were established to evaluate granulocyte‐macrophage colony‐forming cell (GM‐CFC) and macrophage colony‐forming cell (M‐CFC). The apparent shift in maternal erythropoiesis from the bone marrow to the enlarged spleen was reflected by an increase in the numbers of CFU‐E and BFU‐E per spleen and a concomitant decrease in CFU‐E and BFU‐E per femur. Whereas maternal GM‐CFC values per femur increased 36%, maternal GM‐CFC per spleen increased by 172% compared to virgin values. There was a greater decrease in M‐CFC per spleen than per femur in the pregnant animal when values were compared to the virgin animal. Total‐body irradiation to the day‐10·5 pregnant mouse caused a further suppression of day‐14·5 medullary erythropoiesis (i.e. decreased CFU‐E values) compared to the response of the virgin female mouse. An ability of the maternal spleen to support further compensatory erythropoiesis following increasing doses of radiation was demonstrated. 4 d after 1·0 Gy exposure, maternal values for GM‐CFC per femur or spleen decreased to nonirradiated virgin mice values. M‐CFC per maternal femur decreased following 1·5 Gy, but M‐CFC per spleen appeared to be unaffected with doses from 0·5 to 2·0 Gy.
The influence of in utero low-dose ionizing radiation exposure on murine hemopoietic embryogenesis was investigated. In vitro assays such as micro plasma-clot cultures and double-layer soft agar cultures served as sensitive biodosimeters to determine erythropoietic and granulopoietic injuries. Day-10·5, HA/ICR, pregnant mice were irradiated with 0, 50, 100, 150,200, or 300 rads, and day-14·5 fetal livers were studied for colony-forming unit-erythroid (CFU-E), buist-forming unit-erythroid (BFU-E), granulocyte-macrophage colony-forming cell (GM-CFC), and macrophage-colony-forming cell (M-CFC) activity. Fetuses subjected to doses of 200 rads or higher on day 10·5 of gestation responded with a decrease in day-14·5 liver cellularity, reflecting injury to the developing organ and its inability to recover to the nonirradiated values. Difference in response between erythropoietin(EPO)-dependent and EPO-independent CFU-E strongly suggests existence of two populations of erythroid progenitor cells with different radiosensitivities. A dose of 200 rads markedly reduced CFUE recovery, and a dose of 100 rads was sufficient to reduce BFU-E recovery to almost 10% of 0-rad values. Nonirradiated day-14·5 fetal liver had more GM-CFC compared to any of the irradiated fetuses, and a dramatically reduced M-CFC recovery occurred with each increase in dose following 150 rads. Our results showed that (1) fetal liver granulopoiesis is more sensitive to radiation injury compared to erythropoiesis, and (2) fetal liver has a greater potential for erythropoiesis recovery.
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