Fetal murine hemopoiesis following in utero low-dose irradiation.

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 doublelayer 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.