Decrease of erythropoiesis in the fetal liver of X-ray irradiated pregnant mice

To accumulate fundamental knowledge about a possible relationship between severe mental retardation caused by in utero radiation exposure and impaired oxygen transport to fetal brain, the effect of X-ray irradiation on erythropoietic activity in fetal liver of C57BL/6J mice was studied in vivo and in vitro by measuring 59Fe uptake into heme and nonheme fractions of fetal liver. For the in vitro experiments, the mice were irradiated with X-rays at a dose of 189 cGy on day 9, 11, 13 or 15 of gestation. The day after irradiation, fetal livers were dissected, homogenated, and incubated with 59Fe-labeled mouse plasma. 59Fe uptake into the heme fraction of fetal liver was markedly reduced, depending both on the fetal developmental stage at the time of irradiation and the time that had elapsed since irradiation. In the in vivo experiments, pregnant mice were irradiated with X-rays at doses of 24 to 284 cGy on day 15 of gestation. The ratios of the amounts of 59Fe incorporated in the heme and nonheme fractions significantly decreased when mice were irradiated with more than 1 Gy. These results suggested that the necessary amount of oxygen may not be transferred to the fetal brain at the time required. The possible relationship between decreased fetal liver erythropoiesis and severe mental retardation is described.