Evaluation of the effect of gamma-irradiation on fetal erythropoiesis in rats using blood cell volume as the index.

Rat fetuses at day 14 of gestation were irradiated externally with gamma rays at doses of 0.5-8 Gy, and the effect of radiation on the transfer of the erythropoietic site with migration of stem cells from the blood islands of the yolk sac into the liver was investigated. The LD50 was about 5 Gy for 16-day-old fetuses, 2 days after irradiation. Such fetal hematological parameters as the number of blood cells in the liver and the formation rate of micronuclei in erythrocytes, also were affected by irradiation. Two types of blood cells were present in the fetal circulating blood; small blood cells originating in the fetal liver and large blood cells originating in the blood islands of the yolk sac. The number of small blood cells in the circulating blood decreased with the increase in the radiation dose; but, the number of large blood cells remained relatively constant. This suggests that external doses of irradiation of more than 1 Gy impaired the normal transfer of the hematopoietic site (stem cell migration from the blood islands of the yolk sac into the liver.