Prenatal survival of mouse embryos irradiated in utero with fission neutrons or 250 kV X-rays during the two-cell stage of development

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Abstract
Purpose: To investigate the relationship between radiation dose at the two-cell stage and prenatal survival. Materials and methods: Pregnant mice were irradiated with fast neutrons (0.53-1.94 Gy) or X-rays (1.50-5.00 Gy), or sham irradiated. At selected times up to gestation day 16, the mice were killed and the uterine contents examined. Results: At doses up to 0.82 Gy of neutrons and 2.50 Gy of X-rays, all or virtually all the radiation-induced deaths occurred during the period from the time of implantation to gestation day 10. At higher doses an appreciable proportion of the deaths occurred after day 10. Many neutron-induced deaths in the period from implantation to day 10 occurred before day 7. A mathematical model was developed for estimating survival to gestation day 16 as a function of neutron dose. Conclusions: The mortality pattern, in which low radiation doses led to early deaths and high doses to both late and early deaths, suggests the existence of two lethal processes. The relationship between neutron dose and survival to gestation day 7 has been interpreted as indicating that the early deaths involved predominantly a two-event inactivation mechanism. An individual cell of a two-cell embryo was found to be less sensitive to lethal radiation injury than a pronuclear zygote.

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