Abstract
Summary
1. An attempt was made to determine whether there is a maternal influence involved in the lethality of rat ova irradiated on the first day of pregnancy. It was demonstrated that 15OR wholebody irradiation was no more deleterious than irradiation of the pregnant abdominal reproductive organs in rats. Therefore, it was concluded that there is no maternal effect due to irradiation of maternal structures other than abdominal reproductive organs at this stage of gestation and dose of irradiation. If a maternal effect exists it may be due to oviduct irradiation or it may be present with higher doses of irradiation. 2. One hundred fifty Roentgens irradiation on the first day of gestation in the rat did not increase the incidence of exencephaly or gross congenital malformations and did not result in fetal growth retardation. These facts and their significance, reported previously reinforce the discrepancy in the incidence and type of malformations induced in the mouse and rat following irradiation on the first day of gestation. 3. Although irradiation of the mouse during the preimplantation period produces a phenomenon referred to as whole-litter resorptions, this does not occur in the rat. Thus, the exencephally reported by Rugh and the whole-litter resorptions reported by Russell and Brent are produced by irradiating the preimplanted mouse embryo, but do not occur following irradiation of the preimplanted rat embryo. These variations in species response must be explained before attempting to apply any of these data to the human.
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