EMBRYONIC DEATH, DWARFISM AND FETAL MALFORMATIONS AFTER IRRADIATION OF EMBRYOS AT THE ZYGOTE STAGE - STUDIES ON 2 MOUSE STRAINS

Female mice of the BALB/c and CF1 strains were mated and irradiated wi th various doses of X-rays 7 h after presumed fertilization. 18 days l ater, females were killed and their uteri examined for prenatal mortal ity at the different stages of development. Living fetuses were weighe d and examined for the presence of external malformations. A number of them were also examined for skeletal anomalies. Radiation induced mai nly a dose-dependent increase of the preimplantation loss in the BALB/ c strain and of the early postimplantation loss in the CF1 strain. Emb ryos of the BALB/c strain were refractory to the induction of teratoge nic effects after such preimplantation irradiation. In CF1 mice, the f requency of malformed fetuses increased regularly after irradiation, t he difference with controls being significant for the doses of 10, 50 and 100 cGy. Dwarfism occurrence also appeared to be increased by irra diation in this strain, although the importance of this effect varied depending on the criterion chosen for the assessment of dwarfs. With t he definition proposed in the present paper, the increase in the frequ ency of dwarfs paralleled that of malformed fetuses, being significant after doses of 50 and 100 cGy. Irradiation did not increase the frequ ency of skeletal anomalies. A careful examination of the various data obtained to date led us to conclude that radiation may possibly be ter atogenic in several mouse strains, when administered as early as durin g the one-cell stage and, to a lesser extent, during the following pre implantation stages. However, early prenatal mortality will remain by far the greatest risk associated with an exposure to radiation during this period. Moreover, the relativity of the risk of abnormality due t o such irradiation should be considered in the context of the high pre valence of developmental defects spontaneously occurring during human pregnancy.