Influence of ionizing radiation on fetoplacental growth in mice.

The effects of single doses of 60Co whole-body irradiation were studied in about 600 inbred primiparous Swiss-Webster mice on gestational day 9, 10, 11, or 12. The embryos and their placentas were weighted from day 13 to 18. A reference model surveyed the response of the conceptus to varying doses. A significant reduction in the fetal wet weight was observed as follows: day 9, 150-175 r.; day 10, 125-150 r.; day 11, 75-175 r.; day 12, 125-450 r. Beyond the upper-limit doses, a high mortality rate was detected, i.e., 64.5 per cent on day 10 at 175 r. and 63 per cent on day 11 at 200 r. The rapid growth period of the placenta extended from day 13 to 15. By this latter stage it had practically reached its maximum development. The placental index decreased progressively from day 13 to 18; however, this index was higher than the control on day 12 in treated animals, while lower on day 9, 10, or 11.