EFFECTS OF DOSE AND DOSE PROTECTION ON EMBRYOTOXICITY OF 14.1 MEV NEUTRON-IRRADIATION IN RATS

The embryotoxic effects of neutron radiation on rodent embryos are doc umented, but there is disagreement about the dose-response relationshi p and the impact of protracting the dose. Pregnant rats were exposed t o total absorbed doses of 0.15 to 1.50 Gy 14.1 MeV neutrons on day 9.5 after conception, coincident with the most sensitive stage of embryon ic development for the induction of major congenital malformations. In general terms, the incidence of embryotoxic effects increased with in creasing total absorbed dose. However, the dose-response relationship differed depending on the parameter of embryotoxicity chosen, namely, intrauterine death, malformations or very low body weight. In a second study, embryos were exposed to a single embryotoxic absorbed dose (0. 75 Gy) administered at a range of dose rates, from 0.10 to 0.50 Gy/h. The results offer no evidence that protraction of this selected dose s ignificantly increased or decreased the incidence or pattern of embryo toxicity of the neutron exposure used in this study. The results do no t support the hypothesis of a linear dose-response relationship for th e effects of prenatal neutron irradiation that contribute to embryotox icity for total absorbed doses of 0.15 to 1.50 Gy.