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

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.

Dose-incidence relationships for exencephalia, anophthalmia and prenatal mortality in mouse embryos irradiated with fission neutrons or 250 kV X-rays.

Groups of pregnant mice were irradiated at selected times between 10.00 hours on gestation day 7 and 16.00 hours on day 8. Each group received 0.39 Gy of neutrons or 1.60 Gy of X-rays, or was sham irradiated. We identified a period of high susceptibility of the embryos to radiation-induced exencephalia, anophthalmia and prenatal mortality early in gestation day 8. Dose-incidence relationships in this period were investigated with 0.19-0.48 Gy of neutrons and with 0.40-2.00 Gy of X-rays. With increasing neutron dose, incidence of exencephalia in live embryos rose and then declined. This response suggests that embryos with neutron injury of the type that leads to exencephalia are at a greater risk of dying in utero than are similarly irradiated embryos not so injured, and that this risk increases with dose. A model is proposed that accounts for the shape of the neutron dose-incidence curve. X-ray-induced exencephalia showed only an increase with dose. In X-irradiated litters, almost invariably, the incidence of anophthalmia was higher in exencephalic than in nonexencephalic embryos and the ratio of these incidences (relative risk) decreased toward 1 with increasing dose. A model is proposed that accounts for these observations. The incidence of bilateral anophthalmia in X-irradiated embryos was higher than would be expected if the bilateral form resulted solely from independent injury at each of two equally susceptible sites.

Transient and permanent effects of hyperthermia in dogs: a study of a simulated air transport environmental stress.

Heat-induced hyperthermia can be a major problem in dogs shipped during summer months. Dogs shipped by air transport can encounter temperatures as high as 54.4 C. Usually, little concern is given to effects produced by hyperthermia. To assess the heat stress problem, 20 dogs were exposed to a temperature of 54.4 C for 30 minutes--10 dogs at 15% relative humidity and 10 dogs at 35%. Dogs did not die as a result of exposure, but certain transient and permanent changes occurred. All dogs had increased heart rate, rectal temperature, blood pH, hemoglobin concentration, packed cell volume, and erythrocyte count. Body weight and PVCO2, decreased. Differences also were shown between the 2 humidity group for blood PH PVCO2, rectal temperature, and weight loss. The major tissue changes attributed to hyperthermia were fragmentation of the myocardium, acute cortical necrosis in kidney, and marked degenerative changes in the cerebellum and cerebral cortex. Changes in the cerebellum and cerebral cortex were considered severe and permanent.

Fast-neutron irradiation of mouse embryos in the pronuclear zygote stage: mortality curves and neoplastic diseases in 30-day postnatal survivors.

Mouse embryos in the pronuclear zygote stage were either irradiated in utero with a dose of 15 rad of fast neutrons or were sham-irradiated. Those animals that survived at least 30 days after birth were observed until their natural death. We investigated the percentage incidence and mean age at death for each of the principal neoplastic diseases seen on postmortem examination and also cumulative mortality distributions. No statistically significant differences were found between irradiated and sham-irradiated mice of the same sex.