Effects of prenatal x-irradiation on development and postnatal viability of inbred and hybrid mice.

Studies of the effects of prenatal x-irradiation of mammals have emphasized in recent years long-term pathological and functional investigations. These inves tigations have included studies on growth ( Murphree and Pace, 1960 ; Nash and Gowen, 1962 ; Parish, Murphree and Hupp, 1962 ; Rugh, Duhamel, Chandler and Varma, 1964), reproduction (Russell, Badgett and Saylors, 1960 ; Rugh and Jack son, 1958 ; Nash, 1969) , and postnatal mortality and hifespans ( Nash and Gowen, 1965 ; Rugh and Wohlfromm, 1965 ; Sikov, Resta and Lofstrom, 1969). In spite of the obvious significance to human populations, relatively little work has been done to explore the influence of genetic background in conditioning the response of embryos to x-irradiation. Most of the earlier studies either have utilized animals of unknown heterogeneous origin or single strains of uniform origin. A few studies have demonstrated the significance of genetic variability in embryonic response (Rugh, 1958; Callas, 1962; Nash and Gowen, 1962, 1965; Dagg, 1963; Nash, 1969). The recent review of Brill, Nance, Engel, Glasser, and Forgotson (1967) has pointed out the basic similarities between laboratory animal studies and long-term, postnatal effects observed in humans that have been exposed to prenatal irradia tion. The studies reported in the present paper were designed to examine effects of prenatal x-irradiation upon the responses of inbred and hybrid mouse embryos as measured by morphological changes and changes in postnatal viability. The mice that were used in these studies were obtained from first pregnancies of matings within and among three inbred strains: BALB/Gw, K/Gw and S/Gw. Descriptions of the characteristics of the strains are provided in previous papers (Nash and Gowen, 1962, 1965). The matings produced progeny which were either inbred or hybrid, and provided nine different inheritance types. Mated females were examined daily for the presence or absence of a vaginal plug, the plug being the sole criterion used to time the period of gestation and the approximate age of embryos at irradiation. The afternoon of the day on which the plug was observed was considered to be day @ of gestation. Females were irradiated at 4 PM, and the gestational ages of the embryos at the time of treatment were considered to be approximately 6@, 1O@,14@or 17@days. Developmentally, these ages correspond to a time shortly after implantation, a period of major organogenesis, a period of minor organogenesis, and a time of rapid fetal growth, respectively. However, there are a number of factors which 1 This work has received assistance from Contract AT (11-1)—107 from the Atomic En ergy Commission and U. S. PublicHealth ServiceGrant HD—01898from the NationalInsti