Effects of beta radiation from organically bound tritium on cultured mouse embryonic mid brain cells

Effects of beta radiation from four kinds of organically bound tritium compounds were investigated on cultured mouse embryonic mid brain cells, isolated from 11-d-old mouse embryos. The MBC showed a critical time when they were more radiosensitive. Although dose-dependent inhibition was found for both cellular proliferation and differentiation, the differentiation was more sensitive to radiation than proliferation when compared at ID50, the inhibitory dose that reduced assessment value by 50% of the control. Dose-dependent decrease of DNA and protein contents were also observed. The relative biological effectiveness values, ranging from 4.6 to 8.7, of beta ray from organically bound tritium compounds were obtained when compared with x irradiation at their ID50s on the inhibition of cell proliferation and differentiation, and on the decrease of DNA and protein contents of the cultures. The mixed exposure to x ray and one kind of organically bound tritium compound or to any two kinds of organically bound tritium compound resulted in a more efficiently inhibitory effect on differentiation than the exposure to x ray or to any one kind of organically bound tritium compound alone, especially when methyl-3H-thymidine was used. Doses as low as 0.05 Gy (5 cGy) from a mixed exposure resulted in detectable inhibitory effects.