Guinea-pig epidermis was irradiated with 3000 rad of beta rays 1 hr after two injections of [3-H]thymidine 5 hr apart (labeled cells in S phase and G2 phase) or 18 hr after injection (labeled early G1 cells). In nonirradiated epidermis labeled basal cells divided within 24 hr with daughter cells remaining in the basal layer, and approximately 50% of the labeled cells moved into the spinal layer by the 3rd day. Cell division in nonirradiated epidermis diluted the number of silver grains/nucleus, and lightly labeled cells were found in the granular layer by day 7. Beta irradiation inhibited cell division but it did not slow the rate of transit (ca 8 days) of irradiated labeled cells from basal to granular layer, some of these remaining heavily labeled. Although cell division may play some role in upward movement of basal cells in normal epidermis detachment of a basal cell from the basement membrane and its transit to the granular layer is unimpaired in the absence of cell division. These findings suggest that some radioresistant metabolic function(s), not cell division, is responsible for upward movement of basal cells.

This study was designed to investigate radiation-induced vertebral malformations in medaka embryos irradiated with beta particles from tritium. Embryos of two inbred strains (HO4 and HO5) of medaka, Oryzias latipes, were exposed either to different concentrations of tritiated water (9.25-37 MBq/ml) or to 137Cs gamma rays (dose rates of 0.44-1.89 Gy/day) continuously from morula to hatching. The newly hatched fry were removed from the radiation field and kept under usual conditions for 1 month. Young fish were fixed in 10% buffered formalin, cleared in 1% KOH, stained with alizarin red S, and kept in glycerine. There was almost no difference in the response to radiation between medaka strains. No marked reduction of hatching rate was observed after chronic irradiation with beta particles and gamma rays, but a considerable reduction in survival of fry was detected in irradiated groups within 1 month after hatching. From observation of whole-mounted skeleton specimens, the following vertebral malformations were found in irradiated groups: fusion of two or more vertebrae, incomplete formation of vertebrae, and lack of vertebral process. The incidence of vertebral malformations increased significantly in both groups irradiated with tritium beta particles and 137Cs gamma rays. A similarity in the incidences was also observed between beta-particle- and gamma-irradiated groups. The RBE of beta particles relative to gamma rays was estimated to be 1 based on the dose-response relationships observed.

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Embryos of medaka, Oryzias latipes, were exposed to tritiated water and 137Cs gamma rays continuously from the one-cell stage until hatching (10 days at 26 degrees C). Germ cells in the gonads of newly hatched fry were counted in histological sections and compared with controls. The accumulated dose for 50% survival of germ cells was 195 rad for tritium beta rays and 350 rad for 137Cs gamma rays. Female progeny were produced using Yamamoto's method. The 50% survival doses for female germ cells treated in a manner similar to that described above were 140 rad for beta rays and 305 rad for gamma rays. When embryos of medaka were irradiated with gamma rays below an accumulated dose of 475 rad or treated with tritiated water at a concentration of 0.2 mCi/ml or lower, the dose response of the germ cells showed an exponential relationship. It appeared that there was no threshold or significant dose-rate effect for either beta or gamma rays on germ cell survival, and that tritium beta rays were more effective than 137Cs gamma rays in germ cell killing.

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