Susumu Muramatsu

Genetic effects of chronic low-dose irradiation on mice.

SummaryThe genetic effects of radiation on mice were studied by applying chronic gamma-irradiation from conception to reproduction for three successive generations. The frequency of autosomal recessive lethals estimated by Haldanes method, litter-size, rate of early death, and sex-ratio were compared for the offspring of irradiated and non-irradiated ancestors.The dose-rate used was as low as 0·43 r/22 hr.-day, and the accumulated dose for each generation was about 34·4 r.A significant difference was observed in some of the above points.The rates of mutation to various kinds of recessive lethals were calculated.The genetic effect of radiation on mice was demonstrated at a low dose with a low dose-rate. The results may be very significant for the assessment of human radiation hazards.

Relative biological effectiveness of X-rays and fast neutrons in inducing translocations in mouse spermatogonia

Abstract The dose-response relationships for inducing translocations in the spermatogonia of mice were studied, and they were compared for 200 kVp X-rays and 2 MeV fast neutrons. The dose response for fast neutrons was markedly convex; more precisely, the response obtained was linear in the dose range from 24 to 94 rad with a regression coefficient of 11.36·10−4, but decreased for a further increase in dose up to 267 rad. On the other hand, that for X-rays showed a linear dose-response relationship from 48 to 672 rad with a regression coefficient of 2.69·10−4. The relative biological effectiveness for inducing translocations in the spermatogonia of mice was compared for the linear parts of the dose response in both types of radiation, and the relative biological effectiveness (RBE) value was 4.22.

Radiosensitivity and Thyroid Function in Mice

Thyroid function was compared in three inbred strains of mice, RF, CF1, and C57BL/6, whose radiosensitivity was found to be different. The correlation between functional level of the thyroids and radiosensitivity may indicate that the difference in radiosensitivity is due to a physiological difference in the thyroid function and, accordingly, the basal metabolic rate. Protection against radiation was clearly observed on administration of antithyroid agents in a strain with physiologically high thyroid activity. Similarly, sensitization to radiation was demonstrated on the administration of thyroid hormone in a strain with physiologically low thyroid activity.

EFFECTS OF CHRONIC LOW-DOSE IRRADIATION FOR THREE SUCCESSIVE GENERATIONS ON THE BREEDING BEHAVIOUR OF MICE

SummaryThe effects of radiation on the reproductivity of mice were studied under the influence of chronic low-dose irradiation throughout reproductive period for three successive generations. The dose-rate used was 0·43 r/day, and the accumulated dose was 34·4 r for one generation.Mean litter-size increased with each generation in the irradiated series. Sterility and partial sterility were found in the later generations (P2 and P1 generations), but not in the earlier generations, and the increased incidence in the irradiated series was statistically significant. These may suggest that the radiation effects on reproductivity are, in part at least, cumulative at a very low dose-rate.From the incidence of sterility and partial sterility, the minor chromosome-aberration rate including translocation was calculated at 19·8−6·6 × 10−4/r.