Female rats were given tritiated drinking water (3 μCi/ml) from 30 days before mating up to and throughout pregnancy. At this low dose, the course and the outcome of pregnancy were normal. The differences between newborn body and cerebral weights of the treated rats and those of control animals were on the borderline of significance. In contrast, cerebral DNA and cerebral protein were highly significantly lower. In 30-35% of the treated population the DNA and protein values were more than 2 standard deviations (SD) below the mean values for the control population. Thus the number of the progeny of the mothers exposed to tritiated water that were considered to have "outstandingly low" levels of DNA and protein was 14-17 times greater than in the control group. The irradiated population also had 3-5% of severely affected individuals with cerebral DNA and protein values more than 2 SD below the mean of the experimental population. However, even in this irradiated population, a certain number of individuals did not show the effects of radiation as indicated by DNA and protein values that were not lower than the mean values of the control population. These animals may represent those individuals in which normal (control) populations would have cerebral DNA and protein levels well above the average (by 1 to 2 SD), but here, because of prenatal irradiation, were about average. If so, this lack of effect of irradiation cannot be caused by protection against radiation. However, at present, a differential repair mechanism of protection in those animals (or their mothers) that showed little or no effect of irradiation cannot be excluded.

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