[Morphometric and cytogenetic studies of the follicular epithelium thyroid of small mammals under chronic exposure to small doses].

We have detected the genotoxic effect (increase of micronuclei) after chronic exposure to low-level ionizing radiation of the thyroid follicular epithelium of the voles living for many generations in the radioactive territory. At the same time, we also discovered the stimulating effect of chronic low-level ionizing radiation on the activity of morphogenetic processes in the thyroid parenchyma of the animals from natural populations (increased micro-follicles). These data were confirmed by the experiments; chronic irradiation of the thyroid gland of rats at the doses of 5 and 50 cGy revealed an increased induction of micronuclei and the increase in the number of small follicles. An increased proliferative potential of thyroid may be regarded as a non-specific adaptive response to chronicbody exposure to ionizing radiation.