[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.

[Morphometric analysis of follicular structure of the thyroid gland after chronic low-dose gamma-irradiation].

A quantitative study of follicle average cross-sectional diameter distribution was conducted in the thyroid gland (TG) of mouse like rodents (25 tundra voles, 24 CBA mice, 16 Wistar rats) after chronic exposure to low-level external y-radiation both in the environment and under the experimental condition (absorbed dose range 0.05-0.5 Gy). Spectrum analysis of TG follicle cross-sectional diameter distribution in the irradiated animals has demonstrated a universal regularity: in comparison with the unirradiated animals there was a significant (1.3-1.7-fold) increase in content of small follicles (with a cross-sectional diameter lower than 36-41 microm in the studied animal species). A similar phenomenon was reproduced in the model experiments (TG regeneration in rats after hemithyroidectomy). The observed activation of the folliculogenesis processes after chronic low-dose irradiation in small doses may be interpreted as a nonspecific adaptive reaction of TG to radiation induced damage of its parenchyma.

[Cytogenetic effects in follicular epithelium of thyroid gland under prolonged exposure to gamma-radiation at low-doses].

The forming processes of micronucleated follicular thyrocytes in thyroid gland of mature Wistar rats under exposure to the prolonged low-intensity gamma-radiation with 5 and 50 cGy (dose rates: 25, 400 microGy/h; duration: 55, 80 days) were investigated. The chronic exposure to low-intensity gamma-radiation in both doses invokes the frequency of micronuclated thyrocytes three times higher in comparison with control animals. As a result of the small-sized micronuclei formation prevalence in irradiated group, the average size of micronuclei was 1.4-2 times lower than control values. This phenomenon can be reproduced in model experiments with hemithyroidectomized animals exposured to acute gamma-radiation with 2-4 Gy. The obtained results show high sensitivity of micronucleus test to the early determination of radiation-induced genetic damages in follicular epithelium of thyroid gland.

[Morphological analysis of genetically damaged thyrocytes in nodular pathology of the thyroid gland].

The smears of isolated thyrocytes with micronuclei taken from 25 patients with nodular pathology of the thyroid gland were investigated. In all kinds of benign nodular pathology the number of micronucleated thyrocytes comes to 0.1-0.3%. These values correspond to the spontaneous level of the content of aberrant thyrocytes in the thyroid gland of highly specialized cell populations. In papillary carcinoma of the thyroid gland the average occurrence of micronucleated thyrocytes in the tumor nodule was about 0.4%. In the tissue outside the tumor taken from both the same and the opposite lobes, the content of cells with micronuclei proved to be substantially higher--0.93-1%. So, the marked increase of the concentration of genetically damaged cells in the thyroid parenchyma proved to be characteristic of the carcinoma of the thyroid gland.

[Isolation of cells for cytological and cytogenetic studies of the thyroid epithelium].

This paper presents a detailed description of the method for obtaining of high quality smears of thyrocytes from the fragments of rat (30 animals) and human (20 cases) thyroid gland using the method of enzymatic dissociation in 0.25% aqueous solution of collagenase (collagenase for pancreatic islet isolation type XI, collagen digestive activity 1205 units/mg, Sigma, USA) at 37 degrees C during 1; 1.5; 2; 2.5 and 3 hours. Optimal time for dissociation in each individual case should be determined using control smears. This approach permitted to successively perform morphological, morphometric and cytophotometric analysis of the glandular cells, to evaluate the relative proportions of different cell types (mitotically dividing cells, binucleate cells, aberrant forms with the micronuclei) in animal experiments as well as in the various types of human thyroid pathology.