The aim of this paper is to summarize some of our quantitative descriptive and experimental studies, to discuss them in view of the literature data, and to present a synthesis of the topic. The results of stereological analysis of some tissue components of the rat thyroid gland have been compared with the results of topological studies on the parafollicular cells of various mammalian species. Localization of the parafollicular cells in the central regions of the thyroid gland lobes, where the follicular cell activity seems to be greater than in the periphery of the lobes, has led to the hypothesis that the parafollicular cells regulate (stimulate and/or suppress) the activity of the follicular cells. Long-term application and antithyroid drugs to mice and rats has shown that excessive concentrations of thyrotropin provoke hyperplasia of both the follicular cells and the intrathyroid mast cells and, transiently, of the parafollicular cells. This and some of the literature data are congruent with the hypothesis that the parafollicular and mast cells also stimulate the follicular cells by their paracrine secretions. Long-term application of antithyroid drugs to mice and rats has shown that excessive concentrations of cular cells but also probably stimulation of the follicular cells, as judged by the stereological measurements. The biological meaning of the spatial integration of follicular and parafollicular cells seems to be a functional coordination of both epithelial cell lines, supported by intrathyroid mast cells.
In three experiments of 30 weeks' duration, 93 adult female Wistar rats received controlled amounts of calcium with food and water, to produce a state of either hypercalcemia or hypocalcemia. A systematic stereological analysis of the thyroid glands and a radioimmunological analysis of thyroxine, triiodothyronine, and thyrotropine were performed. In the hypercalcemic rats, a reactive hyperplasia of the parafollicular cells was established; this was accompanied by morphological and biochemical signs of hyperfunction of the follicular cells, despite a reduced central stimulation by thyrotropin. In the hypocalcemic animals, no quantitative morphological changes in the parafollicular cells were observed; however, morphological and biochemical signs of hypofunction of the follicular cells were obvious, despite stronger central stimulation by thyrotropin. It is concluded that the extrinsic regulation of follicular cells by the blood calcium level is stronger than the intrinsic regulation by hypothalamo-hypophyseal hormones.
In the introduction the evolution of methods for numerical density estimation of particles is presented shortly. Three pairs of methods have been analysed and compared: (1) classical methods for particles counting in thin and thick sections, (2) original and modified differential counting methods and (3) physical and optical disector methods. Metric characteristics such as accuracy, efficiency, robustness, and feasibility of methods have been estimated and compared. Logical, geometrical and mathematical analysis as well as computer simulations have been applied. In computer simulations a model of randomly distributed equal spheres with maximal contrast against surroundings has been used. According to our computer simulation all methods give accurate results provided that the sample is representative and sufficiently large. However, there are differences in their efficiency, robustness and feasibility. Efficiency and robustness increase with increasing slice thickness in all three pairs of methods. Robustness is superior in both differential and both disector methods compared to both classical methods. Feasibility can be judged according to the additional equipment as well as to the histotechnical and counting procedures necessary for performing individual counting methods. However, it is evident that not all practical problems can efficiently be solved with models
In a 46-week-experiment on 72 female mice the influence of peroral 1.2% sodium perchlorate application, total ionizing irradiation with 8 Gy on 5 consecutive days and their interaction on the pituitary-thyroid axis was studied by histological and stereological methods. It was observed that perchlorate alone caused long-term and strong hypothyroidism with hypertrophic and hyperplastic thyroid epithelial cells as well as pituitary thyrotropic cells. When only irradiation was used, no uniform changes in the structure and function of these cells could be detected. The interaction of perchlorate and irradiation showed similar effects as thyrostatics alone, with some exceptions; paradoxically, minor hyperplasia of thyrotropic as well as of parafollicular cells was observed. A high percentage of the follicular cell carcinoma was found after perchlorate application and after its combination with irradiation. No medullary carcinoma was found.
Seventy-two female mice of BALB/c strain were divided into three control and three perchlorate groups. The perchlorate groups drank 1.2% sodium perchlo-rate solution. After 8 or 32 weeks of the 46-week experiment one control and one perchlorate group were totally irradiated with 0.8 Gy on 5 consecutive days. Ten normal thyroid glands, 10 with hypertrophy and hyperplasia, 8 follicular adenomas and 10 follicular carcinomas were histologically and stereo-logically analysed. The results showed significant differences in the average nuclear volume (p < 0.05) and in the average number of the silver-stained nucleolar organiser regions (AgNORs) per nucleus (p < 0.005) between the follicular adenomas and the follicular carcinomas. The method of counting Ag-NORs per nucleus was more valid, more accurate and more economical than the method of measuring the average nuclear volume.
In this experiment of 11 month-duration, 18 female Wistar rats received controlled amounts of calcium with food and water, to produce a state of either hypocalcemia or hypercalcemia. After a long-term low calcium diet hypocalcemia disappeared. This group of animals showed insignificant increases in the nuclear-cytoplasmic ratio of the parathyroid cells as well as in the total volume of the parathyroid glands, and a significant increase in the volume density of the osteoid. In the group receiving a high calcium diet, hypercalcemia was still present after 11 month. The insignificantly smaller and more numerous C-cells produced more calcitonin than normally. The parathyroid cells were significantly smaller and the numerical areal density of the osteoclasts was significantly lower than in the control group. It can be concluded that the parathyroid glands and C-cells are involved in the maintenance of blood calcium homeostasis during a long-term experiment on rats receiving low or high calcium diet.
FRTL-5 cells grow as a monolayer culture in vitro and they must be detached from the solid surface by trypsin before reseeding. The aim of this study was to examine by light microscopy and by the astereological method the changes that occur in FRTL-5 cells one, two, three or four days after trypsinisation. The most pronounced qualitative and quantitative changes were seen from the first to the second day after trypsinisation, as the area of the cells increased by 119%, their nuclei by 71% and the cytoplasm by 150%, while the nuclear-cytoplasmic ratio decreased by 42%. Significant increases in the average area of the cells, their average nuclear diameter and perimeter were seen also on the third and fourth days, while the average nuclear-cytoplasmic ratio decreased significantly on the first three days after trypsinisation and then remained constant.
For the first time, 3, 7 and 10 days growth of normal thyroid follicular FRTL-5 cell colonies in a semi-solid medium of 0.6% methocel over 1% agar base was morphometrically analyzed. It was found that the areas of FRTL-5 colonies as well as their perimeters and maximum diameters increased, while according to their form factors the FRTL-5 colonies were regular in shape. After 10 days in a semi-solid medium, 83% of the FRTL-5 colonies had maximum diameters greater than 50 microm. It is obvious that after long culturing of FRTL-5 cells under the influence of the pituitary thyroid-stimulating hormone (TSH) these cells are not uniform anymore and that they grow in a semi-solid medium.
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