[Effect of long-term hypokinesia on the C-cell system of the thyroid gland].

The state of C-cells of the thyroid gland of Wistar rats during prolonged (30-165 days) hypokinesia was examined. Histo- and morphometric data pointed to a gradual decline in the function of C-cells during hypokinesia and its return to normal after 2-month readaptation. The decline was most distinct by hypokinesia day 90 (significant decrease in the number and size of nuclei, prevalence of small cells with densely packed granules in the cytoplasm). The decline in the function of C-cells during hypokinesia may be one of the factors leading to increased calcium elimination from bones. In conclusion, the state of C-cells in animals exposed to weightlessness and hypokinesia is compared.