Abstract
The functional activity of the thyroid in laboratory animals exposed to extreme cooling is studied. Male Wistar rats were used. Control animals were kept at 20-22° C, experimental at —10°C for 7 days. Thyroxin and triiodothyronine concentrations in the serum and thyroid hormones and thyroglobulin in the thyroid were measured. Morphometry of the thyroid was carried out. Thyroxin level decreased and the T3/T4 ratio increased in the serum of rats exposed to extreme cooling; the content of thyroid hormones in the gland, mainly triiodothyronine and thyroglobulin, increased under the effect of cold. The thyroid enlarged under the effect of cold. The bulk of follicular epithelium in thyroid tissue increased and colloid volume decreased. Structural transformations of follicles were paralleled by increase of the vascular network and number of degranulated mast cells in the connective tissue thyroid stroma. Therefore, exposure to low temperature results in increase of the thyroid functional activity in rats, despite the exhaustion of the adaptive reactions of the organism.
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