[Morphofunctional changes in the thyroid gland of golden hamsters during acclimatization to a temperature of 4...

Morphological and physiological peculiarities of the thyroid gland have been studied in the golden hamster (Cricetus auratus W.) exposed to prolonged acclimation at +4 degrees C. These heterothermal rodents, kept constantly under laboratory conditions at +18-+20 degrees, show no distinct seasonal changes in the thyroid activity. As demonstrated by morphological findings, a relatively high activity of the gland persists throughout the whole year. At a prolonged acclimation to cold (up to 3 months, +4 degrees), the thyroid activity increases both in golden hamster, and in homothermal rats. Morphological indices of the hyperactivity are as follows: hypertrophy of the gland occurring by the 20th--30th days of exposure and increasing since then; hyperplasy of the granular tissue; colloid vacuolation; strong vessel hyperemy. However, the size of cells is not increased as are likely to retain a partial activity which is evidenced by the presence of tracks. Intensification of the thyroid function is also expressed by the increase in 131(uptake and output rates as well as by the increase in the protein bound iodine content in the blood of hamsters. Changes of the thyroid gland in acclimated animals occur independently of the season and photoperiod. It is shown that the degree of adaptation to prolonged action of cold, is more pronounced in golden hamsters than in rats. It has been also demonstrated that golden hamsters tend to hibernate after a prolonged cold acclimation.