[Importance of thyroid hormones in the realization of the protective effects of cold adaptation].

The possibility of limitation of stress-induced changes of lipid peroxidation (LP) and myocardial antioxidant activity (AA) caused by the combined influence of immobilization and cold during 3 hours was studied in experiments on 128 male rats. Cold adaptation was found to reduce death rates up to 10%, the degree of hypothermia, LP activation and myocardial AA depression under combined stress, significantly elevating the concentration of serum thyroid hormones. Hypothyroidism causes a 2.5-fold decrease in thyroid hormones. It also decreased the concentration of LP products and cardiac AA, and stress in hypothyroid rats resulted in as high as 50% increase in death rates and enhanced hypothermia. This also led to less marked LP stimulation and myocardial AA depression. 50% death of animals, lower hypothermia and the same changes in the content of LP products and cardiac AA, as in non-adapted rats were found in cold-adapter hypothyroid rats during combined stress. It is concluded that thyroid hormones determine the efficiency of cold adaptation to a greater extent.