Influence of the thyroid status of the organism in the realization of the adaptational effect of cold.

The combined three- and six-hour effect of immobilization and cold on euthyroid rats induces suppression of the contractile function and functional reserve of the heart, the death, respectively, of 30 and 80% of the animals, hypothermia, changes in the weight of the adrenals and the spleen, and ulceration of the mucosa of the stomach. Stressing of the hypothyroid rats is accompanied by a substantially more pronounced decrease in the indices of cardiac dynamics and the resistance of the organism after 3 h, and the death of 100% of the animals after 6 h. The periodic effect of cold on euthyroid rats leads to an increase in the strength and speed of contraction and relaxation of the myocardium, as well as to an increase in the relative weight of the spleen. During subsequent stressing, cold adaptation substantially limits the disturbances in contractile function and prevents the decrease in the functional reserve of the heart, increases survival, and decreases the degree of hypothermia, ulcer-formation, and change in the weight of stress-sensitive organs, while the preventive effect of cold adaptation is absent in the hypothyroid animals; this attests to the significance of thyroid status for its realization.