[The dependence of the adaptive effect of brief stress exposures on the thyroid state of the body].

The effectiveness of adaptation to short-term stresses with regard to the level of thyroid hormones was investigated in experiments on isolated hearts of 94 female rats. Adaptation to stress in euthyroid rats (daily immobilization for 15 days) prevented a 2-fold decrease in the blood concentrations of T3 and thyroxine, caused by 6-hour immobilization stress and determined by radioimmunoassay. In hypothyroid rats multiple sessions of short-term immobilization in itself caused a decrease in the coronary dilating reserve by 29%, in the maximum coronary blood flow developing after 60-second discontinuation of perfusion, by 31%, an increase in intraventricular diastolic pressure; subsequent 6-hour immobilization resulted in a further drop of the coronary reserve, maximum coronary blood flow and an increase in diastolic pressure. Thus the effect of preventing stress changes of the coronary blood flow and myocardial contractility by adaptation to short-term stresses depends on body thyroid function.