Cardiovascular Effects of Thyroxine Treatment in Hypophysectomized Rats

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Abstract
Oxygen consumption, weight and rate of the heart, blood pressure, cardiac output and work are restored to normal if rats hypophysectomized two to three months previously are treated with thyroxine over a period of three to five weeks. Although under basal conditions the above parameters in these rats are the same as those in normal rats, the maximum output and work during loading by infusion of polyvinylpyrrolidone into the right side of the heart are less in hypophysectomized rats treated with thyroxine than they are in normal rats. Similarly, if a load is imposed on the heart by constriction of the aorta, cardiac output and work are well below the values measured in normal rats with aortic constriction. It is concluded that thyroxine treatment of hypophysectomized rats can restore to normal the performance of the cardiovascular system under basal conditions but that during loading (polyvinylpyrrolidone infusion, aortic constriction) the performance of the cardiovascular system is less than in normal rats.