Determinants of Thyroxine‐Induced Cardiac Hypertrophy in Mice

Thyroxine was administered to mice to determine whether the cardiac hypertrophy which accompanies experimental thyrotoxicosis is a result of circulatory changes produced by thyroxine, or the result of a hormonal effect on myocardial growth. When mice were fed both reserpine and thyroxine they developed as much cardiac hypertrophy as those fed thyroxine alone, although the circulatory changes associated with thyrotoxicosis were greatly reduced by reserpine treatment. In addition, when mice were injected with synthetic l-thyroxine, the rate of cardiac protein synthesis was increased before any definite circulatory changes were observed. The results suggest an effect of thyroid hormone on cardiac protein synthesis that is independent of the effects of the hormone on the general circulation.