Thyroxine cardiomegaly in rats is not hypertension-bound.

For 13-27 days, male rats were given dried thyroid (Thyreoidin SPOFA) in their food, 0.9% NaCl to drink instead of water, or both. In all the experiments, Thyreoidin induced pronounced cardiomegaly. The blood pressure rose only after 0.9% NaCl combined with Thyreoidin and only in experiments lasting 13 or 16 days (not 25 and 27 days). After three weeks of the experiment, therefore, hypertension disappeared, but cardiomegaly persisted. In all the experimental groups, including the controls, a significant positive correlation was found between heart weight and adrenal weight, but not between heart weight and blood pressure or between adrenal weight and blood pressure. The adrenals may thus participate in some way in the development of thyroxine cardiomegaly.