Abstract
Cowan 1 has recently reported that the administration of thyroxin to rats, while producing an increase in ventricular muscle mass, resulted in a loss of creatine. Before the publication of Cowan's data, we had independently observed the same phenomenon in rats receiving desiccated thyroid. Indeed, the creatine values were depressed to much lower levels in our experiments than in those of Cowan. While it is to be recognized that the response to thyroid varies somewhat in different individuals, and depends upon a variety of factors to be described later, our results have been averaged as outlined in Table I for the purpose of comparison with Cowan's data. The usual daily dose of the powdered thyroid was 200 to 250 mg. per 100 gm. of body weight.
That the increased size of the heart represents a true hypertrophy is indicated by the fact that the water content of the hyperthyroid ventricles was practically the same as that of the normal ventricles (average of 76.48% for 11 hyperthyroid hearts and 76.21% for 6 normal hearts). On histological examination the hearts of the hyperthyroid rats showed hypertrophy, signs of acute degeneration, mononuclear cellular infiltration, and occasionally fatty metamorphosis.
Not infrequently death overtook the thyrotoxic animals in a sitting posture, sometimes following relatively slight exertion, and without being preceded by the usual signs of serious illness.
Our acknowledgment is due to Eli Lilly and Company for their generous cooperation in supplying a part of the desiccated thyroid used in these experiments.
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