An Attempt to Produce Complete Thyroxine Deficiency in the Rat

Removal of the thyroid gland is not always followed by the impressive effects described in text-books of Endocrinology. Thus, thyroidectomized rats routinely kept in this laboratory on a diet of Purina Fox Chow do not show the stunted growth and cretinoid syndrome generally associated with thyroidectomized animals. In man, according to the surgeon Hertzler (1941), complete thyroidectomy seldom produces myxedema symptoms. In fact, Hertzjer claims that most of his patients remained quite normal after thyroid extirpation, only 17% having to take thyroid extract, and very few of them for longer than 6 months. Why then is the classical picture of thyroidectomy missing in such cases? One possible explanation is the presence of thyroid hormone—thyroxine1—in the diet. Thyroxine may be ingested in food of animal origin since this substance is present in muscle, liver, kidney, and other organs (Gross and Leblond, 1950).