STUDIES ON THE MECHANISM OF HYPOTHALAMIC CONTROL OF THYROTROPIN SECRETION: EFFECT OF INTRAHYPOTHALAMIC THYROXINE INJECTION ON THYROID HYPERTROPHY INDUCED BY PROPYLTHIOURACIL IN THE RAT1

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Abstract
A minute amount of thyroxine was injected into the anterior hypothalamus of rats chronically treated with propylthiouracil. The subsequent development of goiter was studied in relation to the hypothesis proposed in a previous paper that the "thyrotropin center" of the anterior hypothalamus is sensitive to alterations in the concentration of circulating thyroid hormone and thus can secondarily control thyrotropin secretion by the pituitary. The development of goiter was markedly inhibited by the injection of systemically ineffective amounts of thyroxine into the anterior hypothalamus but not by saline injections into the same area or by thyroxine injections into other areas of the hypothalamus. Adrenal and testieular weight were not affected by such procedures. It is suggested that thyroxine injection into the anterior hypothalamus specifically affects thyrotropin secretion by the pituitary.