THYROID WEIGHT, MICROSCOPIC STRUCTURE, AND RADIOIODE CONCENTRATION AT VARIOUS LEVELS OF THYROTROPHIN SECRETION IN THE GOITROGEN-TREATED RAT1

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Abstract
IN HYPOPHYSECTOMIZED rats, propylthiouracil has been shown to potentiate the response of the thyroid iodide trap to thyrotrophic stimulation (1). The question of whether or not a similar potentiation of this response occurs in intact rats is of importance in interpreting the fact that, in rats with anterior hypothalamic lesions, there is an apparent dichotomy between the metabolic and growth responses of the thyroid gland to goitrogen treatment (2, 3, 4). This question has been examined by Greer (3), who studied thyroid-serum radioiodide concentration (T/S) ratios and thyroid weights in goitrogen treated intact rats (100 gm. in weight) maintained at three different levels of thyrotrophin secretion. Secretion of this hormone was regulated by daily injections of thyroxine, according to the method of Dempsey and Astwood (5) He found that whereas the T/S and thyroid weight were approximately normal in rats given 3.5 or 5.0 μg. doses of racemic thyroxine daily, both were elevated in rats maintained on 2.5 μg./day.