THYROID HORMONE-LIKE PROPERTIES OF TETRABROMTHYRONINE AND TETRACHLORTHYRONINE*†

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Abstract
ALTHOUGH the important part played by iodine in the action of the thyroid hormone is thoroughly appreciated, its mode of action remains one of the intriguing mysteries of thyroid physiology. Baumann's (1896(1)) discovery of iodine in the thyroid gland, Kendall's (1915(2)) isolation of a substance from the thyroid containing 60 per cent iodine which was capable of abolishing all manifestations of thyroid insufficiency, and the synthesis of crystalline thyroxine by Harington and Barger (1927(3)) are significant landmarks in our increasing knowledge concerning the importance of iodine in thyroid physiology. Harington and Barger concluded from their studies that the physiologic activity of the hormonal compound is dependent upon its content of iodine. Abderhalden and Wertheimer (1928(4)) tested the potency of certain analogs of thyroxine by comparing the effects of these compounds with those of thyroxine on the metamorphosis of tadpoles and axolotls. They found that tetrabromthyronine, a compound in which the iodine atoms of thyroxine are replaced with bromine atoms, had slight activity. They concluded that the molecular structure was an important feature of physiologic activity.