THE COMPARATIVE EFFECTS UPON METABOLISM OF INTRAVENOUSLY INJECTED TYROSINE, DIIODOTYROSINE, DIIODOTHYRONINE AND THYROXINE

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Abstract
Tyrosine (T), diiodotyrosine (DiT), diiodothyronine (DiTh) and thyroxine (Tx) were administered to [3] dogs by intraven. injection, and the effects on the gaseous exchange studied. The maximum rise due to 1 gm. T was 10% of the total metabolism, the effect lasting about 10 hrs., the av. total increase being about 220 cals. per gm. T per kgm. of animal. DiT produced about 7.5 times as much effect as did T; DiTh about 15 times that of DiT; and Tx about 17 times that of DiTh. Generally speaking, the greater the total increase, the more prolonged the effect. The effect of all the substances but Tx began almost at once (not later than 1/2-1 hr. after administration); in the case of Tx an appreciable effect was delayed 4-5 hrs. Though the ratio of the effects of Tx and T is about 2000:1, the data would indicate a step-like progression in stimulating influence as I and the phenyl radical are added to the T molecule in certain positions. The significance of this is not yet clear.

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