1913.] Metabolism in its Relation to the Thyroid Gland. 



557 



The Effect of Thyroid Feeding on the Protein Metabolism. 



This conclusion helps to explain a difficulty, already alluded to in the- 

 in traduction, in the interpretation of the influence of the thyroid hormone on 

 protein metabolism. 



One distinguishes at present with Folin two forms of protein metabolism, 

 the constant endogenous metabolism, which is independent of the protein 

 taken in in the food, and the exogenous metabolism, which varies with the 

 intake of protein in the food. Since thyroid feeding produces an increased 

 protein metabolism even in the fasting organism, it follows that the thyroid 

 hormone acts on the endogenous and not on the exogenous protein metabolism.. 

 One would expect, therefore, to find after thyroid feeding a marked increase 

 in the excretion of uric acid and of creatinin, since both these substances are 

 supposed to represent end-products of endogenous protein metabolism. We 

 found, however, that the increased nitrogen excretion after thyroid feeding is 

 accounted for almost entirely by the increased excretion of urea and ammonia,, 

 while the excretion of creatinin and of uric acid is either not increased at all 

 or only very slightly. 



This difficulty would appear to find its explanation in the fact that thyroid 

 feeding affects carbohydrate metabolism in the manner described above. For 

 the distribution of the urinary nitrogen after thyroid feeding is very similar 

 to that which presents itself when carbohydrates are withheld from the diet.. 

 In the latter case, too, there is a marked increase in the nitrogen excretion,* 

 even when no protein is given in the food, and here, too, the increased 

 nitrogen output is due, almost entirely, to an increase in the excretion of urea 

 and ammonia. f A further similarity is to be found in the appearance of 

 creatin in the urine both after thyroid feeding! and after withdrawal of carbo- 

 hydratesf or in disturbances of carbohydrate metabolism such as diabetes 

 mellitus§ or phlorhizin diabetes.§|| 



In order to demonstrate this similarity as clearly as possible, quantitative 

 analyses of the nitrogenous urinary constituents have been carried out on 

 one of us ; (1) on a diet, creatin,- creatinin- and purin-free, but containing 

 different amounts of carbohydrates, (2) on the same diets after thyroid feeding, 

 (3) on a similar diet without carbohydrates. 



The results are given in Table IV. Experiment 1 shows the effect of 



* Landergren, 'Skand. Archiv f. Physiologie,' 1903, vol. 14, p. 112 ; Kayser, quoted from 

 Landergren. 



t Cathcart, ' Journ. Physiol.,' 1909, vol. 39, p. 311. 



1 Krause and Cramer, ' Phys. Soc. Proc.,' 1912, p. xxiii, ' Journ. Physiol.,' vol. 44. 

 § Krause and Cramer, ibid., 1910, p. lxi, ibid., vol. 40; Krause, 'Quart. Journ. Exp. 

 Physiol.,' 1910, vol. 3, p. 289. 



|| Cathcart and Taylor, ' Journ. Physiol.,' 1910, vol. 41, p. 273. 



