556 Messrs. Cramer and Krause. Carbohydrate [June 10, 



The Effect of Thyroid Feeding on tlie General Metabolism of Carbohydrates. 



In the further study of this phenomenon we have been led by the following 

 considerations. Two possibilities, which appear to be diametrically opposed 

 to each other, suggest themselves as being capable of furnishing an explana- 

 tion of this action of the thyroid hormone on the liver glycogen. Either 

 thyroid feeding primarily increases the oxidation of carbohydrates in the 

 organism or it primarily inhibits the function of the liver to form and store 

 glycogen. In the former case one would expect to find the following com- 

 bination of symptoms : (1) A formation of glycogen in the liver soon after 

 a meal rich in carbohydrates followed by a disappearance of glycogen more 

 rapidly than in the normal animals, (2) an increased tolerance for glucose, 

 (3) a diminution of the blood-sugar, especially in the fasting animal. An 

 inhibition of the liver function, on the other hand, would be reflected, (1) in 

 the relative absence of liver glycogen even soon after a meal rich in 

 carbohydrates, (2) in a diminished tolerance for glucose, (3) in a rise in the 

 blood-sugar especially after a carbohydrate-rich meal. 



Information on the behaviour of the liver glycogen in fed and fasting 

 animals can be gathered from Table I. It will be seen that the effect of 

 thyroid feeding on the glycogen-content of the liver is independent of 

 feeding. 



Experiments on the tolerance for glucose after thyroid feeding were made 

 on dogs. A detailed account of these experiments will be published later ; 

 but the results may be briefly summarised here, as showing that thyroid 

 feeding produces a slight but distinct lowering of the tolerance for glucose. 

 A dog, for instance, which normally could assimilate 100 grm. glucose without 

 any glycosuria supervening and only began to excrete sugar in the urine after 

 the administration of 110 grm. glucose, had its limit of assimilation reduced 

 to 90 grm. glucose after three days' feeding with fresh thyroid. 



The behaviour of the blood-sugar is at present being investigated in this 

 laboratory by Mr. E. J. M. Home. These observations are not yet completed 

 but they are sufficiently far advanced to show that there is at any rate no 

 diminution in the sugar-content of the blood, but rather the reverse. 



One must conclude, therefore, that the internal secretion of the thyroid 

 gland, when administered to normal animals, has an inhibiting influence on 

 the carbohydrate metabolism. But since the utilisation of carbohydrates by 

 the organism is not markedly affected, as is shown by the comparatively slight 

 lowering of the tolerance for glucose, it follows that the thyroid hormone acts 

 specifically on only one aspect of carbohydrate metabolism in so far as it 

 inhibits the formation and storage of glycogen in the liver. 



