THE EFFECT OF IODINE AND IODOTHYRIN ON THE 

 LARVJE OF SALAMANDERS. III. THE ROLE OF 

 THE IODINE IN THE SPECIFIC ACTION OF THE 

 THYROID HORMONE AS TESTED IN THE META- 

 MORPHOSIS OF THE AXOLOTL 



E. UHLENHUTH. 

 (Received for publication September 11, 1921.) 



The role of the iodine in the specific action of the thyroid hor- 

 mone is still an undecided question. The most recent investiga- 

 tions on mammalia have led to the conclusion that the inorganic 

 iodine as such is incapable of bringing about effects identical with 

 the specific effects of the thyroid hormone. 



Kendall 1 has shown that the specific reactivity of the thyroid 

 hormone (thyroxin) as manifested by its capability of abolishing 

 myxedema, mitigating cretinism, and raising metabolism depends 

 chiefly on the presence, in it, of a CO-NH group. Iodine, al- 

 though it may increase the specific reactivity of thyroxin, does not 

 produce it, as is shown by the ineffectiveness of derivatives in 

 which merely the hydrogen on the imino group has been replaced 

 by acetyl without changing the position of the iodine atoms. Ken- 

 dall, therefore, has been forced to conclude that the iodine is not 

 responsible for the specific action of the thyroid hormone. 



Quite in line with Kendall's viewpoint are Leo Loeb's recent 

 experiments on the compensatory hypertrophy of the guinea pig's 

 thyroid. Loeb found that the inhibitive effect in this kind of 

 hypertrophy is specific for the thyroid hormone, 2 while inorganic 

 iodine as such is incapable of preventing the compensatory hyper- 

 trophy of the thyroid gland. Leo Loeb, therefore, claims, like 

 Kendall, that the effect of iodine is not identical with the effect of 

 the thyroid hormone. 



* From the Laboratories of the Rockefeller Institute for Medical Research. 



1 Kendall, E. C, Endocrinology, 1917, i, 153-169, and 1919, iii, 156-163. 

 Plummer, H. S., and Boothby, W. M., Amer. J. Physiol., 1921, lv, 295. 



2 Loeb, L., 7. Med. Res., 1920, xli, 481-494, and 1920, xlii, 77-89. 



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