Formation of Diiodotyrosine and Thyroxine in Thyroidectomized Animals

Thyroxine and diiodotyrosine extracted from the organs were recrystallized five times. In each recrystallization of thyroxine, 10 mg. of nonradioactive diiodotyrosine were added in order to wash out any contaminating radiodiiodotyrosine by dilution. Such a washing-out process is much used in the purification of labeled compounds. In the case of diiodotyrosine rectystallization, 10 mg. of nonradioactive thyroxine were added each time for the same purpose  

The specific activities of both th3rroxine and diiodotyrosine did not change significantly after the second recrystallization. This would be expected to occur only in a case in which the substance giving the radioactivity was identical with the material that underwent repeated recrystallization. 

The completeness of thyroidectomy was checked with great care by histological examination of serial sections of the whole neck and chest regions of the animals, and in some cases by a radioautographic method in which the tissues are rolled out and exposed to an x-ray film. Under such 

Rat No. Body weight, e Interval after thyroid- ectomy, month Oxygen consumption Tissue Time after injection, hr. Administered 311 recovered per % of tissues found as  

At first sight it may be astonishing to find the formation of thyroxine in a thyroidectomized organism, but this is in no way surprising in view of the discoveries of Mutzenbecher (133) and others. By iodination of casein, they obtained preparations that were physiologically active and from which thyroxine could be isolated. Harington and others obtained similar results (72). 

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