THE ANTITHYROXINE ACTIVITY OF THYROXINE ANALOGS*†

Abstract

7 thyroxine analogs were tested for antithyroxine and thyroxine-like activity on rats treated with thiouracil. One of the compounds, 2[image] ,6[image] -diiodothyronine, could antagonize the action of thyroxine in a dose 150 times that of thyroxine. It also showed an action antagonistic to injd. thyro-globulin. Two of the compounds, thyronine and 3-fluorothyronine, had neither thyroxine-like nor antithyroxine activity. The compounds 3[image] -fluoro-3,5-diiodothyronine and 3[image] ,5[image] -difluoro-3,5-dii-odothyronine had weak thyroxine-like activity, the former 1/20-,l/40th, and the latter l/30-l/60th that of thyroxine. 3[image] -Fluoro-5[image]-iodoj3,5-diiodothyronine had an activity close to that of thyroxine. 3/-5/-Diiodo-4(4/-hydroxyphenoxy)-3,5-diiodohippuric acid had very slight thyroxine-like activity.