Antigoitrogenic and Calorigenic Activities of Thyroxine Analogues in Rats¹

The relative potencies of more than forty thyroxinc analogues and a soluble hog thyroglobulin extract were established in parallel goiter-prevention and calorigenic assays against the same thyroxine standard. By both methods of assay twelve of the preparations had activities ranging from 5% to 800% of that of thyroxine. The activities, if any, of the remaining analogues were less than 3% of that of the standard. Analysis of area-under-curve and speed of response in calorigenic assays indicated that all the active analogues and soluble thyroglobulin were qualitatively similar with respect to this parameter of thyromimetic function in normal adult male rats. Thyroglobulin was characteristically more active than expected when its potency, relative to thyroxine, was calculated on the assumption that its thyronine-bound iodine, as determined by the Blau, 1935, procedure, was in the form of thyroxine.