ANTIGOITROGENIC AND CALORIGENIC ASSAY OF THYROGLOBULIN, DESICCATED THYROID ANDl-THYROXINE BY DIFFERENT ROUTES OF ADMINISTRATION IN RATS

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Abstract
By antigoitrogenic assay and assigning the value 100 to the activity of I-thyroxine Na when admn. subcut. the various prepns. and routes of admn. assayed as follows: (a) per [mu]g. "thyroxine" I: soluble thyroglobulin subcut. 349, denatured thyroglobulin Product "A" and desiccated thyroid products "B" and "C" orally 259-229, sol. thyroglobulin orally 183,I-thyroxine Na orally 34; (b) per [mu]g- total organic I: sol. thyroglobulin subcut. 95, products "A," "B," and "C" orally 76-68, sol. thyroglobulin orally 50 I-thyroxine Na orally 34. By calorigenic assay and assigning value of 100 to activity of I-thyroxine Na when admn. subcut. the activities were: (a) per ug. "thyroxine" I: sol. thyroglobulin subcut. 345, products "B" and "A" orally 89-74, sol. thyroglobulin orally 88, 1-thyroxine Na orally 26; (b) per [mu]g. total organic I: sol. thyroglobulin subcut. 96, product "B,"I-thyroxine Na; sol. thyroglobulin and product "A" each admn. orally 28-22. Soluble thyroglobulin was equally active calorigenically when admn. subcut., intraven., and intraperit. These observations on over 800 rats are interpreted as demonstration of the importance of biologic assay when comparing thyroxine and other iodinated thyronines with thyroid prepns. by same or different routes of admn.; confirmation of reports that the activity of thyroglobulin is considerably greater than can be accounted for by its chemically detd. "thyroxine" I or "thyroxine-like" content; evidence that rate of absorption does not explain the difference.