COMPARATIVE PARENTERAL THYROXINE-LIKE ACTIVITY OF NATURAL AND SYNTHETIC THYROPROTEINS STUDIED WITH THE GOITER PREVENTION METHOD1

Abstract
Rats were fed 0.3% thiouracil in their diet and were given parenteral injns. of a DL-thyroxine, of desiccated thyroid, or of iodinated casein. After 15 days the thyroid glands were removed and weighed, the thyroxine-like activity of the prepns. being detd. from the degree of prevention of thiour-acil goiters. Desiccated thyroid showed a 2-fold greater activity than could be attributed to the L-thyroxine that it contained. Iodinated casein not only did not show this excess thyroxine-like potency, but exhibited less activity in terms of its chemically detd. L-thyroxine content.