Relative Activities of l- and dl-Thyroxine

Abstract

We have compared the biological activities of l- and dl-thyroxine in rats receiving 4-methyl-2-thiouracil by determining the ‘thyroxine requirement’ as defined by Griesbach and Purves¹. This method consists of finding the amount of thyroxine which will prevent the pituitary basophil changes, resulting from the thyroxine deficiency produced by the blockage of thyroxine synthesis by the methyl thiouracil. The thyroxine samples used were: (1) l-thyroxine presented by Dr. C. R. Harington, and prepared by the iodination of l-di-iodothyronine²; (2) l-thyroxine presented by Dr. E. P. Reineke, and prepared by, acid hydrolysis of iodinated casein³; (3) l-thyroxine prepared in this laboratory from l-di-iodotyrosine by the method of Harington and Pitt Rivers⁴; (4) dl-thyroxine presented by Burroughs Wellcome and Co., and prepared by alkaline hydrolysis of thyroid substance.