Determination of Thyroxine and Triiodothyronine in Commercial Preparations of Desiccated Thyroid and Thyroid Extract

Abstract

The thyroxine (T4) and triiodothyronine (T3) contents of commercial preparations of desiccated thyroid and thyroid extract have been determined by paper chromatography of butanol extracts of enzymic hydrolysates. Whereas the molar ratio T4:T3 was approximately 2.0 in desiccated thyroid, it was approximately 1.0 in thyroid extract. A calculation of the relative theoretic contribution of biologic activity by T4 and T3 was made on the basis of T3 possessing 4 times the activity of T4 on a weight basis. These calculations indicated that T3 contributes 1.5 and 3.5 times as much of the biologic activity as T4 in desiccated thyroid and thyroid extract, respectively. These findings offer a plausible explanation for the failure of thyroid extract to effect an increase in serum PBI (protein-bound iodine) in myxedema patients showing good clinical response to this therapy. Analyses of 2 clinically ineffective lots of desiccated thyroid revealed low levels of T4 and T3 and an increased amount of monoiodotyrosine.