PHYSIOLOGIC ACTIVITY OF TRIIODO- AND TETRAIODOTHYROACETIC ACID IN HUMAN MYXEDEMA*†

Abstract

The acetic acid derivatives of triiodothyronine and thyroxine were tested on patients with myxedema. When triiodothyroacetic acid was given daily in dosages less than 1.5 mg intravenously, there was a dissociation in the myxedema response, namely, little or no change in the BMR, a distinct drop in the level of serum cholesterol, an increase in the excretion of creatine in the urine, a return of the ecg pattern towards normal, an appreciable weight loss, and definite improvement in the clinical appearance. Failure to affect the BMR may be explained by the fact that a single intravenous dose of triiodothyroacetic acid or tetraiodo-thyroacetic acid produces a transient rise in the BMR over a period of 8-9 hours, with return to pre-treatment levels in 24 hours. A singel intravenous dose of thyroxine produces little or no response in the bassl metabolism during the first 24 hours. Large daily doses of the acetic acid derivatives, given to patients with myxedema, produce an accumulative effect on the BMR characteristic of thyroxine. Tetra-iodothyroacetic acid has about 1/15 the activity of l-thyroxine and triiodothyroacetic acid has 1/4 to 1/6 the activity of l-thyroxine.