The Metabolism of Triiodothyronine in Graves’ Disease*†

Chromatographically pure triiodothyronine (T3) labeled with I131 was given to 12 patients with current or recent hyperthyroidism of Graves′ disease (4 still hyperthyroid, 5 euthyroid, and 3 hypothyroid) and to 8 normal controls. The fate of T3 in these patients was observed by quantitative chromatography carried out on serial samples of blood and urine. In addition, radioactivity over the liver was measured. The behavior of the injected T3 in the patients with Graves′ disease, regardless of their metabolic state, was quite different from that in the controls. During the first forty-eight hours, the labeled T3 remained in the serum of patients with Graves′ disease in greater amounts than in the controls. More radioactivity was excreted in the urine by patients with Graves′ disease than by the controls; this difference was largely owing to free iodide. There was also slightly more unaltered T3 in the urine of patients with Graves′ disease. Measurement of radioactivity over the liver revealed maximal concentration within a few minutes after injection of T3, followed by a marked fall. A subsequent secondary rise occurred in the patients with Graves′ disease, but not in the controls. The liver/serum-T3 ratio indicated that, considering the level of T3 in serum, the livers of the patients with Graves′ disease held less radioactivity than did the livers of the normal subjects.