THE METABOLISM OF 3 : 3′ :5′-TRIIODOTHYRONINE IN MAN*

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Abstract
1131-labeled 3:3[image]:5[image]-triiodothyronine was administered intravenously to 10 euthyroid hospital patients. Disappearance from the serum and accumulation in the urine were measured. 3:3[image]:5[image]-Triiodothyronine was rapidly degraded and its iodide appeared as free iodide in the serum. The mean serum half-time of the injected compound was of the order of thirty minutes. Within twenty-four hours, more than 50 per cent of the administered labeled iodine was usually eliminated in the urine. Practically all was free iodide. Only a slight amount was excreted as the parent compound. No intermediate degradation products were found in the blood or urine. The rapid metabolic degradation of 3:3[image]:5[image]-triiodo-thyronine makes improbable its existence as a naturally occurring thyroid hormone in man.