3,3′,5′-Triiodothyronine and 3,37′-Diiodothyronine: Partially Deiodinated Intermediates in the Metabolism of the Thyroid Hormones

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Abstract
3,3′,5′-Triiodothyronine (T3) and 3,3′-diiodothyronine (T2) labeled with I131 in the 3′ or 5′ position have been administered to normal dogs, to dogs with biliary fistulas, to dogs after total hepatectomy, and to rats with biliary fistulas. Both of these partially deiodinated derivatives of thyroxine (T4) were metabolized rapidly by dogs and rats, and a variety of products were formed. In the dog, stepwise deiodination led to the formation of 3,3′T2 and 3′-monoiodothyronine (Tl) from 3,3′,5′T3, and of 3′Tl from 3,3′T2; these products were found chiefly in conjugated form in bile or, after hepatectomy, in urine. Deiodination from the beta ring and excretion of radioactive iodide in the urine occurred more slowly from 3,3′,5′T3 and 3,3′T2 than from T4 or 3, 5, 3′T3 in the dog. Deiodination from the beta ring of all these substances was greatly diminished after total hepatectomy. Deiodination from the beta ring of these compounds was fairly rapid in the rat with a biliary fistula, and large amounts of radioactive iodide were excreted in the urine.