Biliary Excretion and Metabolism of Radioactive L-Triiodothyronine

Dogs with biliary fistulas metabolized triiodothyronine rapidly to inorganic iodide, as did normal dogs. The amount and distribution of I131 compounds in the urine were not greatly altered by withdrawal of the bile, which contained about one-fourth of the I131 administered. Dogs with biliary obstruction excreted more of compounds b, iodide and the conjugate than normal dogs. The absence of enterohepatic circulation of metabolic products of triiodothyronine usually excreted in the bile did not appreciably alter the products or rate of metabolism of triiodothyronine. Some of the same products of triiodothyronine appeared in both bile and urine but there was very little inorganic iodide in the bile and much more of the glucuronide and the water-soluble, column residual fraction.