Biliary Excretion and the Metabolism of Radioactive L-Thyroxine

¹ From the Sections of Biochemistry and Surgical Research, Mayo Clinic and Mayo Foundation, Rochester, Minnesota

Dogs excreted the same compounds in the urine after injections of radioactive thyroxine whether they were normal or had a biliary fistula or biliary obstruction. Dogs with biliary fistulas excreted more of the conjugate in the urine than did normal dogs. Dogs with biliary obstruction excreted the largest amounts of the conjugate and also showed increased levels of the conjugate in the blood. All the changes were minor, however, compared to those found after hepatectomy. No evidence was found for conversion of thyroxine to triiodothyronine or tetraiodothyroacetic acid, but the present studies would not exclude the possibility that these substances are rapidly transformed intermediates in the metabolism of thyroxine.