Conjugation of Thyroid Hormones and Analogs by the Gunn Rat

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Abstract
The metabolism of the thyroid hormones and analogs, particularly the conjugation of these substances with glucuronic acid, has been studied in the homozygous Gunn rat, which is jaundiced due to inability to conjugate bilirubin with glucuronic acid. The effect of butyl-hydroxydiiodobenzoate (BHDB) on the metabolism of these substances also has been studied in the Gunn rat, because this drug produces a great increase in the amount of thyroxine (T4) glucuronide excreted in bile by the normal rat. I131-labeled L-thyroxine (T4), 3,5,3[image]-triiodothyronine (T3), tetraiodothyroacetic acid (tetrac), 3,5,3)-triiodothyroacetic acid (triac), 3[image],3[image],5-triiodothyronine (T3[image]) and 3-3-diiodothyronine (T2) were given by single intravenous injection to unanesthetized Gunn and normal rats with biliary fistulas. Large variations were found in the ability of the Gunn rats to conjugate these different iodine compounds. Conjugation of T4 with glucuronic acid was greatly impaired in the Gunn rat and very little tetrac was conjugated by these rats. They conjugated T3 more rapidly than T4 and triac with glucuronic acid much more rapidly than T4. After the administration of BHDB, twice as much T4 was conjugated by the Gunn rat, and much larger increases were found in the conjugation of tetrac and triac. Conjugation of T3 with sulfate was increased.

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