Metabolism of Oral Iodide and 3,5-Diiodosalicylic Acid in the Pregnant Cow

Tbree near-term pregnant cows were studied. Two of these were each given simultaneous oral tracer doses of I ~ as 3.5diiodosalicylic acid (DI~S) and I ~. The third cow was given both radioisotopes as iodide. One was sacrificed at 144 and two at 168 hr after dosage. For the animals given DI~:~S, the percentage of dose of each isotope excreted (urinary and fecal) in 144 hr was 11~, 83.6%; F ~, 43.1%. The average percentage of the dose in the thyroids at the time of sacrifice was I ~1 in the maternal thyroid, 2.3%; I ~ in the fetal thyroid, 2.1%; I ~ in the maternal thyroid, 18.0%; I ~5 in the fetal thyroid, 15.9%. Iodine fed as DIS was not as available to either maternal or fetal thyroid and did not cross the placenta as readily as iodine fed as iodide. The animal given both isotopes as iodide exhibited no differences between the two isotopes in excretion or in concentrations in the various tissues.