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

Abstract

Three near-term pregnant cows were studied. Two of these were each given simultaneous oral tracer doses of I131 as 3.5-diiodosalicylic acid (DI131S) and I125. 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 DI131S, the percentage of dose of each isotope excreted (urinary and fecal) in 144 hr was I131, 83.6%; I125, 43.1%. The average percentage of the dose in the thyroids at the time of sacrifice was I131 in the maternal thyroid, 2.3%; I131 in the fetal a thyroid, 2.1%; I125 in the maternal thyroid, 18.0%; I125 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.