Changes of the Radioactive Iodine Uptake and in the Iodoamino Acids Pattern of Thyroid in Rats in the Course of Advancement of Iodine Deficiency

Hourly changes of 131I uptake and the changes in several indices of thyroid at different time intervals after beginning of an iodine deficient diet with or without propylthiouracil were determined. An amino acid mixture was used as the protein source in the present experiments. The magnitude of iodine uptake and the ratio of monoiodotyrosine to diiodotyrosine increased according to the length of time on low iodine diet. The earlier appearance and more enlargement of peak of the ratio of monoiodotyrosine to diiodotyrosine in rats treated with small dose of propylthiouracil than in those untreated suggested that propylthiouracil might also bring about the lack of iodine by inhibiting the iodination at substrate level.