METABOLIC FATE OF RADIOACTIVE THYROID HORMONES IN NORMAL AND PROPYLTHIOURACIL-TREATED RATS1

Abstract

Wistar rats treated with propylthiouracil plus dried thyroid powder for 10 months, and normal control animals, were injected with thyroxine or triiodothyronine labeled with Il31. After 24 hours, their thyroid, liver, skeletal muscle and pituitary tissues were extracted, and the amounts and identities of free radioactive substances were determined. In all groups, skeletal muscle and liver were found to contain appreciable amounts of the respective labeled thyroid hormones administered. Following the injection of labeled thyroxine, triiodothyronine was one of the principal radioactive substances identified in these tissues. Similar findings were obtained in the thyroid glands of the rats treated with propylthiouracil and thyroid powder, whereas the thyroid glands of the normal rats showed radioactivity almost exclusively in the inorganic iodide fraction. No appreciable radioactivity could be detected in the pituitary glands.