INHIBITION BY PROPYLTHIOURACIL OF THE EXTRATHYROIDAL FORMATION OF TRIIODOTHYRONINE FROM THYROXINE

Abstract

Thyroidectomized rats were injected daily with 1.9 μg/100 g body weight of ¹²⁵I-labelled L-thyroxine (T*₄). When isotopic equilibrium was attained, half the experimental group was injected twice with 2 mg of propylthiouracil at a 24 h interval. Animals were killed 7 h after the last dose and the amounts of T*₄ and labelled iodide and T₃ in peripheral tissues were determined after extraction and paper chromatography. The amount of T₃ derived from T₄ is significantly lower in tissues of rats receiving PTU.