A STUDY OF THE ABSORPTION CHARACTERISTICS OF IODINE-131 LABELED IODINATED CASEIN IN SOME MAMMALS1

Abstract

Iodocasein labeled with I131 was administered to sheep and rats by various routes. When labeled iodocasein was administered intraven. in sheep only about 10% of the radioactivity present immediately after injn. could be detected in the blood 7 hrs. later. Greater levels of blood radioactivity in sheep were obtained when the material was administered orally than when it was introduced directly into the ventral rumen sac or the small intestine. There was very little absorption from the cecum. High levels of blood radioactivity were maintained for at least 48 hrs. following admn. Following oral admn. of labeled iodocasein approx. 10% of the plasma radioactivity appeared to be in the thyroxine fraction and 39% in the diiodotyrosine-inorganic I fraction. 50% of the activity of the material was not extractable with butyl alcohol, indicating that I131 was present in some other form. The presence of thyroxine was established by the carrier technic. Similar results were obtained with rats. The skimmilk of ewes given labeled iodocasein orally showed considerable radioactivity. 80% of the iodine compounds present in the skimmed milk was extractable with butyl alcohol, 30% was found in the thyroxine fraction, and 50% in the diiodotyrosine-inorganic I fraction.