Sites of Gastrointestinal-Blood Passage of Iodide and Thyroxine in Young Cattle

A nonabsorbed marker technique (Ce TM) has been used to determine the net absorption snd endogenous secretion of orally administered radioiodide in young aninmls. The rumen appears to be a major site of absorption and the abomasum a major site of endogenous secretion. Net absorption occurred from the second section of the small intestine throughout the remainder of the tract. Following intravenous administration of labelled NaI one-half hour prior to slaughter, a significantly greater concentration of radioactivity was found in the abomasum than in the first part of the small intestine. The reverse was true for iodine from 1-thyroxine.