Absorption and excretion of the mono-sodium salt of thyroxine labelled with radioactive iodine

Publisher Website
Google Scholar
Abstract
Single doses of the mono-sodium salt of DL-thyroxine labelled with radioactive iodine in the 3[image]- and 5 - positions were admd. either in soln. or as a suspension, orally or subcut., to rats; the subsequent excretion in urine and feces was detd. over a 4-day period. The final distribution of radioactive iodine in the carcass was studied. Thyroxine in soln. and as a suspension is metabolized in the same way and is absorbed from the gastro-intestinal tract. Radioactive iodine in the urine was present almost entirely as iodide; that in the feces was present in both organic and inorganic forms. Single physiol. doses of labelled mono-sodium DL-thyroxine were admd. intraduodenally, subcut., or intraven. to anesthetized cats; the subsequent radioactive iodine blood levels and urinary and biliary excretion rates were measured over a 6-hr. period. Distribution of labelled thyroxine and its breakdown products was studied. For all routes of admn., the amt. of radioactive iodine in the bile was related to the blood concns.; that in the bile was present in approx. equal proportions as thyroxine and iodide. Appreciable amts. of I were secreted into the stomach. Rat thyroids, in contrast to cat thyroids, contained appreciable quantities of radioactive I; very little of the radioactive I in the rat thyroids was present as thyroxine.