The Behavior of Labeled Iodocasein in Human Myxedema*

STUDIES of the distribution and transformation of calorigenic, iodine-containing substances have been handicapped by the fact that pharmacologic doses of material were usually required in order to obtain a concentration of iodine in tissue or body fluids sufficiently high to be measured satisfactorily by current chemical methods. The availability of radioiodine (I131) has made it possible to reinvestigate the metabolism of calorigenic iodine compounds in animals and man under physiologic conditions. Radioiodine can be incorporated into calorigenic materials so as to obtain biologically active compounds with high specific activity. This not only permits the use of physiologic amounts of material, but also permits determination of the distribution of the material and its derivatives with greater accuracy and sensitivity than was previously possible. In addition, radioiodine and substances containing it can, to some extent at least, be observed in vivo by means of a Geiger counter directed at various parts o...