¹ From the Department of Medicine, University of Colorado Medical School, Denver. Dr. Zizza was a Research Fellow of the American Heart Association during this work.
² From the Department of Medicine, University of Colorado Medical School, Denver.

When I¹³¹-albumin is given intravenously to rabbits, the radioactive breakdown products that are released into the plasma and urine can be extracted into acetone. Paper chromatography and paper electrophoresis show that about 80 per cent of these are I¹³¹-iodide and the remainder are organic I¹³¹-iodine compounds. When I¹³¹-iodide is given to rabbits taking iodide in their drinking water, the radioactivity is quantitatively excreted, without being accumulated in the tissues and without becoming attached to the plasma proteins. The rate of excretion can be defined by a first order rate process with a rate constant, a, ranging between 1 and 3day^-1. The organic I¹³¹-iodine compounds liberated during the metabolism of I¹³¹-albumin can be closely matched by a mixture of the organic I¹³¹-iodine compounds liberated during the metabolism of I¹³¹-monoiodotyrosine, I¹³¹-diiodotyrosine, and the amino acids released by digestion from I¹³¹-albumin. These organic I¹³¹-iodine compounds are not accumulated in the body and their radioactivity does not become attached to the plasma proteins. Their radioactivity is excreted as fast or faster than that of I¹³¹-iodide, and, to a satisfactory approximation, the same equations describing the excretion of I¹³¹-iodide with the same constants may be used for describing the excretion of the organic I¹³¹-iodine. These results permit improved estimates of the distribution and catabolism of I¹³¹-albumin.

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