The fractionation of urinary iodine. 2. Metabolites excreted during treatment of carcinoma of the thyroid

The nature and rates of excretion of radioactive breakdown products of I131-albumin in the rabbit

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.

The disposition of SK&F L-94901, a selective thyromimetic in rat, dog and cynomolgus monkey

SK&F L-94901 is a novel thyromimetic, structurally related to thyroxine. The absorption, distribution, excretion and metabolism of radiochemically labelled [14C]-SK&F L-94901 has been investigated in the rat, dog and cynomolgus monkey. Oral absorption from solution was low or moderate in all three species. The compound was widely distributed and rapidly excreted, although traces of radioactivity were still evident in some tissues at 7 days post-dose, particularly in the kidney where radioactivity was located in an area approximating to the corticomedullary junction. Elimination of [14C]-SK&F L-94901 was both metabolic, mediated by the liver, and renal. The major metabolic routes of elimination were via oxidative deamination to lactate and acetate derivatives.

Determination of iodide in metabolic studies of 125I-labeled compounds

Methods capable of measuring inorganic iodide in the presence of other highly polar metabolites were developed in support of studies concerning the metabolism of 125I-labeled compounds. The methods included separation of iodine on a weakly basic resin paper followed by gamma-counting, methyl iodide exchange, and reverse isotopic dilution.