Conversion of Iodate to Iodide in Vivo and in Vitro
Alvin Taurog 1, Earl M. Howells 1, and Harold I. Nachimson 1
From the
1 From the Department of Pharmacology, The University of Texas Southwestern Medical School, Dallas, Texas 75235
Iodate is almost immediately reduced to iodide following its intravenous administration to rats or rabbits. Even when it is given in relatively large doses, reduction is complete within 2 to 3 min. Following oral administration also, radioiodate is so rapidly transformed to radioiodide that 2-hour thyroid 131I uptakes in rats that received radioiodate by stomach tube were not significantly different from those of rats that received radioiodide by the same route. These findings support the view that iodate can substitute for iodide in all instances in which supplementary iodine is required for human or animal nutrition.
Whole blood, resuspended washed red cells, and various tissue extracts reduce iodate to iodide very rapidly in vitro. However, plasma is much less effective than whole blood in reducing iodate.
Iodate is rapidly reduced by glutathione at pH 7.4, but not by a number of other biological reducing agents. The stoichiometry of the reaction between GSH and iodate indicates that the reaction proceeds as follows.
6 GSH + IO3- 
3 G—S—S—G + I- + 3 H2O
Because red cells and most tissues contain a fairly high concentration of GSH, it might appear that GSH is the active agent in blood and tissues responsible for reducing iodate. However, the iodate-reducing capacity of red cells and of tissue extracts far exceeds their potential GSH content, and it is suggested that —SH groups in hemoglobin and in other proteins may also be oxidized by iodate.
Results of incubations carried out at 0° suggest that iodate reduction in blood is not enzymatic, at least for iodate levels below 1 x 10-3 m.
Submitted on March 8, 1966
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