Conversion of Iodate to Iodide in Viva and in Vitro*

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 13rI 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 tidings 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.