Figure 1.

The Wolff-Chaikoff Effect.

Panel A shows a propsed mechanism of the acute Wolff-Chaikoff effect. During the the first day of iodine exposure, the sodium-iodide symporter transports the excess iodine into the thyroid, resulting in transient inhibition of thyroid peroxidase (TPO) and a decrease in thyroid hormone synthesis. Panel B shows the mechanism that turns off the acute Wolff-Chaikoff effect: a dramatic decrease in sodium-iodide symporter expression results in decreased iodine transport and the subsequent resumption of thyroid hormone synthesis. DIT denotes diiodotyrosine, I iodide, MIT monolodotyrosline, T₃ triiodothyronine, and T₄ thyroxine. Reprinted from P. Pramyothin et al: Clinical problem-solving. A hidden solution. N Engl J Med. 2011;365:2123–2127 (26), with permission. © Massachusetts Medical Society.