Acute Wolff—Chaikoff effect

Acute excess iodine ingestion has long been known to result in a transient decrease in iodine organification, termed the Wolff—Chaikoff effect (Wolff and Chaikoff, 1948). With sustained excess iodine exposure, however, most individuals thyroid glands escape from acute Wolff— Chaikoff effect, despite continued excess iodine exposure, and resume synthesis of normal amounts of T4 and T3. The mechanism responsible for this escape or adaptation to the iodine load probably involves a decrease in the Na /H symporter protein, resulting in a decrease in thyroid iodide content (Eng et ai, 1999). In some individuals... 

It is well known that thyroidal radioiodine uptakes decrease when dietary iodide increases and when the dose of iodide reaches a certain levels, the administration of perchlorate and thiocyanate discharges acutely administered tracer radioactive iodide from the thyroid, indicating that organification of intrathyroidal iodide is inhibited. However, there is no evidence that thyroidal organic iodide uptake is actually decreased by iodide. There is no evidence for an acute Wolff Chaikoff effects in normal human thyroids. 

What we would like to know more precisely is the duration of the preventive effect of a single injection of iodized oil in women on the incidence of cretinism in the offspring. More information is also needed on the possible adverse effects of iodized oil. The possibility that this therapy could induce a Wolff-Chaikoff effect in the fetus has been raised (85) but never conclusively demonstrated. The hypothesis has also been proposed (86), but never confirmed, that an acute increase in iodine supply could trigger thyroid autoimmunity. 

Acute inhibitory effects of excess iodide was first demonstrated in vitro in 1944 by Morton, Chaikoff and Rosenfeld (i) and in vivo in 1948 by Wolff and Chaikoff (Wolff-Chaikoff effect) (2). As shown in Fig. 1, they injected 100 pg of iodide per rat with a tracer dose of and determined pleisma inorganic iodide concentration, total thyroidal iodine uptake and thyroidal organic iodine uptake until 50 hours after the injection of iodide. Thyroidal organic iodine... 

However, in 1949, the same authors have shown that the acute inhibitory effect is transient. When a high level of plasma iodide was maintained by the administration of repeated doses, the inhibitory effects disappeared and organification of intrathyroidal iodide increased This is the so called escape from Wolff-Chaikoff effect. 

Wolfi ChaikofF effect. Raben (1949) showed that this effect was dependent on the amount of iodine in the thyroid gland and not on the plasma concentration of iodine. The acute inhibitory effect of iodine overload is usually transient. Intrathyroidal iodine decreases within a few days despite a high plasma iodine concentration and thyroid hormone synthesis then returns to the previous level. This resumption of the organification of iodine is known as the escape phenomenon (Wolff, 1969), and it means that hypothyroidism will not develop in most individuals despite excessive iodine intake. 

---