Patients occasionally have thyroid enlargement either because of goitrogenic substances in their diet or because of drugs that have been given for other conditions (53). Feeding rats with minute doses of a natural goitrogen over many months will result in the same kind of response. Similar results have been obtained using combinations of the three most prevalent goitrogens contained in cabbage. The explanation for the effect of such substances is that the goitrogen is much more effective at the level of iodothyronine synthesis than at earlier steps in hormone production such as iodide trapping. Thus, the RAIU may be high, but with a block in hormone synthesis the stage would be set for the production of a goiter. This possibility remains to be proved in humans, but one might surmise that, if true, it would operate most effectively in a situation of borderline iodine supply. The goitrogen thiocyanate potentiates the effect of severe iodine deficiency in endemic areas of Africa (53).
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