Wolf Chaikoff effect -

Ans. is 'a' i.e., Excess iodine intake causes hypothyroidism o The effect of iodine on thyroid function is quite complex.o The most obvious effect of administering a high dose of iodine is a decrease in the release ofthyroid hormones.This effect is very prompt and is quicker than the action of antithyroid drugs.Hence, iodine ivas used in the treatment ofthyrotoxicosis and is still used in preparing patients for thyroid surgery.o However, the effect is not observed on repeated administration of iodine a phenomenon called "iodine escape" the cause of which is not understood.o Administration of iodine has a triphasic response on the organification of iodine.o Inhally there is a brief increase in iodine organification.o Shortly therafter, the high intrathyroid iodide concentration inhibits iodine organification an effect known as wolff-ch iakoffeffect.o Prolonged adminstration of high dose of iodine, however produces an escape from the wolfchiakoff effect (not to be confused with iodine escape) due to autoregulation of iodine uptake by the thyroid.When iodine organification decreases due to the wolfchiakoff effect it results in inthrathyroid accumulation of iodine.The rise in intrathyroid iodide, reduces the iodine uptake (due to autoregulation).The intrathyroid iodide therefore reduces and with it the wolf-chiakoff effect subsides.If however the autoregulation is absent due to thyroid dysfuntion the wolf-chiakoff effect will persist and keep the iodine organification suppressed.Increased concentrationof plasma iodide|Increased uptake ofiodide by thyroid|iIncreased conceniraionof intrathyroid iodine|Increased organificationof iodine|Increased synthesis of T, and T4|Increased release of F, and T,