Objective   To make a comparative study on effect of iodine and iodide excess on thyroid function and morphology in Wistar rats without iodine deficiency.

  Methods   Serum TSH was measurd with solid phase radioimmunoassay(IRMA)and TT₄, TT₃, rT₃ and thyroid TT₄ with radioimmunoassay(RIA).Cer-Arsenite colormetric method were used to measure median urinary iodine(MUI).Thyroid morphological changes were observed under optical and electronic microscope.Metamorph imaging system was used to measure the height of thyrocytes and the areas of thyroid follicular cavities.

  Results   Intake of 840μg/L iodine for 90 days could increase serum TSH without significant difference; Serum TT₄ values were markeldy higher than those in DDW group, P < 0.05.Serum TT₄ was not significanlty different from the groups of iodine and iodide with the same dosage.In the iodine excess groups, the following morphological changes can be seen under microscope; increase of the area of follicular cavity, flat follicular cells, darker nucleus staining, broken and combined follicles, formation of giant follicles, reduction of capillary, enlargement of endoplasmic reticulum of thyroid follicular cells, increase of the number of secondary lysosomes, chromatin condensation, cytoplasmic vesicularisation, reduction of microvilli.When iodine intake was > 840μg/L for 90 days, the height of thyrocytes was makedly lower than those of DDW group and the areas of thyroid follicular cavities were markedly larger than those of DDW groupP < 0.05.

  Conclusion   Iodine intake of 840μg/L for 90 days may increase serum TT₄ and inhibit the function of most of thyroid follicular cell.No significant difference was found between the effect of iodine and iodide excess on thyroid.