Abstract:Objective To study the morphological and functional alterations of the thyroid gland in the second filial generation (F2) of Balb/c mice subjected to different levels of iodine intake. MethodsThe mice were randomly divided into five groups［less iodine group (LI), normal iodine group (NI), 5-fold excessive iodine group (5HI), 10-fold excessive iodine group (10HI), and 50-fold excessive iodine group (50HI)］ and given drinking water containing iodine in different concentrations ［daily intake<0.25 μg (LI), 1.5 μg (NI), 7.5 μg (5HI), 15 μg (10HI), 75 μg(50HI)］. After three months, the mice were mated and their 20-day and 40-day old second filial generations were observed. Stereological parameters including the thickness of the epithelial layer (L), the area of the follicle (SA), the area of follicular lumen (SB), and the ratio of follicular lumen and follicle volume VA) were measured using a photo analytic system to provide a basis for the quantitative evaluation of thyroid gland changes. ResultsThe serum thyroxin T4 level in the 20-day old and 40-day old F2 mice of the LI and 50 HI groups were significantly lower than the normal control group. Histopathological examination revealed that in the NI group, the thyroid gland follicles were of median size, and the most follicular epithelium consisted of a single-layer of cuboidal epithelial cells. In the LI group, there was apparent follicular hyperplasia, and the epithelium was columnar and stratified. In the 50HI group, the epithelium was more flat than that in the NI group, and plenty of colloid was accumulated in the follicular lumen. Assessment of the stereological parameter showed that in the LI group, L and SA were increased, VA was decreased. The data of the 5HI and 10HI groups were similar to those of the NI group. In the 50HI group, L was significantly decreased, and SA, SB and VA were significantly increased.ConclusionsBoth iodine deficiency and excess may cause hypothyroidism in the second filial generation mice. Iodine deficiency produces apparent follicular hyperplasia goiter, and long-term excessive iodine intake may result in colloid cumulative goiter, but the enlargement of thyroid by iodine excess is much less than that by iodine deficiency．The second filial generation mice have a high tolerance of excessive iodine. Obvious morphological changes often occur when the iodine intake excess reaches 50-fold higher than that in normal mice.