| Iodine is also a necessary element for human being.Iodine deficiency disease (IDD) is a serious disease and many countries of the world have been take steps to control it including China.Our government has established the law of universal salt iodized (USI) from 1996.In order to acknowledge the situation of thyroid disease in population,we have taken an cross-section study in three different iodine intake areas. The results show the increasing incidence of hypothyroidism and thyroid carcinoma.The mechanism of iodine-induced hypothyroidism is a hot topic in the world recently.We found 121 cases of subclinical hypothyroidism and 70% thyroid function disorder of them may be related with the increasing iodine intake,but the role is still not known.Iodine, an essential component of thyroid hormones,is concentrated by the thyroid gland 20-40fold with respect to the iodide concentration in plasma.Active iodide uptake across the basolateral membrane of the thyroid follicular cell is mediated by the sodium/iodide symporter (NIS).TSH regulates every step of thyroid iodide metabolism.Iodine uptake has been demonstrated to be under the control of TSH.The changes of iodine intake can also have effects on the expression of NIS.A high iodine intake can decrease the level of NIS protein and may cause an abnormal transportation of iodine.So does it take part in the development of hypothyroidism.In the present study we compared the the relationship between TSH and FT3, FT4 and other factors in normal in three different iodine intake areas.Moreover, we observed the effects of high iodine intake on thyroid function and the expression of NIS in SD rats.We hope to explain the non-autoimmune mechanism of iodine-induced hypothyroidism.Materials and Methods1. Epidemical studyIn three areas with deficient, moderate, and excess iodine intakes (Panshan, Zhangwu,and Huanghua respectively), we selected residents randomly, tested their serum TSH (IMMULITE, the third generation assay) , TPOAb, TGAb, TG, FT3, FT4 and urinary iodine, and scan their thyroids with ultrasonic scanning. Those with a history of thyroid diseases, familial thyroid diseases, or with positive TPOAb, TGAb or abnormal levels TG or abnormal thyroid ultrasonic scanning were excluded. Then 650, 728 and 550 subjects from three areas were determined as normal subjects for the further study on the relationship between serum TSH and iodine intakes and its related influencing factors such as sex, age and TG.2. AnimalsSprague Dawley (SD) rats (160g-220g) were used in the experiments and were maintained on lab diet from the animal department of China Medical University.The rats were divided into 4 groups: control (given distilled water) and three different iodine treatment water (given 600g/L , 1200g/L and 2000g/L iodized distill water respectively).Thyroid gland from rat were removed immediately,snap frozen and stored at -70 C for measurements.Other thyroid glands were fixed in 4% PFA for 3 days and then removed to 30% sucrose for another 3 days for preparing the ice section.Blood from rats were collected and the serum was frozen for later measurement of serum TSH, FT3, FT4. Fasting urinary sample from rats were collected before the killed day and stored at -20 C.3. TSH, FT3, FT4, TPOAb, TGAb, TG of population was all determined by chemiluminescent immunoassay kits (IMMULITE, Diagnostic Products Corporation; USA ) ; Urinary iodine and tissue iodine concentration were determined using the Ce/As method after digestion by alkine ashing.Serum TT3, TT4 of rats were measured by RIA ( DPC,USA ) and TSH was by IRMA ( DPC,USA ) .4. Immunohistochemical stainingImmunohistochemical staining was performed on frozen tissue section ( 7m ).The expression of NIS protein was studied by SP method of immunohistochemistry in different period of iodine treatments.5. Western BlotTotal protein from thyroid gland was extracted.Homogenization was perform using amechanical device and centrifuged at 15,000 g...
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