Experimental Study Of Iodine Excess On The Morphology Of TSH Cells In Rats

ObjectivesTo observe the morphology change of TSH cells in Wistar rats after fed with different concentration iodine diet for 12 and 24 weeks, then to study the mechanism of the effect of iodine excess on pituitary-thyroid axis. MethodsOne month Wistar rats weighted 80~100gram, half of male and female, were divided into six groups randomly: low iodine group(LI group), normal iodine groups(NI group), 5,10,50 and 100 times of normal iodine group respectively(5HI, 10HI,50HI and 100HI group). The animals of LI group were fed with diet derived from endemic goiter area containing iodine of 50 u g/kg, and drank deionized water. The other rats were fed with standard diet containing iodine of 300 u g/kg. Tap water containing iodine of 5 u g/L,25 u g/L,50 u g/L and 250 u g/L were drank by the rats of NI,5HI,50HI and 100HI groups respectively. All rats were sacrificed at 12 and 24 weeks respectively, and randomly selected 10 of them from each group for study. TSH cells of selected rats were determined by immunohistochemistry, and analyzed the change of volume density (Vv)and numerical density on area (Na) based on the theory of stereology. In addition , two pituitaries of each group rats were observed by the electron microscope at the experimental time of 12 weeks. Results1.Compared with NI group rats, the weight of pituitary in LI group were increasing following the time of iodine deficiency. The change in weight of pituitary was insignificant in all high iodine groups, but showing a tendency ofincreasing with different concentration of iodine.2.Most TSH cells assembled in the central area of adenohypophysis. The numberof TSH cells stained with TSH by immunohistologychenistry was increasingwith iodine excess diet.3. Vv and Na of TSH cells in iodine excess groups rats were lower than LI groupat 12 weeks. Compared with NI groups animals, Vv and Na of TSH cells in5HI,10HI and 50HI groups animals changed insignificantly but higher in 100HIgroup. Compared with LI group rats ,Vv and Na of TSH cells in iodine excessgroups were lower at 24 weeks and presented increasing tendency with iodineexcess concentration, while Vv and Na of TSH cells in 50HI and 100HI groups ishigher than that of NI group rats.4.The ultrastructure of TSH cells were studied by electron microscope at 12weeks, and our findings were: The change of TSH cell in 10HI group rats wasslightly swelling. The structure of TSH cells in 50HI group rats was damaged butthe function was in the condition of compensation. The function anabolism andsecretion of TSH cells in 100HI group rats was unactive.Conclusions1 .There isn't obviously changed in the structure and function of TSH cells in 5HIand 10HI groups rats, which showed that thyroid can maintain it's normalfunction under such condition.2.TSH cells in 50HI group rats is active , which partly compromises the restraintof iodine excess on thyroid.3.It's poor that thyroid responses to TSH cells and thyroid can not maintain it'snormal function through autoregulation in 100HI group rats.4.TSH cells can be damaged for rats when long-term drank water containing iodine over 250ug/L.