Effects Of Iodine Excess On The Morphology Of TSH Cells And Thymus In Postnatal Rats

ObjectivesTo observe the morphology change of TSH cells in postnatal Wistar rats of 20 days and 60 days fed with different concentration iodine diet , then to study mechanism of the effect of iodine excess on pituitary-thyroid axis in postnatal rats. MethodsWistar rats,one month after stopping laction ,were divided into six groups randomly: low iodine group(LI group), normal iodine group(NI group), 5,10,50 and 100 times of normal iodine group respectively(5HI, 10HI, 50HI and 100HI group). The rats of LI group were fed with diet derived from endemic goiter area containing iodine of less than 50 μ g/kg, and drank deionized water. The other rats were fed with standard diet containing iodine of 300 μ g/kg.The rats of NI group drank tap water. Tap water containing iodine of 820 μ g/L,1845 μ g/L,10045 μ g/L and 20295 μ g/L were drunk by the rats of 5HL10HL50HI and 100HI groups respectively. After three months, the female and male rats were mated by 1:1 and produced postnatal rats.The feeding of postnatal rats was the same as that of parental rats. When the postnatal rats were 20 days and 60 days , we measured the relative weights of pituitary and analyzed volume density (Vv) and numerical density(NA) on area of TSH cells. We also measured the relative weights of thyroids and the number of the strong positive TSH cells of the 60-day postnatal rats . Results 1. Compared with NI group rats, the change in the relative weight of pituitary wasinsignificant in all iodine excess groups and LI group in 20-day and 60-day postnatal rats. The change in the relative weight of thyroid was also insignificant in all iodine excess groups in 60-day postnatal rats ,but the relative weight of thyroid of LI group was higher than that of NI group.2. Most TSH cells assembled in the central area of adenohypophysis. The number of TSH cells was increasing with iodine excess diet.3. Vv and Na of TSH cells in LI group were higher than those in NI group in 20-day and 60-day postnatal rats. Compared with NI group ,Vv of TSH cells in 5HI ,10HI and 50HI groups changed insignificantly while Vv of TSH cells in 100HI group was higher than that in NI group and Na of TSH cells in all iodine excess groups did not change in 20-day postnatal rats. Vv and Na of TSH cells in 5HI and 10HI groups changed insignificantly while Vv and Na of TSH cells in 50HI and 100HI groups were higher than those in NI group in 60-day postnatal rats.4. The number of the strong positive TSH cells in 50HI and 100HI groups is higherthan that in NI group in the 60-day postnatal rats . Conclusions1. In 20-day postnatal rats, Vv of TSH cells in 100HI group is higher than that in NI group.2. In 60-day postnatal rats, iodine excess did not induce goiter though Vv and Na of TSH cells and the number of the strong positive TSH cells in 50HI and 100HI groups are higher than those in NI group.3. Thyroid is resistance to iodine excess in 60-day postnatal rats.