Effect Of Chronic Iodine Excess On Thyroid Anti-Oxidation Of Wistar Rats

To investigate the effect of chronic iodine excess on thyroid oxidative injury and antioxidation ability and thyroid function of Wistar rats fed with iodine deficient diet and normal diet originally. In order to ensure supplied iodine concentration being in the experimentation objectives, urinary iodine was inspected.Methods1. Group and treatment of experimental animals (1)Iodine deficient animal: 160 Wistar rats with 4 weeks old were fed with iodine deficient diet and double distilled water for three months to made iodine deficient goitrous model. Then 10 rats were killed, the remaining 150 rats were divided randomly into three groups: iodine deficient control group , iodine deficient I group and iodine deficient II group , which were fed with double distilled water, potassium iodate solutions with iodine concentrations as 100 and 330ug/L respectively. 10 rats of each group were killed at 1, 2, 4, 8 and 24 weeks after treatment. (2)Normal iodine intake animal: 150 Wistar rats, 4 weeks old, were fed with iodine sufficient diet and double distilled water for three months, then were divided randomly into three groups: normal control group , high iodine I group and high iodine II group , fed with double distilled water, potassium iodate solutions with i-odine concentrations as 300 and 660ug/L respectively. 10 rats of each group were killed at 1, 2, 4, 8 and 24 weeks after treatment.2. Animal sample collection and preparation (1) Urine: Rats were put in cage for one day with free access to food and water before killed in order to collect urine for 24 hours. Urine were then stored in refrigeration at - 20C. (2) Plasma: Rats were weighted and then anaesthetized by aether. Whole blood wascollected after cardiac puncture. Plasma was separated from blood by centrifu-ging at 3000 x g for 20 minutes and stored at - 20C. (3)thyroid homogenation: Thyroid were removed quickly after cardiac pumcture, weighted by electric balance , cooled in liquid nitrogen and stored at -70C. Thyroid were diluted with 0.9% sodium chloride to 5 percent thyroid homogenate and then centrifuged at 3000 x g for 15 minutes. The supernatant was collected for analysis.3. Index determination (1)Urinary iodine: AS(III) - Ce4+ catalytic spectro-photometry method was used. (2)Index of antioxidation: MDA was determined by TBA method; GSH-PX was determined by glutathione peroxidase method; SOD was determined by xanthine oxidase method; H2O2 was determined by molybdate amine method; Tissue pretein was determined by Coomassie brilliant blue method. Kits were provided by Institute of Nanjing Jiancheng Biological Engineering. (3)Thyroid function: Radioimmunoassay was used to determined rats TSH whose kit was provided by Amersham company in UK. Radioimmunoassay was also used to determined TT4(double antibody method) and TT3(coat method) whose kits were purchased from DPC company in U. S. A.Results1. Concentration of urinary iodine was postivly relate to concentration of iodine supplied in water significantly. Correlation coefficient of normal iodine intake animals and iodine deficient animals was 0. 936 and 0. 973 respectively. Average of MUI was 165. 9ug/L in normal control group, while it was about three and six times in high iodine I group and high iodine II group respectively compared with normal control group. Average of MUI was 19. 2ug/L in iodine deficient control group while it was about half and three times in iodine deficient I group and iodine deficient II group respectively compared with normal control group.2. Thyroid weight and thyroid relative weight in iodine deficient control group increased significantly. Thyroid weight and thyroid relative weight decreased obviously after iodine supplement in iodine deficient I group and iodine deficient II group as compared with those in iodine deficient control group. Thy-roid weight and thyroid relative weight had no significant difference between iodine deficient I group and iodine deficient II group. There was also no significant difference among three groups...