Effect of combined excess-iodine and low-protein diet on growth, metabolism and morphological changes in thyroid of Wistar rats / 中华地方病学杂志

ABSTRACT

Objective To establish an animal model of high-iodine and low-protein in Wistar rats,and to observe the effect of combined excess-iodine and low-protein diet on growth,metabolism and morphological changes in thyroid.Methods According to body weight[(110 ± 10)g] and sex(half male and half female),one hundred and ninety-two Wistar rats,1 month after weaning,were randomly divided into ① normal iodine control group (NI),② 10-fold excess-iodine group (10HI),③ 50-fold excess-iodine group (50HI),④ 100-fold excess-iodine group (100HI),⑤ low-protein control group (LC),⑥ low-protein and l 0-fold excess-iodine group (L10HI),⑦low-protein and 50-fold excess-iodine group (L50HI),⑧ low-protein and 100-fold excess-iodine group(L100HI).Twenty-four rats were in each group,with the experimental period of 6 months.The iodine content of NI and LC groups was 4.65 μg/d; 10HI,50HI and 100HI groups were 46.50,232.50 and 465.00 μg/d,respectively.The animal's body weight,water and feed consumption were recorded weekly.At the end of 60,120,180 days,urine and blood samples were collected from eight rats in each group.Urinary iodine was tested by arseni cerium catalytic spectrophotometry; serum iodine was tested by the method of chloric acid.Histological change of the thyroid gland was observed by transmission electron microscopy and hematoxylin-eosin (HE) staining at the end of 6 months; apoptosis of thyroid was tested by terminal-deoxynucleoitidyl transferase mediated nick end labeling (TUNEL) method.Results At the end of 4,8,16,18,22 and 24 weeks,the differences of body mass of rats among groups were statistically significant(F =4.26,3.75,4.98,4.09,3.28,3.95,all P ＜ 0.05).At the end of 60,120,180 days,the differences of iodine concentration in urine and blood among groups were statistically significantly (H =5.37,6.03,all P ＜ 0.05).Light microscopy showed that thyroid follicular epithelial cells became flattened,and follicles became distended with colloid following increasing of iodine concentration.Electron microscopy showed increased glial vesicles,condensation of nuclear chromatin,karyopyknosis,and karyolysis with increasing of iodine concentration.The differences of apoptotic indexes among groups were statistically significant (F =4.59,P ＜ 0.01).The apoptotic indexes of L50HI and L100HI groups [(21.50 ± 5.20)‰,(26.70 ± 6.40)‰] were higher than those of 50HI and 100HI groups [(11.20 ± 4.30)‰,(19.40 ± 4.80)‰,P ＜ 0.01 or ＜ 0.05].Conclusion Excessiodine and low-protein can cause growth retardation,abnormal iodine metabolism,and thyroid follicular epithelium damage in Wistar rats.