| Objective:Build rat models of Iodine excess and low-protein diet, to study the effect of iodine excess and low-protein diet on rats' growth, metabolism and thyroid function, discuss the possible pathology.Methods:The Wistar strain rats were divided into 8 groups on the basis of weight and gender:①ormal control group(NI):feed normal diet and drink normal water;②10HI group:drink 10 multiple excess Iodine water;③50HI group:drink 50 multiple excess Iodine water;④100HI group:drink 100 multiple excess Iodine water;⑤Low-protein control group(LC): feed low-protein diet and drink normal water;⑥L10HI group:drink 10 multiple excess Iodine water;⑦L50HI group:drink 50 multiple excess Iodine water;⑧L100HI group:drink 100 multiple excess Iodine water.24 rats in each group. To weigh rats'body weights weekly, note the water and feed consumption. Collect urine at 2,4 and 6 months later. Take 8 rats from each group randomly at 2,4 and 6 months later, get blood from eyeground vein and fetch thyroid. The concentrations of urine iodine, serum iodine, TT4, TT3, FT4, FT3, TSH and the levels of anti-oxidation capability(SOD, GSH-Px, MDA) were tested. To observe the structure of thyroid by electron microscope and detect the apoptosis by TUNEL after 6 months. Data were analyzed with normal ANOVA using the SPSS software(SPSS, version 16.0).Results:1. There was no statistical difference in water and feed consumption among groups (P>0.05). The body weights of the rats fed with low-protein diet and normal water were decreased when compared with the NI group, demonstrating statistics difference (P<0.01 or P<0.05). In the condition of the same iodine concentration, the urine iodine levels of the groups fed with low-protein diet and iodine excess water increased significantly compared with that of the groups fed with normal diet and iodine excess water(P<0.01), the serum iodine levels of the groups fed with low-protein diet and iodine excess water decreased significantly compared with that of the groups fed with normal diet and iodine excess water(P<0.01).2. After 2 months, serum levels of FT4 in L1OOHI group were higher than that of 100HI group, showing statistical difference(P<0.05). After 4 months, in the condition of the same iodine concentration, serum levels of TT4 and FT4 in the groups fed with low-protein diet and iodine excess water increased significantly compared with that of the groups fed with normal diet and iodine excess water(P<0.01), serum levels of TSH in the groups fed with low-protein diet and iodine excess water decreased significantly compared with that of the groups fed with normal diet and iodine excess water(P<0.01). After 6 months, in the condition of the same iodine concentration, serum levels of TT4, FT4, TT3 and FT3 in the groups fed with low-protein diet and iodine excess water decreased significantly compared with that of the groups fed with normal diet and iodine excess water(P<0.05 or P＜0.01). Serum levels of TSH in L10HI and L50HI groups increased significantly when compared with that of 10HI and 50HI groups(P<0.01).3. After 2 months, the activity of GSH-Px in L100HI group decreased significantly when compared with that of 100HI group(P<0.05). After 4 months, the activity of GSH-Px and SOD in L100HI group decreased significantly when compared with that of 100HI group(P<0.05), the MDA level in L1OOHI group increased significantly when compared with that of 100HI group(P<0.05). After 6 months, in the condition of the same iodine concentration, the activity of GSH-Px in L100HI and L50HI groups decreased significantly when compared with that of 100HI and 50HI groups(P<0.05 or P＜0.01). the MDA level in L100HI and 50HI groups increased significantly when compared with that of 100HI and 50HI groups(P<0.05).4. In the condition of the same iodine concentration, the comparative weights of thyroids in groups fed with low-protein diet and iodine excess water increased significantly compared with that of the groups fed with normal diet and iodine excess water. By optical microscope, we found that thyroid follicles were much bigger in groups fed with low-protein diet and iodine excess water, epithelia showing flat and the thyroid follicles were full of dark colloid. By electron microscope, we found that the thyroid follicles epithelia nucleus became flat, colloid vesicles increased and there were vacuoles in endoplasmic reticulum and mitochondria. Apoptomic cells could also be observed.5. Detect the apoptosis by TUNEL,we found a great quantity of apoptotic cells in groups fed with low-protein diet and iodine excess water, the apoptotic cells distributing irregularly, apoptosis index increased significantly (P<0.05 or P＜0.01)Conclusion:In conclusion, by building rat models of iodine excess and low-protein diet for 6 months, we got results as follows:1. The rats had fairly toleration to simple iodine excess water or low-protein diet. The rats in groups fed with low-protein diet and iodine excess water showed physical retardation, higher urinary iodine and lower serum iodine compared to the normal groups with excess iodine.2. In the condition of the same iodine concentration, in short term, the serum levels of TT4 and FT4 in the groups fed with low-protein diet and iodine excess water increased significantly compared with that of the groups fed with normal diet and iodine excess water, showing high fatalness to hyperthyreosis. In long term, the serum levels of TT4, FT4, TT3 and FT3 in the groups fed with low-protein diet and iodine excess water decreased significantly compared with that of the groups fed with normal diet and iodine excess water, showing hypothyroidism symptom. The low-protein diet could aggravate effect to the thyroid function induced by iodine excess water.3. In the condition of the same iodine concentration, compared with that of the groups fed with normal diet and iodine excess water, the activity of antioxidant in the groups fed with low-protein diet and iodine excess water decreased significantly, the MDA level increased, inducing peroxide in body.4. In the condition of the same iodine concentration, compared with that of the groups fed with normal diet and iodine excess water, the comparative weight of thyroids in the groups fed with low-protein diet and iodine excess water increased significantly, the thyroid follicular epithelial cells showed anormal structure, apoptomic cells increased. In summery, iodine excess and low-protein diet could induce physical retardation, higher urinary iodine and lower serum iodine, do injury to thyroid function.
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