A study on the thyroid injury induced by combined deficiency of selenium,protein and vitamin E in rats

Objective To explore the effect of associated deficiency of selenium,protein and vitamin E(VE)on the thyroid iniury and thyroid hormone metabolism of the rats in a long-term.Methods The Wistar rats were randomly divided into four groups:Group A with selenium deficiency and low protein and VE;Group B with selenium deficiency,low protein but adequate VE;Group C,adequate selenium and protein but low VE;Group D,adequate selenium.protein and VE.The rats were killed at the end of 26th week.Glutathione peroxidase(GSH-Px)activity in the rat blood and type I 5'-deiodinase activity of the rat liver were determined.The content of triiodothyronine(T3),tetraiodothyronine(T4),thyrotropic-stimulating hormone(TSH),activated oxygen(ROS)and malonaldehyde(MDA)were detected in serum. The changes of thyroid histopathology were observed under light microscope.Results ①The interactive effect of selenium+protein and VE was not significant on GSH-Px and ID I activity(F=0.003,0.871,P＞0.05),but it was significant on MDA and ROS content(F=13.057,6.706,P＜0.05 or＜0.01). ②Selenium+protein and VE could influence T3 and T4 content(F=431.977,28.271,6.570,41.419,P＜0.05).The interactive effect of selenium±protein and VE was not significant on T3 and T4 content(F=0.871,0.136,P＞0.05).Whether in the condition of low selenium and protein or supplementary,T4 contents of supplementary VE group[(79.095±12.199),(64.392±6.261)μg/L]were respectively higher than the low VE group[(61.068±6.648),(44.176±7.090)μg/L],the difference being statistically significant(t = 3.670,6.045, P ＜ 0.01). In the condition of low VE, T3[(0.718 ± 0.079)μg/L] and T4[(44.176 ±7.090)μg/L] content of supplementary selenium and protein group was lower than that in the low selenium and protein group[ (0.966 ± 0.156), (61.068 ± 6.648)μg/L], the difference being statistically significant (t = 4.568,4.916, P ＜0.01 ). With supplementary VE, T4 content of supplementary selenium and protein group[ (64.392 ± 6.261 )μg/L] was lower than that in the low selenium and protein group [(79.095 ± 12.199)μg/L], the difference being statistically significant (t = 3.033, P ＜ 0.01 ). ③Degeneration and necrosis of follicular epithelial cell were induced by diet of low selenium, protein and VE, which could be relieved by supplymentary VE. The sparseness of intracavitary glue was observed occationally in the supplementary selenium and protein but low VE group. Conclusions Long-term deficiency of selenium, protein and VE results in the decrease of the selenoenzymes of rats, which causes accumulation of the oxidative products, as well as thyroid pathological injury and thyroid hormone metabolism disorder, but supplement of adequate VE can reduce the oxidative damage in rats having low selenium and protein diet. Key words: Selenium;  Proteins;  Vitamin E;  Deficiency diseases;  Thyroid gland;  Oxidative stress