Effects of iodine excess on TPO and NIS genes mRNA expression in rats

Objective To observe the effects of iodine excess on thyroid morphology,the expression of thyroid peroxidase and sodium iodide symporter mRNA and to explore their mechanisms.Methods One-month SD rats were divided into three groups:control iodine(CI),high iodine Ⅰ(HI Ⅰ)and high iodineⅡ(HI Ⅱ)and were fed with water containing iodine in different concentrations by adding K103(5,5000,10 000μg/L)respectively.Rats were sacrificed after being fed for six months.The morphology of thyroid was investigated under light microscopy and electron microscopy,the serum thyroid hormones and ratio of TPO/β-actin and NIS/β-actin were measured by radio-immunoassay and RT-PCR method.Results The major changes were increased follicles with colloid accumulation in HI groups.The levels of serum thyroid hormones TT3 and TT4 were decreased gradually from CI[(75.68±13.99,1.45±0.49)nmol/L]to HI Ⅰ[(73.82±16.48,1.34±0.31)nmol/L]and HIⅡ groups[(70.65±11.43,1.15±0.39)nmol/L],but there were no significant differences among three groups(F=O.371,l.163,P＞0.05).The TPO and NIS mRNA expressions in HI Ⅰ(1.28±0.10,0.56±O.17)and HI Ⅱ(1.14±0.04,0.39±0.06)were significantly lower(F=30.863,62.62.675,P＜O.05)than those of control group(1.39±0.08,0.71±0.13).Conclusions Chronic iodine excess leads to definite histological changes in rat thyroid,and inhibits the expressions of TPO and NIS mRNA as well as thyroid hormone synthesis,which in turn acts as a protective mechanism against iodine excess. Key words: Iodine; Thyriod; Thyriod peroxidase; Sodium iodide symporter