Effects of different levels of iodine concentration on sodium/iodide symporter mRNA expression of thyroid and breast in lactating rats

Abstract

Objective To study the effects of different levels of iodine concentration on sodium/iodide symporter(NIS) mRNA expression of thyroid and breast in lactating rats, and to explore their mechanisms. Methods Thirty Wistar female rats weighted 40-60 g, having been weaned for one month, were randomly divided into three iodine(HI, 10 rats). Synthetic fodder and deionized dringking water containing iodine of 0, 150 and 3000 μg/L were respectively fed to the rats in 3 groups. After fed for 3 months, the rats mated and had offspring. Their mammary glands, thyroids and serum were sampled at lactation day 5. The serum iodine of lactating rats was determined by moderate acid digestion method. T_3, T_4 levels were determined by radioimmunoassay method. The expressions of NIS mRNA of mammary glands and thyroids were determined by real-time fluorescence quantitative PCR assay. Results Serum iodine, T_3, T_4 and expression of NIS mRNA in lactating rats were statistically significant between 3 groups(F=499.94,16.67,8.49, H=7.58, all P < 0.05). The mean value of serum iodine of LI group[(17.38±3.27)μg/L] was lower than that Of AI group[(43.42±6.92)μg/L, P< 0.05], and the value of HI group[(350.10±38.46)μg/L] was higher than that of AI group(P < 0.05). Serum T_3 level in LI group[(1.11± 0.25)μg/L] and HI group[(1.61±0.33)μg/L] reduced obviously compared with that of AI group[(2.18±0.46) μg/L, all P< 0.05]. Serum T_4 level in LI group[(33.40±11.11)μg/L] and HI group[ (56.54±10.38)μg/L] had no statistical significance, but the level of serum T_4 in LI group was lower than that in HI group(P < 0.05). The NIS mRNA expression of thyroid in LI group(0.280±0.030) was higher than that in AI group(0.240±0.030, P<0.05), but it was lower in HI group (0.069±0.037). NIS mRNA expression of lactating mammary in HI group (0.027±0.007) was lower than that in AI group(P < 0.05). Conclusions Mild iodine deficiency can increase the level of NIS mRNA expression of thyroid and protect the mother from damage caused by low-iodine, but no obvious protective effect on the next generation has been found. High-iodine inhibits NIS mRNA expression in thyroid and breast, thus protecting mother and its next generation from the high-iodine hazards. Key words: Iodine; Thyroid; Breast; Sodium/iodide symporter