Effect of excessive iodine intake on sodium-iodide symporter mRNA and protein expression of breast in lactating rats

Objective To study effect of excessive iodine intake on sodium-iodide symporter(NIS)mRNA and protein expression of breast in lactating rats.Methods 60 Wistar rats,having been weaned for one month,were randomly divided into three groups according to their body weights,I.e,①normal iodine(NI,30 rats);②ten fold high iodine(10 HI,15 rats);③one hundred fold high iodine(100 HI,15 rats).Eating food containing iodine of 300μg/L and drinking water of iodine at 5,1845,20 295μg/L,respectively.After fed for 3 months,the rats mated and had offspring,and urine and milk iodine of lactating rats were determined by As-Ce-catalytic spectrophotometric method.Their marmnary glands were sampled at lactation day 10.Then NIS mRNA expression by RT-PCR was determined and NIS protein by immunohistochemistry(SABC)was observed.Results The urine iodine of 10 HI group(3597.5μg/L)and 100HI group(25 404.3μg/L)increased obviously compared with that of NI group(344.7μg/L).The milk iodine of 10HI group(27.1×103μg/L)and 100HI group(191.0×1μg/L)was higher than that of NI group(6.0×103μg/L),but the increased fold of milk iodine was not paralleled with that of urine iodine.Difference of NIS mRNA expression was significant(F=24.19,P＜0.01)among the groups,and the NIS mRNA expression in 10HI(1.250±0.034)and 100HI(1.272±0.039)group were less than that in NI (1.532±0.044)group(P＜0.01).The breast NIS mRNA expression in lactating rats(1.532±0.044)was significantly higher than that in unlactating rats(0.879±0.018,P＜0.01).With the increasing iodine uptake,NIS protein expression decreased.Conclusions The NIS mRNA and protein in rat breasts is down-regulated by excessive iodine intake.So increasing extent of milk iodine concentration is inhibited,which is important to prevent off-spring from getting excessive iodine intake from parental generation. Key words: Iodine;  Mammary glands.animal;  Sodium-iodide symporter