碘过量对大鼠脑神经元特异性烯醇化酶基因表达的影响

目的 观察碘过量对大鼠脑神经元特异性烯醇化酶(NSE)基因表达的影响.方法 选用150只断乳1月龄的健康Wistar大鼠,按5×2析因设计分为10组.每组15只.按摄碘量分为正常碘(NI)、5倍碘(5HI)、10倍碘(10HI)、50倍碘(50HI)、100倍碘(100HI)5个水平,饲喂时间为3、6个月.实验期满后,取全部大鼠血样,用放射免疫分析方法测定血清总甲状腺素(TT4)、总三碘甲状腺原氨酸(TT3)、游离甲状腺素(FT4)、游离三碘甲状腺原氨酸(FT3)、反三碘甲状腺原氨酸(rT3)水平;取大鼠脑组织,采用RT-PCR方法检测脑组织NSE mRNA的表达.结果 各碘水平组TT4、TT3变化明星(F值分别为18.867、27.287,P<0.01),时间和碘水平对TT4存在交互作用(F=2.486,P<0.05);100HI组TT4、TT3均低于同时间NI、5HI、10HI、50HI组(P均<0.01).血清FT4、FT3、rT3水平,在3、6个月时变化明显(F值分别为4.968、27.046、59.776,P<0.05或<0.01),各碘水平组间变化明显(F值分别为33.058、28.420、17.482,P均<0.01),时间和碘水平对FT3、rT3存在交互作用(F值分别为6.894、5.233,P均<0.01);100HI组FT4、FT3、rT3低于同时间其他组(P<0.01或<0.05).各碘水平间NSE mRNA变化明显(F=29.006,P均<0.05);3、6个月100HI组大鼠脑中NSE mRNA水平(0.61±0.19、0.61±0.22),与NI(0.73±0.13、0.72±0.26)、5HI(0.72±0.15、0.72±0.16)、10HI(0.73±0.32、0.70±0.13)、50HI(0.71±0.18、0.69±0.31)组比较降低(P均<0.05).3、6个月时血清FT3、FT4与NSE mRNA水平均存在相关关系(r值分别为0.987、0.969及0.890、0.910,P均<0.05).结论 NSE基因的表达对过量碘摄入呈现出耐受性且有一定的阈值;当过量碘摄人为正常100倍时,在转录水平影响NSE基因的表达,表现为抑制NSE mRNA水平;在过量碘引发NSE转录减低的调控中,FT4和FT3可能均起着重要作用.

Expression of neuron specific enolase gene in the brains of rats induced by iodine excess

Objective To observe expression of neuron specific enolase (NSE) gene in the brain of rats induced by iodine excess. Methods One hundred and fifty one-month weaning Wistar rats were divided into ten groups according to 5 × 2 factorial experiment. Rats were fed with normal feedstuff and water of a series of iodine concentration by adding potassium iodide respectively: norrmal iodine (NI), five-fold high iodine (5HI), ten-fold high iodine(10HI), fifty-fold high iodine(50HI) and one hundred-fold iodine(100HI). After these rats were fed for three or six months, rat serum thyroid hormones were measured by radioimmunoassay including TT4, TT3, FT4, FT3, rT3 and the mRNA level of NSE in rat brain tissue was studied using RT-PCR technique. Results The levels of serum TT4 and TT3 were significantly different in five iodine level groups(F values were 18.867,27.287, both P < 0.01). The interaction between time and iodine level in TT4 was significant in our study(F values were 2.486, P < 0.05). The levels of TT4 and TT3 of 100 HI group at third and sixth month were lower than those of NI, 5HI, 10HI, 50HI groups in the same period (all P < 0.01). The levels of serum FT4, FT3 and rT3 were significantly different at different time(F values were 4.968,27.046,59.776 respectively, P < 0.05 or < 0.01) and in different iodine level groups(F values were 33.058,28.420,17.482 respectively, all P < 0.01). Moreover, the interaction between time and iodine level in FT3 and rT3 was significant in our study(F values were 6.894,5.233 respectively, both P < 0.01). FT4, FT3 and rT3 in 100HI group were lower than that of other iodine dosage groups at the same time (P < 0.05 or < 0.01). The levels of NSE mRNA in brain tissue was significantly different in five iodine level groups (F values were 29.006, P < 0.05). The levels of mRNA NSE of 100HI group in both three and six months (0.61 ± 0.19,0.61 ± 0.22) were all lower than that of any other groupsNI(0.73±0.13 and 0.72 ±0.26), 5HI (0.72 ± 0.15 and 0.72±0.16), 10HI (0.73 ±0.32 and 0.70±0.13), 50HI(0.71±0.18 and 0.69±0.31), all P < 0.05]. The results of correlation analyses show that the levels of serum FT3 and FT4 had correlations with the levels of NSE mRNA (P < 0.05) both in three and six months(r values were 0.987, 0.969 in three month, and 0.890, 0.910 in six month respectively). Conclusions The expression of NSE gene can tolerant the excess of iodine to a certain extent. Exposure to heavy excess iodine(100HI) can decrease the mRNA level of NSE gene. FT4 and FT3 may both have important roles on the regulation of NSE mRNA induced by excess iodine.