不同碘营养水平对大鼠肝脏组织中Ⅰ型5’脱碘酶的影响

The influence of iodine nutrition on type 1 deiodinase in rat liver

目的研究不同碘营养水平对大鼠肝脏组织中Ⅰ型5’脱碘酶（DI）表达及活性的影响。方法正常2月龄Wistar大鼠根据碘摄入量不同分为6个组：低碘（LI）组、适碘（NI）组、5、10、50、100倍高碘（5HI、10HI、50HI、100HI）组，分别于饲养3、6、12个月时处死。放免法测定血清甲状腺激素水平；提取肝组织总RNA，以β-actin为内对照，半定量RT-PCR分析DI基因的表达水平：改进的Chopra法测定肝组织匀浆液中DI活性。结果与NI组相比，因碘供给量及给予时间的不同，100HI组及LI组大鼠血清甲状腺激素水平有不同程度的降低．而50HI组则无明显变化。肝DI基因表达水平，LI组随低碘持续时间的不同有所波动，各HI组则与NI组无显著差别。肝DI活性：3个月时与碘供给量成反比；饲养6、12个月时LI组则显著低于NI组（P〈0．05），各高碘组与NI组相比较，差异没有统计学意义（P〉0．05）。结论在碘缺乏早期，大鼠出现以低L为主要表现的甲状腺功能低下症（甲低），并导致DI活性和DI基因表达水平代偿性上调，以维持足够的T3水平来避免周围组织出现器官性甲低；长期碘缺乏后，动物表现为失代偿性的甲低和肝DI活性及DI基因表达水平的降低。机体对碘过量有一定的耐受阈值，若碘摄入量为正常量的50倍以内，甲状腺功能可保持正常，当超过50倍时，甲状腺功能出现失代偿。长期（12月）高碘状态下．机体又会出现对高碘的耐受，而表现为甲状腺功能逐渐恢复正常．肝DI的活性和基因表达水平也趋于正常。

Objective To study the effect of iodine supply on thyroid gland function, activity and gene expression of type 1 iodothyronine deiodinase （DI） in rat liver. Methods 2-month old normal Wistar rats were randomly divided into 6 groups and supplied with different amount iodine. 3, 6 and 12 months after iodine supply, mice of different groups were sacrificed respectively. Serum thyroid hormone was determined by RIA. DI gene mRNA level was measured by semi-quantitative RT-PCR and the activity of DI was also detected by improved Chopra＇s method. Results Compared with NI group, serum thyroid hormone levels decreased in LI and 100HI groups, but did not alter a lot in 50HI due to the difference of the amount of iodine supply and the time phrase, however, no significant difference was shown in any HI group. In the 3rd months, it was increased compared with NI group（P 〈 0.05）, while it was decreased in 50HI and 100HI（P 〈 0.05）. However DI activity decreased in LI group after the rats were fed for 6 and 12 months, no significant differences was found among other groups （P 〉 0.05 ）. Conclusions In the early stage of iodine deficiency, hypothyroidism happens presenting with T4 decrease. In order to maintain T3 and avoid organic hypothyroidism, gene expression and activity of DI in rat liver are increased compensatively. After a long-term of iodine deficiency, decompensated hypothyroidism appears and both DI gene expression and DI activity are decreased. Iodine excess is somewhat tolerated within a threshold. When iodine excess is 50 times less of normal value, thyroid can maintain its normal function. But when the iodine excess exceeding 50 times hypothyroidism happens and the DI activity decreases. After a long term of iodine excess （12 month）, animals become tolerated to iodine excess, indicated by the recovery of thyroid function and DI activity to normal level.