不同碘摄入水平对仔鼠大脑2型脱碘酶活力与髓鞘碱性蛋白和突触蛋白Ⅰ表达的影响

Type 2 Iodothyronine Deiodinase Activity and Expressions of MBP and Synapsin I in Brain of Young Rats with Iodine Deficiency and Excess

目的研究不同碘摄入水平对仔鼠大脑2型脱碘酶(D2)活力、髓鞘碱性蛋白(MBP)、突触蛋白Ⅰ表达的影响。方法将 SPA-VAF 级 Wistar 大鼠60只随机分为低碘组(LI 组)、正常碘组(NI 组)、5、10、50、100倍高碘组(HI 组),每组10只,雌、雄各半。经饮水给予碘酸钾,使其每日总碘摄入量分别为1、6.15、30.75、61.5、307.5、615μg。喂养3个月后雌、雄交配,仔鼠在出生后28 d 处死,以竞争结合放射免疫分析(RIA)法测定血清甲状腺激素(TH),以强阳离子交换层析法测定大脑 D2活力,以免疫组化方法检测 MBP 及突触蛋白Ⅰ表达的变化。结果与 NI 组比较,LI 组各血清 TH 水平均显著降低,差异有统计学意义(P<0.05,P<0.01);各 HI 组随着碘摄入量的增加各血清 TH 水平均呈降低趋势,其中 TT_4、FT_4在615μg/d 碘组降低,差异有统计学意义(P<0.05)。LI 组与各 HI 组的 D2活力较 NI 组有升高的趋势,但均无统计学意义(P>0.05)。与 NI 组比较,LI 组和各 HI 组胼胝体 MBP 蛋白表达均减少,海马 CA3区突触蛋白Ⅰ表达均增多。结论碘缺乏和重度碘过量(615μg/d 碘组)仔鼠表现出甲状腺功能减退,碘缺乏引起的甲状腺功能减退程度和对髓鞘与突触发育的影响比碘过量更为严重。

Objective To study the activity of type 2 Iodothyronine deiodinase （D2） and the expressions of myelin basic protein（MBP） and synapsin I in the brain tissue of young rats fed on a diet with different levels of iodine. Methods Wistar rats were fed on a diet with different doses of KIO3 for 3 months and then mated randomly. The serum TH and the brain D2 activity were measured in 28 days old pups. The protein expressions of MBP and Synapsin I in their brains were determined by immunohistochemistry staining. Results Compared with normal iodine group （NI）, the serum TH levels of low iodine group （LI） were lower, while those of iodine excess groups were gradually decreased with their increase of iodine intake, especially in 100-fold high iodine group （100 HI）, TT4 and FF4 were significantly decreased（P〈0.05）. The activity of D2 was moderately increased without statistical significance in LI and all iodine excess groups compared with NI （P〉0.05）. The immunohistochemistry staining showed weakly positive reactivity of MBP in corpus callosum and stronger of synapsin I in hippocampus CA3 in LI group compared with NI. The similar alterations were also found in all iodine excess groups with their increase of iodine intake. But MBP reactivity was stronger in 100 HI rats than the LI ones. Conclusion Iodine deficiency and iodine excess can cause hypothyroidism in degrees in the young rats, more severe hypothyroid and retarded myelin sheath and synapses can be caused in iodine deficiency compared with iodine excess.