硒缺乏降低大鼠组织中5′-脱碘酶活性

用不同硒含量的半合成饲料(试验组饲料含硒0.005ppm,对照组饲料含硒0.105ppm),饲喂断奶的Hooded Lister大鼠6周,研究了在不同硒营养状态下,大鼠肝、肾、脑、垂体及褐脂中5′-脱碘酶活性的变化。试验进行2、4、6周后,试验组大鼠组织中GSH-Px及5′-脱碘酶活性比对照组显著降低。按组织中GSH-Px及5′-脱碘酶活性下降幅度的大小,可把各组织分别排序为:肝>肾>褐脂>垂体>脑和肝>肾>褐脂>脑>垂体。硒耗竭2、4、6周后,肝脏GSH-Px活性下降94％、99％、及99.2％,肝脏5′-脱碘酶活性下降的幅度分别为62％80％及90％。硒调节5′-脱碘酶活性可能因为硒是Ⅰ型脱碘酶的辅助因子;而Ⅱ型脱碘酶活性的变化则可能是缺硒导致组织局部T_4水平升高的间接作用。硒缺乏降低5′-脱碘酶活性会导致大鼠循环T_4水平升高,而循环T_3水平降低。

5'-DEIODINASE ACTIVITIES DECLINE BY SELENIUM DEFICIENCY IN RAT TISSUES

Male weanling Hooded Lister rats were used as an animal model, which were fed semi-synthetic diets with different selenium content (0.005 ppm Se in basal diet, and 0.105 ppm Se in control diet) for six weeks. The influence of selenium nutritional status on the iodothyronine 5'-deiodinase activities in rat liver, kidney, brain, pituitary and brown adipose tissue (BAT) were studied. After 2, 4, and 6 weeks, GSH-Px and 5'-deiodinase activities in selenium deficient rat tissues were significantly lower than that in control. In liver, the GSH-Px activity decreased 94%, 99% and 99.92%, while the 5'-deiodinase activity decreased 62%,80% and 90%, after six weeks's selenium depletion. The magnitude of declinement of GSH-Px activity in various tissues was in the following order: liver>kidney>BAT>pituitary>brain; in respect to 5'-deiodinase activity, the order was. liver>kidney>BAT>brain> pituitory. Modulation of type Ⅰ iodothyronine 5'-deiodinase activity by selenium is probably due to selenium's direct role as a cofactor of the enzyme; lower type Ⅱ iodothyronine 5'-deiodinase activity might be caused indirectly by selenium deficiency through elevating local T4 level in tissues and circulating T4 level. It's the lowered iodothyronine 5'-deiodinasl (type Ⅰ and typeⅡ) activities under selenium deficient conditions that cause plasma T4 level elevated and plasma T3 level declined.