PHYSIOLOGICAL ROLES OF SELENIUM WITH SPECIAL REFERENCE TO GUINEA PIGS

为了阐明硒作为抗氧化剂的生理作用，我们研究了硒蛋白在豚鼠体内的表达和功能。豚鼠有两个明显的特点：谷胱甘肽过氧化物酶(GPX)活性极低，不能合成维生素C。我们发现，豚鼠体内大量表达比GPX更多的硒蛋白，如磷脂过氧化氢谷胱甘肽过氧化物酶和硫氧还蛋白还原酶(TrxR)。这表明并不是所有的硒蛋白在豚鼠体内的表达都受到抑制。在维生素C含量最高的肾上腺中，TrxR的活性最高。我们证实了TrxR在硫氧还蛋白存在下还原脱氢抗坏血酸(DHA)的能力。豚鼠组织中TrxR活性在低硒饲料中几乎没有降低。同样，低硒对豚鼠DHA的还原几乎没有影响。这些结果与大鼠TrxR活性和DHA-还原活性的显着降低形成鲜明对比。因此，豚鼠体内含Se的TrxR可能在维持维生素C的还原形式中发挥重要作用。

To elucidate physiological roles of selenium (Se) as an antioxidant, the expression and functions of selenoproteins in guinea pigs were examined. The guinea pigs have two distinct characteristics ; i.e., extremely low activity of glutathione peroxidase (GPx), which is the major selenoprotein in other mammals, and an inability of synthesizing vitamin C.We found that othter selenoproteins than GPx such as phospholipid hydroperoxide glutathione peroxidase and thioredoxin reductase (TrxR) are expressed substantially in guinea pigs. This suggests that the expression of not all selenoproteins is suppressed in guinea pigs. The highest activity of TrxR was found in adrenal glands, which had the highest concentration of vitamtin C.We confirmed the ability of TrxR for reducing dehydroascorbic acid (DHA) in the presence of thioredoxin. The activity of TrxR in guinea pig tissues hardly decreased when subjected to a Se-deficient diet. Similarly, DHA-reducing was hardly affected by Se deficiency in guinea pigs. These results were in contrast with a marked reduction of both activities of TrxR and DHA-reduction in rats. Thus, Se-containing TrxR in guinea pigs may play an important role in maintaining a reduced form of vitamin C.