TAILIEUCHUNG - Encyclopedia Of Animal Science - V

Từ điển khoa học động vật vần V | Vitamin E Selenium and Their Interrelationship Donald C. Mahan The Ohio State University Columbus Ohio . Duane E. Ullrey Michigan State University Okemos Michigan . INTRODUCTION Vitamin E is a fat-soluble nutrient found in body fat depots plasma lipoproteins and cell membrane phospholipids where it serves as an important antioxidant. Selenium Se fulfills an antioxidant role as a component of glutathione peroxidases GSHPx . Se is widely distributed in the body but the most labile reservoir is in the liver. It is found in body tissue principally as selenomethionine SeMet or as selenocysteine SeCys the latter found in GSHPx. Both nutrients are discussed together because of their related functions and similar deficiency signs. However Se and vitamin E each have unique metabolic roles and the factors that alter the oxidative state of an animal may differentially affect their dietary needs. VITAMIN E Vitamin E is a collective term used for eight compounds synthesized by plants and found principally as free alcohols in lipid-containing fractions of green leaves and seeds. 1 2 Four are designated a- b- g- and 8-tocopherols or tocols and four are designated a- - g- and 8-tocotrienols differing from the tocopherols in unsaturation of the phytyl side chain. Of the various isomers RRR-a-tocopherol formerly D-a-tocopherol has the highest biological activity in preventing fetal resorption in rats. The biological ranking of the tocopherols and tocotrienols as antioxidants is based on their ability to scavenge peroxyl radicals. Although a-tocotrienol has only about one-third of a-tocopherol s ability to prevent fetal resorption it reportedly is equal in antioxidant activity. 3 4 Tocopherols and tocotrienols are absorbed by mechanisms generated from fat digestion requiring bile and pancreatic secretions. Vitamin E esters are hydrolyzed by pancreatic esterases. The dietary free alcohols and those released from the esters are subsequently incorporated into chylomicrons .

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