Circadian rhythmicity of absorption of a lipid compound (vitamin K-1) in vivo

Hollander, Daniel; Kielb, Michael; Rim, E

doi:10.1016/0016-5085(78)93173-6

Cited by 1 publication

(1 citation statement)

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“…Pancreatic esterases and bile acids allow the formation of micelles into which tocopherols and other hydrophobic molecules become solubilized. Vitamin E is absorbed in the proximal small intestine, where it is transported across the brush border by passive diffusion (41). In human, the fractional absorption of atocopherol has been estimated to be 70% (48,56) and in rat 65% (83), these percentages being decreased when the amount of vitamin E given is enhanced.…”

Section: Metabolismmentioning

confidence: 99%

Vitamin E: action, metabolism and perspectives

Herrera

Barbas

2001

J. Physiol. Biochem.

341

197

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Natural vitamin E includes four tocopherols and four tocotrienols. RRR-alpha-tocopherol is the most abundant form in nature and has the highest biological activity. Although vitamin E is the main lipid-soluble antioxidant in the body, not all its properties can be assigned to this action. As antioxidant, vitamin E acts in cell membranes where prevents the propagation of free radical reactions, although it has been also shown to have pro-oxidant activity. Non-radical oxidation products are formed by the reaction between alpha-tocopheryl radical and other free radicals, which are conjugated to glucuronic acid and excreted through the bile or urine. Vitamin E is transported in plasma lipoproteins. After its intestinal absorption vitamin E is packaged into chylomicrons, which along the lymphatic pathway are secreted into the systemic circulation. By the action of lipoprotein lipase (LPL), part of the tocopherols transported in chylomicrons are taken up by extrahepatic tissues, and the remnant chylomicrons transport the remaining tocopherols to the liver. Here, by the action of the "alpha-tocopherol transfer protein", a major proportion of alpha-tocopherol is incorporated into nascent very low density lipoproteins (VLDL), whereas the excess of alpha-tocopherol plus the other forms of vitamin E are excreted in bile. Once secreted into the circulation, VLDL are converted into IDL and LDL by the action of LPL, and the excess of surface components, including alpha-tocopherol, are transferred to HDL. Besides the LPL action, the delivery of alpha-tocopherol to tissues takes place by the uptake of lipoproteins by different tissues throughout their corresponding receptors. Although we have already a substantial information on the action, effects and metabolism of vitamin E, there are still several questions open. The most intriguing is its interaction with other antioxidants that may explain how foods containing small amounts of vitamin E provide greater benefits than larger doses of vitamin E alone.

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Section: Metabolismmentioning

confidence: 99%