Occurrence, absorption and distribution of vitamin A

Pa, Plack

doi:10.1079/pns19650027

Cited by 16 publications

(10 citation statements)

References 28 publications

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“…Higher animals must obtain vitamin A from the diet. The main dietary forms of preformed vitamin A are carotenoids in fruits and vegetables and long-chain FA esters of retinol in foods of animal origin (145). Carotenoids are either cleaved to generate retinol or absorbed intact, whereas retinyl esters must be completely hydrolyzed within the intestinal lumen to release free retinol before retinol can be taken up by enterocytes.…”

Section: Vitamin Ementioning

confidence: 99%

Intestinal lipid absorption

Iqbal¹,

Hussain²

2009

American Journal of Physiology-Endocrinology and Metabolism

651

484

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Our knowledge of the uptake and transport of dietary fat and fat-soluble vitamins has advanced considerably. Researchers have identified several new mechanisms by which lipids are taken up by enterocytes and packaged as chylomicrons for export into the lymphatic system or clarified the actions of mechanisms previously known to participate in these processes. Fatty acids are taken up by enterocytes involving protein-mediated as well as proteinindependent processes. Net cholesterol uptake depends on the competing activities of NPC1L1, ABCG5, and ABCG8 present in the apical membrane. We have considerably more detailed information about the uptake of products of lipid hydrolysis, the active transport systems by which they reach the endoplasmic reticulum, the mechanisms by which they are resynthesized into neutral lipids and utilized within the endoplasmic reticulum to form lipoproteins, and the mechanisms by which lipoproteins are secreted from the basolateral side of the enterocyte. apoB and MTP are known to be central to the efficient assembly and secretion of lipoproteins. In recent studies, investigators found that cholesterol, phospholipids, and vitamin E can also be secreted from enterocytes as components of high-density apoB-free/apoAI-containing lipoproteins. Several of these advances will probably be investigated further for their potential as targets for the development of drugs that can suppress cholesterol absorption, thereby reducing the risk of hypercholesterolemia and cardiovascular disease.intestine; dietary fat; triacylglycerol; cholesterol; phospholipids; fat-soluble vitamins; microsomal triglyceride transfer protein DIETARY FATS CONSIST OF A WIDE ARRAY of polar and nonpolar lipids (32, 33). Triacylglycerol (TAG) is the dominant fat in the diet, contributing 90 -95% of the total energy derived from dietary fat. Dietary fats also include phospholipids (PLs), sterols (e.g., cholesterol), and many other lipids (e.g., fatsoluble vitamins). The predominant PL in the intestinal lumen is phosphatidylcholine (PC), which is derived mostly from bile (10 -20 g/day in humans) but also from the diet (ϳ1-2 g/day). The predominant dietary sterols are cholesterol (mostly of animal origin) and ␤-sitosterol (the major plant sterol). Although ␤-sitosterol accounts for 25% of dietary sterols, it is not absorbed by humans under physiological conditions.Researchers have been investigating the various steps involved in lipid digestion, absorption, and metabolism to identify factors that could serve as targets for the development of drugs capable of reducing the risk of lipid-associated disorders, including dyslipidemias and cardiovascular disease. In so doing, they have explored key aspects of lipid digestion hydrolysis, emulsification, and micelle formation. They have also explored key issues of absorption, e.g., the uptake of the products of lipid hydrolysis by enterocytes (the epithelial cells lining the walls of the intestinal lumen) and their transport to intracellular compartments, where fatty acids and sterols are...

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Section: Vitamin Ementioning

confidence: 99%

Intestinal lipid absorption

Iqbal¹,

Hussain²

2009

American Journal of Physiology-Endocrinology and Metabolism

651

484

View full text Add to dashboard Cite

show abstract

“…Susceptibility is reduced by the presence of antioxidants (Plack, 1965). Ames (1969) reports that in vitamin E-deficient rats oral supplementation with d-a-tocopherol increased the utilization of orally administered vitamin A approximately six fold.…”

Section: Review Of Literaturementioning

confidence: 99%

“…Low protein levels presumably decrease the activity of certain enzymes involved in vitamin A metabolism (Plack, 1965) and reduce the number of intestinal epithelial cells .…”

Section: Review Of Literaturementioning

confidence: 99%

“…Bile salts and lecithin aid the absorption of vitamin A by dispersing the fat in the intestine (Plack, 1965), although the absorption of retinol is less dependent on the specific nature of the detergent than is the absorption of g-carotene (Olson, 1964b).…”

Section: Review Of Literaturementioning

confidence: 99%

“…Vitamin A Vitamin A occurs in foods chiefly as alltrans retinyl esters (Plack, 1965). These dietary retiny1 esters appear to be totally hydrolyzed in the lumen before absorption (Mahadevan et , 1963a;Ganguly, 1969).…”

Section: Review Of Literaturementioning

confidence: 99%

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