Author
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HARRISON, EARL |
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Submitted to: Annual Review of Nutrition
Publication Type: Review Article Publication Acceptance Date: 5/13/2005 Publication Date: 8/2/2005 Citation: Harrison, E.H. 2005. Mechamisms of digestion and absorption of dietary vitamin a. Annual Review of Nutrition. 25:87-103. Interpretive Summary: Interpretative summary is not required. Technical Abstract: Mechanisms involved in the digestion and absorption of dietary vitamin A require the participation of several proteins. Dietary retinyl esters are hydrolyzed in the intestine by the pancreatic enzyme, pancreatic triglyceride lipase, and intestinal brush border enzyme, phospholipase B. Unesterified retinol taken up by the enterocyte is complexed with cellular retinol-binding protein type 2 and the complex serves as a substrate for re-esterification of the retinol by the enzyme lecithin:retinol acyltransferase (LRAT). The retinyl esters are then incorporated into chylomicrons, intestinal lipoproteins containing other dietary lipids, such as triglycerides, phospholipids, and free and esterified cholesterol, and apolipoprotein B. Chylomicrons containing newly absorbed retinyl esters are then secreted into the lymph. While under normal dietary conditions much of the dietary vitamin A is absorbed via the chylomicron/lymphatic route, it is also clear that under some circumstances there is substantial absorption of unesterified retinol via the portal route. There is evidence supporting the idea that the cellular uptake and efflux of unesterified retinol by enterocytes is mediated by lipid transporters, but the exact number, identity and role of these proteins is not known and is an active area of research. |
