Retinol animals

Vitamin A (retinol) Animal tissue, liver, green plants Component of the pigment involved in vision... 

Vitamin A is manufactured by Hoffmaim-La Roche (Switzerland), BASF (Germany), and Rhc ne-Poulenc (France), as well as by some smaller suppliers in India, China, and Russia. The worldwide production is estimated to be 2500 to 3000 metric tons. About three-quarters of this production is for animal feed the remainder is for food fortification and pharmaceuticals (qv). The main trade names of feed products are Rovimix, Lutavit, and Microvit. Prices depend on appHcation forms and are approximately 60— 70/10 lU retinol (1995) ie, 200— 233/10 RE. One lU is equivalent to 0.300 )lg of aH-Zra/ j -retinol and 1 RE is equivalent to 1 ) g of all-retinol. 

Retinoids are alcohols and accordingly soluble in ethanol, isopropanol, and polyethylenglycol. Major sources of natural retinoids are animal fats, fish liver oil (retinylesters) and yellow and green vegetables (carotenoids). Ingested retinylesters (RE) are hydrolyzed to retinol by enteral hydrolases in the intestine. ROL and carotenoids are absorbed by intestinal mucosa cells. 

Subsequent studies have confirmed that the reason for this discrepancy is that the rat is able to rapidly metabolise P-carotene to retinol in the intestine, through the action of intestinal dioxygenase. In contrast humans absorb P-carotene systemically such that plasma levels of P-carotene increase to levels not found in the rodent. A more appropriate animal model is the ferret, which shows a similar metabolism to humans. High levels of plasma P-carotene in the ferret induce the cellular transcription factors c-fos and c-jun, and squamous metaplasia is seen in the lung with or without exposure to cigarette smoke (SCF, 2000). Even after the investment of all these resources it has not been possible for the EU Scientific Committee on Food to set an ADI. 

Gundersen and Blomhoff (1999) used online dilution with online SPE to measure vitamin A (retinol) and other active retinoids in animal plasma. The intention of online dilution in this application was on optimizing SPE extraction conditions rather than on peak focusing during analytical separation. An SPE cartridge packed with Bondapak C18 materials (37 to 53 jt/M, 300 A, Waters, Milford, Massachusetts) and a reversed-phase analytical column (250 x 2.1 mm inner diameter, Superlex pkb-100, Supelco, Bellefonte, Pennsylvania) were controlled by a six-port switching valve (Rheodyne, Cotati,... 

The a-, (3- and y-carotenes, which are found in most plants, are vitamin A provitamins and are converted to vitamin A alcohol (all- ran,v-retinol), which is usually called vitamin Aj (Figure 12.8) by oxidative mid-point cleavage. Retinol and its fatty acid esters are the main forms in which vitamin A is stored in animals and humans, and its oxidation product, 1 1-c/s-retinal (vitamin A, aldehyde), is required for the visual process. 

T.W. Knight and A.F. Death, Effects of oral and injected vitamin A (retinol) supplements on liver vitamin A and plasma carotenoid and cholesterol concentrations in cattle. Animal Sci. 69 (1999) 607-612. 

Vitamin Ai (retinol) is derived in mammals by oxidative metabolism of plant-derived dietary carotenoids in the liver, especially -carotene. Green vegetables and rich plant sources such as carrots help to provide us with adequate levels. Oxidative cleavage of the central double bond of -carotene provides two molecules of the aldehyde retinal, which is subsequently reduced to the alcohol retinol. Vitamin Ai is also found in a number of foodstuffs of animal origin, especially eggs and dairy products. Some structurally related compounds, including retinal, are also included in the A group of vitamins. 

This class includes both vitamin A and the provitamin A carotenoids. All the compounds related to all-trani-retinol (Figure 19.11) are known as vitamin A. These compounds, together with their metabolites and synthetic derivatives, exhibiting the same properties are called retinoids. Vitamin A is found in animal products as retinyl esters (mainly palmitate). 

In animal foods, vitamin A is present in Uver, eggs, butter, cheese, milk, fish and meat. Fish Uver oil are the richest source of retinol. 

Altered vitamin A homeostasis, primarily manifested as decreased hepatic storage of vitamin A, is another established effect of PBBs in animals. Vitamin A is essential for normal growth and cell differentiation, particularly differentiation of epithelial cells, and some PBB-induced epithelial lesions resemble those produced by vitamin A deficiency. Because it is the primary storage site for vitamin A, the liver has a major role in retinol metabolism. Esterification of dietary vitamin A, hydrolysis of stored vitamin A, mobilization and release into the blood of vitamin A bound to retinol-binding protein, and much of the synthesis of retinol-binding protein occurs in the liver. 

Vitamin A (retinol, 6.1) is the parent of a range of compounds known as retinoids, which possess the biological activity of vitamin A. In general, animal foods provide preformed vitamin A as retinyl esters (e.g. 6.5, which are easily hydrolysed in the gastrointestinal tract) while plant foods provide precursors of vitamin A, i.e. carotenoids. Only carotenoids with a /3-ionone ring (e.g. /1-carotene) can serve as vitamin A precursors. /3-Carotene (6.6)... 

The concentration of vitamin A and carotenoids in milk is strongly influenced by the carotenoid content of the feed. Milk from animals fed on pasture contains higher levels of carotenes than that from animals fed on concentrate feeds. There is also a large seasonal variation in vitamin A concentration summer milk contains an average of 62 fig retinol and 31 fig carotene per 100 g while the values for winter milk are 41 and 11 fig per... 

Retinol A primary alcohol containing a p-ionone ring with an unsaturated side chain, retinol is found in animal tissues as a retinyl ester with long-chain fatty acids. 

Retinyl esters and retinol are found in certain animal tissues. 

Reproduction Retinol and retinal are essential for normal repno duction, supporting spermatogenesis in the male and preventing fetal resorption in the female. Retinoic acid is inactive in maintain ing reproduction and in the visual cycle, but promotes growth and differentiation of epithelial cells thus, animals given vitamin A only as retinoic acid from birth are blind and sterile. 

In food, vitamin A exits in two forms preformed vitamin A (retinol and retinyl esters) in animal products and pro-vitamin A carotenoids... 

VITAMIN A. This substance also has been referred to as retinol, axerophthol, biosterol, vitamin Ai, anti-xerophthalmic vitamin, and anti-infective vitamin. The physiological forms of the vitamin include Retinol (vitamin A ) and esters 3-dehydroretinol (vitamin A2) and esters 3-dehydroretinal (retinme-2) retinoic acid neovitamin A neo-b-vitamin Ai. The vitamin is required by numerous animal species. All vertebrates and some invertebrates convert plant dietary carotenoids in gut to vitamin Ai. which is absorbed. Most animal species store appreciable amounts... 

The leveisal of the oxidative pathway of vitamin A (retinol —r retinal —>-retinoic add) does not occur in the body, When retinoic acid is feci to animals, even in relatively large doses, there is no storage and, in fact, die molecule is rapidly metabolized and cannot be found several hours after administration. The metabolic products have not been fully identified. Several fractions from liver or intestine, isolated after administering retinoic add marked with carbon-14, have been shown to have biological activity. 

Vitamin A is a necessary micronutrient in the diet for vision, growth, tissue differentiation, reproduction, and maintenance of the immune system. A deficiency of vitamin A affects reproduction in both male and female experimental animals. In the male, retinol is required for normal spermatogenesis in the female, the vitamin is necessary for both conception and normal development of the fetus. 

The liver of meat animals is a rich source of vitamin A, for this organ is the body s main storage site of the vitamin. Fish liver oils, particularly halibut liver oil, are incredibly rich in the vitamin and are too potent to be consumed as foods. Typical food sources of vitamin A (in /ag retinol equivalents/100 g) are sheep and ox liver, 15,000 butter, 830 cheese, 320 eggs, 140 herring and... 

For food labeling purposes, which require the actual amounts of vitamin A in the food rather than the nutritional value, data obtained by physicochemical assay are expressed on a weight basis. In plant-derived foods, the appropriate units are /3-carotene equivalents expressed in micrograms of /3-carotene. By definition, 1 /3-carotene equivalent is equal to 1 fig of all-trans-/3-carotene or 2 fig of other, largely animal-derived foods, the units are either micrograms of retinol or retinol equivalents (32). 

Vitamin A is an essential nutrient for humans and other vertebrates. Dietary sources of vitamin A are provided either by retinol esters, which are present in foods of animal origin and are hydrolyzed in the intestine to form retinol, or by plant carotenoids. More than 600 carotenoids have been identified in nature, of which 50 to 60 possess provitamin A properties and 10 have nutritional relevance (De Flora et al., 1999). 

It is obtained from retinols in animal products or p-carotene in plant foods. 

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