Vitamin Retina

Berges, D., G. Schmitt et al. (1959). The effects of helenien and vitamin A on the primary sight process. III. A flame photometric determination of the potassium and sodium content of the retina (German). Z. Biol. Ill 220-227. 

RPE plays numerous functions essential for proper structure and function of retinal photoreceptors. They include the maintenance of the blood-retina barrier, selective uptake and transport of nutrients from the blood to the retina and removal of waste products to the blood, enzymatic cleavage of P-carotene into vitamin A, storage of vitamin A and its metabolic transformations, phagocytosis and molecular renewal of POS, expression and secretion of growth factors and immunomodulatory cytokines (Aizman et al., 2007 Aleman et al., 2001 Crane et al., 2000a,b Elner et al., 2006 Holtkamp et al., 2001 Leuenberger et al., 2001 Lindqvist and Andersson, 2002 Maminishkis et al., 2006 Momma et al., 2003 Strauss, 2005). 

Recent data indicate that SR-BI is a nonspecific receptor for many lipophilic molecules (Lorenzi et al., 2008 Reboul et al., 2007b). Apart from HDLs, rodent SR-BI also binds to LDL, VLDL, acetylated LDL, oxidized LDL, and maleylated bovine serum albumin. SR-BII has a similar ligand specificity and function to that of SR-BI (Webb et al., 1998). However, it has been shown that vitamin E (which like carotenoids is carried in the bloodstream mainly by LDL and HDL) is transported more efficiently into the endothelial cells from HDLs than from LDLs (Balazs et al., 2004 Kaempf-Rotzoll et al., 2003 Mardones and Rigotti, 2004). This is in striking contrast to cholesterol, which is taken up much more efficiently from LDLs than HDLs by the RPE to the retina (Tserentsoodol et al., 2006b). It remains to be shown which lipoproteins are the main carriers for carotenoids transported from blood into the RPE. 

We have mentioned microwave ovens a few times already. Although we might employ such an oven regularly, no one has actually seen microwave radiation. The photons are wholly invisible. The phenomenon of sight can be simplified to the photo-effected transformation of a pigment related to retinal within the retina at the back of the eye. Retinal is derived from vitamin A. 

Retention time, in chromatography, 6 374-375, 409-410 ( )-Reticuline, 2 90 Retina, 7 307-308 Retinal, 25 787. See also Vitamin A carotenes and, 25 790 Retinitis pigmentosa, 17 659 Retinoic acid, 25 787-789, 790. See also Vitamin A... 

GSH synthesis. GLUT1 transports dehydroascorbic acid, an oxidized form of vitamin C, to supply the retina with ascorbic acid [47],... 

In the absence of sufficient vitamin A, one consequence is a vision defect termed night blindness or, more technically, xerophthalmia. The rod cells in the retina are largely responsible for vision in low light. If they have too little retinal, they cannot do their job and night blindness, the inability to see in low light, results. If the condition persists, it is characterized by extreme dryness of the conjunctiva and can result in permanent blindness. 

A deficiency of vitamin A leads to vision defects, including a visual impairment at low light levels, termed night blindness. For the processes of vision, retinol needs to be converted first by oxidation into the aldehyde retinal, and then by enzymic isomerization to cw-retinal. c -Retinal is then bound to the protein opsin in the retina via an imine linkage (see Section 7.7.1) to give the red visual pigment rhodopsin. 

Vitamin A is essential for proper functioning of the retina, for the integrity of epithelial tissue, for growth and bone development and for reproduction. For vision the active vitamin appears to be retinal as the chromophore of both rods and cones is 11-cis-retinal which, in combination with the protein opsin, forms the photoreceptor rhodopsin. Retinoic acid is the active form associated with growth, differentiation, and transformation. Both all-trans and 9-cis retinoic acid act as a steroid hormone to affect cellular differentiation, especially for morphogenesis, reproduction and for immune responses. At... 

H hstract. Until recently, all ocular photoreception was attributed to the rods and cones of the retina. However, studies on mice lacking rod and cone photoreceptors (rdjrdcl), has shown that these mice can still use their eyes to detect light to regulate their circadian rhythms, suppress pineal melatonin, modify locomotor activity and modulate pupil size. In addition, action spectra for some of these responses have characterized a novel opsin/vitamin A-based photopigment with a 480nm. Electrophysiological... 

Mechanism of Action A fat-soluble vitamin that may act as a cofactor in biochemical reactions. Therapeutic Effect Is essential for normal function of retina, visual adaptation to darkness, bone growth, and testicular and ovarian function preserves integrity of epithelial cells. 

It is vital for the functioning of retina. Vitamin A is essential for differentiation and growth of epithelial tissue. It enhances function of immune system and protect against development of certain malignancies. Different forms of vitamin A mediate different functions. 

In 1912, Hopkins reported a factor m milk needed for the growth of rats. In 1913, Osborne and Mendel demonstrated that milk factor is fat soluble, and present in other fats also, McCollum and Davis, in 1913-1915, identified milk factor (fat-soluble A) in butter and egg yolk. In 1917, McCollum and Simmonds found xerophthalmia in rats due to lack of fat-soluble A. In 1920, Drummond renamed fat-soluble A, vitamin A. In 1930, Moore determined that carotene is a precursor of vitamin A. See also . During 1930-1937, Karrer et al, isolated and synthesized vitamin A. In 1935, Wald reported visual purple in retina to be a complex of protein and vitamin A. 

In higher plants, carotenoids are produced in green leaves. In animals, conversion of carotenoids to vitamin A occurs in the intestinal wall. Storage is in the liver also kidney in rat and cat. Target tissues are retina, skin, bone, liver, adrenals, germinal epithelium. Commercial Vitamin A supplements are obtained chemically by extraction of fish liver or synthetically from citral or /3-ionone. 

Unusual features of riboflavin as recorded by some researchers include (1) High levels in liver inhibit tumor formation by azo compounds in animals (2) free radicals are formed by light or dehydrogenation flavine semiquinone dihydroflavin+ (3) free vitamin is found only in retina, urine, milk, and semen (4) substitution of adenine by other purines and pyrimidines destroys activity of flavin adenine dinucleotide (FAD) ... 

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