Retinyl Stearate Research Articles

Determination of retinol and retinyl esters in human plasma by high-performance liquid chromatography with automated column switching and ultraviolet detection

A HPLC method with automated column switching and UV detection is described for the simultaneous determination of retinol and major retinyl esters (retinyl palmitate, retinyl stearate, retinyl oleate and retinyl linoleate) in human plasma. Plasma (0.2 ml) was deproteinized by adding ethanol (1.5 ml) containing the internal standard retinyl propionate. Following centrifugation the supernatant was directly injected onto the pre-column packed with LiChrospher 100 RP-18 using 1.2% ammonium acetate–acetic acid–ethanol (80:1:20, v/v) as mobile phase. The elution strength of the ethanol containing sample solution was reduced by on-line supply of 1% ammonium acetate–acetic acid–ethanol (100:2:4, v/v). The retained retinol and retinyl esters were then transferred to the analytical column (Superspher 100 RP-18, endcapped) in the backflush mode and chromatographed under isocratic conditions using acetonitrile–methanol–ethanol–2-propanol (1:1:1:1, v/v) as mobile phase. Compounds of interest were detected at 325 nm. The method was linear in the range 2.5–2000 ng/ml with a limit of quantification for retinol and retinyl esters of 2.5 ng/ml. Mean recoveries from plasma were 93.4–96.5% for retinol (range 100–1000 ng/ml) and 92.7–96.0% for retinyl palmitate (range 5–1000 ng/ml). Inter-assay precision was ≤5.1% and ≤6.3% for retinol and retinyl palmitate, respectively. The method was successfully applied to more than 2000 human plasma samples from clinical studies. Endogenous levels of retinol and retinyl esters determined in female volunteers were in good accordance with published data.

Serum concentrations of vitamin D metabolites, vitamins A and E, and carotenoids in six canid and four ursid species at four zoos

Nutritional status for six captive canid species ( n=34) and four captive ursid species ( n=18) were analyzed. The species analyzed included: African wild dog ( Lycaon pictus), arctic fox ( Alopex lagopus), gray wolf ( Canis lupus), maned wolf ( Chrysocyon brachyurus), Mexican wolf ( Canis lupus baleiyi), red wolf ( Canis rufus), brown bear ( Ursus arctos), polar bear ( Ursus maritimus), spectacled bear ( Tremarctos ornatus), and sun bear ( Ursus malayanus). Diet information was collected for these animals from each participating zoo (Brookfield Zoo, Fort Worth Zoo, Lincoln Park Zoological Gardens, and North Carolina Zoological Park). The nutritional composition of the diet for each species at each institution met probable dietary requirements . Blood samples were collected from each animal and analyzed for vitamin D metabolites 25(OH)D and 1,25(OH) 2D, vitamin A (retinol, retinyl stearate, retinyl palmitate), vitamin E (α-tocopherol and γ-tocopherol) and selected carotenoids. Family differences were found for 25(OH)D, retinol, retinyl stearate, retinyl palmitate and γ-tocopherol. Species differences were found for all detectable measurements. Carotenoids were not detected in any species. The large number of animals contributing to these data, provides a substantial base for comparing the nutritional status of healthy animals and the differences among them.

Influence of increased vitamin A supplements on α‐tocopherol and retinoids in serum and lipoproteins of Shetland ponies

SummaryThe effects of feeding 75 versus 750 IU vitamin A/kg body mass (BM) per day to eight healthy pony geldings were studied in a cross‐over design experiment for 20 weeks. The vitamin E intake was 2 mg/kg BM per day. α‐tocopherol and retinoid distribution was examined in serum and lipoproteins. No effect was seen on retinol, α‐tocopherol, cholesterol, triglycerides, phospholipids and protein. The α‐tocopherol was distributed between high‐density lipoprotein (69%), low‐density lipoprotein (LDL; 22%) and very‐low‐density lipoprotein (VLDL; 9%). A retinol dose response (RDR)‐test was carried out in both experimental groups to analyse the vitamin A status. The RDR‐test indicated in some cases a false insufficient supply in spite of increased dietary vitamin A. However increased retinyl ester concentrations were found in serum and lipoproteins. Therefore concentrations of retinyl esters seems to be an excellent indicator for the vitamin A status of ponies. In lipoproteins, retinyl ester were measurable in VLDL and LDL. The main ester was retinyl stearate followed by retinyl palmitate. Data suggest that feeding increased concentration of vitamin A did not influence the serum vitamin E status and lipid parameters in ponies, but increased the retinyl esters in serum, VLDL and LDL.

Fatty acid, carotenoid and vitamin A composition of tissues of free living gulls

The aim of this study was to investigate fatty acid and carotenoid profile as well as vitamin A (retinol and retinol esters) content in gull ( Larus fucus) tissues. Palmitic (16:0) and stearic (18:0) fatty acids were major saturates in all the tissues studied. Oleic acid (18:1n-9) was the major monounsaturate in the tissue phospholipids varying from 11.9% (liver) up to 18.2% (lung). Arachidonic acid (20:4n-6) was the major unsaturate in the phospholipid fraction in all the tissues. Liver contained the highest total carotenoid concentration which was 5 and 7 fold higher compared to kidney and pancreas. In the liver β-carotene was major carotenoid. In contrast, in all other tissues β-carotene was minor fraction with lutein being major carotenoid. Zeaxanthin, canthaxanthin, β-cryptoxanthin and echinenone were also identified in the gull tissues. Liver and kidney were characterised by the highest vitamin A concentrations (1067.5 and 867.5 μg/g, respectively). Retinol comprised from 55.3% (pancreas) down to 8% (kidney) of the total vitamin A but was not detected in the abdominal fat. Retinyl palmitate was the major retinyl ester in the liver, kidney and heart (44.2; 38.1 and 46.0% of total retinyl esters). In muscles and abdominal fat retinyl stearate was the major retinyl ester fraction. Therefore high proportions of β-carotene were found in gull liver and peripheral tissues were enriched by lutein and zeaxanthin compared to the liver, a very high concentration of retinyl esters in the kidney was observed and tissue-specificity in retinyl ester proportions in peripheral tissues was found.

Retinyl Palmitate in Macaque Retina-Retinal Pigment Epithelium-Choroid: Distribution and Correlation with Age and Vitamin E

Retinyl palmitate (RP) and retinyl stearate (RS) are of central importance in the visual cycle because they are the major storage molecules for retinol. In some tissues (e.g. liver) the amount of vitamin A (mostly in the form of retinyl ester) is positively correlated with both the amount of α-tocopherol (α-T) and age. Furthermore, α-T is a noncompetitive inhibitor of the hydrolysis of RP. We measured RP, RS, α-T and β+g-tocopherol (β+g-T) as functions of distance from the foveal center (eccentricity) in the retina-RPE-choroid (NRC) of rhesus monkeys using high-pressure liquid chromatography.It was found that the central and peripheral NRC differed with respect to these parameters. The concentration (pmoles sq mm−1) of RP was higher in the central NRC than in the peripheral NRC and was at a maximum in the region of the fovea. Furthermore, although in the peripheral NRC, RP was well correlated with age and α-T (similar to other tissues), in the central NRC, RP per sq mm was more clearly related to photoreceptor density. These differences imply that the central NRC controls the concentration of RP within it, while the concentration of RP in the peripheral NRC is determined by its environment (e.g. nutrients available from blood) and the age of the individual.

Characterization and identification of an adrenal age-related nonpolar fluorescent substance.

The adrenal cortexes of humans and rodents accumulate lipofuscin with age, but the chemical nature of the substance that produces lipofuscin fluorescence in the gland is not known. Analysis of rat adrenal nonpolar lipids revealed a fluorescence profile with increased intensity in the lipids extracted from older animals (23-24 months > 6 months > 6 weeks). The peak occurred at a wavelength of 470 +/- 5 nm(n = 26) when excited at 340 nm. After sucrose density gradient centrifugation, the fluorescent substance was primarily concentrated in subcellular lipid droplets rather than supernatant or particulate. Prolonged stimulation of rats with ACTH for 7 consecutive days caused 14-51% decreases in the fluorescence levels, with a tendency of return to control levels poststimulation regardless of age. In contrast, the nonpolar lipids of mouse adrenal tumor (Y1) cells, which contain no lipofuscin, did not display this fluorescence in the presence or absence of ACTH. The chromatographic characteristics of the substance in a silica gel-60 column resembled those of authentic retinyl palmitate and cholesteryl oleate. Analysis of the substance by HPLC demonstrated at least three prominent peaks, designated XI-3 in order. X1 and X2 were minor peaks; X3 was the major peak. Whereas none of the peaks comigrated with cholesteryl esters, X1 comigrated with authentic retinyl palmitate. Determination of the fatty acid component of the major fluorescent substance X3 by gas-liquid chromatography disclosed stearic acid. Retinyl stearate was, therefore, synthesized. The fluorescent profiles, HPLC retention time and mass spectrometric fragmentation of purified X3 substance were all identical to those of the synthetic compound. In contrast, the rat liver principally accumulated retinyl palmitate with age. Thus, we conclude that 1) the major nonpolar fluorescent substance accumulated in the rat adrenal with age is retinyl stearate, which may be a fluorophore of adrenal lipofuscin; 2) ACTH action may be related to this accumulation; and 3) the type of retinyl ester accumulated in aged animals is organ specific.

Simultaneous determination of retinyl esters and retinol in human livers by reversed-phase high-performance liquid chromatography.

A high-performance liquid chromatographic method for the simultaneous determination of retinol and retinyl esters in human liver samples is presented. The free retinol and the prevalent retinyl esters (retinyl palmitate, oleate and stearate) are resolved within less than 30 min, using an octasilyl (C8)-substituted column and an isocratic elution with methanol-water as mobile phase. This method allows to determine in duplicate all retinyl ester concentrations in small liver samples (3-10 mg of fresh tissue). The results obtained from thirteen patients without liver disease are described.

Fetal, Neonatal, and Long-Term Alterations in Hepatic Retinoid Levels Following Maternal Polychlorinated Biphenyl Exposure in Rats

This study was undertaken to investigate the effects of perinatal polychlorinated biphenyl (PCB; Aroclor 1254) exposure on hepatic and plasma retinoid levels in fetal rats, their dams, and neonatal and adult offspring. Pregnant Wistar rats were treated with 0, 5, or 25 mg Aroclor 1254/kg body wt from Days 10 to 16 of gestation. Hepatic retinoid (retinol, retinyl palmitate, and retinyl stearate) levels were determined in fetuses and dams from Day 20 of gestation, in male and female neonates 21 days postpartum, and in young adult offspring 90 days after birth. Retinol levels were determined in fetal and maternal plasma (Gestation Day 20) and plasma from the offspring 21 and 90 days after birth. Maternal and fetal plasma retinol levels were decreased by 35 and 38% on Day 20 of gestation following exposure to the highest dose of Aroclor 1254. Male, but not female, neonatal plasma retinol levels were significantly decreased (23%) in the high-dose group. No effects of PCB treatment were seen on plasma retinol levels in the offspring 90 days after birth. Only slight reductions in fetal and maternal hepatic retinol and retinyl palmitate concentrations were observed after prenatal PCB exposure. Male neonatal hepatic retinyl palmitate levels were reduced by 25 and 50% in the 5 and 25-mg Aroclor 1254/kg dose groups, respectively, while female neonatal hepatic retinyl palmitate levels were significantly reduced only in the high-dose group. Ninety days after birth, male hepatic retinyl palmitate levels were only slightly reduced in the highest dose group; however, hepatic retinol concentrations were significantly reduced by 50% in both PCB treatment groups. Female adult offspring exhibited significant reductions in hepatic retinyl palmitate levels (25%) in both PCB treatment groups, while hepatic retinol levels exhibited an unusual increase of more than 100% of controls in the low-dose group, while levels in the high-dose group were similar to controls. This study demonstrates that even a relatively low maternal dose of Aroclor 1254 results in long-term alterations in retinoid status of the offspring in the rat.

Intestinal vitamin A metabolism: coordinate distribution of enzymes and CRBP(II)

In the mucosal layer of the small intestine, we found nearly identical gradients of CRBP(II), retinal reductase, and LRAT levels down the duodenal-ileal axis, suggesting coordinate regulation of these three proteins. In all cases the level of binding protein or enzyme activity was greatest in the proximal intestine and then decreased sharply in the distal half. This pattern fits with the known capacity of the intestine to absorb vitamin A. In addition, the retinal reductase activity was found predominantly in the intestinal mucosa, while LRAT activity was found in both the intestinal mucosa and muscle. An even distribution of LRAT activity along the longitudinal axis of the intestinal muscle was consistent with an even distribution of CRBP in that tissue. In conjunction with LRAT activity and CRBP, we found endogenous retinyl ester stores in the intestinal muscle layer. The patterns of retinyl ester produced by LRAT in vitro and found in vivo were similar, with retinyl palmitate predominating and a high percentage comprised of retinyl stearate. We also observed a bile salt-independent retinyl ester hydrolase activity in intestinal muscle whose distribution paralleled the retinyl ester stores and LRAT levels. This hydrolase appears to be distinct from retinyl ester hydrolases described from other organs as its activity was insensitive to retinyl ester chain length, the presence of bile salts, or the addition of apo-CRBP. This activity was inhibited by diethyl-p-nitrophenyl-phosphate (IC50 100 microM) and diethylpyrocarbonate (IC50 10 microM), demonstrating a requirement for active serine and histidine residues. In addition, we describe an activity present in some intestinal microsomal preparations that can perturb determinations of reductase and LRAT activity and must be avoided.

β-Carotene, Retinol and Retinyl Ester Concentrations in Serum and Selected Tissues of Ferrets Fed β-Carotene

The concentrations of β-carotene, retinol and retinyl esters in serum and selected tissues of ferrets fed diets supplemented with β-carotene (80 μg/g wet diet) for 3 wk were determined. The initial concentration of serum β-carotene was 0.011 ± 0.006 μmol/L (mean ± SEM); at the end of the experimental period it was 5.75 ± 1.60 μmol/L. No significant differences in serum retinol and total retinyl esters were observed between β-carotene-fed and control ferrets that had been fed an unsupplemented diet. The predominant retinyl esters in serum were retinyl stearate (53%) and retinyl palmitate (35%). Of the tissues analyzed after β-carotene feeding, the liver contained the highest concentration of β-carotene (78.8 ± 18.8 nmol/g). Other tissues that contained β-carotene in amounts ranging from 17 to 20 nmol/g were adrenals, small intestine, stomach and colon; lesser amounts (6.9 nmol/g) were found in kidneys. Amounts ranging from 1.2 to 2.3 nmol/g were found in muscle, bladder, adipose tissue, lungs and skin; only 0.37 and 0.34 nmol/g were present in brain and eyes, respectively. Thus, like humans, ferrets have the capacity to absorb intact β-carotene and to store this compound in tissues, especially the liver. However, compared with humans, ferrets have elevated concentrations of retinyl esters in serum, liver and other tissues.

Quantitative plasma disposition of retinol and retinyl esters after high-dose oral vitamin A administration in the cynomolgus monkey

A solid-phase extraction technique followed by automated high-performance liquid chromatography sample elution was successfully used to evaluate the effect of three pharmaceutical parameters on the plasma profile of various forms of vitamin A after an oral dose to cynomolgus monkeys. The three parameters evaluated were the chemical form of vitamin A (retinol versus retinyl acetate), the vehicle (acetone/Tween 20/water versus acetone/soybean oil), and the retinol dose (2, 10, and 50 × 10 3 retinol equivalents/kg). The form of the administered compound, retinol or retinyl acetate, appeared to have no major effect on the formation of nonpolar retinoids. The ester profile in plasma differed depending on whether the dose was administered in the water-based or the oil-based vehicle. Irrespective of the vehicle type the predominant retinoid formed was retinyl palmitate/oleate. However, retinol doses in the water-based vehicle formed relatively high concentrations of retinyl laurate and retinyl myristate but no retinyl linolenate. The retinol dose in the oil-based vehicle formed consistent, but relatively minor, concentrations of retinyl linolenate, higher relative concentrations of retinyl linoleate, and no retinyl laurate or myristate. The dose of retinol administered had an impact on the diversity of the nonpolar retinoid profile. The low dose led to the presence of almost exclusively retinyl palmitate/oleate and retinyl stearate, whereas at higher doses the other retinyl esters became major retinol constituents. These findings are consistent with the hypothesis that, at low doses, the principle esterification pathway is via lecithin:retinol acyltransferase (LRAT) which produces retinyl palmitate, but at higher doses acyl-CoA:retinol acyltransferase is a prominent esterification enzyme, due to the saturation of the LRAT pathway, producing a more diverse profile of retinyl esters.

Quantitative Plasma Disposition of Retinol and Retinyl Esters after High-Dose Oral Vitamin A Administration in the Cynomolgus Monkey

A solid-phase extraction technique followed by automated high-performance liquid chromatography sample elution was successfully used to evaluate the effect of three pharmaceutical parameters on the plasma profile of various forms of vitamin A after an oral dose to cynomolgus monkeys. The three parameters evaluated were the chemical form of vitamin A (retinol versus retinyl acetate), the vehicle (acetone/Tween 20/water versus acetone/soybean oil), and the retinol dose (2, 10, and 50 × 103 retinol equivalents/kg). The form of the administered compound, retinol or retinyl acetate, appeared to have no major effect on the formation of nonpolar retinoids. The ester profile in plasma differed depending on whether the dose was administered in the water-based or the oil-based vehicle. Irrespective of the vehicle type the predominant retinoid formed was retinyl palmitate/ oleate. However, retinol doses in the water-based vehicle formed relatively high concentrations of retinyl laurate and retinyl my-ristate but no retinyl linolenate. The retinol dose in the oil-based vehicle formed consistent, but relatively minor, concentrations of retinyl linolenate, higher relative concentrations of retinyl linoleate, and no retinyl laurate or myristate. The dose of retinol administered had an impact on the diversity of the nonpolar retinoid profile. The low dose led to the presence of almost exclusively retinyl palmitate/oleate and retinyl stearate, whereas at higher doses the other retinyl esters became major retinol constituents. These findings are consistent with the hypothesis that, at low doses, the principle esterification pathway is via lecithin:retinol acyltransferase (LRAT) which produces retinyl palmitate, but at higher doses acyl-CoA:retinol acyltransferase is a prominent esterification enzyme, due to the saturation of the LRAT pathway, producing a more diverse profile of retinyl esters.

Alterations in β-carotene and vitamin e status in rats fed β-carotene and excess vitamin A

The effects of feeding various levels of vitamin A with and without various levels of β-carotene on vitamin E and β-carotene status and hepatic biodegradation capacity were examined. Male weanling Sprague-Dawley rats, 10/group, were fed ad libitum for 8 wk diets containing vitamin A and β-carotene in a 3×3 factorial experimental design. Vitamin A palmitate was given at the National Research Council's recommended requirement level of 4,000 IU/kg of diet (control), 10 times the requirement (vitamin A1) and 100 times the requirement (vitamin A2). Each of these groups was given β-carotene at either 0,48 (BC1) or 480 mg/kg (BC2) of diet. Liver vitamin A levels increased dramatically and were 100-fold higher in vitamin A2 groups than in the control group. Retinyl esters increased in the liver; retinyl stearate increased as a result of β-carotene treatments. Liver β-carotene levels were significantly reduced in vitamin A1-BC2 and vitamin A2-BC2 groups compared to the control-BC2 group. In the vitamin A2-BC2 group, plasma vitamin E was reduced 77% compared to the control group; hepatic microsomal cytochrome P-450 and its isozyme, benzephetamine demethylase, were significantly lower; and the specific activity of glutathione S-transferase was increased. These findings suggest that vitamin E status can be altered by ingesting excessive vitamin A or β-carotene and that vitamin A and β-carotene changed the biodegradation and detoxification capacity of the liver in rats.

Effect of Feeding on Vitamin A Concentrations in Blood Plasma of Dogs

The effects of different concentrations of vitamin A in food as well as different food compositions on serum vitamin A levels in dogs were investigated. Contrary to current knowledge for all other species, vitamin A levels in dogs were clearly affected by the daily vitamin A supply as well as the type of food. This behavior, similar to that of vitamin E, can be explained by the fact that dogs and other carnivores transport most of their vitamin A in blood as retinyl esters (mainly retinyl stearate) bound to lipoproteins. The differences in the retinyl ester pattern between vitamin A in liver and in blood indicates that the mobilization of vitamin A from the liver involves selective mechanism. The possible importance of nonspecific, lipoprotein-bound vitamin A esters in the blood of dogs is discussed.

The majority of vitamin A is transported as retinyl esters in the blood of most carnivores

1. 1. In canines and mustelides total vitamin A was 10–50 times higher compared to other species due to a high amount of retinyl esters (40–99% of total vitamin A) in blood plasma. The dominant vitamin A ester was in most species retinyl stearate. 2. 2. In Ursidae, Procyonidae, Viveridae and Felidae, total vitamin A was much lower. When present, however, retinyl esters also represented 10–65% of total vitamin A in plasma. 3. 3. Only retinol was detected in plasma of the family, Hyaenidae, and the suborder, Pinnipedia. 4. 4. In maned wolf cubs it was found that retinol, retinyl esters and α-tocopherol increased with the age of the animals, reaching values comparable to adult animals at the age of 5 months.

The effect of high vitamin a intake on fatty acid composition of rat liver retinyl esters and total liver fatty acids

Female Fischer 344 rats fed AIN-76 diet plus 7 μmoles (2.3 mg) retinyl acetate in corn oil daily for 17 d (vitamin A-supplemented) showed markedly enhanced liver vitamin A levels compared with control animals fed AIN-76 diet plus corn oil (6.6 μmol/g liver vs. 0.21 μmole/g, p<0.001) and lower serum retinol (0.55 μM vs. 0.99 μM, p<0.001). As mole per cent of liver retinyl esters, retinyl palmitate increased on vitamin A supplementation (from 61.1% to 75.5%, p<0.001), retinyl stearate and laurate plus arachidonate (unresolved) decreased (from 19.2% to 10.4%, p<0.001, and 5.5% to 1.8%, p<0.001, resp.), and retinyl oleate did not change (5.0% to 4.8%). The fatty acid composition of total liver lipids showed similar changes. In general, the ratios of more unsaturated to less unsaturated fatty acids increased, while those of elongated to unelongated fatty acids fell. Thus, high intakes of vitamin A clearly influence the overall fatty acid metabolism of the liver, possibly by stimulating desaturation reactions and by inhibiting elongation.

Esterification by rat liver microsomes of retinol bound to cellular retinol-binding protein.

We have investigated the esterification by liver membranes of retinol bound to cellular retinol-binding protein (CRBP). When CRBP carrying [3H]retinol as its ligand was purified from rat liver cytosol and incubated with rat liver microsomes, a significant fraction of the [3H]retinol was converted to [3H]retinyl ester. Esterification of the CRBP-bound [3H]retinol, which was maximal at pH 6-7, did not require the addition of an exogenous fatty acyl group. Indeed, when additional palmitoyl-CoA or coenzyme A was provided, the rate of esterification increased either very slightly or not at all. The esterification reaction had a Km for [3H]retinol-CRBP of 4 +/- 0.6 microM and a maximum velocity of 145 +/- 52 pmol/min/mg of microsomal protein (n = 4). The major products were retinyl palmitate/oleate and retinyl stearate in a ratio of approximately 2 to 1 over a range of [3H]retinol-CRBP concentrations from 1 to 8 microM. The addition of progesterone, a known inhibitor of the acyl-CoA:retinol acyltransferase reaction, consistently increased the rate of retinyl ester formation when [3H]retinol was delivered bound to CRBP. These experiments indicate that retinol presented to liver microsomal membranes by CRBP can be converted to retinyl ester and that this process, in contrast to the esterification of dispersed retinol, is independent of the addition of an activated fatty acid and produces a pattern of retinyl ester species similar to that observed in intact liver. A possible role of phospholipids as endogenous acyl donors in the esterification of retinol bound to CRBP is supported by our observations that depletion of microsomal phospholipid with phospholipase A2 prior to addition of retinol-CRBP decreased the retinol-esterifying activity almost 50%. Conversely, incubating microsomes with a lipid-generating system containing choline, CDP-choline, glycerol 3-phosphate, and an acyl-CoA-generating system prior to addition of retinol-CRBP increased retinol esterification significantly as compared to buffer-treated controls.

Vitamin A is stored as fatty acyl esters of retinol in the lacrimal gland.

Many tissues which require vitamin A store the vitamin as long-chain fatty acyl esters of retinol. As part of a study designed to characterize vitamin A metabolism in the lacrimal gland, which transports retinol from blood to lacrimal gland fluid, extracts from lacrimal glands of rabbits and rats were analyzed by non-aqueous high performance liquid chromatography. Retinyl linoleate, retinyl palmitate, and retinyl stearate were identified in these extracts by their co-elution with standards, their retention time relative to retinyl palmitate, and their susceptibility to hydrolysis by saponification. Retinyl palmitate was present in rabbit lacrimal gland at 51.0 +/- 10.1 ng/g tissue. After treatment of vitamin A-deficient rabbits with orally administered [11,12-3H] retinyl acetate, the radiolabeled esters retinyl linoleate, palmitate, and stearate were extracted from the lacrimal glands. These data show that the lacrimal gland stores vitamin A as fatty acyl esters of retinol.

Quantitative determination of vitamin A in liver and liverwurst using high pressure liquid chromatography (HPLC)

Samples of liver sausage and liver tissue from slaughtered animals were analysed for pre-formed vitamin A. A sensitive reversed phase HPLC method with fluorescence detection was used to determine the amount of free and esterified retinol in extracts of these samples. Under our chromatographic conditions retinyl myristate and linoleate run together as do retinyl palmitate and oleate. The contents of all forms of vitamin A were expressed in milligrams of all-trans retinol per 100 g wet weight. The average concentrations of total vitamin A for turkey, pig, calf, beef, and chicken liver were 42.31, 38.15, 22.74, 14.98, and 13.22, respectively. In addition to these differences, the fatty acid composition of liver retinyl esters, as well as the amount of retinol, also varied considerably among species. Approximately 95% of the hepatic vitamin A was present as retinyl ester with retinyl palmitate/oleate as the main ester fraction. The second most abundant fatty acid in the retinyl ester fraction of calf, beef, and chicken liver was stearic acid followed by myristic/linoleic acid. An increment of retinol, however, was also found in these tissue samples. By contrast, in turkey liver the retinol fraction was increased and therefore both retinyl stearate and retinol were present in nearly equal amounts, whereas the retinyl ester fatty acids from pig liver contained relatively more myristate/linoleate and less stearate than those from liver of the other domestic animals (apparently a hallmark of pig liver). The retinol and retinyl ester pattern present in liver sausage was similar to, but not identical with, that of pig liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary vitamins A and E influence retinyl ester composition and content of the retinal pigment epithelium

Experiments were conducted to determine the influence of dietary levels of vitamin levels A and α-tocopherol on the amounts and composition of retinyl esters in the retinal pigment epithelium of light-adapted albino rats. Groups of rats were fed diets containing α-tocopherol and either no retinyl palmitate, adequate retinyl palmitate, or excessive retinyl palmitate. Other groups of rats received diets lacking α-tocopherol and containing the same three levels of retinyl palmitate. Retinoic acid was added to diets lacking retinyl palmitate. After 27 weeks, the animals were light-adapted to achieve essentially total visual pigment bleaches, and the neural retinas and retinal epithelium-eyecups were then dissected from each eye for vitamin A ester determinations. Almost all of the retinyl were found in the retinal pigment epithelium-eyecup portions of the eyes, mainly as retinyl palmitate and retinyl stearate. Maintaining rats on a vitamin A-deficient, retinoic acid-containing diet led to a significant reductions in retinal pigment epithelial retinyl ester levels in rats fed both the vitamin E-supplemented and vitamin E-deficient diets; contrary to expectations, the effect of dietary vitamin A deficiency was more pronounced in the vitamin E-supplemented rats. Vitamin A deficiency in retonic acid-maintained animals also led to significant reductions in retinyl palmitate-to-stearate ester ratios in the retinal pigment epithelia of both vitamin E-supplemented and vitamin E-deficient rats. Excessive dietary intake of vitamin A had little, if any, effect on retinal pigment epithelial retinyl ester content or composition. Vitamin E deficiency resulted in significant increases in retinal pigment epithelial retinyl palmitate content and in palmitate-to-stearate ester ratios in rats fed all three levels of vitamin A, but had little effect on retinal pigment epithelial retinyl stearate content. In other tissues, vitamin E deficiency has been shown to lower vitamin A levels, and its widely accepted that this effect is due to autoxidative destruction of vitamin A. The increase in retinal pigment epithelial vitamin A ester levels in response to vitamin E deficiency indicates that vitamin E does not regulate vitamin A levels in this tissue primarily by acting as antioxidant, but rather may act as in inhibitor of vitamin A uptake and/or storage. The effect of vitamin E on pigment epithelial vitamin A levels may be mediated by the vitamin E-induced change in retinyl palmitate-to-stearate ratios.