Search PubMed⌕ Search

Biomedical subjects

J G Bieri

Publications and source records attributed to J G Bieri.

At least 37 records · Page 2Linked to original sources
PubMed1982

The roles of vitamin E and unsaturated fatty acids in the visual process.

Relatively high proportions of long-chain, polyunsaturated fatty acids seem to be required in rod photoreceptor membranes in order to provide the precise microenvironment for the proper function of the visual pigment rhodopsin. At the same time, such high levels of lipid unsaturation put the photoreceptor membranes at a high risk for autoxidation. The antioxidant vitamin E which can minimize autoxidation of polyunsaturated fatty acids is found in rather high concentrations in the outer segment membranes. Dietary deficiency in vitamin E induces disintegration of rod outer segment membranes, probably by increasing autoxidation. Also, it greatly accelerates the accumulation of aging pigments in the retinal pigment epithelium, probably because these lipofuscin granules do indeed represent the end products of lipid peroxidation. Vitamin E supplements, up to threefold normal levels, appear to provide no significant protection of the retina from light damage produced either by short but acute or by long-term, low level exposures to light. This is not consistent with current theories which implicate lipid peroxidation in the destruction of rod outer segments in light damaged retinas; more work is needed before any relation between retinal light damage and vitamin E levels can be assessed. Surprisingly, the amount of lipofuscin granule accumulation in the retinal pigment epithelium is influenced dramatically by dietary levels of vitamin A. Even retinas lacking a source of polyunsaturated fatty acids from rod outer segments still may accumulate massive lipofuscin if dietary vitamin A is provided. Perhaps vitamin A, which has such a dynamic relationship with the retinal pigment epithelium, becomes oxidized, and then contributes to the formation of a lipofuscin-like pigment. Centrophenoxine, a drug claimed to be effective in reversing the accumulation of age-related lipofuscin in the central nervous system, has no obvious effect in the eye or uterus in removing the lipofuscin granules induced by vitamin E deficiency. Microperoxisomes are abundant in the retinal pigment epithelium, and may be associated with rapid lipid turnover and/or utilization of lipid soluble vitamins. Their potential roles, however, need further documentation and clarification. Recently developed techniques and new discoveries in lipid research open the way for many fruitful studies on the interactions and precise roles of lipids and lipid-soluble vitamins in vision.

Animals↗
PubMed1982

Intrinsic, light-independent, regional differences in photoreceptor cell degeneration in vitamin A-deficient rat retinas.

The retinas of retinol-deficient rats reared in darkness or cyclic light were examined to determine whether regional degeneration of photoreceptor cells was induced by environmental lighting or resulted from intrinsic differences between ocular hemispheres. Weanling male Sprague-Dawley rats were fed a retinol-adequate or retinol-deficient diet and were reared in either cyclic light or darkness through 29 weeks. The nasal retinal quadrants were examined by light microscopy and the number of photoreceptor nuclei was counted in a 630 micron segment beginning 200 micron from the optic nerve. Retinol-deficient rats reared in darkness for 29 weeks lost 24% of their photoreceptors in the inferior nasal quadrant but only 11% in the superior nasal quadrant. Deficient rats reared in cyclic light for 29 weeks lost 39% of their photoreceptor cells in the inferior nasal quadrant and only 16% in the superior nasal quadrant. Photoreceptor cells degenerated faster in the inferior nasal quadrant than in the superior nasal quadrant in darkness or cyclic light. These results indicate that regional differences in rate of photoreceptor cell loss in retinol-deficient rats are not induced by the lighting conditions but occur as a result of intrinsic differences between the ocular hemispheres.

Animals↗
PubMed1981

Expressing dietary values for fat-soluble vitamins: changes in concepts and terminology.

The 9th ed. of the Recommended Dietary Allowances has abandoned the use of international units for expressing the food values for vitamins A, D, and E, and has set forth expressions based on absolute weights, including vitamin K. These changes will necessitate a revision in the manner in which both experimental and applied nutritionists deal with these vitamins. In this review, the background and rationale for these changes are presented in an effort to aid investigators in their transition to this new concept. Changes in the nomenclature of vitamin E are also explained.

Animals↗
PubMed1981

Reduced intestinal absorption of vitamin E by low dietary levels of retinoic acid in rats.

It was observed that rats fed a low dietary level of retinoic acid had markedly lower plasma concentrations of alpha-tocopherol than did rats fed the same amount of retinol. In this report, the possible mechanisms by which retinoic acid alters vitamin E metabolism has been investigated. Weanling male rats were fed a complete purified diet with either retinol or retinoic acid at 4 mg/kg diet; plasma and tissues were analyzed after 2-5 weeks. The plasma alpha-tocopherol concentration in rats ingesting retinoic acid was one-half that of rats ingesting retinol, and this difference also occurred in the liver and adipose tissue. Similar effects occurred in chicks. This low dietary level of retinoic acid had no effect on plasma triglyceride concentration, as has been reported for higher intakes, and plasma cholesterol and total lipids were also unaffected. Retinoic acid did not affect the rate of decrease in endogenous alpha-tocopherol in normal rats fed a vitamin E-free diet for 3 weeks. In rats with mesenteric lymph cannulas, dietary retinoic acid caused a reduced absorption of 3H-labeled alpha-tocopherol. In chicks fed retinoic acid, plasma and liver radioactivity 2.5 hours after an oral dose of 3H-alpha-tocopherol was one-fifth that of chicks fed retinol. More oxidation of alpha-tocopherol occurred during absorption in rats fed retinoic acid than in those fed retinol, as evidenced by more alpha-tocopherylquinone in the collected lymph. We postulate that dietary retinoic acid reduces the intestinal absorption of alpha-tocopherol and may also promote its oxidation.

Animals↗
PubMed1981

Effects of moderate-intensity light on vitamin A-deficient rat retinas.

The effects of moderate-intensity light (150 to 200 ft-cd) on retinal structure were compared between retinol-adequate and retinol-deficient rats after 1 to 6 days of light exposure during the 12 hr light phase of the cycle. Both damage to the outer segments and loss of photoreceptor cells were accelerated in retinol-adequate rats. Outer segments in retinas of retinol-adequate rats showed an abnormal staining pattern and disruption of disc structure in the distal portion about 2 days before those of retinol-deficient rats. After 4 days of exposure 24% of the photoreceptor cells had degenerated in the retinol-adequate retinas, but only 6% in the retinol-deficient retinas. By 6 days 65% and 41% of the photoreceptors had degenerated in the retinol-adequate and retinol-deficient retinas, respectively. Thus light exposure induced more rapid degeneration of photoreceptor cells in rats receiving adequate retinol than in those deficient in this vitamin.

Animals↗
PubMed1981

Effects of sunflower seed supplements on reproduction and growth of RCS rats with hereditary retinal dystrophy.

Both control and dystrophic pink-eyed RCS rats reproduced poorly when they were fed a standard laboratory rodent diet and were housed in conventional animal rooms unshielded from pathogenic influences. More prolific reproduction and improved growth of young were obtained with a commercial unsterilized closed formula pelleted rodent ration, supplemented with 25% sunflower seed kernels. The sunflower kernels contained a high concentration of vitamin E and 47% fat which was mostly unsaturated. Linoleic acid was 75% of the unsaturated fatty acids. The kernels also contained a higher concentration of selenium (0.8 mg/kg) than standard rodent diets. Effective absorption of the high vitamin E of the diet was shown by analyses of blood plasma of 50-day-old dystrophic and control rats, in which the alpha-tocopherol level was three-fold that in animals fed standard laboratory rodent diet. Dams fed the diet had calmer temperaments and improved lactation. Litters of 8-13 pups were produced, and the pups grew rapidly to weaning with 95% survival of the control strains and 75% survival of the dystrophic strain. Progeny fed the diet for 8-10 months after weaning did not manifest cataracts, which occurred in 23% of the pink-eyed dystrophic animals fed standard rodent diets.

Animal Feed↗
PubMed1980

Lipofuscin in vitamin E deficiency and the possible role of retinol.

This study was designed to determine if the vitamin A status of rats could affect the degree of lipofuscin formation in vitamin E deficient rats, inasmuch as an earlier report proposed a retinoyl complex in human brain lipofuscin pigment. Female rats were depleted of vitamin E from weaning while being maintained on different intakes of vitamin A (0, 0.8 and 8.0 mg/kg diet). The amount of lipofuscin present in the uterus was estimated at intervals between 2 and 8 months by visual observations, by histological fluorescence and by organic solvent extractable fluorescence. There was no difference in pigment deposition by any of the three criteria used, whether the animals were made retinol deficient and maintained on retinoic acid or were fed a low or high intake of retinol. Organic solvent extractable fluorescence was a poor indicator of the degree of pigment deposition in the uterus. It appears unlikely that retinol is a significant component of lipofuscin pigment in this tissue.

Animals↗
PubMed1980

Ineffectiveness of testosterone and FSH in maintaining the vitamin A deficient rat testis.

The combined administration of follicle-stimulating hormone and testosterone to sexually mature male rats whose testes were in the early stages of damage from retinol deficiency did not prevent the continued degeneration of the germinal epithelium. It is concluded that the action of retinol on the testis is probably not mediated through, nor influenced by, the pituitary or steroid hormones.

Animals↗
PubMed1980

An overview of the RDAs for vitamins.

The allowances for vitamins have undergone re-evaluation with emphasis being given to the information used to establish them. As noted, some allowances are still not as clearly delineated as desired. However, it is unlikely that future editions will make marked changes for any of the vitamins. In other words, we are in the right "ball park," not in the outfield but in the infield. Small fluctuations from edition to edition generally have little effect in the use for which RDAs were originally intended, namely, meal planning. However, small changes can have a significant impact for some of the broader applications for which they are now being used. This raises the question being heard more frequently, namely: Should we have different standards for these other applications, such as assessing nutritional adequacy or planning food assistance programs?

Ascorbic Acid↗
PubMed1980

Deficiencies of vitamins E and A in the rat. Retinal damage and lipofuscin accumulation.

The interrelationships of vitamins E and A in maintaining various structural components of the retina were studied in four groups of weanling female rats fed purified diets adequate or deficient in each vitamin: +E, +A; -E, +A; +E, -A; and -E, -A. Groups deficient in retinol (-A) were supplemented with retinoic acid. After 14, 21, and 35 weeks, the retinas were examined histologically and ultrastructurally. At 35 weeks, the doubly deficient rats (-E, -A) had lost 92% of their rod nuclei, whereas rats deficient in vitamins A (+E, -A) or E (-E, +A) alone had lost only 34% and 20%, respectively. Vitamin E deficiency resulted in extensive lipofuscin deposits in the retinal pigment epithelium as early as 21 weeks, but the presence of vitamin A doubled the number of lipofuscin granules (-E, +A vs. -E, -A) and induced an even greater increase in their autofluorescence. Another clear influence of vitamin A was seen when +E, +A retinas autofluoresced not only much more than +E, -A retinas, which had similar numbers of granules, but also more than -E, -A retinas, which had about twice as many lipofuscin granules. In the retina, unlike the uterus, the lipofuscin-specific autofluorescence and lipofuscin granule number were not proportional. Moreover, the numbers of granules were influenced by both vitamins E and A, whereas the intensity of lipofuscin-specific autofluorescence was determined almost exclusively by vitamin A. Probably the accelerated loss of photoreceptor cells in -E, -A retinas resulted from both oxidation of membranes and oxidation of retinal vitamin A stores in the absence of vitamin E protection.

Animals↗
PubMed1979

Simultaneous determination of alpha-tocopherol and retinol in plasma or red cells by high pressure liquid chromatography.

This paper describes a rapid, microprocedure for the simultaneous determination of alpha-tocopherol (vitamin E) and retinol (vitamin A) in plasma, and of alpha-tocopherol alone in red cells since cells do not contain retinol. A total lipid extract from 0.1 ml plasma or 0.125 ml red cells and containing internal standards of alpha-tocopheryl acetate and retinyl acetates is injected onto a high pressure liquid chromatography with a reverse phase column developed with methanol-water. An ultraviolet detector with 280-nm filter is used. The chromatogram is complete in 8 min and the alpha-tocopherol and retinol are quantitated by the peak height ratio method. Comparison of results with both plasma and red cells gave excellent agreement with conventional methods for these vitamins. The procedure should be particularly useful for clinical studies and nutrition surveys.

Chromatography, High Pressure Liquid↗
PubMed1979

AIN-76 diet.

Explore the source record for details and available documents.

Animal Nutritional Physiological Phenomena↗
PubMed1979

Structural and biochemical changes in vitamin A--deficient rat retinas.

The levels of rhodopsin and opsin were investigated in relation to the maintenance of retinal structure in retinas of vitamin A--deficient rats in low levels of cyclic illumination (1.5 to 2 foot-candles). Rhodopsin levels decreased in the deficient retinas to approximately 20% of control at 9 weeks, and this level was retained through 39 weeks on the deficient diet. Opsin levels decreased at a slower rate but reached about 20% of control levels at 32 weeks. Despite the decrease in rhodopsin levels, obvious deterioration of disc structure was not observed until 16 weeks of deficiency, when opsin levels had already decreased to 60% to 70% of control. The structural disruption of photoreceptor outer segments was localized initially in discs of the distal third. Rod cell degeneration preceded cone cell degeneration in vitamin A--deficient retinas. Most of the rods and cones persisted in the posterior retina at 23 weeks on the deficient diet; however, by 40 weeks, only 11% of the rod nuclei remained. In contrast, about 63% of the cone nuclei were present at 40 weeks of deficiency. The photoreceptor cells were affected by the deficiency to a greater extent in the inferior hemisphere than in the superior hemisphere of the eye.

Animals↗
PubMed1979

Vitamin E deficiency and the retina: photoreceptor and pigment epithelial changes.

To investigate the role of normal vitamin E levels and the interrelationships between vitamin E and A in maintaining the visual cells of the retina, weanling female Sprague-Dawley rats were fed vitamin E-free diets differing tenfold in their vitamin A content (0.8 and 8.0 mg of retinol per kilogram of diet). Rats on vitamin E-free diets with the higher vitamin A level exhibited marked disruption of photoreceptor outer segment membranes and a fivefold increase in the number of lipofuscin granules in the pigment epithelial cells which ingest these membranes. Rats on vitamin E-free diets with the lower vitamin A level showed the same retinal damages plus significant loss of photoreceptor cells compared to age-matched rats on control diets. Rods and cones were involved equally, and their pattern of loss was not like that found in vitamin A deficiency. Normal levels of vitamin E probably protect photoreceptor membranes from oxidative damage and retard the accumulation of their remnants and other products of lipid breakdown in the pigment epithelium. The vitamin A status of rats has a significant influence on the extent of damage induced by vitamin E deficiency.

Animals↗