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Biomedical subjects

D Sklan

Publications and source records attributed to D Sklan.

At least 109 records · Page 6Linked to original sources
PubMed1990

Effects of hard fats on in vitro and in vivo rumen fermentation, milk production and reproduction in dairy cows.

Adding 0, 5, 15, and 20% of substrate as prilled or unprilled fatty acids [palmitic (47 to 48%), stearic (36 to 37%), and oleic (14%) acids] to an in vitro rumen fermenter had no effect on total VFA production. Acetate:propionate ratio was reduced by fatty acid concentrations of 15 and 20% (prilled and unprilled). In a 4 x 4 Latin square, increasing dietary prilled fatty acids (0, 3, 6, or 9% of DM) decreased DM intake, increased percentage of milk fat, and had no effect on percentage of milk protein. Milk volume and FCM increased with 3% but decreased with 6 and 9% dietary fatty acids. Rumen fluid acetate:propionate decreased with increasing dietary fatty acids. Holstein cows in three herds in Pennsylvania and Friesian cows in an Israeli herd were assigned randomly to receive, from 0 to 110 to 150 d postcalving, diets containing 0 or 2% of DM prilled fat. In Israel, dietary fat increased milk yield, FCM, and fat percentage during the first 90 d postcalving. In Pennsylvania, prilled fat had variable effects on milk composition and little effect on milk yield and FCM. Conception rate was improved in cows consuming rations containing prilled fat: first service, 59.1 versus 42.6%; all services, 59.3 versus 40.7%. The inclusion of prilled fat at 2% of DM in dairy cattle rations had slight effects on rumen fermentation, variable effects on milk yield and composition, and beneficial effects on conception rate.

Animals↗
PubMed1990

Effect of moderate semi-starvation on plasma lipids.

The effect of a daily intake of 200 kcal for 6 days on blood lipid levels of normal and obese subjects was examined. Subjects exhibited a decrease in body weight of 5.9 percent. Plasma glucose levels decreased with no change in insulin levels. FFA and cholesterol did not change significantly with the low caloric intake. Triglyceride and phospholipid concentrations, elevated in obese subjects before the dietary period, decreased significantly with low caloric intake. In contrast no significant changes were observed in triglycerides or phospholipids in normal subjects. Serum uric acid increased during diet in normal but not in obese subjects. These results show different patterns of changes in plasma lipids in normal and obese subjects on very low caloric intake and raise the possibility of differences in utilization of lipid and protein stores, and may also hint at a role for phospholipids in energy metabolism. Very low calorie and carbohydrate diets may be beneficial for weight reduction in obese subjects without increasing blood lipids.

Adult↗
PubMed1989

Feeding calcium soaps of fatty acids to lactating cows: effect on production, body condition and blood lipids.

Ca soaps of fatty acids (CSFA, 0.5 kg/d) were added to the diet of lactating cows for 170 d, and production, body condition score and blood lipids were examined. Production of fat-corrected milk was increased by 1.5 kg/d owing to increase in both milk and fat production. Over 250 d lactation, production of fat-corrected milk was enhanced by 1.3 kg/d. Body condition scores were lower in cows fed CSFA in early lactation, but tended to exceed those of control cows after 80 d lactation. Reproductive performance was improved in cows fed CSFA. Serum total lipids, phospholipids and cholesterol were increased in CSFA cows at 15 and 29 d but not at 59 d post partum. The cholesterol increase was mainly in the high density lipoprotein fraction.

Analysis of Variance↗
PubMed1989

Impaired T lymphocyte immune response in vitamin A depleted rats and chicks.

Vitamin A deficiency results in decreased immune responses; the objective of the present study was to investigate the involvement of T lymphocytes in the depression of immune responses resulting from vitamin A depletion. This objective was achieved by evaluating antigen-specific T lymphocyte proliferative responses in vitro as vitamin A depletion developed. The evaluation was performed in both rat and chick to examine the generality of immune effects due to vitamin A depletion. Our findings show that vitamin A depletion led to severe impairment of T lymphocyte activity in both animal models, and that this was directly related to the vitamin A status in both species. Immune response impairment was found to precede other manifestations of vitamin A deficiency, and was rapidly corrected by feeding retinyl acetate boluses. This implied a possible regulatory, rather than constitutive, role of vitamin A in immune responsiveness.

Animals↗
PubMed1989

Antigen-specific immune response impairment in the chick as influenced by dietary vitamin A.

The effects of a broad range of dietary vitamin A levels on antigen-specific immune responses of the chick were studied. Vitamin A deficiency and long-term excess caused impairment of the immune response as demonstrated by antigen-specific antibody production and T-lymphocyte proliferation in vitro. Immune responsiveness was correlated with both hepatic and blood vitamin A levels, and was affected prior to other physiological manifestations of hypo- or hypervitaminosis. In contrast to the effects of long-term vitamin excess, a large vitamin A bolus did not cause immune response impairment and, on the contrary, restored normal immune functions in previously vitamin A-depleted chicks. This finding implied a regulatory role for vitamin A in the immune system rather than a constitutive one.

Animals↗
PubMed1989

The effects of vitamin A, beta-carotene and canthaxanthin on vitamin A metabolism and immune responses in the chick.

Chicks were fed diets containing, 0, 0.85 and 350 mg/kg vitamin A and 1 g/kg beta-carotene or canthaxanthin from hatching. Carotene increased and canthaxanthin depressed plasma and hepatic vitamin A concentrations. High vitamin A levels decreased the concentration of both carotenoids. Neither carotene nor canthaxanthin affected intestinal carotene cleavage in vitro. T-lymphocyte proliferative responses were decreased at low vitamin A intakes and enhanced at the high vitamin A intake. Carotene and canthaxanthin fed with 0.85 mg/kg vitamin A had no effect on immune response and with 350 mg/kg vitamin A prevented the enhancement of the proliferative response. It is concluded that immune response in the chick is modulated by vitamin A; carotene and canthaxanthin effects are probably due to influences on vitamin A metabolism.

Animals↗
PubMed1988

Some characteristics of a high molecular weight lipid-protein aggregate and its possible role in intracellular fatty acid metabolism.

Several physical aspects of a high molecular weight lipid-protein aggregate separated by gel chromatography from chick and rat liver cytosol and its possible role in intracellular fatty acid metabolism were investigated. Electron microscopic examination of the high molecular weight lipid-protein aggregate indicated spherical particles with a diameter range of 200-600 A. This structure is consistent with a microemulsion particle of triglyceride encapsulated by phospholipid and protein. Uptake of fatty acids by microsomes occurred from the same lipid-protein aggregate, and the triglycerides synthesized in microsomes also became associated with these particles in the cytosol. The lipid-protein aggregate prepared by different homogenization methods showed identical ratios of components, but these ratios changed following incubation. These findings lend support to the concept that this aggregate plays a physiological role in intracellular lipid metabolism, and may be identifiable with previously reported subcellular fatty acid and triglyceride pools.

Animals↗
PubMed1987

Inhibition of arachidonic acid oxidation by beta-carotene, retinol and alpha-tocopherol.

Prostaglandin and hydroxyeicosatetraenoic acid (HETE) production from arachidonic acid in bovine seminal vesicles and kidney as influenced by the addition of beta-carotene, retinol or alpha-tocopherol was studied. The major product formed was prostaglandin E2 (approximately 85% prostaglandin E2 of control), and its proportion decreased with increasing concentration of the additives, while the proportion of HETE increased. Prostaglandin and HETE production was considerably inhibited by beta-carotene and retinol, and to a lesser extent by alpha-tocopherol; HETE production was inhibited less than that of prostaglandin. It appears that beta-carotene, retinol and alpha-tocopherol influence both the cyclooxygenase and lipoxygenase pathways; this modulation of arachidonic acid oxidation by physiological compounds may have important in vivo implications.

Animals↗
PubMed1987

Absorption of protein, fatty acids and minerals in young turkeys under heat and cold stress.

1. Absorption of protein, fatty acids, calcium, phosphate and potassium by young turkeys maintained at thermoneutral (24 degrees C), hot (35 degrees C) and cold (8 degrees C) conditions was examined. 2. Non-acclimatised, heat-stressed birds absorbed less potassium and phosphate, whereas absorption of nitrogen, fatty acids and calcium was not altered, as compared with birds at 24 degrees C. Non-acclimatised, cold-stressed birds absorbed less calcium than control birds and more nitrogen than non-acclimatised, heat-stressed birds. 3. Heat acclimatization might reduce the adverse effect of heat stress on potassium and phosphate absorption.

Animals↗
PubMed1987

Synthesis of retinol-binding protein and transthyretin in yolk sac and fetus in the rat.

Levels of retinol-binding protein (RBP) and transthyretin (TTR) were determined in rat maternal livers, placenta, yolk sac, whole fetuses and fetal livers at different stages of gestation. Yolk sac concentrations of RBP and TTR expressed as micrograms per mg protein were three- to fivefold higher than liver values. TTR (moles) in the whole fetus was higher than RBP at all stages of gestation. Fetal hepatic RBP concentration was relatively constant throughout gestation, where fetal hepatic TTR concentration was low until close to parturition. RBP was observed in fetal microsomes at 12 d gestation. Incorporation of labeled amino acids into both RBP and TTR in vitro was observed in the yolk sac. In the 20-d fetal liver, incorporation to RBP and TTR was observed, whereas at 14 d gestation, incorporation only to RBP was observed. A small amount of synthesis of both proteins was also observed in the placenta. In the fetal circulation at 20-21 d gestation, no TTR-RBP complex was observed; instead a broad peak of RBP was found eluting at 20,000-40,000 daltons on gel chromatography. Incubation of fetal serum with maternal TTR resulted in an RBP peak eluting with an Mr of approximately 40,000. Treatment of the fetal serum with either lysozyme, neuraminidase or endoglycosidase H resulted in a 20,000 dalton RBP peak and following incubation with maternal TTR, a 70,000 dalton RBP-TTR complex was formed. Yolk sac, fetal liver and amniotic fluid on gel filtration exhibited a 40,000-20,000 dalton RBP peak. It is suggested that retinol transport in the fetus may involve RBP and TTR synthesized in the yolk sac as well as in fetal tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

The effect of different dietary levels of vitamin A on metabolism of copper iron and zinc in the chick.

Chicks were fed on diets containing either no added vitamin A or 3300 micrograms/kg or 330,000 micrograms/kg retinol equivalents for 30 d. Concentrations of copper, iron and zinc were higher in liver and lower in plasma at low and high intakes of vitamin A. Haemoglobin, packed cell volume and erythrocyte levels were depressed by both low and high vitamin A intake and could be related to vitamin A levels by quadratic equations. The Zn and Fe levels in erythrocytes and serum albumin and ceruloplasmin were also affected in a similar fashion by low or high vitamin A diets. Hepatic activity of alcohol dehydrogenase (EC 1.1.1.1) and cytochrome oxidase (EC 1.9.3.1) paralleled Zn and Cu concentrations respectively. Superoxide dismutase (EC 1.15.1.1) and hydrolysis of triolein and retinyl palmitate were not correlated significantly with concentrations of metals but were correlated negatively with log vitamin A concentration. No changes in bone concentrations of Cu, Fe or Zn were detected. It is suggest that vitamin A influences metabolism of Cu, Fe and Zn possibly, in part, due to a decrease in secretion of transport proteins by the liver.

Alcohol Dehydrogenase↗
PubMed1987

Vitamin A in human nutrition.

Vitamin A, an unsaturated 20 carbon cyclic alcohol, has a variety of physiological functions including a role in vision, reproduction, growth and maintenance of epithelial and bone structures. The main sources of vitamin A are from preformed vitamin A in animal foods or from -carotene in green plants. Carotene is cleaved in the intestinal mucosa to retinol, which is transported in chylomicrons mainly to the liver which is the major storage site of vitamin A, where stores are mainly of retinyl palmitate. Utilization of vitamin A appears to be a highly regulated process; retinol is transported in the serum bound to a specific binding protein. There also may be some control of the level of retinol in cells possibly through membrane receptors or of excretion from the cell. Intracellular cytosolic retinol binding proteins transport retinol to the nucleus where specific receptors for retinol have been found. Intracellular binding proteins for retinoic acid and retinal, metabolites of retinol have also been found, and an interstitial protein transporting retinol is present in the eye. Vitamin A deficiency causes cessation of growth, night blindness, and renders the organism more susceptible to infection, and vitamin A supplementation has been shown to enhance immune response. Epidemiological studies have shown low vitamin A and carotene to be correlated with incidence of cancer. Excess vitamin A intake results in hypervitaminosis with severe detrimental effects. Vitamin A requirements appear to be met in most developed countries although in the populations at greatest risk, newborns and pregnant and nursing women, cases of deficiency are observed. However, in large areas of the world vitamin A deficiency is endemic, causing widespread blindness and mortality.

Biological Transport, Active↗
PubMed1986

Ruminal fermentation in vivo as influenced by long-chain fatty acids.

Responses of ruminal microbes to long-chain fatty acids in forms of free acids, calcium salts, or triglycerides were measured in trials with rumen cannulated heifers. Addition of fatty acids at 10% to a basal diet of 50% corn silage and 50% grain increased fat content 3 to 10 to 12%. Long-chain fatty acids with a high melting point (stearic acid) and calcium salts of long-chain fatty acids (vegetable fat and tallow) decreased acetate:propionate by about 20%. Long-chain fatty acids with a low melting point (oleic acid) and the triglyceride form of long-chain fatty acid (tallow) decreased acetate to propionate ratio by 50 to 60%. Even though they were not completely inert in the rumen, responses with the hard long-chain fatty acids (stearic acid) and with calcium salts of long-chain fatty acids confirm that these are efficacious for protecting ruminal microbes from adverse effects of fat. With calcium salts of long-chain fatty acids, dietary buffers may be needed to maintain ruminal pH so that dissociation of salts does not occur. Long-chain fatty acid supplementation at 10% of the diet is probably more than the amount needed to optimize productivity and health. With most diets, 6 to 8% supplemental long-chain fatty acid is probably sufficient.

Animals↗
PubMed1985

Retinol transport proteins and concentrations in human amniotic fluid, placenta, and fetal and maternal sera.

1. The proteins binding retinol, and retinol concentrations, were determined in amniotic fluid, placental cytosol and in the fetal and maternal circulation. 2. In non-pregnant women, plasma retinol was almost exclusively found in a transthyretin-retinol-binding-protein complex whereas, in pregnant women, retinol-binding-protein-bound retinol was observed not complexed to transthyretin. This latter fraction increased in concentration with fetal age. These two fractions were the major retinol-protein complexes in amniotic fluid and their relative amounts changed with progress of gestation. 3. In fetal blood both of these fractions were again found, with higher proportions of retinol-binding-protein-bound retinol in the umbilical artery than in the umbilical vein.

Amniotic Fluid↗
PubMed1985

Placental transport of retinol in ewes fed high intakes of vitamin A.

Twelve ewes were fed retinyl propionate equivalent to 12,000 micrograms retinol/kg body weight per day for the last two trimesters of pregnancy (group fed high vitamin A). Four ewes received a control level of 120 micrograms/kg body weight per day. Indwelling catheters were implanted surgically in fetal jugular veins and carotid arteries. Ewes or fetal lambs received [3H]retinol intravenously, and blood was sampled until parturition. The ewes fed large amounts of vitamin A maintained viable fetal lambs for 6 d less than did controls. Plasma retinyl ester concentrations were elevated in the ewes fed a high level of vitamin A but not in their fetal lambs. Rates of plasma retinol transport and clearance increased with vitamin A intake in ewes and their fetal lambs. Efficiency of placental retinol transport in the group fed high levels of vitamin A was less than one-quarter that for controls. However, placental transport rate was approximately 100 micrograms/d greater than that of controls with an equivalent amount retained by the fetoplacental unit in the group fed high vitamin A. These data indicate that placental transport of retinol is partially regulated. High maternal vitamin A intake results in high retinol transport to the fetus.

Animals↗
PubMed1985

Movement and absorption of major minerals and water in ovine gastrointestinal tract.

Movement of calcium, chloride, magnesium, potassium, sodium, and water in the intestine of sheep was determined with cerium-141 as an unabsorbed reference substance. Net secretion of phosphorus and sodium, but not of potassium and calcium, was observed to the rumen. Water disappeared from the omasum and was secreted in the abomasum. Chloride secretion occurred in the omasum and more in the abomasum. Extensive secretion in the duodenum increased flows of sodium and potassium 8 to 9 times; of calcium, chloride, and phosphorus 3 to 6 times; of magnesium 1.3 times; and of water 12 times. Reabsorption was rapid in the small intestine, the major site of disappearance of all ions. Rates of disappearance decreased with increasing distance from the pylorus. Little further net disappearance of calcium, phosphorus, magnesium, or potassium was found in the large intestine, whereas water, sodium, and chloride disappearance continued. Overall absorption of sodium, potassium, and chloride was approximately 90%, of phosphorus 63%, of calcium 38%, and of magnesium 71%. This study highlights the importance of endogenous secretions in mineral absorption in the sheep.

Animals↗
PubMed1985

Digestion and absorption of lipids and bile acids in sheep fed stearic acid, oleic acid, or tristearin.

Sheep were fed diets containing 7.5% added stearic acid, oleic acid, or tristearin for 21 days. In addition, 50 microCi/kg cerium-141 was included for the last 10 days on experimental diets as an unabsorbed reference substance. In the rumen dietary triglycerides were approximately 50% hydrolyzed, and hydrogenation resulted in saturation of the free fatty acid fraction. Some net synthesis of phospholipids, presumably microbial phospholipids, occurred in the rumen. In the intestine immediately distal to the pylorus, extensive secretion of bile acids, cholesterol, phospholipids, triglycerides, free fatty acids, and lipase occurred. This resulted in doubling of fatty acid fluxes through the duodenum. These endogenous secretions were reabsorbed rapidly however, with the major site of lipid and bile acid absorption in the region .6 to 4 m distal to the pylorus. Additional but less absorption occurred in the more distal segments of the small intestine. Overall absorption of stearic acid, oleic acid, and tristearin supplements was in the range 60 to 70%, and no differences were apparent between fats. Unsaturated fatty acids were over 90% absorbed as compared with 55 to 65% for saturated fatty acids. No significant effect of any of the supplements was observed on ruminal total volatile fatty acids, ratios of volatile fatty acids, or on overall cellulose or caloric digestion.

Abomasum↗