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Biomedical subjects

D Sklan

Publications and source records attributed to D Sklan.

At least 127 records · Page 7Linked to original sources
PubMed1985

Digestion and absorption of protein along ovine gastrointestinal tract.

Digestion and absorption of protein were determined in ovine gastrointestinal tract with cerium-141 as an unabsorbed reference substance. Nitrogen flows changed little in rumen and reticulum, but in the proximal small intestine flows increased because of secretion of .9 g nitrogen per day per kg body weight. This secretion included trypsin, chymotrypsin, elastase, and carboxypeptidases A and B; maximal activity was in proximal segments of the small intestine and decreased with distance from the pylorus. Activity of chymotrypsin decreased more rapidly than that of trypsin. Amino acid flows reflected the influx of protein in the duodenum; absorption was approximately 55% in the terminal ileum. No major changes of proportions of individual amino acids were observed. Overall nitrogen absorption was 72.6% of which 6% was in the large intestine. The major soluble protein fraction in the gastrointestinal tract consisted of peptides with molecular weight 7,000 to 14,000 daltons. Soluble high molecular weight protein was observed only in rumen and duodenum. Low molecular weight peptides and amino acids accumulated only in the proximal small intestine. Solubilization of protein and breakdown of peptides of 7,000 to 14,000 molecular weight appear to be rate limiting for protein absorption in sheep.

Abomasum↗
PubMed1985

Energy disappearance in hindgut of sheep.

Digestibility and disappearance of energy in the large intestine of sheep fed 75% concentrates was investigated with Cerium-141 as an unabsorbed reference substance. Cecal fermentation increased acetic acid and decreased propionic acid compared with ruminal fermentation. This situation was associated with cellulose disappearance in the lower gut and accounted for 26% of total cellulose disappearance from the entire alimentary tract. Energy disappearance in the hindgut accounted for 13% of energy disappearance in the gastrointestinal tract.

Acetates↗
PubMed1984

A low molecular weight zinc-copper lipolytic protein from chick liver.

A lipolytic zinc-copper protein has been isolated from the cytosol of chick liver. This material had a molecular weight of 6000 daltons, contained four atoms of zinc and one atom of copper per molecule. The 6000 dalton fraction aggregated at high ionic strength or in the presence of sodium dodecyl sulphate. Lipolytic activity was observed towards triolein, tripalmitin , phosphatidyl choline and retinyl palmitate, and was stimulated by cholate, Ca and high NaCl concentrations, and was inhibited by sulphydryl reagents, inhibitors of serine esterases, alkaline phosphatase and chelating agents. It appears that this copper-zinc protein is distinct from metallothionein which has no lipolytic activity.

Animals↗
PubMed1984

Intestinal absorption and plasma transport of lipids in chicks and rats.

Labelled oleic acid was introduced into the duodenum of chicks in which the pancreatic-duodenal vein and brachial artery had been cannulated, and blood samples were withdrawn. Similar experiments were performed in rats which had not been venously cannulated. In rat plasma, over 92% of the label was found in the triglycerides, whereas in the chick 64% of the label was in the triglycerides and 27-31% in the free fatty acids. In the rat, over 85% of the lipid label circulating in the plasma was found in lipoproteins with hydrated density less than 1.006, whereas in the chick only 25% of the label was in this fraction and the majority of label was found with density greater than 1.063. It thus appears that both release and transport of fatty acids from the intestinal mucosa in chicks differs from the rat.

Animals↗
PubMed1984

Retinoid binding lipoprotein in neoplastic cells.

A lipid-protein aggregate (LPA), binding both retinol and retinoic acid, was detected in the cytosols of several human and murine tumor cells by gel filtration after incubation of cell extracts with labelled retinoids. In addition to this high Mr lipoprotein (Mr 2 X 10(6)) the cytosols also contained low Mr retinoid binding proteins (Mr 14,500). The amounts of retinoids bound to these 2 distinct components were similar and both bound some 40-200-fold more retinol than retinoic acid. Retinyl palmitate hydrolase, copper and zinc were found in association with LPA. The LPA may be involved in subcellular compartmentalization, transport and function of retinoids.

Animals↗
PubMed1984

Vitamin A metabolism in chick liver: some properties of the cytosolic lipid-protein aggregate.

Incubation of hepatic microsomes with retinol resulted in formation of retinyl esters and glucuronides. The presence of the cytosolic lipid-protein aggregate (LPA) in the system in addition induced release of holo-retinol-binding protein from the microsomes. The extent of these reactions was influenced by the addition of coenzyme A and ATP, or uridine diphosphate glucuronic acid. Incubation of hepatic microsomes containing labelled retinyl esters with the LPA resulted in the appearance of the labelled retinyl esters in the LPA. Small amounts of retinoic acid were formed on incubation of retinol with microsomes (approximately 1% of added retinol); this was found to be associated with a protein of approximately 14 500 molecular weight, and less than 10% was associated with the LPA. This is in contrast to retinol, which was found to be almost completely associated with the LPA. The cytosolic LPA was associated both with carotene-cleavage activity and alcohol dehydrogenase (NAD(P)+) (EC 1.1.1.71) activity. These findings lend some support to the concept of a specific role for hepatic LPA.

Animals↗
PubMed1984

Rumen fermentation in vitro as influenced by long chain fatty acids.

Responses of rumen microbes to fatty acids were evaluated by production of total volatile fatty acid and ratio of acetate to propionate. Fermentations were under carbon dioxide for 20 h in 50-ml Erlenmeyer flasks in a Dubnoff metabolic shaking incubator. Flasks contained 20 ml medium, 1 ml reducing solution, 750 mg substrate (450 mg hay plus 300 mg grain), and varying amounts of long-chain fatty acids supplied as free acids, as calcium salts, or as triglycerides. They were inoculated with 5 ml rumen fluid obtained from a cow fed 3.6 kg grass hay, 2.3 kg grain, and .2 kg tallow daily. Volatile fatty acid production was decreased by long-chain fatty acids that contained less than 18 carbon atoms and by unsaturated long-chain fatty acids with 18 carbon atoms. Lauric acid decreased volatile fatty acid production by 69% and induced unusual acetate/propionate ratio (40:1). Stearic acid, however, did not affect volatile fatty acid production or acetate/propionate ratio. Within two series of long chain fatty acids (myristic, palmitic, stearic, arachidic; stearic, oleic, linolenic), melting point accounted for 93 to 95% of the variation of volatile fatty acid production and acetate/propionate. As calcium salts, long chain fatty acids caused small changes of fermentation. Our data support the proposition that hard fats and calcium salts of long-chain fatty acids do not interfere with ruminal fermentation.

Acetates↗
PubMed1984

Vitamin A and carotene in animal nutrition.

Vitamin A, an unsaturated 20 carbon cyclic alcohol, subserves a number of important physiological functions. However, the biochemical basis of these roles is not well understood. The main sources of retinol are liver, egg yolk and milk fat. Several carotenoids show vitamin A activity. The conversion of beta-carotene to retinol is affected by copper-containing dioxygenase and zinc-containing retinene reductase. The efficiency of conversion varies in different species. The latter is defined in units as the daily dose required to produce a weight gain of 3 g/week in young rats between the 4th and 8th week. Retinol is unstable on exposure to light or heat, particularly in the presence of heavy metal ions and water. Much recent work has focused on the absorption, metabolism and excretion of vitamin A. It is now recognized that plasma vitamin A levels do not reflect the nutritional status except in severe hypo- and hypervitaminosis A. Also, many dietary factors may influence vitamin A metabolism. These basic and applied aspects of vitamin A are reviewed.

Absorption↗
PubMed1983

Retinol homeostasis in lambs given low and high intakes of vitamin A.

Four groups of lambs were fed on a low-carotene basal diet. One group received no supplemental vitamin A (mildly deficient). Remaining groups were supplemented daily with vitamin A acetate equivalent to 100 (control) 9000 (mildly intoxicated) and 18000 (severely intoxicated) microgram retinol/kg body-weight. After 16 weeks lambs received a bolus of [15-3H]retinol intravenously; blood, urine and faeces were sampled for 48 h. Plasma retinol was complexed to a protein of 20000 molecular weight (MW), which in turn was complexed to a protein of 65000 MW; these proteins correspond respectively to retinol-binding protein and prealbumin. Plasma retinol concentration reached plateau values in intoxicated lambs, but plasma retinyl ester concentrations increased rapidly when liver contents of both retinol and retinyl esters exceeded approximately 10 and 100 mg respectively and kidney contents of both retinol and retinyl esters exceeded 30 micrograms. Labelled compounds, more polar than retinol, were found in plasma; their concentration increased tenfold in intoxicated lambs within 48 h. Plasma retinol transport rates were 0.1, 10.5 and 11.8 times control values, and clearance rates were 0.3, 14.1 and 14.3 times control values in mildly-deficient, and mildly- or severely-intoxicated lambs respectively. Turnover of retinol increased rapidly when liver contents of retinol and retinyl esters exceeded approximately 10 and 100 mg respectively and kidney contents of both retinol and retinyl esters exceeded approximately 30 micrograms. Plasma clearance of retinyl esters was unchanged with intake. Faecal excretion of tracer increased linearly with plasma retinol clearance. Our findings identify several variables that appear to be involved in retinol homeostasis, including plasma retinol clearance and excretion.

Animals↗
PubMed1983

Vitamin A absorption and metabolism in the chick: response to high dietary intake and to tocopherol.

Absorption of 14C-labelled retinol was determined along the gastrointestinal tract of chicks, using 141Cerium as a non-absorbed reference substance, as influenced by high dietary vitamin A and the addition of tocopherol to the diet. The site of major vitamin A absorption was the proximal small intestine and high intake of vitamin A reduced slightly the percentage over-all absorption. Labelled glucuronides were secreted into the duodenum and were 50-60% reabsorbed in the small intestines. High-vitamin-A intakes enhanced the duodenal flow of retinyl glucuronides. In vitro hepatic retinol esterification and glucuronide production were enhanced in chicks given high dietary vitamin A. Plasma transport and clearance of retinol were enhanced by feeding high levels of vitamin A and further enhanced when tocopherol at high concentrations was present in the diet. Dietary tocopherol had no effect on absorption, increased hepatic vitamin A stores and in vitro retinol esterification, and decreased retinyl glucuronide flows through the duodenum.

Animals↗
PubMed1983

Effect of high vitamin A or tocopherol intake on hepatic lipid metabolism and intestinal absorption and secretion of lipids and bile acids in the chick.

The effect of high dietary vitamin A or tocopherol, or both, on lipid absorption and secretion in the gastrointestinal tract and on serum and hepatic lipids was determined in the chick. High dietary vitamin A increased secretion of cholesterol, bile acids, phospholipids and fatty acids to the duodenum, and tocopherol enhanced cholesterol and bile acid secretion to the duodenum. No differences in over-all absorption were observed. Serum cholesterol was depressed by vitamin A and hepatic lipids were enhanced, except phosphatidyl choline which was depressed. Tocopherol increased hepatic triglycerides and cholesterol. In vitro fatty acid synthesis from lactate by liver homogenates was enhanced by vitamin E and cholesterogenesis enhanced by both vitamin A and tocopherol. delta 9 Desaturation was also enhanced by vitamin E. It is concluded that both vitamin A and tocopherol affect the hepatic synthesis and catabolism of cholesterol and that vitamin E also influences fatty acid metabolism.

Animals↗
PubMed1983

Carotene-cleavage activity in chick intestinal mucosa cytosol: association with a high-molecular-weight lipid-protein aggregate fraction and partial characterization of the activity.

A fluorescent high-molecular weight lipid-protein aggregate was isolated from the cytosol of chick intestinal mucosa or liver by gel filtration on columns of Sepharose 4B or 6B. This aggregate exhibited carotene-cleavage activity. On incubation of this aggregate, dissociation occurred and low-molecular weight fractions containing Cu and Zn and exhibiting carotene-cleavage activity were found. This fraction appeared on sodium dodecyl sulphate polyacrylamide electrophoresis to have a molecular weight of 7000-11000 and resembled the previously described Cu chelatins in amino acid composition. Carotene cleavage may be effected by a copper-zinc metalloprotein of low-molecular weight, associated in intestinal cytosol with a lipid-protein aggregate.

Animals↗
PubMed1983

Carotene Cleavage Activity in the corpus luteum of cattle.

Carotene cleavage has been demonstrated in the corpus luteum of cattle, and activity characteristics are compared to the intestinal mucosa. At mid-ovulation, specific activity of the carotene cleavage enzymes was two-fold greater in the corpus luteum than in the intestine. In the corpus rubicans and in the regressing corpus luteum, the specific activity appeared to be lower than that observed in mid-ovulation.

Animals↗
PubMed1982

Association of acylglyceride and retinyl palmitate hydrolase activities with zinc and copper metalloproteins in a high molecular weight lipid-protein aggregate fraction from chick liver cytosol.

A lipid-protein aggregate fraction of molecular weight approx. 1.8 . 10(6) was isolated by gel filtration from chick liver cytosol. This aggregate fraction had a hydrated density range of 1.06-1.13, was 45% lipid, contained zinc and copper and was associated with triolein, phosphatidylcholine and retinyl palmitate hydrolase activity. Hydrolytic activities were stimulated by albumin and cholate, but not by dihydroxy bile acids, and inhibited by serine esterase and sulphydryl inhibitors. Incubation of the aggregate with fatty acid-labelled acylglycerides resulted in protein-binding fatty acid fractions with molecular weights of 150,000, 60,000, 13,000 and approx. 2000. Incubation of the aggregate with [3H]retinyl palmitate yielded retinol-containing fractions with molecular weights of 150,000, 60,000 and 15,000. The latter peak appears, on the basis of amino acid composition, to be similar to the cellular retinol-binding protein. In addition, on incubation of the aggregate fraction, zinc and copper peaks are found with molecular weights of 150,000, 60,000 and 12,000-8000. The latter were further purified to yield a copper-rich metalloprotein similar to 'copper-chelatin' and a zinc-rich metalloprotein, possibly zinc-metallothionein. Both these metalloprotein fractions had acyl hydrolase activity which was depressed in zinc-depleted animals. This may provide a possible explanation for the documented nutritional interactions between zinc and retinol.

Animals↗
PubMed1982

Serum and intracellular retinol in the equine.

1. Serum and intracellular distribution of retinol was determined in equines maintained on four levels of vitamin A intake. 2. The form of retinol transported in serum was determined by gel filtration and chromatography to be a complex of retinol bound to a protein of molecular weight (MW) of approximately 20000, which was in turn complexed probably with prealbumin to yield a complex with a MW of 75000 to 80000. 3. Increasing dietary vitamin A levels enhanced the concentration of lipoprotein-bound retinyl esters in the plasma. 4. Vitamin A in the liver cytosol was found predominantly as retinyl esters in a lipid-protein aggregate of MW approximately 2 X 10(6) and hydrated density of 1.063-1.111. In the kidney and adrenal gland, two lipid-protein entities were found with MW of approximately 1.8 X 10(6) and 1.7 X 10(6) respectively. These fractions contained approximately 40 and 20% lipid respectively and had densities of 1.063-1.111 and approximately 1.21. 5. All lipid-protein aggregates were associated with retinyl palmitate hydrolase activity and guanidine treatment released a 15000 MW material, presumably intracellular retinol-binding protein. 6. Increasing dietary vitamin A enhanced the proportion of retinol in the 1.7 X 10(6) fraction. 7. Findings in equine plasma and liver resemble previous observations in other species. The characterization of two new lipid-protein aggregates in equine kidney and adrenal glands, which have hydrolase activity, may be important in intracellular retinal transport and metabolism, especially in animals subjected to high intakes of vitamin A.

Animals↗
PubMed1982

Placental transport of retinol in sheep.

Six ewes in the last trimester of pregnancy were maintained on adequate intakes of vitamin A. Indwelling catheters were implanted surgically in fetal jugular veins and carotid arteries. Three ewes and three fatal lambs received intravenous [15-3H] retinol 19 days prior to parturition, followed by sequential sampling of maternal and fetal blood. Fetal plasma retinol was found to be complexed with retinol-binding protein and another protein other than prealbumin, with a total molecular weight of 30,000 to 35,000. Transfer of labeled retinol from ewe to fetus peaked at 24 hours after maternal injection. Calculation of plasma retinol transport rate from the areas under the radioactivity-time curves showed that transport in the fetus averaged 5% of that in the ewe. Approximately 250 microgram of retinol was transferred daily from ewes to fetal lambs and 50 microgram/day carried back to mothers. The study suggested that the carrier system of retinol in blood may not be the same in the fetal lamb as in adults, and demonstrated that retinol transfer is appreciable from fetus to ewe.

Animals↗