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Biomedical subjects

A C Beynen

Publications and source records attributed to A C Beynen.

At least 199 records · Page 11Linked to original sources
PubMed1994

Dietary calcium chloride vs. calcium carbonate reduces urinary pH and phosphorus concentration, improves bone mineralization and depresses kidney calcium level in cats.

The effect of dietary calcium chloride vs. calcium carbonate on mineral metabolism was studied in cats. Ovariectomized cats and female kittens were fed purified diets with a normal calcium level (9.5 mmol Ca/MJ) but containing either calcium carbonate or calcium chloride, or were fed diets with a high calcium level (17.7 mmol Ca/MJ) containing either calcium carbonate alone or equimolar amounts of both calcium carbonate and calcium chloride. A 4 x 4-wk cross-over study using adult cats and a 31-wk parallel study using kittens were conducted. Calcium, phosphorus and magnesium balances were established regularly. In the course of the experiment with the kittens, blood samples were taken and X-ray photographs of the tibiae made. At the age of 39 wk, the kittens were killed, and organs and bones were collected. In both adult cats and kittens fed the high calcium diets, urinary concentrations of magnesium and phosphorus and apparent absorption of these minerals were lower than after feeding the normal calcium diets. Urinary pH and phosphorus concentration were lower in cats and kittens fed diets with calcium chloride instead of calcium carbonate. Body weight gain and tibia growth in the kittens tended to be greater after feeding the diets with calcium chloride. Calcium chloride vs. calcium carbonate and also supplemental calcium chloride in the high calcium diet significantly stimulated femur density and reduced renal calcium concentration.

Aging↗
PubMed1994

Increasing calcium intakes lower urinary concentrations of phosphorus and magnesium in adult ovariectomized cats.

The effect of dietary calcium level on the fecal and urinary excretion of calcium, phosphorus and magnesium was studied in adult cats. Ovariectomized cats were fed purified diets containing 3.2, 4.8, 9.5 or 19.3 mmol calcium/MJ in a 4 x 4 wk crossover study. During the experiment, balance studies were performed and blood samples were taken. The adult ovariectomized cats maintained calcium balance at all four levels of calcium tested. Extra dietary calcium, in the form of CaCO3, caused a slight increase in urinary pH. Urinary concentrations of phosphorus and magnesium dropped, but that of calcium remained unchanged, when the cats were fed diets with increasing calcium levels. The percentages of apparent absorption of phosphorus and magnesium fell when calcium intake was raised. The dietary calcium level did not affect plasma concentrations of calcium, magnesium and phosphorus or plasma activity of alkaline phosphatase.

Absorption↗
PubMed1994

Effects of dietary corn and olive oil versus coconut fat on biliary cholesterol secretion in rats.

We have studied the effects of dietary corn and olive oil versus coconut fat on bile formation and fluidity of hepatic plasma membranes in rats. After 4 weeks of feeding the purified diets containing 9% (w/w) of the test fats, there was no difference in plasma cholesterol concentration between the dietary groups. The amount of free and esterified cholesterol in the liver was significantly higher in rats fed either corn oil or olive oil as compared with coconut fat. In the rats fed olive oil, but not in those fed corn oil this was associated with lower rates of biliary phospholipid excretion. Bile flow was not differently influenced by the three dietary fats. Hepatic plasma membranes of the rats fed corn or olive oil contained more cholesterol and less phospholipids than those on coconut fat, which was, however, not accompanied by changes in fluidity of the membranes. These results indicate that in rats the type of dietary fat can induce considerable changes in hepatic cholesterol metabolism without affecting plasma cholesterol concentrations, and without consistent effects on biliary cholesterol secretion.

Animals↗
PubMed1993

Plasma activities of lecithin:cholesterol acyltransferase, lipid transfer proteins and post-heparin lipases in inbred strains of rabbits hypo- or hyper-responsive to dietary cholesterol.

Plasma lipoproteins, plasma activities of lecithin:cholesterol acyltransferase (LCAT), phospholipid transfer protein (PLTP), cholesteryl ester transfer protein (CETP) and post-heparin lipases were measured before and after cholesterol challenge in two inbred strains of rabbits with either a high (hyper-responders) or a low (hyporesponders) response of plasma cholesterol to dietary cholesterol. The purpose of this study was to provide clues about the mechanisms underlying the effect of dietary cholesterol on lipoprotein levels and composition, and particularly those underlying the strain difference of this effect. Cholesterol feeding (0.15 g of cholesterol/100 g of diet) caused increased plasma total cholesterol concentrations and an increased ratio of cholesteryl esters:triacylglycerol in all lipoprotein particles in both strains; these effects were significantly greater in hyper- than hypo-responsive rabbits. Feeding on the high-cholesterol diet lowered plasma triacylglycerols in hyper-responders, but caused increased plasma triacylglycerol levels in hyporesponders. This was accompanied by significantly greater increases in the activities of hepatic triacylglycerol lipase and lipoprotein lipase in hyper- than in hypo-responders. Both strains showed a dietary-cholesterol-induced rise in plasma CETP as well as in PLTP activity. The increase in PLTP activity was greater in the hyper-responders, but that of CETP was less. There was no effect of dietary cholesterol on LCAT activity. It is hypothesized that the lipases are involved in the removal of cholesterol-rich lipoproteins.

Animals↗
PubMed1993

Characterization of rat plasma esterase ES-1A concerning its molecular and catalytic properties.

To characterize esterase ES-1A from rat plasma with regard to its molecular and catalytic properties, the enzyme was purified. The degree of purification, as measured by a densitometric gel scanning assay for ES-1 activity, was about 142-fold with a recovery of 9%. The ES-1A preparation was free of other plasma esterases but not of other plasma proteins. The enzyme shows microheterogeneity after staining for esterase activity in gradient polyacrylamide gel electrophoresis and isoelectric focusing. The native ES-1A protein is a carboxylesterase (EC 3.1.1.1) with a molecular mass of about 59 kDa as determined by gel filtration and gradient polyacrylamide gel electrophoresis. ES-1A exhibits a pI of 4.73 and optimum pH of 8.6 for p-nitrophenylbutyrate hydrolysis. With various p-nitrophenyl esters as substrate for ES-1A, it was found that the Michaelis constant decreased with increasing number of C atoms of the unbranched fatty acid moiety, whereas the maximum reaction velocity peaked with p-nitrophenylvalerate. The high degree of similarity of the properties of rat ES-1A with those reported earlier for mouse ES-2B, rabbit EST-2F, and human ESB2 suggests that these four esterases have a common evolutionary origin.

Animals↗
PubMed1993

Plasma esterase activities in rats fed magnesium-deficient diets.

In a study with rats it was determined whether dietary magnesium concentration affects plasma esterase activities. The feeding of a diet with 0.01% (w/w) instead of 0.04% magnesium reduced plasma magnesium concentration by 50%. Plasma total esterase, arylesterase and butyrylcholinesterase activities were significantly decreased in the magnesium-deficient rats. In rats fed a diet containing 0.02% magnesium, plasma magnesium concentration was lowered by 30%, and group mean plasma total esterase activity was decreased, but not the activities of arylesterase and butyrylcholinesterase.

Animals↗
PubMed1993

Iron and zinc status in rats with diet-induced marginal deficiency of vitamin A and/or copper.

The hypothesis was tested that there are interactions of marginal copper and vitamin A deficiency regarding iron and zinc status. Copper restriction (1 vs 5 mg Cu/kg diet) significantly lowered copper concentrations in plasma and tissues of rats and reduced blood hemoglobin, hematocrit, and iron concentrations in tibia and femur, but raised iron concentrations in liver. Vitamin A restriction (0 vs 4000 IU vitamin A/kg diet) reduced plasma retinol concentrations and induced a fall of blood hemoglobin and hematocrit. Neither copper nor vitamin A restriction for up to 42 d affected feed intake and body wt gain. There were no interrelated effects of vitamin A and copper deficiency on iron status. Copper deficiency slightly depressed liver, spleen, and kidney zinc concentrations. Vitamin A deficiency lowered zinc concentrations in heart, but only when the diets were deficient in copper.

Animals↗
PubMed1993

Dietary fructose vs glucose lowers copper solubility in the digesta in the small intestine of rats.

The hypothesis was tested that dietary fructose vs glucose lowers copper solubility in the digesta in the small intestine of rats, which in turn causes a decreased copper absorption. Male rats were fed adequate-copper (5 mg Cu/kg) diets containing either fructose or glucose (709.4 g monosaccharide/kg) for a period of 5 wk. Fructose vs glucose significantly lowered copper concentrations in plasma and the liver, but did not alter hepatic copper mass. Fructose feeding resulted in a significantly lesser intestinal solubility of copper as based on either a smaller soluble fraction of copper in the liquid phase of small intestinal contents or a lower copper concentration in the liquid phase. The latter fructose effect can be explained by the observed fructose-induced increase in volume of liquid phase of intestinal digesta. After administration of a restricted amount of diet extrinsically labeled with 64Cu, rats fed fructose also had significantly lower soluble 64Cu fraction in the digesta of the small intestine. Although this study shows that fructose lowered intestinal copper solubility, only a slight reduction of apparent copper absorption was observed. It is suggested that the fructose-induced lowering of copper status in part counteracted the fructose effect on copper absorption at the level of the intestinal lumen.

Animals↗
PubMed1993

Influence of dietary fish proteins on plasma and liver cholesterol concentrations in rats.

The effects of amount and type of dietary fish proteins on plasma and liver cholesterol concentrations were evaluated in female rats. The isonitrogenous diets used contained 10 g cholesterol/kg and were carefully balanced for residual fat, cholesterol, Ca, Mg and P in the protein preparations. Cod meal, soya-bean protein or casein was incorporated into the diets as the only source of dietary protein at three levels: either 24, 48 or 72 g N/kg diet. Extra protein was added to the diet at the expense of the glucose component. In a second experiment soya-bean protein, casein, cod meal, whiting meal or plaice meal was added to the diet at a level of 24 g N/kg. When compared with casein, cod meal and soya-bean protein decreased plasma and liver cholesterol concentrations. A further cholesterol-lowering effect was achieved by increasing the proportion of either soya-bean protein or cod meal in the diet. Substitution of casein for glucose did not influence plasma and liver cholesterol concentrations. Plaice meal in the diet produced lower group mean plasma cholesterol concentrations than did whiting meal. In rats fed on the diet containing plaice meal, liver cholesterol concentrations were significantly lower than those in their counterparts fed on either cod meal or whiting meal. The present study demonstrates that different fish proteins in the diet have different effects on cholesterol metabolism and that the cholesterol-influencing properties of cod meal can be enhanced by the incorporation of higher proportions of this protein in the diet.

Animals↗
PubMed1993

Urinary excretion of magnesium and calcium as an index of absorption is not affected by lactose intake in healthy adults.

The effect of lactose on the urinary excretion of Mg and Ca, as an index of absorption, was studied in a double-blind, crossover study during three 1-week periods. Twenty-four healthy, lactose-tolerant, adult volunteers maintained their habitual diets with the exception that all lactose-containing dairy products in the diet were replaced by 600 g/d of three specially prepared dairy products. These products were based on either lactose-enriched cow's milk or lactose-enriched, lactase (EC 3.2.1.23)-treated cow's milk, with or without added Mg, and were given in turn during 1 week. Lactose intake was increased by 127 mmol/d (46 g/d) while taking the lactose-enriched products. While taking the Mg-enriched products, Mg intake was increased by 2.8 mmol/d (69 mg/d) which was equivalent to 17% of the habitual Mg intake. Apart from the lactose and Mg intake, nutrient intake was comparable during the three dietary periods. Urinary excretions of Mg and Ca were used as indicators for their absorption. Mg supplementation significantly increased urinary Mg excretion by 0.97 mmol/d (equivalent to an increase of 18%, P < 0.001), indicating that urinary Mg excretion is a valid indicator for intestinal Mg absorption. Hydrolysis of lactose did not affect urinary excretion of Mg and Ca, which implies that lactose intake does not affect the absorption of Mg and Ca in healthy adults.

Adult↗
PubMed1993

Lowering effect of dietary milk-whey protein v. casein on plasma and liver cholesterol concentrations in rats.

The effect of dietary whey protein v. casein on plasma and liver cholesterol concentrations was investigated in female, weanling rats. Balanced, purified diets containing either whey protein or casein, or the amino acid mixtures simulating these proteins, were used. The high-cholesterol diets (10 g cholesterol/kg feed) had either 150 or 300 g protein or amino acids/kg feed. The diets were fed for 3 weeks. At the low dietary protein level, whey protein v. casein did not affect plasma total cholesterol, but lowered the concentration of liver cholesterol. At the high dietary protein level, whey protein significantly lowered plasma and liver cholesterol and also plasma triacylglycerols. The hypocholesterolaemic effect of whey protein was associated with a decrease in very-low-density-lipoprotein cholesterol. At the high dietary protein concentration, whey protein reduced the faecal excretion of bile acids when compared with casein. The effects of intact whey protein v. casein were not reproduced by the amino acid mixtures simulating these proteins. It is suggested tentatively that the cholesterol-lowering effect of whey protein in rats is caused by inhibition of hepatic cholesterol synthesis.

Animals↗
PubMed1993

Dietary fructose v. glucose lowers ferrous-iron absorption in rats.

The effect of dietary fructose v. glucose on Fe solubility in the small intestine and apparent Fe absorption was studied in rats. Female rats were fed for 4 weeks on low-Fe (10 mg Fe/kg) or normal-Fe (40 mg Fe/kg) diets containing either fructose or glucose (709.4 g monosaccharide/kg). Fe was added to the diets in the form of FeSO4. The low-Fe diets did not lower levels of haemoglobin and packed cell volume, but significantly lowered Fe concentration and Fe mass in the liver, kidney and spleen. Fructose v. glucose also lowered Fe concentrations in these organs, but did not alter absolute Fe contents. Low Fe intake reduced the amount of Fe in the intestinal lumen. The total amount of Fe and Fe concentration in the liquid phase of the proximal intestinal lumen were depressed by fructose irrespective of Fe intake. Fructose also lowered the amount of Fe in the liquid phase of the distal intestine. In keeping with these observations, dietary fructose significantly lowered apparent absorption of Fe at the two levels of Fe intake. Decreasing the intake of Fe raised the percentage of apparent Fe absorption.

Animals↗
PubMed1993

Thyroid function in rats with iodine deficiency is not further impaired by concurrent, marginal zinc deficiency.

The hypothesis tested was that Zn deficiency aggravates impaired thyroid function as induced by I deficiency. In two separate experiments male rats were fed on diets either deficient in Zn or in I, or deficient in both. An identical, restricted amount of food was given to each rat so that body-weight gain of the experimental groups was comparable. Zn deficiency was evidenced by reduced tibial Zn concentrations. I deficiency was evidenced by goitre, reduced urinary I excretion, reduced plasma thyroxine concentrations and reduced absolute amounts and concentrations of thyroxine in the thyroid. Zn deficiency had no effect on the raised thyroid weight as induced by I deficiency. Zn restriction from 184 mumol Zn/kg diet to 31 mumol Zn/kg diet, but not to 92 mumol Zn/kg diet, significantly lowered plasma thyroxine concentration. There were no interrelated effects of Zn and I deficiencies on thyroid hormone levels. These results indicate that marginal Zn deficiency does not influence thyroid hormone metabolism in I deficiency.

Animals↗
PubMed1993

Dietary cholesterol lowers the activity of butyrylcholinesterase (EC 3.1.1.8), but elevates that of esterase-1 (EC 3.1.1.1) in plasma of rats.

The question addressed is whether an increased intake of cholesterol affects esterase-1 (EC 3.1.1.1; ES-1) and butyrylcholinesterase (EC 3.1.1.8) activity in plasma. Rats were fed on a purified diet either without or with cholesterol (10 g/kg) added at the expense of the carbohydrate source. Dietary cholesterol significantly decreased plasma butyrylcholinesterase activity, but raised plasma ES-1 activity. Evidence is discussed, suggesting that plasma butyrylcholinesterase is involved in plasma cholesterol metabolism, whereas esterase-1 is involved in intestinal cholesterol absorption.

Animals↗
PubMed1993

Ileal pH and apparent absorption of magnesium in rats fed on diets containing either lactose or lactulose.

The hypothesis was tested that dietary lactose v. glucose stimulates Mg absorption in rats because lactose lowers pH of the ileal lumen, which improves Mg solubility which in turn enhances Mg availability for transport across the ileal epithelium. For comparison, the effects of lactulose were studied because it shares with lactose the characteristic of being poorly digestible. Replacement of glucose by lactose (100 g/kg) significantly stimulated apparent absorption of Mg. Apart from Mg absorption, lactulose also significantly enhanced absorption of Ca and phosphate. Lactose v. glucose lowered the pH of the ileal lumen from 7.5 to 7.2, whereas lactulose significantly reduced it to 7.0. In in vitro incubations a decrease in pH within the range of fluctuation in vivo was found to cause an improved solubility of Mg, and to a lesser extent also of Ca and phosphate. The smaller fall of ileal pH induced by feeding lactose instead of lactulose may explain why lactose improved Mg absorption only. For all individual rats combined there were negative relationships between ileal pH and apparent absorption of minerals, the relationship being strongest for Mg. Neither lactose nor lactulose was found to raise ileal solubility of minerals, which could relate to the possibility that the time of sampling was not appropriate. It is suggested that lactose-induced stimulation of Mg absorption in rats is caused by a lowering of ileal pH.

Animals↗
PubMed1993

Iron status in rats fed on diets containing marginal amounts of vitamin A.

Severe vitamin A deficiency in rats is known to cause anaemia associated with growth retardation and impaired water retention. However, study of the effect of marginal vitamin A intake is of more interest because such intake may mirror the situation in humans in many developing countries. Therefore, in two experiments, the effect of marginal vitamin A deficiency on Fe status was investigated in male rats. After 28 d of feeding either low- or high-vitamin A diets (0 or 120 v. 1200 retinol equivalents/kg feed), body weight and feed intake were not influenced by the level of vitamin A in the diet. Liver weight was lowered by vitamin A deficiency. Water intake was not influenced in rats fed on a low-vitamin A diet. Plasma retinol concentrations were decreased in rats fed on diets low in vitamin A. Marginal vitamin A deficiency produced slightly lower blood haemoglobin concentrations; it did not systematically affect packed cell volume. The concentration of Fe in liver was significantly higher when diets low in vitamin A were fed, but hepatic Fe mass was not affected. Significantly lower Fe levels were observed in femurs of rats with vitamin A deficiency. The effects on liver and femur Fe concentrations were seen with diets adequate in Fe but not with diets deficient in Fe. The efficiency of apparent Fe absorption was significantly increased by low intakes of vitamin A, provided that the dietary Fe concentration was adequate. It is speculated that depressed uptake of Fe by bone marrow is the primary feature of altered Fe status in rats with marginal vitamin A deficiency.

Animals↗
PubMed1993

Dietary native resistant starch but not retrograded resistant starch raises magnesium and calcium absorption in rats.

The effects on calcium and magnesium absorption of dietary native and retrograded cornstarch were studied in rats. Uncooked high amylose starch granules (35% of total glucose equivalents as enzyme-resistant starch) and cooked and cooled (-20 degrees C) high amylose starch (24% of total glucose equivalents as retrograded resistant starch) were used as test starches, and cooked normal starch (3% of total glucose equivalents as resistant starch) was used as control starch. Native vs. control starch raised the amount of polymerized glucose in ileum, but not in feces. Retrograded starch produced more polymerized glucose than control starch in both ileum and feces. When compared with control starch, ileal pH was significantly lowered by native starch and tended to be raised by retrograded starch. Cecal pH was lowered by the two preparations rich in resistant starch. Apparent absorption of calcium and magnesium was raised by native starch but not by retrograded resistant starch. Calcium concentrations in the liquid phase of the ileum tended to be elevated by native starch but were significantly lowered by retrograded starch relative to control starch. Magnesium and calcium concentrations in liquid cecal contents tended to be raised with native starch; they were unchanged with retrograded starch. It is suggested that native resistant starch raised calcium and magnesium absorption because it tended to enhance the solubility of these minerals in ileal and cecal digesta.

Absorption↗