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Biomedical subjects

A C Beynen

Publications and source records attributed to A C Beynen.

At least 235 records · Page 13Linked to original sources
PubMed1992

The use of three ferguson-plot-based calculation methods to determine the molecular mass of proteins as illustrated by molecular mass assessment of rat-plasma carboxylesterases ES-1, ES-2, and ES-14.

The molecular masses of three rat-plasma carboxylesterases (ES-1, ES-2, and ES-14) were estimated by transverse-gradient polyacrylamide gel electrophoresis and subsequent application of Ferguson-plot-based calculation methods. Two electrophoretic buffer systems were used and the data subjected to either weighted or unweighted regression analysis. The Tris-boric acid buffer system produced significantly higher retardation coefficients than the Tris-glycine system. Molecular mass estimates were significantly higher with the Tris-glycine buffer system. Unweighted instead of weighted analysis produced significantly higher molecular mass estimates. Molecular mass estimates also depended on the calculation method, that is, the choice of calibration relationship with molecular size as a function of retardation coefficient. Three commonly used calibration relationships were compared. On the basis of their accuracy, both the weighted log[retardation coefficient] versus log[molecular mass] plot and the square root of retardation coefficient versus molecular radius were found suitable, provided that the Tris-boric acid buffer was used for electrophoresis. Using the former calibration relationship, the molecular masses of rat-plasma ES-1, ES-2, and ES-14 were 55.5, 61.1, and 65.3 kDa, respectively.

Animals↗
PubMed1992

Is dietary ergotamine atherogenic in the rabbit?

The effect of dietary ergotamine on pre-lesional indicators of atherosclerosis was studied in rabbits. The experimental purified diets contained 0.08% (w/w) cholesterol and either 0, 40 or 200 mg ergotamine-tartrate/kg. After 6 wk, serum total cholesterol concentration and the ratio of serum total cholesterol: high-density lipoprotein-cholesterol were significantly increased by ergotamine in a dose-dependent manner. Dietary ergotamine raised the total level of glycosaminoglycans and the relative proportion of chondroitin sulphate in the abdominal aorta. It is suggested that dietary ergotamine is atherogenic in the rabbit.

Animals↗
PubMed1992

Inhibitory effect of high protein intake on nephrocalcinogenesis in female rats.

Increased intakes of protein have been shown to reduce kidney calcification (nephrocalcinosis) in female rats. Two questions were addressed in the present study. First, can protein-induced inhibition of nephrocalcinosis be demonstrated when the diets used are balanced for calcium, magnesium and phosphorus in the added protein? Second, can the protein effect be explained by the frequently observed magnesiuria after giving high-protein diets? Nephrocalcinosis was induced in female rats by giving purified diets containing 151 g casein/kg and either an increased concentration of P (6 v. 2 g/kg) or a decreased concentration of Mg (0.1 v. 0.4 g/kg). To these diets 151 g ovalbumin/kg was added at the expense of glucose, and the diets were balanced for Ca, Mg and P in ovalbumin. The diets were given for 29 d. In rats fed on the diet containing 151 g protein/kg, an increased intake of P or a decreased intake of Mg caused nephrocalcinosis as measured chemically by analysis of kidney Ca as well as histologically by scoring kidney sections stained according to Von Kossa's method. The addition of ovalbumin to the diet prevented the induction of nephrocalcinosis. High P intake and low Mg intake with the low-protein diets induced enhanced loss of albumin in urine, suggesting that nephrocalcinosis caused kidney damage. Increased protein intake with a non-calcinogenic diet also caused increased albumin excretion in urine. Irrespective of the composition of the background diet, increased protein intake caused increased urinary excretion of Mg. When all dietary groups were considered, differences in nephrocalcinosis and urinary Mg output were not proportionally related.

Animals↗
PubMed1992

Influence of amount of dietary fat and protein on esterase-1 (ES-1) activities of plasma and small intestine in rats.

The objective of the present study was to characterize nutritionally esterase-1 (ES-1). For this purpose, the effects of replacement of dietary carbohydrates by isoenergetic amounts of either fat or protein on ES-1 activities of plasma and small intestine were studied in male rats. Purified diets differing in the amounts of maize starch plus dextrose, casein and various types of fat were used. Plasma and jejunal ES-1 activities were found to be increased with increasing fat intakes. As to the type of fat, increasing plasma ES-1 activities were induced by coconut fat, olive oil, maize oil and medium-chain triacylglycerols, in this order. Maize oil induced higher jejunal ES-1 activities than coconut fat and olive oil, but had similar effects to medium-chain triacylglycerols. Maize oil was more powerful in increasing plasma ES-1 activity than isoenergetic amounts of casein, but with respect to jejunal ES-1 activity these dietary components were equally effective. It is concluded that the amounts of fat and protein in the diet are important determinants of ES-1 activities in plasma and jejunum.

Animals↗
PubMed1992

Bioavailability of magnesium and calcium from cow's milk and soya-bean beverage in rats.

The milk components lactose and casein enhance the apparent absorption of magnesium and possibly also of calcium, whereas phytate, which occurs in soya-bean products, has an inhibitory effect. This implies that soya-bean beverage v. cow's milk could lower bioavailability of Mg and Ca. This hypothesis was tested in two experiments with growing rats. Feeding soya-bean beverage v. cow's milk consistently lowered body-weight gain, enhanced bone turnover, as measured by increased plasma alkaline phosphatase (EC 3.1.3.1) activity and increased urinary hydroxyproline excretion, and decreased Mg and Ca concentrations in the femur. Because the mineral compositions of the soya-bean beverage and the cow's milk were different, the intake of Mg was higher in rats fed on soya-bean beverage, whereas that of Ca was higher in rats fed on cow's milk. Supplementation of the soya-bean beverage either with phosphorus and Ca or with P, Ca and methionine, to concentrations identical to those in milk, restored growth and bone mineralization. When using diets carefully balanced for Mg, Ca, P, sodium, potassium and methionine, soya-bean beverage v. cow's milk in the diets decreased apparent absorption and urinary excretion of Mg and Ca. Hydrolysis of lactose in milk decreased absorption and urinary excretion of Mg; it did not significantly affect Ca absorption but lowered urinary Ca excretion. The present study shows that soya-bean beverage v. milk depresses Mg and Ca bioavailability, as would be predicted on the basis of reported effects of their purified components.

Alkaline Phosphatase↗
PubMed1992

Influence of ascorbic acid supplementation on copper metabolism in rats.

An attempt was made to unravel further the mechanism by which high dietary concentrations of ascorbic acid influence copper metabolism. The addition of ascorbic acid to the diet of rats caused about a twofold increase in plasma ascorbate concentrations and reduced group mean plasma and tissue concentrations of Cu. The effect of 10 g ascorbic acid/kg diet was greater than that of 1 g/kg. Ascorbic acid feeding reduced blood haemoglobin concentrations and packed cell volume values. Dietary ascorbic acid caused a significant decrease in apparent Cu absorption from the intestine. Ascorbate, intravenously administered together with 64Cu, caused an increase in 64Cu in the liver. Ascorbate, at concentrations occurring in plasma after ascorbic acid feeding, promoted the uptake of 64Cu by isolated hepatocytes. Thus, ascorbate stimulated the efficiency of hepatic uptake of Cu. Ascorbate, intravenously administered together with 64Cu, stimulated accumulation of 64Cu in bile of rats with a bile duct cannula. In rats fed on ascorbic acid, intravenously administered 64Cu was recovered in bile at increased rates. Dietary ascorbic acid enhanced the recovery of intraperitoneally administered 64Cu in faeces. The ascorbate-induced stimulation of biliary 64Cu excretion may reflect an increased hepatic uptake of 64Cu and be caused by an increased specific activity of Cu in liver pools. It is suggested that dietary ascorbic acid reduces tissue Cu concentrations primarily by interfering with intestinal Cu absorption. Ascorbate increases the efficiency of hepatic uptake of Cu, but this effect may not be causatively related with the reduced tissue Cu concentrations after ascorbic acid feeding.

Animals↗
PubMed1992

Plasma esterase-1 (ES-1) activity in rats is influenced by the amount and type of dietary fat, and butyryl cholinesterase activity by the type of dietary fat.

In previous work, we studied, under conditions of ad libitum food consumption, the effect of amount and type of dietary fat on plasma esterase-1 (ES-1) and butyryl cholinesterase activity in rats. This was done by the isoenergetic replacement of dietary fat by carbohydrates or by another fat source. The observed change in enzyme activity could theoretically be determined by either the dietary omission or the addition or by the combination. In the present work, we studied under restricted feeding conditions the effect of supplemental energy in various forms to determine the effect of the supplement alone. Supplemental coconut fat, but not isoenergetic amounts of either glucose or casein, raised plasma ES-1 activity. None of these supplements influenced butyryl cholinesterase activity. In a second experiment, we demonstrated that the ES-1 enhancing effect of supplemental coconut fat also occurred with fish oil, whereas the stimulatory effects of olive oil and corn oil were less pronounced. Supplemental fish oil, but not the three other fats, significantly reduced the depression in butyryl cholinesterase activity. Plasma cholesterol concentration was negatively associated with butyryl cholinesterase activity, but was not related to ES-1 activity. The two esterases were not correlated with plasma triglyceride concentration. We conclude that both the amount and type of fat in the diet of rats have specific influences on plasma ES-1 activity and that butyryl cholinesterase activity is affected by the type of fat.

Animal Feed↗
PubMed1992

Increasing intake of soybean protein or casein, but not cod meal, reduces nephrocalcinosis in female rats.

Female weanling rats were fed diets with soybean protein, casein or cod meal at 171, 342 or 513 mmol nitrogen/100 g for 3 wk. The diets were isonitrogenous and balanced for fat, cholesterol, calcium, magnesium and phosphorus. Cod meal feeding at 171 and 342 mmol nitrogen/100 g diet produced lower kidney calcium concentrations than the feeding of either soybean protein or casein. Increasing protein intakes were associated with reduced kidney calcium concentrations in the rats fed either soybean protein or casein but not in those fed cod meal. The anti-nephrocalcinogenic effect of increasing intakes of soybean protein may relate to the lowering of urinary phosphorus concentration. Increasing intakes of casein probably inhibited nephrocalcinogenesis by lowering urinary pH and raising urinary magnesium concentration. Increasing cod meal concentrations in the diet lowered urinary pH and raised urinary magnesium and calcium concentrations, but the effects on nephrocalcinogenesis of these changes probably counteracted each other.

Animals↗
PubMed1992

Fat intake and clofibrate administration have interrelated effects on liver cholesterol concentration and serum butyryl cholinesterase activity in rats.

Rats were fed for 15 d purified diets with different amounts of coconut fat, and with or without clofibrate. Fat was added at the expense of an isoenergetic amount of glucose. The hypolipidemic action of clofibrate was not influenced by the amount of fat in the diet. Clofibrate did not affect liver cholesterol concentration in rats fed the low fat diet, but it counteracted the rise in liver cholesterol seen in rats fed the high fat diet. This could relate to the observed raised intestinal clofibrate-hydrolyzing activity of rats fed the high fat diet, because hydrolysis of clofibrate gives rise to its biologically active form. In rats fed the low fat diet, but not in those fed the high fat diet, clofibrate raised the activity of serum esterase-1, which (unlike esterase-2) does not hydrolyze clofibrate. Possibly, the dramatic stimulatory effect of fat feeding on serum esterase-1 activity had overruled any influence of clofibrate. Clofibrate elevated serum butyryl cholinesterase activity, with this effect being amplified by fat feeding. High levels of dietary fat in the absence of dietary clofibrate did not alter serum butyryl cholinesterase activity. Clofibrate did not change butyryl cholinesterase and esterase-1 activities in small intestine. The high fat diet caused slightly higher levels of butyryl cholinesterase activity in small intestine, but markedly raised intestinal esterase-1 activity. This study shows that certain effects of clofibrate and a high fat diet are interrelated.

Animals↗
PubMed1992

Excessive cholesterolemic response in analbuminemic rats fed a cholesterol-rich diet containing casein.

Female Nagase analbuminemic rats and Sprague-Dawley rats were fed purified diets with or without 1% cholesterol and containing either soybean protein or casein. After consuming the cholesterol-free diets, the analbuminemic rats had significantly higher plasma cholesterol and triglyceride concentrations than the Sprague-Dawley rats. The higher plasma cholesterol levels were essentially in the low density and high density lipoproteins. Based on the fact that the analbuminemic rats excreted more bile acids in feces it is possible that the higher baseline plasma cholesterol concentrations in Nagase analbuminemic rats were partly caused by overproduction of cholesterol. The Nagase analbuminemic rats displayed a greater cholesterolemic response to cholesterol feeding than Sprague-Dawley rats, but only if casein was the protein source in the diet. Casein vs. soybean protein in either cholesterol-free or high cholesterol diets reduced bile acid excretion in Sprague-Dawley but not in Nagase analbuminemic rats. The increased sensitivity to casein plus cholesterol feeding in Nagase analbuminemic rats may be caused by a lack of inhibition of de novo cholesterol synthesis.

Animals↗
PubMed1992

Interaction of calcium and phosphate decreases ileal magnesium solubility and apparent magnesium absorption in rats.

We tested the hypothesis that increased intakes of calcium and phosphate lower magnesium solubility in the intestinal lumen, causing a decreased magnesium absorption. In in vitro experiments at a constant magnesium concentration, increasing calcium concentrations reduced magnesium solubility. This effect did not occur in the absence of phosphate. Increasing phosphate concentrations decreased the solubility of magnesium in the presence, but not in the absence, of calcium. These results suggest that the formation of an insoluble calcium-magnesium-phosphate complex determines magnesium solubility. To extend this concept to in vivo conditions, rats were fed purified diets containing a constant concentration of magnesium (16.4 mumol/g) but different concentrations of calcium (25, 100 or 175 mumol/g) and phosphate (58, 103 or 161 mumol/g). Increased intakes of calcium decreased magnesium solubility in the ileal lumen and lowered magnesium absorption. The latter result occurred only if the dietary phosphate concentration was at least 103 mumol/g. Increasing dietary phosphate concentrations reduced both magnesium solubility in the ileum and magnesium absorption, but only if the dietary calcium concentration was at least 100 mumol/g. These results support those obtained in vitro. We conclude that increased intakes of calcium and phosphate decrease magnesium absorption by the formation of an insoluble calcium-magnesium-phosphate complex in the intestinal lumen.

Animals↗
PubMed1992

Hyperresponsiveness to dietary cholesterol in inbred rabbits is not associated with enhanced reduction in binding of beta-VLDL to liver membranes.

In two inbred strains of rabbits with high or low response of serum cholesterol to dietary cholesterol, binding of rabbit beta-VLDL to hepatic membrane preparations was determined. The objective was to test the hypothesis that after cholesterol feeding, hyperresponders show a more dramatic reduction in hepatic apolipoprotein (apo) B/E receptors, which may explain the development of the high degree of cholesterolemia in these animals. The number of hepatic high affinity receptors for beta-VLDL in hyperresponders fed a diet without added cholesterol was, on average, 20% lower than that in hyporesponders. After the addition of increasing amounts of cholesterol to the diet, liver cholesterol concentrations were elevated to a greater extent in hyper- than in hyporesponsive rabbits. Liver free cholesterol concentrations were negatively associated with maximal binding of beta-VLDL to liver membranes. With increasing liver free cholesterol concentrations, maximal binding was less effectively depressed in hyper- than hyporesponders. We conclude that in the inbred strains of rabbits, hyperresponsiveness to dietary cholesterol is not caused by enhanced depression of hepatic apo B/E receptors.

Animals↗
PubMed1992

Secretion of lipoprotein cholesterol by perfused livers from rabbits hypo- or hyperresponsive to dietary cholesterol: greater dietary cholesterol-induced secretion in hyperresponsive rabbits.

In two inbred strains of rabbits with high or low response of plasma cholesterol to dietary cholesterol, secretion of lipoprotein cholesterol by perfused livers was determined. The perfused rabbit livers secreted cholesterol into the perfusate at essentially constant rates between 30 and 120 min of perfusion. Most of the secreted cholesterol resided in VLDL. Addition of cholesterol to the diet of the donor rabbits caused a higher cholesterol:triglyceride ratio of lipoproteins secreted by the perfused liver. Such a rise was also seen in the plasma lipoproteins of cholesterol-fed rabbits. Plasma and perfusate lipoproteins differed in that the former had a higher cholesterol:triglyceride ratio. Cholesterol feeding produced a higher output of lipoprotein cholesterol by the perfused liver, the increment being greater in hyper- than in hyporesponders. Cholesterol-fed hyperresponders had higher liver cholesterol concentrations than their hyporesponsive counterparts. There was a direct relationship between the rise of liver cholesterol concentrations and the rise of hepatic secretion of lipoprotein cholesterol; this relationship was identical for hypo- and hyperresponders. We conclude that the higher cholesterolemic response to cholesterol feeding in the hyperresponders, when compared with the hyporesponders, can be explained, at least partly, by a greater cholesterol-induced hepatic secretion of lipoprotein cholesterol.

Animals↗
PubMed1992

Inbred strains of rats have differential sensitivity to dietary phosphorus-induced nephrocalcinosis.

The degree of nephrocalcinosis after increasing the dietary phosphorus concentration from 0.2 to 0.5 g/100 g was measured in weanling female rats of 10 inbred strains. Based on kidney calcium concentrations and histological kidney calcification scores, there were considerable strain differences in nephrocalcinogenesis; 86% of the strain variability in nephrocalcinosis was attributable to genetic factors. Two strains with the most extreme nephrocalcinogenic responses were retested and the strain difference was found to be reproducible. Mean plasma phosphorus concentrations after phosphorus feeding were lower in the sensitive strain than in the insensitive strain. The high phosphorus diet produced greater urinary phosphorus concentrations, with the increase being greater in the sensitive strain. The strain difference in the response of urinary phosphorus concentrations after raising dietary phosphorus level may determine the strain difference in phosphorus-induced nephrocalcinosis. After consuming the high phosphorus diet, RP rats housed in groups in solid-floored cages had significantly higher degrees of nephrocalcinosis than their counterparts housed individually in metabolism cages with wire-mesh bases.

Animals↗
PubMed1992

Inhibitory effect of soybean protein vs. casein on apparent absorption of magnesium in rats is due to greater excretion of endogenous magnesium.

Apparent magnesium absorption is depressed in rats fed diets containing soybean protein or enriched with sodium phytate or phosphate in comparison with casein, whereas it is raised in rats fed lactose. However, the possibility that changes in apparent absorption are caused by changes in fecal excretion of endogenous magnesium cannot be excluded. We studied the effects of casein, soybean protein, sodium phytate, lactose and phosphate on apparent and true absorption of magnesium. True magnesium absorption was measured with the use of oral and intraperitoneal administration of tracer doses of 28Mg. Fecal excretion of endogenous magnesium was calculated from apparent and true absorption. True magnesium absorption was not affected by either substitution of soybean protein for casein or by the addition of sodium phytate to a diet containing casein. Endogenous magnesium excretion in feces was significantly increased by soybean protein and sodium phytate. Thus the observed impairment of apparent magnesium absorption in rats fed soybean protein or sodium phytate is due to enhanced fecal excretion of endogenous magnesium. With the other dietary treatments, enhanced fecal excretion of endogenous magnesium was not associated with a discrepancy in the effects on apparent and true magnesium absorption. Dietary lactose vs. dextrose and supplemental phosphate both stimulated fecal excretion of endogenous magnesium, but lactose raised both true and apparent magnesium absorption, and phosphate depressed both true and apparent magnesium absorption.

Absorption↗
PubMed1992

Intestinal, segmented, filamentous bacteria.

Segmented, filamentous bacteria (SFBs) are autochthonous, apathogenic bacteria, occurring in the ileum of mice and rats. Although the application of formal taxonomic criteria is impossible due to the lack of an in vitro technique to culture SFBs, microbes with a similar morphology, found in the intestine of a wide range of vertebrate and invertebrate host species, are considered to be related. SFBs are firmly attached to the epithelial cells of the distal ileal mucosa, their preferential ecological niche being the epithelium covering the Peyer's patches. Electron microscopic studies have demonstrated a considerable morphological diversity of SFBs, which may relate to different stages of a life cycle. Determinants of SFB colonization in vivo are host species, genotypical and phenotypical characteristics of the host, diet composition, environmental stress and antimicrobial drugs. SFBs can survive in vitro incubation, but do not multiply. On the basis of their apathogenic character and intimate relationship with the host, it is suggested that SFBs contribute to development and/or maintenance of host resistance to enteropathogens.

Animals↗
PubMed1992

Histological changes in the orbital region of rats after orbital puncture.

To contribute to the assessment of the degree of discomfort in rats after orbital puncture, we have examined the histological changes in the intraorbital tissues caused by this technique of blood sampling. Orbits were studied from rats euthanized either within 1 min, 4 days, 28 days or 56 days after puncture while under diethyl-ether anaesthesia. The techniques of 2 animal technicians were compared, one using a broken haematocrit capillary and the other using an intact Pasteur's pipette. Non-punctured orbits served as controls. Microscopic slides containing the eye in situ at 2 horizontal levels in the orbital region were examined for 37 parameters; the slides were scored blind and in random order. Orbital puncture caused haemorrhages in the puncture track and, depending on the technique used, also in the periosteum. Four days after puncture, inflammatory reactions were present in the puncture track. Depending on the technique of puncture, these reactions were also seen in the eye muscles and periosteum or in the Harderian gland. Within 4 weeks after puncture, the lesions had healed without detectable scars. The different histological effects of the 2 techniques of orbital puncture are discussed in the light of the characteristics of these techniques.

Animals↗