Rat Serum Lipoproteins Research Articles

Hepatic Secretion of Lipids and Apolipoproteins in Rats Fed Soybean Phospholipid and Soybean Oil

Dietary phospholipid (PL) containing phosphatidylethanolamine alters serum lipoproteins in rats. To clarify the underlying mechanism for the alteration of serum lipids and apolipoproteins, secretions of lipids and apolipoproteins from isolated perfused livers in rats fed soybean PL or soybean oil were compared in this study. Soybean PL significantly decreased the rates of accumulation of apolipoprotein A-I (apoA-I) and cholesterol in the liver perfusate. The secretion of newly synthesized apoA-I labeled with [3H]lysine into the perfusate also significantly decreased in rats fed soybean PL. The secretion patterns of triglyceride and apolipoproteins other than apoA-I were similar for rats fed either diet. Constant infusion of oleic acid into the liver perfusion medium did not alter the response of the secretion of lipids and apolipoproteins to soybean PL feeding. In rats injected with Triton WR-1339, concentrations of serum triglyceride and high-molecular-weight apoB at 20 hours after injection were significantly increased by soybean PL feeding, whereas until 2 hours postinjection the accumulation of serum triglyceride was similar for rats fed either diet. Thus, soybean PL affects not only secretion of hepatic lipoproteins but also metabolism of triglyceride-rich lipoproteins derived from the liver.

Effects of dietary trans-fat on biliary and fecal steroid excretion and serum lipoproteins in rats.

Rats were fed cholesterol-free or cholesterol-enriched diets containing olive oil or partially hydrogenated corn oil at the 10% level for ca. 30 days (c-18:1, 77.0% in the former diet and c-18:1,24.7% and t-18:1,42.5% in the latter). The linoleic acid content of these fat diets was made equivalent (1.7 energy %). After feeding cholesterol-free diets, trans fat compared to cis fat showed (a) no untoward effects on growth parameters, (b) a reduction of serum cholesterol levels without influencing concentrations of serum apolipoproteins A-1, B and E, (c) no effects on the bile flow and the concentration of biliary cholesterol and bile acids, (d) an increasing trend of fecal excretion of neutral and acidic steroids, both in terms of mg/day and mg/g feces, and (e) rather equivocal change in the composition of fecal, but not biliary steroids. Similar response patterns were also observed when cholesterol-enriched diets were fed except for a decrease in serum apo B and an ineffectiveness to increase fecal acidic steroids. Together with the results obtained from experiments simultaneously performed with safflower oil and completely hydrogenated corn oil, it seems that the steroid metabolism can be specifically modified by the geometry of dietary fats.

Characterization of a triphenylethylene-antiestrogen-binding site on rat serum low density lipoprotein.

Several laboratories have reported the presence of an intracellular, high affinity [dissociation constant (Kd), 1-2 nM] antiestrogen-specific binding site in estrogen target tissues. In this report, we describe the binding properties and characteristics of an additional triphenylethylene antiestrogen-binding site in the serum of rats. By using saturation and competitive binding analyses with [3H]tamoxifen as the radio-labeled ligand, we have determined that rat serum contains a relatively high affinity (Kd, 28 nM), protease-sensitive binding site that is specific for antiestrogens of the triphenylethylene type (clomiphene and nafoxidine). Since this serum site has little affinity for the benzythiophene antiestrogens (LY 117018 and 156758), we have chosen the name of triphenylethylene-antiestrogen binding site (TABS). The concentration of serum TABS (picomoles of [3H]tamoxifen bound per ml serum) is roughly the same in males and females but is significantly greater in both sexes at days 5, 10, and 15 of age (400-500 pmol/ml) than in newborn or adult animals (100-200 pmol/ml). Preliminary characterization studies indicated that the serum TABS is probably a serum lipoprotein. Separation of rat serum lipoproteins on potassium bromide density gradients revealed that the serum TABS migrated with rat low density lipoprotein (LDL). Furthermore, rat LDL purified by density gradient centrifugation has an affinity and specificity for [3H]tamoxifen that is similar to the TABS found in whole serum. In contrast, the rat liver intracellular TABS does not have these density gradient characteristics. These data suggest that the rat serum TABS is LDL; however, the role of this serum lipoprotein in the mechanism of action of antiestrogens remains to be determined.

Effect of lactose content of nonfat milk diets on male rat serum lipids and lipoproteins.

The lactose content of a semisynthetic diet containing 45% of calories as nonfat milk powder was modified by enzymatic hydrolysis with beta-galactosidase or bacterial fermentation with yogurt cultures. Three milk-based diets and a stock diet were fed for 28 days to male rats derived from the Sprague-Dawley strain. Energy consumption, growth rate, feed efficiency, liver weight, liver cholesterol and liver triglyceride concentrations were not significantly different between the four diets. At day 28 serum cholesterol and serum triglyceride concentrations were not different between the milk-based diets. No hypocholesterolemic effect of the milk-based diets was seen at any time compared to the stock diet. Two of four electrophoretic lipoprotein fractions varied with the lactose content of the milk-based diet. The faster alpha lipoprotein decreased while the slower alpha lipoprotein increased with decreasing content of dietary lactose. These data indicate that lactose differs from its constituent monosaccharides, galactose and glucose, in its effect on lipoprotein levels, even though total serum cholesterol and triglycerides do not differ.

Effect of dietary polyunsaturated phospholipid on the chemical composition of serum lipoproteins in rat.

The effect of soybean phospholipid (SP), given at the rate of 100/g/kg diet for 2-3 weeks, on the chemical composition of serum lipoprotein in rats was examined. Soybean oil (SO) containing almost comparable amounts of linoleic acid was used as a control diet. SP significantly decreased the concentration of serum cholesterol and apolipoprotein A-I (apo A-I) and increased apolipoprotein B (apo B). There was no significant change in the concentration of serum apolipoprotein E (apo E) and the other lipids. The reduction of cholesterol levels in all the lipoprotein fractions was observed. The reduction of the serum apo A-I was brought about by the addition of SP at the level of 1% while that of the cholesterol at the level of 4%. The subunit composition of apo A-I, but not apolipoprotein C, in high density lipoprotein (HDL) was also altered by SP. The high molecular weight of apo B was responsible for the increment of apoproteins in the low density lipoprotein (LDL). The triglyceride, but not the cholesterol ester, also increased in LDL. there was no significant difference between the groups in the fatty acid compositions of serum triglyceride and phospholipid. In the liver, SP significantly increased the concentration of cholesterol ester and decreased triglyceride. These results are discussed in the context of the role of the lipoprotein and apoprotein in the regulation of serum cholesterol concentration.

Relationship between the nutritional status of zinc and cholesterol concentration of serum lipoproteins in adult male rats

The effect of zinc status on the distribution of serum cholesterol among the major serum lipoproteins was assessed in adult male rats fed a zinc-deficient diet (0.37 ppm Zn) as compared with those of pair-fed and ad libitum-fed zinc-supplemented controls (41 ppm Zn). All data were collected within the first 4 wk of dietary treatment before the manifestation of any external symptoms of zinc deficiency. The acute zinc depletion produced a significant reduction in total serum cholesterol; the reduction was primarily due to the selective decline in high-density lipoprotein-cholesterol. Zinc depletion per se produced no significant alterations in very low-density lipoprotein- or low-density lipoprotein-cholesterol level. In addition, linear regression analysis based on the 36 pairs of serum zinc and high-density lipoprotein-cholesterol values showed a significant positive correlation (r = + 0.81; p less than 0.01) between these two parameters. The data also indicated a significant correlation between the ratio of zinc/copper and total serum cholesterol. This relationship was, however, solely dependent upon serum zinc status rather than serum copper. The serum levels of copper were not affected by zinc depletion over the period of 4 wk. These results present new evidence for the close association between the nutritional status of zinc and high-density lipoprotein concentration in adult male rats and draw attention to the potential significance of zinc nutriture in relation to cardiovascular health.

Serum and hepatic nascent lipoproteins in normal and hypercholesterolemic rats.

The lipids and apoproteins of serum, hepatic Golgi cisternae, and secretory vesicle lipoproteins from hypothyroid, hypercholesterolemic rats were analyzed and compared to homologous lipoprotein fractions from euthyroid rats fed a low fat chow diet in order tao determine the nature of the nascent lipoprotein particles and indicate post-secretory modifications. Normal rat hepatic Golgi and secretory vesicles contained predominantly triglyceride-rich very low density lipoprotein (VLDL) which had little associated apoC-II or C-III and was deficient in apoE when compared to serum VLDL. Small quantities of cholesteryl ester-enriched low density lipoprotein (LDL) containing apoB and apoE were also present. Hepatic fractions from hypercholesterolemic rats contained cholesteryl ester- and apoE-rich, triglyceride-depleted VLDL of similar size, immunodiffusion characteristics, ratio of immunoassayable apoB to apoE, and lipid composition, to hypercholesterolemic serum VLDL. Hepatic levels of LDL in hypercholesterolemic rats were markedly elevated and enriched in cholesteryl ester and apoE when compare to normal hepatic LDL. Cholesteryl ester-rich hepatic VLDL and LDL increased in size and in cholesteryl ester and apoE content during transit from the Golgi cisternae into the secretory vesicles. Triglyceride-rich VLDL only acquired apoE which was further supplemented upon secretion. Nascent VLDL and LDL represented LpB-LpE association complexes and no deficiency in any apoE isoprotein within the cholesteryl ester-rich serum lipoproteins was observed. Thus, dietary-induced hypercholesterolemia in hypothyroid rats results in a fatty liver whose lipoprotein secretory products contribute to the plasma pool of abnormal cholesteryl ester- and apoE-enriched lipoproteins.

Metabolism of chromatographically separated rat serum lipoproteins specifically labeled with 125I-apolipoprotein E.

Radioiodinated apolipoprotein E, added in small amounts to rat serum, rapidly associates with the serum very low density lipoproteins and high density lipoproteins in proportion to their content of endogenous and apolipoprotein E. The labeled lipoproteins can be separated, without ultracentrifugation, by molecular sieve chromatography. When these labeled lipoproteins are injected intravenously into intact rats, the labeled apolipoprotein E rapidly exchanges with apolipoprotein E in the alternate lipoprotein fraction and is removed from the blood at a slow rate, comparable to that observed for apolipoprotein A-I in similarly labeled high density lipoproteins. No evidence was found for a rapidly turning over component of high density lipoproteins containing apolipoprotein E. When very low density lipoproteins, labeled endogenously with [3H]cholesterol and with radioiodinated apolipoprotein E, are added to perfusates of isolated rat livers, the labeled cholesteryl esters and apolipoprotein E are removed from the perfusate rapidly and at the same rate. Therefore, the slow removal of labeled apolipoprotein E in very low density lipoproteins in vivo is the result of rapid exchange with apolipoprotein E in high density lipoproteins.

Two‐dimensional immunoelectrophoresis of rat serum apolipoproteins

AbstractA two‐dimensional crossed immunoelectrophoretic method for the determination of the specificity of antibodies raised against rat serum lipoproteins and apolipoproteins (Apo) is described. The method may also be used for the detection of as yet undesignated apoproteins, associated with the serum lipoprotein fractions, and exploits the superior resolving capacity of 7m urea 10% polyacrylamide gel electrophoresis for the first dimension separation and minimizes physical separation of polyacrylamide and agarose in the second dimension electrophoresis by use of low electroendosmotic flow agarose. The use of polyacrylamide instead of cellulose acetate in the first dimension permits the analysis of larger amounts of antigen protein, crossed imunoelectrophoresis of Apo E which binds to cellulose acetate, and the crossed immunoelectrophoresis of antigens previously focused to their isoelectric points in polyacrylamide gels containing ampholytes.

Effects of 17 alpha-ethinyl estradiol on the serum lipoproteins of cholesterol-fed diabetic rats.

Large doses of 17 alpha-ethinyl estradiol were administered to rats made diabetic by administration of streptozotocin and fed a diet containing 2% cholesterol and 1% cholic acid. Before estrogen treatment, these rats were severely hypercholesterolemic and had high concentrations of lipoproteins of d < 1.006 g/ml (very low density lipoproteins, VLDL), d = 1.006 to 1.03 g/ml (intermediate density lipoproteins, IDL), and d = 1.03 to 1.063 g/ml (low density lipoproteins, LDL), and low concentrations of lipoproteins of d = 1.063 to 1.21 g/ml (high density lipoproteins, HDL). The VLDL contained two populations of particles with a mean diameter of 1150 and 350 A, respectively. The IDL contains only the latter particles. These particles are unusual in that they contain apolipoprotein A-I in addition to their usual complement of apolipoproteins. After estrogen treatment, the concentrations of both large and smaller particles in VLDL were greatly decreased as were the concentrations of IDL and LDL; apo A-I was no longer present in the residual VLDL and IDL. HDL phospholipid, protein, and cholesterol increased 7-fold, 4-fold, and 2-fold, respectively. Studies by others have shown that large doses of estrogen enhance uptake of LDL by the liver and this is associated with an increase in the saturable binding sites for LDL on liver membranes. The present studies suggest that these binding sites recognize lipoproteins other than LDL. Furthermore, the enhanced uptake of these lipoproteins appears to result in transfer of their surface components to HDL.

Interaction of unilamellar liposomes with serum lipoproteins and apolipoproteins

The effect of rat whole blood plasma, serum, serum lipoproteins, and apolipoproteins on the stability of unilamellar liposomes prepared with French pressure cell was evaluated by measuring the release of entrapped carboxyfluorescein and by electron microscopy. In the absence of serum components, dye escaped very slowly (hours) from egg phosphatidylcholine and phosphatidylcholine-cholesterol (43 mol % cholesterol) vesicles without apparent change in liposomal structure. This slow release was both temperature- and size-dependent. serum and some of its constituents induced a far more rapid (seconds) loss of entrapped dye from phosphatidylcholine liposomes, associated with structural changes. For equal masses of protein the order of potency of this induced activity was: free apolipoproteins (apo A-I, apo E) > isolated lipoproteins (HDL and VLDL) > whole serum or whole plasma. Substantial activity was found in three preparations of bovine serum albumin. This activity could be attributed to small and variable amounts of contaminating lipoprotein-like particles and apolipoprotein A-I. Induced release of dye from liposomes by apolipoproteins was usually associated with rapid formation of discs although other structures were sometimes formed. Purified rat apolipoproteins A-I and E appeared to interact identically with liposomes to induce dye release. This effect was progressively impaired for both apoproteins by increasing amounts of cholesterol and was completely inhibited when liposomes contained 37 mol % cholesterol.

Serum lipoproteins of diabetic rats fed a high cholesterol diet.

Feeding a diet containing 2% cholesterol and 1% cholic acid (wt/wt) to rats made diabetic by administration of streptozotocin (45 mg/kg) produced marked hypercholesterolemia characterized by high concentrations of very low density lipoproteins (VLDL) and intermediate density lipoproteins (IDL) and a reduction in concentration of high density lipoproteins (HDL). The VLDL was unique in that it contained apo A-I and apo A-IV in addition to its usual complement of apoproteins: apo B, apo E, and the C apoproteins. IDL had a similar apoprotein composition. The HDL from these rats was deficient in apo E. Nondiabetic rats fed the same diet exhibited similar qualitative changes in lipoprotein concentration and composition but with lesser increases in VLDL and IDL concentrations. The altered apoprotein composition suggested that the hyperlipoproteinemia associated with cholesterol feeding in the rat is due to an inadequate rate of removal of lipoproteins of intestinal origin, and that this is greatly exacerbated by diabetes.

Serum lipoproteins of diabetic rats fed a high cholesterol diet

Serum lipoproteins of diabetic rats fed a high cholesterol diet

Drug-induced dyslipoproteinemia: a report of two cases.

We describe two cases of atypical dyslipoproteinemia due to drug-induction. This secondary form of lipoprotein abnormality is unique because the newly available drug, miconazole, apparently directly delipidated the alpha-lipoproteins in the bloodstream. On closer study we found that the delipidation was caused by the vehicle rather than the fungicide--more specifically, only by the polyethoxylated castor oil in the vehicle. It affects serum lipoproteins both in vitro and in vivo, and the effect is species-specific. In vitro studies indicate that it preferentially delipidates high-density lipoprotein rather than low-density lipoprotein. Because its effects on the serum lipoproteins of rats resemble those on man, and because aortic lesions were produced in rats injected daily (90 mL/L) with this substance, caution is indicated in long-term use of drugs containing this chemical component in the vehicle.

Drug-induced dyslipoproteinemia: a report of two cases.

Abstract We describe two cases of atypical dyslipoproteinemia due to drug-induction. This secondary form of lipoprotein abnormality is unique because the newly available drug, miconazole, apparently directly delipidated the alpha-lipoproteins in the bloodstream. On closer study we found that the delipidation was caused by the vehicle rather than the fungicide--more specifically, only by the polyethoxylated castor oil in the vehicle. It affects serum lipoproteins both in vitro and in vivo, and the effect is species-specific. In vitro studies indicate that it preferentially delipidates high-density lipoprotein rather than low-density lipoprotein. Because its effects on the serum lipoproteins of rats resemble those on man, and because aortic lesions were produced in rats injected daily (90 mL/L) with this substance, caution is indicated in long-term use of drugs containing this chemical component in the vehicle.

Effect of serum lipoproteins of bile obstructed rats on 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase activity in perfused rat liver

Total lipoproteins as well as fractionated VLDL + LDL and HDL from fasted control rats and bile-ligated rats were tested in liver perfusion for their effect on 3-hydroxy-3-methylglutaryl CoA reductase activity in normal rat livers. The total lipoproteins of bile-obstructed rats had 3 times greater capacity to increase 3-hydroxy-3-methylglutaryl CoA reductase activity than that of the control total lipoproteins. When the fractionated lipoproteins were tested from fasted control rats, it was found that the major stimulating activity was in the HDL fraction with minor activity in the VLDL + LDL fraction. When these plasma components isolated from fasted bile-ligated rats were tested, it was found that the major activity had shifted to the VLDL + LDL fraction with the HDL having only a minor stimulatory role. The possible mechanism of action of the abnormal lipoproteins associated with bile obstruction in regulating 3-hydroxy-3-methylglutaryl CoA reductase activity is discussed.

The Interactive Effect of Dietary Glycerol and Corn Oil on Rat Liver Lipids, Serum Lipids and Serum Lipoproteins

The Interactive Effect of Dietary Glycerol and Corn Oil on Rat Liver Lipids, Serum Lipids and Serum Lipoproteins

Biochemical studies on fatty liver. IX. Serum lipoproteins in rats with amino acid imbalance-induced fatty liver.

Serum lipoproteins in rats with fatty liver, which was induced by feeding an amino acid imbalanced diet containing 8% casein supplemented with 0.3% of DL-methionine, were analyzed. Three classes of serum lipoproteins, VLDL, LDL and HDL, were isolated by flotation in the ultracentrifuge and their concentration and chemical composition were determined. In serum VLDL of the imbalanced group, the concentration of TG was significantly higher than those for the control group, and that of apoprotein was maintained at the normal level. These results suggest that this type of fatty liver is not due to a block in the transport of hepatic TG to the plasma. On the contrary, the administration of DL-ethionine resulted in a reduced level of TG of VLDL.

Mechanism of heparin and serum lipoprotein interaction: Effects of calcium, phosphorylcholine, and a serum fraction

The mechanism of formation of an insoluble complex between heparin and rat serum lipoprotein has been studied. Optical density changes during the reaction, counting of the fatty acid labelled lipoproteins in the precipitates, and complexing of [14C]palmitate-labelled lipoprotein with heparin-CNBr-Sepharose were used to quantitatively determine the formation of insoluble complexes. The maximal heparin--lipoprotein complex formation requires 25--30 mM of Ca2+, but with micromolar amounts of phosphorylcholine, the reaction was saturated at only 10 mM of Ca2+. The effect of phosphorylcholine in promoting the reaction was lost when purified chylomicrons or very low density lipoproteins were used. The effect of phosphorylcholine in promoting the interaction between heparin and pure chylomicrons or very low density lipoproteins was regained when a crude serum protein factor of unwashed chylomicrons was added to the system, suggesting that rat serum contains a protein factor(s) which normally inhibits the heparin--lipoprotein interaction by raising the requirement of Ca2+. Phosphorylcholine counteracted the effect of this protein, thereby favouring the precipitation reaction in the presence of much lower concentration of Ca2+. The results have been discussed with special reference to the possibility of a relationship between mucopolysaccharides, Ca2+, lipoproteins, and arterial phospholipids in the pathogenesis of atherosclerosis.

Eicosenoic and docosenoic acid incorporation in serum lipoproteins in rats fed rapeseed oil.

Rats were fed rapeseed oil rich in eicosenoic (20:1) and docosenoic (22:1) acids for 7 days, and the fatty acid composition of the lipid classes of serum and serum lipoproteins was determined. Concentrations of 20:1 and 22:1 acids in the lipid classes were variable, especially among lipoproteins, and were a direct function of the alimentary state of the animal. The results suggest differences in the incorporation of the above acids among the major lipoprotein types and various lipid classes within a given lipoprotein type. The quick partial disappearance of very low density lipoproteins (VLDL) and of low density lipoproteins (LDL) containing 20:1 and 22:1 acids upon starvation and the preferential incorporation of these acids in the triacylglycerols of high density lipoproteins (HDL) are discussed.