Density Lipoprotein In Rats Research Articles

Postprandial Changes in High Density Lipoproteins in Rats Subjected to Gavage Administration of Virgin Olive Oil

Background and AimsThe present study was designed to verify the influence of acute fat loading on high density lipoprotein (HDL) composition, and the involvement of liver and different segments of small intestine in the changes observed.Methods and ResultsTo address these issues, rats were administered a bolus of 5-ml of extra-virgin olive oil and sacrificed 4 and 8 hours after feeding. In these animals, lipoproteins were analyzed and gene expressions of apolipoprotein and HDL enzymes were assessed in duodenum, jejunum, ileum and liver. Using this experimental design, total plasma and HDL phospholipids increased at the 8-hour-time-point due to increased sphingomyelin content. An increase in apolipoprotein A4 was also observed mainly in lipid-poor HDL. Increased expression of intestinal Apoa1, Apoa4 and Sgms1 mRNA was accompanied by hepatic decreases in the first two genes in liver. Hepatic expression of Abcg1, Apoa1bp, Apoa2, Apoe, Ptlp, Pon1 and Scarb1 decreased significantly following fat gavage, while no changes were observed for Abca1, Lcat or Pla2g7. Significant associations were also noted for hepatic expression of apolipoproteins and Pon1. Manipulation of postprandial triglycerides using an inhibitor of microsomal transfer protein -CP-346086- or of lipoprotein lipase –tyloxapol- did not influence hepatic expression of Apoa1 or Apoa4 mRNA.ConclusionAll these data indicate that dietary fat modifies the phospholipid composition of rat HDL, suggesting a mechanism of down-regulation of hepatic HDL when intestine is the main source of those particles and a coordinated regulation of hepatic components of these lipoproteins at the mRNA level, independently of plasma postprandial triglycerides.

Influence of dietary fat saturation on lipid peroxidation of serum and low density lipoprotein in rats

The purpose of this study was to investigate the influence of different P/S (polyunsaturated/saturated) ratios on lipid peroxidation of plasma, liver and low-density lipoprotein (LDL) in rats, using dietary fats with different saturation levels. Male Sprague-Dawley rats weighing about 300 g were randomly divided into five groups and fed a semisynthetic diet containing 10% (w/w) fat for 6 weeks. The fat was composed of 100, 75, 50, 25, 0% corn oil and 0, 25, 50, 75, 100% lard (CO100, CO75, CO50, CO25 and LA groups, with P/S ratios of 3.81, 2.13, 1.21, 0.64, and 0.28, respectively) respectively. The body and liver weight of rats fed dietary fat with different P/S ratios were comparable among 5 groups. The CO100 group had higher plasma TBARS (thiobarbituric acid-reactive substances) than the CO25 and LA groups. The TBARS of LDL in LA and CO25 groups were lower than those of the other (CO100, CO75 and CO50) groups. In addition, the rats fed P/S ratio ≦1.21 (i.e., CO50, CO25, and LA groups) had lower LDL TBARS than rats fed P/S ratio >1.21 (i.e., CO100 and CO75 groups) when LDL were incubated with Cu 2+ at 37 °C for 2 or 5 h. On the other hand, rats fed diets with P/S ratio ≦1.21 experienced significantly increase lag time of conjugated diene formation in LDL than those fed P/S >1.21. The fatty acid content of 18:2 (n-6) in LDL was reduced by decreasing the ratio of P/S in dietary fat. The ratio of linoleic acid content to oleic acid content was inversely correlated with the lag time of LDL oxidation. However, different P/S ratio in the diet did not affect 18:1 (n − 9), vitamin E levels and the TBARS values in liver of rats. The results suggested that P/S ratios in the diet influenced the LDL oxidation, and the lipid peroxidation might have a threshold of P/S ratios between 1.21 and 0.64.

Effect of human apolipoprotein A-I gene on vasoactive properties of high density lipoproteins in rats of different age

Vasodilatory activity of high density lipoproteins and the content of apolipoprotein A-I in these particles decreases in senescent rats in comparison with adult animals. Implantation of human apolipoprotein A-I gene increases the content of this apolipoprotein in high density lipoproteins and improves their vasodilatory effect.

2.P.86 Effects of silymarin and silybin on lipoprotein cholesterol levels and oxidizability of low density lipoprotein in rats

2.P.86 Effects of silymarin and silybin on lipoprotein cholesterol levels and oxidizability of low density lipoprotein in rats

Oxidized lipids in the diet are incorporated by the liver into very low density lipoprotein in rats

Previous studies have shown that the quantity of oxidized lipids in the diet directly correlates with the level of oxidized chylomicrons in mesenteric lymph and the level of oxidized lipids in endogenous lipoproteins such as very low density lipoprotein (VLDL) and low density lipoprotein (LDL). The aim of the present study was to determine whether oxidized fatty acids in the diet are delivered via chylomicrons to the liver and whether these lipids are repackaged and secreted in VLDL. In these experiments, oxidized [14C]linoleic acid was utilized as a marker for oxidized dietary fats. When we determined the metabolism of nonoxidized and oxidized [14C]linoleic acid-labeled chylomicrons, we found that hepatic uptake was similar with 13.57 +/- 0.84% of nonoxidized and 13.40 +/- 0.96% of oxidized linoleic acid delivered to the liver 30 min after chylomicron administration. Additionally, uptake by the extrahepatic tissues was also similar. When the hepatic secretion of VLDL was determined in an in vitro perfusion system after the administration of nonoxidized and oxidized linoleic acid-labeled chylomicrons to intact animals, we found that oxidized linoleic acid was utilized for the formation and secretion of VLDL. After the administration of labeled nonoxidized and oxidized linoleic acid, 0.86 +/- 0.07% and 0.70 +/- 0.09% of the administered label was found in the liver perfusate at 2 h, respectively. The presence of oxidized linoleic acid in oxidized VLDL was confirmed by demonstrating the presence of hydroperoxide-derived hydroxy octadecanoic acid. Thus, our findings demonstrate that oxidized dietary lipids are delivered to the liver via chylomicrons where they are utilized for synthesis of endogenous lipoproteins such as VLDL.

Copper deficiency increases hepatic parenchymal cell's maximal binding capacity and impairs Kupffer cell's internalization of apolipoprotein E-free high density lipoprotein in rats

The binding and internalization of apolipoprotein (apo) E-free high density lipoprotein (HDL) by hepatic parenchymal and Kupffer cells were examined with cells and HDL derived from rats fed copper (Cu)-deficient (II nmol/g) and -adequate (126 nmol/g) diets. After 8 weeks of dietary treatment, plasma apo E-free HDL was isolated by a combination of ultracentrifugation, gel filtration, and heparin-Sepharose affinity chromatography. Liver parenchymal and Kupffer cells were obtained by collagenase perfusion and purified by centrifugal elutriation. Freshly isolated cells were incubated with 125I-apo E-free HDL, either from the same treatment group or in a crossover design, to establish if treatment differences were associated with cells, HDL, or both. Binding studies performed at 0° C with increasing apo E-free HDL concentrations demonstrated increases in specific binding and maximum binding capacity (B max) in parenchymal cells from Cu-deficient rats. In addition, cell association studies at 37° C indicated that the amount of apo E-free HDL bound to the cell surface (trypsin releasable) was greater, but the amount internalized (trypsin resistant) was not altered in parenchymal cells from Cu-deficient rats. In contrast, the amount of apo E-free HDL internalized was reduced and that bound to the cell surface was unaltered in Kupffer cells from Cu-deficient rats. Thus Cu deficiency may exert different effects on HDL metabolism in hepatic parenchymal and Kupffer cells. Furthermore, the crossover design demonstrated for the first time that the source of cells from Cu-deficient rats, not HDL, was responsible for the enhanced B max and altered internalization. The results of the present study also support the contention that the hypercholesterolemia associated with the copper-deficient rat model is not the result of decreased HDL uptake by the liver.

Different fate in vivo of oxidatively modified low density lipoprotein and acetylated low density lipoprotein in rats. Recognition by various scavenger receptors on Kupffer and endothelial liver cells

Human low density lipoprotein was oxidized (Ox-LDL) by exposure to 5 microM Cu2+ and its fate in vivo was compared to acetylated low density lipoprotein (Ac-LDL). Ox-LDL, when injected into rats, is rapidly removed from the blood circulation by the liver, similarly as Ac-LDL. A separation of rat liver cells into parenchymal, endothelial, and Kupffer cells at 10 min after injection of Ox-LDL or Ac-LDL indicated that the Kupffer cell uptake of Ox-LDL is 6.8-fold higher than for Ac-LDL, leading to Kupffer cells as the main liver site for Ox-LDL uptake. In vitro studies with isolated liver cells indicated that saturable high affinity sites for Ox-LDL were present on both endothelial and Kupffer cells, whereby the capacity of Kupffer cells to degrade Ox-LDL is 6-fold higher than for endothelial cells. Competition studies showed that unlabeled Ox-LDL competed as efficiently (90%) as unlabeled Ac-LDL with the cell association and degradation of 125I-labeled Ac-LDL by endothelial and Kupffer cells. However, unlabeled Ac-LDL competed only partially (20-30%) with the cell association and degradation of 125I-labeled Ox-LDL by Kupffer cells, while unlabeled Ox-LDL or polyinosinic acid competed for 70-80%. It is concluded that the liver contains, in addition to the scavenger (Ac-LDL) receptor which interacts efficiently with both Ac-LDL and Ox-LDL and which is concentrated on endothelial cells, an additional specific Ox-LDL receptor which is highly concentrated on Kupffer cells. In vivo the specific Ox-LDL recognition site on Kupffer cells will form the major protection system against the occurrence of the atherogenic Ox-LDL particles in the blood.

Probucol Promotes Hepatic Uptake of High Density Lipoprotein in Rats

Probucol significantly reduced high density lipoprotein (HDL)-cholesterol and apolipoprotein AI in rats. Hepatic uptake of radiolabelled human HDL3 increased significantly in vivo and in the isolated perfused rat liver preparation. In vivo, uptake of HDL3 by the adrenal glands also increased significantly. Hepatic cholesterol content in probucol-treated rats tended to increase, whereas newly synthesised cholesterol decreased significantly. The results of the present study suggest that enhanced uptake of HDL is one of the mechanisms of lowering serum HDL with probucol treatment.

Effects of triton WR 1339 and heparin on the transfer of surface lipids from triglyceride‐rich emulsions to high density lipoproteins in rats

The influence of lipolytic mechanisms on the transfer of phospholipids and unesterified cholesterol from artificial emulsions, serving as chylomicron models to other plasma lipoproteins, mainly high density lipoproteins (HDL) were tested in vivo. The emulsions labeled with radioactive lipids were injected into the bloodstream of rats (controls) and the results were compared with those obtained from rats that had previously been treated with Triton WR 1339 or heparin. Plasma clearance and the distribution of cholesteryl esters, phospholipids and unesterified cholesterol in the different plasma lipoprotein fractions were then determined. Whereas virtually no cholesteryl esters were found in d greater than 1.006 g/mL density fraction of the three experimental groups, 2.8 +/- 1.3% of the injected phospholipids were in the 1.063-1.210 g/L density fraction of the Triton treated rats, and 12.6 +/- 5.4% of the heparin treated rats, as compared to 10.1 +/- 1.7% in controls. This indicates that lipolysis directly influences phospholipid transfer to HDL. In contrast, free-cholesterol transfer to HDL, besides being less pronounced than phospholipid transfer, was enhanced by Triton and diminished by heparin, indicating that lipolytic mechanisms were not important determinants in this process.

Metabolism of very low density lipoproteins in rats with isotretinoin (13-cis retinoic acid)-induced hyperlipidemia.

A significant rise in plasma triacylglycerols from the control level of 0.89 mmol/l to 1.88 mmol/l (P less than 0.001) was observed in male Sprague-Dawley rats treated for 11 days with isotretinoin (oral dosing; 10 mg/day). This rise was due to an increased level of plasma very low density lipoproteins (VLDL). When VLDL from untreated rats were labeled with 125I-labeled tyramine-cellobiose and injected intravenously into rats treated for 10 days with isotretinoin (n = 6) and in control rats (n = 6), it was found that the disappearance of radioactivity from the blood was dramatically retarded in the treated animals. The disappearance could be divided into two phases, a rapid (alpha) phase dominated the first 5 min and was followed by a slower (beta) phase. The half-life of the beta-phase increased significantly from 53 +/- 7 min in the controls, to 120 +/- 62 min after isotretinoin. VLDL prepared from isotretinoin-treated animals (n = 6) had about the same half-life in control animals (62 +/- 8 min) as had ordinary VLDL. The elimination of tracer from the blood was mainly due to uptake by the liver. The amount of radioactivity in the liver after 30 min of circulation was significantly reduced from 34 +/- 7% of injected dose in controls to 24 +/- 5% in the isotretinoin group (P = 0.013). The uptake in other organs was less than 3% per organ and was essentially unaffected by the treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced catabolism of low density lipoproteins in rat by lactosaminated Fab fragment. A new carrier of macromolecules to the liver.

Proteins conjugated with lactose residues exhibit enhanced hepatic uptake mediated by the galactose receptor. In this study, we demonstrate that lactosaminated Fab fragments (lac-Fab) of IgG can induce hepatic catabolism of specific antigens, especially low density lipoproteins (LDL). lac-Fab and human LDL-lac-Fab complex exhibited specific uptake in isolated rat hepatocytes. In vivo in the rat, lactosamination enhanced plasma clearance of Fab fragments 2-fold and hepatic localization 20-fold. Fab fragments retained their affinity after lactosamination. Hepatic uptake of rat 125I-IgG complexed in vitro with anti-rat lac-Fab was increased almost 5-fold, compared to rat 125I-IgG alone. Injection of rats with anti-LDL lac-Fab induced plasma clearance and hepatic uptake of tracer amounts of previously injected human 125I-LDL, which decreased 50% 10 min after injection of lac-Fab, with 30% present in the liver. Asialofetuin completely inhibited these processes. After a bolus of 6 mg of human LDL, administration of anti-LDL lac-Fab reduced the serum cholesterol of rats to basal values within 2.5 h. These findings suggest that lactosaminated Fab fragments of specific IgGs are effective reagents for inducing hepatic uptake of macromolecules through the galactose receptor. lac-Fab specific for LDL may be an effective hypocholesterolemic agent in vivo.

In vivo interaction of synthetic acylated apopeptides with high density lipoproteins in rat.

The metabolism of synthetic peptide analogues of high density lipoprotein (HDL) apoproteins has been studied in the rat. These compounds are 15-amino acid lipid associating peptides (LAPs) bearing acyl chains of various lengths (0-16 carbon units). After injection of each 125I-LAP, the serum decay curves suggested a two-compartment process with a clearance rate decreasing when the acyl chain lengths increased. The similarity between the apparent half-life of C16-LAP and that of apoprotein A-I as well as the chromatographic analysis of rat serum were consistent with a partitioning of the LAPs between HDL and the aqueous phase. This was strongly dependent upon the acyl chain length of the LAPs. The distribution volumes of the 125I-LAPs in organs were measured 10 min after injection. The results were analyzed using a model explicitly predicting the organ distribution volumes of HDL and the equilibrium constant (Keq) of the binding of each LAP to HDL. HDL distributed significantly in the adrenals (250 microliters/g), liver (80 microliters/g), and ovaries (55 microliters/g), but not in the kidneys. This suggests that the binding of HDL apoproteins to kidneys, reported by others, was due to the uptake of free apoproteins. The Keqs exhibited a log-linear relationship with respect to the acyl chain length of the LAPs. Each carbon unit added to the acyl chain decreased the free energy of association by a constant value (0.3 kcal mol-1). This clearly showed a strict hydrophobic effect similar to that previously observed in vitro.

Catabolism of Newly Formed Triglyceride-Rich Lipoproteins and Serum High Density Lipoproteins in Rats Fed Soybean Phospholipid and Soybean Oil

Previous research has shown that serum cholesterol and apolipoprotein (apo) A-I were lower and serum apoB was higher in rats fed soybean phospholipid (PL) than in rats fed soybean oil. Secretion of cholesterol and apoA-I, but not apoB, from the liver and intestine was lower in rats fed soybean PL. In the present study catabolism of newly formed triglyceride (TG)-rich lipoproteins, from the liver and intestine, and of serum high density lipoproteins (HDL) were compared in rats fed soybean PL and in rats fed soybean oil. The following results were seen: Feeding of soybean PL was related to more TG and less cholesterol in intestinal lymph chylomicrons (CM) and hepatic very low density lipoproteins (VLDL) than was feeding of soybean oil. A lesser amount of the TG, labeled with [3H]oleate in CM and hepatic VLDL, was incorporated into the adipose tissue and muscle in vivo. The clearance of CM-TG from plasma was higher, but that of VLDL-TG and apoB labeled with [3H]lysine was lower. The catabolism of 125I-labeled HDL from the plasma was lower while hepatic uptake of 125I-labeled HDL, in vivo and in vitro, was higher. These results indicate that soybean PL modifies the catabolism of the respective serum lipoproteins. Therefore, we suggest that changes in both the catabolism and secretion of lipoproteins are responsible for the altered serum lipid and apolipoprotein patterns found in rats fed soybean PL.

Effect of Copper Deficiency on the Apolipoprotein E-Rich High Density Lipoproteins in Rats

Twenty-four male weanling Sprague-Dawley rats were randomly divided into two treatments, namely a copper-adequate (8 mg Cu/kg diet) or a copper-deficient (0.85 mg Cu/kg diet) group. Feed and distilled-demineralized water were provided ad libitum. After 7 wk, plasma high density lipoproteins (HDL) were isolated by ultracentrifugation and agarose column chromatography. A heparin-Sepharose affinity column chromatographic method was used to subfractionate HDL into apolipoprotein E (apoE) -rich and apoE-poor subfractions. Significantly higher protein and cholesterol contents of HDL and the second retained (RII) subfraction (apoE-rich) were observed in copper-deficient than in control rats. The apoE contents of HDL and the apoE-rich (RII) subfraction were about threefold higher in copper-deficient rats. The increase in apoE in the HDL fraction was due primarily to the increased apoE concentration of the RII subfraction. In addition to a higher apoE concentration, apolipoprotein A-I concentration was also higher in the RII subfraction of the copper-deficient rats as compared to controls. However, the percentage of these apolipoproteins remained unaltered by copper deficiency. The present data suggest that the hypercholesterolemia observed in copper deficiency was associated with marked increases in cholesterol and apolipoprotein contents of the apoE-rich HDL.

Different Effects of Zinc and Copper Deficiency on Composition of Plasma High Density Lipoproteins in Rats

Male Sprague-Dawley rats (six per group) were fed an egg white-based diet containing 0 or 5 µg/g Cu with 1, 10, 100 or 1000 µg/g Zn. After 6 wk of feeding, the rats were killed, and the tissues were processed for trace element, lipid and lipoprotein analysis. Copper deficiency was associated with a higher concentration of plasma free cholesterol, high density lipoprotein (HDL) cholesterol and HDL apolipoproteins. Plasma total cholesterol was not significantly affected. No significant differences were noted in HDL lipid composition. However, HDL apo E and apo A–I concentrations were higher with copper deficiency. Lecithin:cholesterol acyltransferase (LCAT) was not affected in a consistent manner by copper status. Varying the amount of zinc in the diet did not produce significant changes in plasma total cholesterol, plasma free cholesterol, HDL cholesterol, or HDL apolipoprotein concentrations. However, HDL from zinc-deficient rats were enriched in free cholesterol and depleted in triglycerides. Furthermore, the concentration of HDL apo C increased as the level of dietary zinc increased.

Composition of High Density Lipoproteins in Rats Fed Various Dietary Fibers

Several studies have suggested that dietary fibers, especially water-soluble sources, are effective agents for lowering plasma cholesterol. This study was undertaken to determine the effect of various fibers on the composition of apoproteins in high density lipoproteins. Rats were fed experimental diets that contained either 20% wheat bran, oat bran or cellulose or 5% pectin or guar gum for 4 weeks. Final body weight was similar among groups. HDL cholesterol and total apoprotein concentrations were not significantly altered by diet. The percentage of apo A-I was significantly elevated and apo E and the apo C's were significantly lower in the guar gum group relative to the wheat bran group. Lecithin cholesterol acyl transferase activity and the C-II-to-C-III ratio were highest in the guar gum group. Differences in the absorption and subsequent metabolism of lipid could account for differences in HDL composition.

Tissue sites of degradation of native and reductively methylated [14C]sucrose-labeled low density lipoprotein in rats. Contribution of receptor-dependent and receptor-independent pathways.

Low density lipoprotein (LDL) is catabolized by both receptor-dependent and receptor-independent pathways; methylated LDL (MeLDL) is catabolized only by receptor-independent mechanisms. Rats were injected with either LDL or MeLDL labeled with [14C]sucrose and the tissue sites of degradation were determined 24 h later. On degradation, the 14C-labeled ligand remains trapped intracellularly as a cumulative measure of degradation. The fractional catabolic rate (FCR) of [14C]sucrose-MeLDL was lower than that of [14C]sucrose-LDL (0.056 +/- 0.015 versus 0.118 +/- 0.025 h-1, p less than 0.01). Liver was the predominant site of catabolism of both LDL and MeLDL; more than 85% of catabolism was attributable to parenchymal cells in both cases. The fraction of the plasma LDL pool "cleared" per tissue weight per unit of time was determined for individual tissues. The differences in these rates for LDL and MeLDL are an approximation of receptor-mediated uptake of LDL. According to this method, 67.4% of hepatic uptake was attributable to receptors, as was 69.5% of adrenal, 65.4% of ovarian, 52.4% of intestinal, and 44.2% of renal uptake. In other studies, rats were continuously infused with LDL to down-regulate and saturate receptor prior to injection of labeled LDL or MeLDL. Rats infused with LDL exhibited a lower FCR for [14C]sucrose-LDL compared to controls (0.077 versus 0.120 h-1); the FCR for sucrose-MeLDL was unchanged by LDL infusion. The fractional degradation rate of [14C]sucrose-LDL by individual tissues was lowered by LDL infusion in liver, adrenal, ovary, and intestine (41.4, 57.3, 23.1, and 32.4% lower than controls, respectively). The determination of receptor dependency by this independent approach supports the conclusions reached using [14C]sucrose-LDL and [14C]sucrose-MeLDL in normolipemic animals.

Tissue sites of catabolism of rat and human low density lipoproteins in rats

We have determined the sites of degradation of low density lipoprotein in rats using covalently linked [ 14C]sucrose as tracer. On degradation, 14C is trapped intracellularly as a cumulative measure of the amount of protein catabolized by each tissue. [ 14C]Sucrose-labeled rat low density lipoprotein ( d 1.02–1.05 g/ml) was cleared from the plasma at a rate (0.092 ± 0.003 h −1) similar to that for 125I-labeled LDL (0.096 ± 0.22 h −1). Tissues were examined for total 14C content 24 h after injection of 14C-labeled lipoprotein. At death, animals were perfused thoroughly to remove trapped plasma. Recovery of 14C in tissues was 100 ± 23% of catabolized 14C-labeled lipoprotein (calculated from plasma decay kinetics). In three test tissues, leakage of 14C over 5 day s was less than 10%/day; leakage from liver was 10%/day, predominantly into bile; 14C content of kidney increased slightly. Thus, 14C trapping was adequate. The 14C-labeled lipoprotein was catabolized 66.8 ± 2.5% by liver. No other organ catabolized more than 8%. Liver, adrenal and ovary were the most active per unit wet weight, followed by spleen. Urinary excretion, in 24 h, was 3% and biliary excretion was 7% of catabolized. Human low density lipoproteins were similarly examined with similar results; this similarity may be due to exchange of rat apolipoproteins onto human lipoprotein in the circulation.

Quantification of the hepatic contribution to the catabolism of high density lipoproteins in rats.

Isolated rat livers were perfused for four hours in a recirculating system containing washed rat erythrocytes. Biologically screened radioiodinated rat high density lipoproteins (1.090 < d < 1.21 g/ml) were added to the perfusate with different amounts of whole serum to supply unlabeled rat high density lipoproteins. The protein moiety of the lipoprotein contained more than 95% of the radioiodine. The fraction of apolipoprotein mass degraded during the perfusion was quantified by the linear increment of non-protein-bound radioiodine in the perfusate, corrected for the increment observed during recirculation of the perfusate in the absence of a liver. The small amount of (131)I secreted into bile was added to calculate the fractional catabolic rate. The fractional catabolic rate ranged from 0.22 to 0.63% per hour in 12 experiments and was inversely related to the size of the perfusate pool of high density apolipoprotein. The absolute catabolic rate of high density apolipoprotein (fractional catabolic rate x pool size) in three livers in which the concentration of rat HDL in the perfusate approximated that in intact rats was 69.5 +/- 10.4 micro g hr(-1) (mean +/- SD). The rate of disappearance of cholesteryl esters of rat high density lipoproteins (labeled biologically by injecting donor rats with [5-(3)H]mevalonic acid) from the liver perfusate did not exceed that of the apoprotein component. These rates were compared with catabolic rates for rat high density lipoproteins in intact rats. Fractional catabolic rate in vivo, obtained by multicompartmental analysis of the disappearance curve of (131)I-high density apolipoprotein from blood plasma, was 11.9 +/- 1.3% hr(-1) (mean +/- SD). Total catabolic rate in vivo (fractional catabolic rate x intravascular pool of high density apolipoprotein) was 986 +/- 145 micro g hr(-1) (mean +/- SD). The results suggest that only a small fraction of high density lipoproteins in blood plasma of rats is degraded directly by the liver.-Sigurdsson, G., S-P. Noel, and R. J. Havel. Quantification of the hepatic contribution to the catabolism of high density lipoproteins in rats.

Interaction of lipopolysaccharides with plasma high density lipoprotein in rats: M.A.Freudenberg 1, T.C.B∅g Hansen 2, U.Back 3, E.Jirillo 1 and C.Galanos 11Max Planck Institut für Immunbiologie, Freiburg, West Germany 2The Protein Laboratory, University of Copenhagen, Copenhagen, Denmark 3The Collaboratory Centre for Reference and Research on Escherichia (WHO), The State Serum Institute, Copenhagen, Denmark

Interaction of lipopolysaccharides with plasma high density lipoprotein in rats: M.A.Freudenberg 1, T.C.B∅g Hansen 2, U.Back 3, E.Jirillo 1 and C.Galanos 11Max Planck Institut für Immunbiologie, Freiburg, West Germany 2The Protein Laboratory, University of Copenhagen, Copenhagen, Denmark 3The Collaboratory Centre for Reference and Research on Escherichia (WHO), The State Serum Institute, Copenhagen, Denmark