Normolipidemic Rabbits Research Articles

The Effects of Aromatic Water of Salix aegyptiaca L. and its Major Component, 1,4-Dimethoxybenzene, on Lipid and Lipoprotein Profiles and Ethology of Normolipidemic Rabbits.

We earlier reported that 1,4-dimethoxybenzene (DMB) was major component of aromatic water (AW) of Salix aegyptiaca L, Salicaceae, (SA). Here, Forty-eight male albino rabbits were divided into six equal groups: negative control (NC) group was gavaged with distilled water; positive control (PC) group was gavaged with simvastatin (0.6 mg/kg);SA1X and SA3X groups were gavaged with AW contains 1 mg/dl and 3 mg/dl essential oil, respectively and DMB1X and DMB3X were gavaged with 0.6 mg/dl and 1.8 mg/dl DMB, respectively. Serum total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) concentrations increased after 28 days in DMB-treated groups compared with NC group. The AW decreased TC level similar to the simvastatin-treated groups. DMB and SA intake did not positively modify highdensity lipoprotein cholesterol (HDL-C) and triacylglycerides (TGs) levels compared to NC group and similar levels of very low-density lipoprotein cholesterol (VLDL-C), HDL-C and LDL-C in SA-treated groups compared to NC showed that SA could not positively modify lipoprotein profile in normolipidemic rabbits. The atherogenic index level was higher in DMB3X group compared to NC and SIM groups. Stereotypies like body whirling, biting, escaping attempt and head shaking behaviors have been observed in DMB-treated groups.

The influence of social environment on endocrine, cardiovascular and tissue responses in the rabbit

Previous work from our lab demonstrated that social environment influences the progression of atherosclerosis in genetically hyperlipidemic rabbits. The purpose of the current study was to examine behavioral and physiological responses associated with these distinct chronic social conditions. Normolipidemic rabbits were exposed to one of three social environments for 4hours/day over 20weeks: 1) an Unstable Group in which animals were paired weekly with a different unfamiliar rabbit, 2) a Stable Group in which rabbits were paired with the same littermate for the entire study, and 3) an Individually Caged Group in which animals were socially isolated. It was found that the Unstable Group, characterized by increased agonistic behavior and relatively less affiliative behavior, exhibited physiological responses indicative of chronic stress (increased urinary norepinephrine, plasma cortisol, splenic weight, and decreased visceral fat and body weight compared to the other groups). These animals also had increased acute plasma oxytocin responses relative to the other groups 10minutes into the social pairing. In contrast, the Stable Group exhibited more affiliative behavior and less stressful physiological and tissue responses. The Individually Caged Group had elevated urinary norepinephrine relative to the Stable Group, and they exhibited higher heart rates at the end of the study compared to the other groups, suggesting that this social environment is also associated with chronic sympathetic arousal. It was concluded that distinct social contexts lead to different patterns of behavioral and physiological responses, and these responses are relevant to the pathophysiology of atherosclerosis and cardiovascular disease.

Apolipoprotein CI is a physiological regulator of cholesteryl ester transfer protein activity in human plasma but not in rabbit plasma

Plasma cholesteryl ester transfer protein (CETP) activity is high in rabbits, intermediate in humans, and nondetectable in rodents. Human apolipoprotein CI (apoCI) was found to be a potent inhibitor of CETP. The aim of this study was to compare the ability of rabbit and human apoCI to modulate the interaction of CETP with HDLs and to evaluate to which extent apoCI contributes to plasma cholesteryl ester transfer rate in normolipidemic humans and rabbits. Rabbit apoCI gene was cloned and sequenced, rabbit and human apoCI were purified to homogeneity, and their ability to modify the surface charge properties and the CETP inhibitory potential of HDL were compared. It is demonstrated that unlike human apoCI, rabbit apoCI does not modulate cholesteryl ester transfer rate in total plasma. Whereas both human and rabbit apoCI readily associate with HDL, only human apoCI was found to modify the electrostatic charge of HDL. In humans, both CETP and apoCI at normal, physiological levels contribute significantly to the plasma cholesteryl ester transfer rate. In contrast, CETP is the sole major determinant of cholesteryl ester transfer in normolipidemic rabbit plasma as a result of the inability of rabbit apoCI to change HDL electronegativity.

Hyaluronan Accumulation Is Elevated in Cultures of Low Density Lipoprotein Receptor-deficient Cells and Is Altered by Manipulation of Cell Cholesterol Content

The extracellular matrix molecule hyaluronan (HA) accumulates in human atherosclerotic lesions. Yet the reasons for this accumulation have not been adequately addressed. Because abnormalities in lipid metabolism promote atherosclerosis, we have asked whether disrupted cholesterol homeostasis alters HA accumulation in low density lipoprotein receptor-deficient cell cultures. Cultured aortic smooth muscle cells (ASMC) from Watanabe heritable hyperlipidemic (WHHL) rabbits and skin fibroblasts from homozygous patients with familial hypercholesterolemia accumulated 2-4-fold more HA than corresponding cells from age- and sex-matched normolipidemic rabbits and individuals. This occurred in both cell-associated and secreted HA fractions and was independent of cell density or medium serum concentration. WHHL ASMC cultures synthesized twice the proportion of high molecular mass HA (>2x10(6) Da) as normal rabbit ASMC but showed a lower capacity to degrade exogenous [3H]HA. Most importantly, cholesterol depletion or blocking cholesterol synthesis markedly reduced HA accumulation in WHHL ASMC cultures, whereas cholesterol replenishment or stimulation of cholesterol synthesis restored elevated HA levels. We conclude the following: 1) maintaining normal HA levels in cell cultures requires normal cell cholesterol homeostasis; 2) HA degradation may contribute to but is not the predominant mechanism to increase high molecular mass HA accumulation in low density lipoprotein receptor-deficient WHHL ASMC cultures; and 3) elevated accumulation of HA depends on cellular or membrane cholesterol content and, potentially, intact cholesterol-rich microdomains.

Influence of Dyslipidemia on Moxidectin Distribution in Plasma Lipoproteins and on its Pharmacokinetics

We studied the influence of dyslipemia on the distribution of moxidectin, a potent antiparasitic drug of the macrocyclic lactone (ML) family, in plasma lipoproteins and on its pharmacokinetic behaviour. Plasma samples from normolipidemic or dyslipidemic subjects were spiked with moxidectin (20 ng/ml). Rabbits fed with standard (n = 5) or cholesterol-enriched diet (n = 5) were injected subcutaneously with moxidectin (300 microg/kg) and blood samples were collected over 32 days. Lipoproteins were separated from plasma samples by ultracentrifugation on density gradients. Moxidectin and lipids were measured in plasma and in lipoproteins and the pharmacokinetic parameters calculated. In normolipidemic subjects or rabbits, the drug bound preferentially to HDL. In hyperlipidemic samples, moxidectin shifted to the VLDL-LDL fraction. In addition, hyperlipidemic rabbits had a 2.8-fold higher area under the plasma concentration versus time curve (AUC) and a lower clearance and volume of distribution when compared with controls. Dyslipidemia led to major changes in moxidectin plasma distribution and in drug disposition. Therefore, a high variability in moxidectin disposition might be expected in humans or animals liable to develop dyslipidemia, with a possible impact on the efficacy and safety of this class of drugs.

Mechanisms underlying dysfunction of carotid arteries in genetically hyperlipidemic rabbits

In the present study we compared the vascular reactivity and integrity of the nitric oxide (NO)-cyclic 3',5'-guanosine monophopsphate (cGMP) pathway in carotid arteries of hyper- and normolipidemic rabbits. Vasodilation to acetylcholine, nitroglycerin, and sodium nitroprusside was desensitized in hyperlipidemia, but the nitroprusside-induced relaxation was normalized by an NO synthase inhibitor in endothelium-intact and -denuded vessels. Hyperlipidemic carotid arteries exhibited increased basal NO (detected by EPR spin-trapping) and reactive oxygen species formation (detected by chemiluminescence), whereas acetylcholine-induced NO formation was nearly abolished. Hyperlipidemia increased NADPH-dependent superoxide formation in carotid membranes, and carotid cryosections stained with the fluorescent dye dihydroethidium revealed increased endothelial and medial reactive oxygen species formation. Hyperlipidemia elicited macrophage invasion into the carotid wall, as detected by a dot-immunoblot. The basal activity of cGMP-dependent proteinkinase, the nitroprusside-stimulated activity of soluble guanylyl cyclase, and its protein expression were decreased by hyperlipidemia. The cGMP phosphodiesterase activity was marginally increased by hyperlipidemia, such that the ratio of cGMP-forming vs. -degrading capacity was decreased by 2-fold. Hyperlipidemia triggers infiltration of macrophages into the carotid wall and endothelial as well as smooth muscle superoxide formation. Consequently, relaxation of the carotid arteries are impaired due to smooth muscle and endothelial dysfunction.

Intravascular ultrasound imaging in the assessment of atherosclerotic plaques in rabbit abdominal aorta: comparison with histologic findings.

To examine the correlation between the echogenicity and the components of atherosclerotic plaques in rabbit. The atherosclerotic plaque formation in the abdominal aortas of hyperlipidemic or normolipidemic rabbits was stimulated by inserting polyethylene tubing. Intravascular ultrasound (30-MHz, 4.5 F catheter) investigation was performed at locations in the vessel. The intravascular ultrasound images of the plaques were evaluated and compared with the histologic findings. Ultrasound images delineated areas showing hyperechoic or hypoechoic ultrasound beams in the plaques. Histologic studies revealed that the hyperechoic areas were closely associated with a dense fibrous extracellular matrix, whereas the hypoechoic areas corresponded to lesions showing a marked accumulation of foamy macrophages or proteoglycan-rich loose myxoid extracellular matrix with smooth muscle cell proliferation. A good correlation between ultrasound images and histologic features was observed. These results suggest that intravascular ultrasound imaging could provide useful information for assessing the tissue characteristics of atherosclerotic lesions.

Marked neointimal lipoprotein lipase increase in distinct models of proclivity to atherosclerosis: a feature independent of endothelial layer integrity

Lipoprotein lipase (LPL) in the arterial wall has been proposed to enhance the retention of apoB-containing lipoproteins, an early event in atherosclerosis. As the neointima is considered the primary site of lipid accumulation in atherogenesis, the arterial expression and location of LPL was investigated in distinct experimental models of neointimal formation in normolipidemic rabbits and rats. Neointima elicited by balloon aortic denudation or raised beneath an anatomically intact endothelial layer by placing a silastic collar around the common carotid artery, both showed a striking LPL immunostaining that mostly co-localized with neointimal smooth muscle cells. Besides, increased LPL protein and mRNA in deendothelialized aortas was demonstrated by Western and Northern blot analysis, respectively, suggesting an enhanced expression of LPL in injured arteries. It was concluded that LPL is increased in neointima developed in either denuded vessels or arteries with a preserved endothelium, a finding which suggests that LPL abundance may be an attribute of the neointima, whatever the stimulus that promotes its formation. On the basis of former evidence concerning the role of LPL in lipid retention, this study provides a possible explanation for the injury-induced vessel susceptibility to atherosclerosis, and the particular proneness of the neointimal layer to lipid accretion.

ACAT inhibitor F-1394 prevents intimal hyperplasia induced by balloon injury in rabbits

Acyl-CoA:cholesterol acyltransferase (ACAT) is thought to contribute significantly to lipid deposition in macrophages, which subsequently leads to the initiation and progression of atherosclerosis. The aim of the present study was to examine the influence of hypercholesterolemia on arterial hyperplasia induced by endothelial denudation and the direct effect of ACAT inhibition on lesion formation. Rabbits were fed either a cholesterol diet or a regular diet for 4 weeks, and then the left common carotid arteries were denuded of endothelium. After the operation, all rabbits were kept on the regular diet for 2;-6 weeks. Two weeks after the denudation, the degree of intimal thickening and the number of proliferating cells (which were immunohistologically identified to be smooth muscle cells) were similar in hypercholesterolemic and normolipidemic rabbits. After that, both parameters progressively increased in hypercholesterolemic rabbits but declined in normolipidemic rabbits. Macrophages were apparent in the lesions only in hypercholesterolemic rabbits. Next, the effect of the ACAT inhibitor, (1S,2S)-2-[3-(2,2-dimethylpropyl)-3-nonylureido] cyclohexane-1-yl 3-[(4R)-N-(2,2,5,5-tetramethyl-1,3-dioxane-4-carbonyl)amino]propionate (F-1394), on neointimal formation in hypercholesterolemic rabbits was examined. Oral administration of F-1394 significantly reduced neointimal thickening and the extent of macrophages in lesions without affecting serum cholesterol levels. These results suggest that hypercholesterolemia causes macrophage-derived foam cell accumulation in lesions, and that the progression of lesions is accelerated by the presence of macrophages. Moreover, the study shows that F-1394 prevents neointimal formation even in the presence of hypercholesterolemia, indicating that F-1394 may be useful for treating restenosis after percutaneous translumenal coronary angioplasty in hyperlipidemic patients.

Increased metabolism of peroxynitrite-modified [125I] beta-VLDL by monocytes from hypercholesterolemic rabbits.

The metabolism (uptake and degradation) of peroxynitrite-modified beta-VLDL and native beta-VLDL labeled with [125I]iodine was studied in monocytes isolated from peripheral blood of hypercholesterolemic (HC) and normolipidemic rabbits (NC). The peroxynitrite-modified beta-VLDL uptake and degradation was up to 2-fold higher in monocytes from HC rabbits than monocytes from NC rabbits. In addition, monocytes from HC rabbits took up and degraded significantly more peroxynitrite-modified beta-VLDL than native beta-VLDL. In contrast, monocytes from NC rabbits took up both lipoproteins in a similar rate and degraded more native beta-VLDL than peroxynitrite-modified beta-VLDL. Our results suggest that hypercholesterolemia can affect monocyte metabolism enhancing foam cell formation by increasing the influx of peroxynitrite-modified beta-VLDL.

Effect of hypolipidemic drugs on key enzyme activities related to lipid metabolism in normolipidemic rabbits

The effect of atorvastatin (3 mg kg −1 day −1), simvastatin (3 mg kg −1 day −1) and bezafibrate (100 mg kg −1 day −1) administered for 4 weeks to male New Zealand white rabbits on enzyme activities related to lipid metabolism has been studied. Only the statins reduced plasma cholesterol values, while none of the drugs modified plasma triglyceride or high density lipoprotein (HDL)-cholesterol concentrations, nor the activity of enzymes such as hepatic diacylglycerol acyltransferase, lipoprotein lipase or hepatic lipase, directly involved in triglyceride metabolism. Both statins elicited similar increases in the hepatic microsomal 3-hydroxy-3-methyl-glutaryl Coenzyme A (CoA) reductase activity (147 and 109% induction for simvastatin and atorvastatin, respectively), and none of the drugs assayed modified hepatic acyl-coenzyme A:cholesterol acyltransferase activity significantly. Only bezafibrate induced a significant 57% reduction in the activity of hepatic microsomal cholesterol 7 α-hydroxylase. Regarding the rate limiting enzyme of phosphatidylcholine biosynthesis, CTP:phosphocholine cytidylyl transferase, atorvastatin and bezafibrate behaved similarly, decreasing the enzyme activity in the liver by 45% and 54%, respectively; simvastatin induced no modification of this activity. The reduction of CTP:phosphocholine cytidylyl transferase activity is not caused by a direct inhibition of the enzyme by bezafibrate and atorvastatin. Further, the inhibitory effect of atorvastatin appears to be unrelated to the inhibition of 3-hydroxy-3-methyl-glutaryl CoA reductase elicited in vivo.

1.P.111 The relationships between serum lipids metabolism and ACE activity in normolipidemic and cholesterol-fed rabbits

1.P.111 The relationships between serum lipids metabolism and ACE activity in normolipidemic and cholesterol-fed rabbits

Residence time of low-density lipoprotein in the normal and atherosclerotic rabbit aorta.

Previous results from this laboratory found that the arterial low-density lipoprotein (LDL) residence time in lesion-prone aortic sites was longer in hyperlipidemic rabbits before lesion formation than in the corresponding sites in normolipidemic rabbits. The calculation of residence time in the previous study assumed that the arterial wall was homogeneous; the present study reexamines the issue using a method that does not require such an assumption. The concentration of radiolabeled arterial LDL was measured in New Zealand White rabbits killed at several different times (0.5 to 72 hours) after injection of labeled LDL. Using a stochastic analysis, arterial LDL residence time was calculated from the pooled labeled arterial LDL measurements from these rabbits. In these studies, the arterial LDL residence times in normolipidemic and hyperlipidemic rabbits before lesion formation were similar in both the lesion-prone and -resistant sites. However, immediately upon development of early fatty streak lesions, the arterial LDL residence time increased dramatically. After only 16 days of cholesterol feeding, the residence time was 10 times longer in the lesioned aortic arch compared with similar tissue from normolipidemic rabbits (4 to 45 hours). After 21 days of cholesterol feeding, the residence time of LDL in the lesioned aortic arch increased to > 25-fold that of normolipidemic tissue. Similar results were observed in the lesioned tissue of the abdominal branchings. This early retention of LDL suggests that significant changes are taking place within the arterial wall during this critical stage of early lesion development.

Injury produces early rise in lipoprotein lipase activity in rabbit aorta

The mechanisms following intimal injury predisposing towards atherosclerotic changes have not been fully elucidated. We speculated that a local increase in the enzyme lipoprotein lipase (LPL) might explain a higher susceptibility of the damaged intima to lipid accretion, and so we investigated the effect of balloon endothelial denudation on LPL activity and cholesterol content (LPL a and Chol c, respectively), in aortas from normolipidemic male New Zealand white rabbits. Arteries were obtained from injured and control animals after 2, 6, 8 and 10 weeks to evaluate the shortest period after de-endothelialization necessary to detect LPL a changes. Injury resulted in a 4-fold LPL a rise ( P < 0.01), as early as 2 weeks, and the enzymatic activity remained increased throughout the study period. A mild but significant 22% Chol c increase ( P < 0.03) was found after 2 weeks of injury, even in this normolipidemic rabbit model. We conclude that physical damage to the intima markedly and soon increases LPL a. This finding might account for the higher lipid accumulation by injured vessels, providing additional support to the hypothesis of LPL as an atherogenic mediator.

Effect of cholesterol feeding on the susceptibility of lipoproteins to oxidative modification

In previous studies we have shown that the liver endothelial and Kupffer cells in hypercholesterolemic rabbits are very active in endocytosis of low-density lipoprotein (LDL) and β-very-low-density lipoprotein (β-VLDL) (Nenseter et al. (1992) J. Lipid Res. 33, 867–877; Gudmundsen et al. (1993) J. Lipid Res. 34, 589–600). These data raised the question whether subfractions of LDL and β-VLDL were modified in vivo to forms recognized by the scavenger/oxidized LDL receptors of the non-parenchymal liver cells. The purpose of the present study was to address this question by assessing the effect of cholesterol feeding on the susceptibility of the lipoproteins to oxidative modification in vitro. In addition, the effect of HDL on the lipid peroxidation of LDL was evaluated. LDL and β-VLDL were isolated from rabbits given a diet supplemented with cholesterol (2% w/w) for 3 weeks. The extent of Cu 2+-catalyzed oxidation of the lipoproteins was compared with that of LDL from control-fed rabbits. Extent of oxidation assessed by formation of conjugated dienes, lipid peroxides, thiobarbituric acid-reactive substances, relative electrophoretic mobility and uptake of lipoproteins by J774 macrophages suggested that LDL and β-VLDL from the hypercholesterolemic rabbits were more susceptible to oxidation than LDL from normolipidemic rabbits. HDL protected LDL and β-VLDL from lipid peroxidation in vitro. Taken together, the increased susceptibility of LDL and β-VLDL to oxidative modification in vitro, combined with the low levels of α-tocopherol, and the reduced ratio of HDL to LDL cholesterol observed in the hypercholesterolemic rabbits, and the protective effect of HDL on the lipid peroxidation of LDL, support the probability that oxidative modification of LDL and β-VLDL occur in vivo in the hypercholesterolemic rabbits.

Plasma HDL Levels Are Regulated by the Catabolic Rate of Large Particles of Lipoprotein Containing APO-A-I

Lp-A-I was isolated by immunoaffinity chromatography and then separated into two fractions of large and small Lp-A-I particles by conventional ultracentrifugation with a cut-off density of 1.125 g/ml. The large and small particle-rich fractions were then radiolabeled with [125I]-Na and [131I]-Na, respectively. Both of the labeled lipoproteins were injected (20 μCi, i.v.) simultaneously into normolipidemic rabbits. The FCR of the large Lp-A-I particles was much less than that of the small Lp-A-I particles (0.801 ± 0.026/day vs. 2.227 ± 0.067/day, P<0.0001). These data indicate that the two particles have distinctly different metabolic pathways and that the lower FCR of larger Lp-A-I particles can effectively raise plasma HDL levels.

Endothelial cell morphometry of atherosclerotic lesions and flow profiles at aortic bifurcations in cholesterol fed rabbits.

Observations on shapes of endothelial cells both in sudanophilic and nonsudanophilic regions at bifurcations of the brachiocephalic (BC) and left subclavian (SA) arteries in hyperlipidemic rabbits were performed under a SEM. The stagnation point of flow and leading edges of flow dividers were nonsudanophilic and covered by round and long fusiform endothelial cells, respectively. The hips of flow dividers of both branchings, proven to be relatively low shear stress regions, by movement of microspheres in steady flow, were sudanophilic and covered by ellipsoidal cells. Similar studies were carried out in normolipidemic rabbits. It might be concluded that lipid deposition in hyperlipidemic rabbits occurs in relatively low shear stress regions, where endothelial cells are functionally activated, rather than in laminar high shear stress regions at the flow divider.

Concentration and distribution of apolipoproteins A-I and E in normolipidemic, WHHL and diet-induced hyperlipidemic rabbit sera

Two sandwich-type enzyme immunoassays have been developed to measure apolipoproteins A-I and E in rabbit serum. Specific goat antibodies were purified by affinity chromatography and used both for coating and for preparing antibody-peroxydase conjugates. The sensitivity of these assaysis sufficient to allow studies of apo A-I and E distribution in lipoproteins fractionated by gel filtration from 50 μl of serum. In WHHL rabbits, apo A-I is 5-fold lower (5.2 ± 2.5 mg/dl) and apo E is 8-fold higher (9.9 ± 3.5 mg/dl than in normolipidemic rabbits (29 ± 4.3 mg/dl and 1.3 mg/dl, respectively). In hyperlipidemoc rabbits, fed 2 months on a 0.5% cholesterol diet, the apo A-I level was similar (32 ± 12 mg/dl) to that of normolipidemic rabbits, apo E level is 12-fold higher (15.1 ± mg/dl). In addition, HDL particles were enriched with cholesterol and apo E. The bulk of apo E and cholesterol is located in large β-VLDL in diet-induced hyperlipidemia, whereas they are mainly located in smaller size β-VLDL in WHHL rabbits. In normolipidemic rabbits apo E occurs mainly in HDL, and cholesterol is distributed in the main three lipoprotein fractions VLDL, LDL and HDL. Interestingly, HDL of WHHL rabbit are deficient in apo A-I. These results are compatible with profound perturbations of lipoprotein composition and metabolism in atherogenic hyperlipidemia.

Platelet Function in Watanabe Heritable Hyperlipidemic Rabbits, a Model for the Progression of Atherosclerosis

Platelet function in a strain of rabbits designated as Watanabe heritable hyperlipidemic (WHHL) rabbits was examined. When compared to normolipidemic rabbits, the platelet aggregation induced by ADP and collagen were significantly higher in WHHL rabbits (P<0.01 or 0.05). Furthermore, platelet sensitivity for ADP was significantly higher in WHHL rabbits than in normolipidemic rabbits (P<0.01). The platelet aggregation among resuspended platelet in normolipidemic rabbit plasma was singnificantly higher in WHHL rabbits than in the normolipidemic rabbits (P<0.01). Furthermore, the botrocetin induced platelet agglutination (BIPA) as von Willebrand factor (vWF) activity was significantly higher in WHHL rabbits than in normolipidemic rabbits (P<0.01). As for change of platelet function with aging, the platelet aggregation induced by ADP increased with age and the BIPA were higher in WHHL rabbits than control rabbits at almost all ages and decreased between 5 and 8 months of age. These findings suggest that increased platelet function and vWF activity in WHHL rabbits are associated with the thrombotic complications and accelerated atherogenesis of WHHL rabbits.

Reversible inhibitory effects of apo-B-carrying lipoproteins on acid lipase activity of mononuclear leukocytes from cholesterol-fed rabbits.

Acid lipase (AL) activity of mixed mononuclear leukocytes from cholesterol-fed rabbits exhibited reduced values when compared with that of normolipidemic rabbits. The observed suppression of the AL activity was reversed commensurate with a fall in the plasma concentrations of cholesterol and lipid peroxides (LPO) after the rabbits were returned to a basal diet. The AL activity was negatively correlated with both plasma cholesterol and LPO levels in rabbits. This reversible inhibition was caused by apo-B-carrying lipoproteins from the hypercholesterolemic rabbits, and protective effects were produced by preincubation of lipoproteins with anti apo-B serum. The increase in plasma LPO in the hypercholesterolemic rabbits suggests that the observed reversible inhibition of the AL activity might be due to an increase in free radicals produced in the process of lipid peroxidation in the hypercholesterolemic state. The current findings also suggest that, through the combined effects of suppression of lysosomal hydrolysis and stimulation of microsomal synthesis of esterified cholesterol, β-migrating very low density lipoprotein in cholesterol-fed rabbits accelerates hypercholesterolemia and causes accumulation of esterified cholesterol in cells.