Secretion of very low density lipoproteins by cultured rabbit hepatocytes with hypercholesteremia, induced by purified cholesterol and containing autooxidation products

To evaluate the impact of oxidized derivatives of cholesterol on the development of hypercholesterolemia in rabbits, the secretion of very low density lipoprotein (VLDL) apoproteins and lipids was studied in cultures of hepatocytes obtained from: i) control rabbits, ii) rabbits fed on purified cholesterol (PCH), and, iii) rabbits fed on old commercial cholesterol (OCH) containing 5% of oxidized cholesterol derivatives. The rabbits fed on OCH for 6 weeks revealed a 5-fold increase in the serum cholesterol level compared with that in PCH-fed rabbits. The secretion of VLDL apoproteins and lipids by hepatocytes of two cholesterol-fed groups was similar, but was 2-3 times as high as that of cells from control rabbits. The cholesterol ester content in hepatocytes and the secretion of VLDL cholesterol esters by hepatocytes from OCH-fed rabbits was dramatically increased in comparison with hepatocytes from control and PCH-fed rabbits. These effects appear to be caused by the activation of cholesterol esterification by oxidized cholesterol derivatives. The rapid development of hypercholesterolemia in OCH-fed rabbits is at least partly associated with the stimulation of hepatic VLDL production.     

Does a HDL injection reduce the development of serum hyperlipidemia and progression of fatty streaks in cholesterol fed rabbits?

The influences of homologous (rabbit) or heterologous (human) high density lipoprotein (HDL) on the development of serum hyperlipidemia and progression of fatty streaks were studied in cholesterol fed rabbits. Three groups of New Zealand rabbits were fed a 0.5% cholesterol rich diet for 8 weeks. Additionally into these animals the following solutions were injected intravenously two times per week: group 1 (control): saline; group 2: human HDL dissolved in saline; group 3: rabbit HDL dissolved in saline. The animals of group 2 had lower serum cholesterol levels during the dietary period than rabbits of group 1 (p < 0.05) but the surface of intima covered with fatty streaks was the same as in group 1. On the other hand, the serum cholesterol level in rabbits of group 3 was the same as in group 1 during the whole experimental period, but the surface of aorta covered with fatty streaks was significantly lower (p < 0.05) in group 3 than in group 1. The results of this study support the hypothesis of an antiatherogenic action of HDL, which seems to be independent of the influence of HDL on the serum lipids but depends on the source of HDL.     

Development and partial metabolic characterization of a dietary cholesterol-resistant colony of rabbits

A colony of New Zealand white rabbits has been developed which, when fed a cholesterol-supplemented diet, exhibit unusual resistance to hypercholesterolemia and atherosclerosis, disorders usually observed in normal cholesterol-fed rabbits. When resistant rabbits (RT) were fed a normal low cholesterol diet (ND), their plasma lipoprotein patterns were significantly different from those of normal rabbits (NR) fed the same diet. The low density lipoprotein cholesterol (LDL-c)/high density lipoprotein cholesterol (HDL-c) ratio and LDL-c/very low density lipoprotein cholesterol (VLDL-c) ratio were lower in the resistant rabbits. The hydrated density of HDL of the normal-responsive rabbits was greater than that of the resistant rabbits. LDL from resistant rabbits contained a lower proportion of esterified cholesterol and protein than LDL from normal rabbits. Peripheral mononuclear cells from resistant rabbits bound about 30% more 125I-labeled rabbit LDL than mononuclear cells from normal rabbits. These results demonstrate that the plasma cholesterol levels of these animals is at least partly under genetic control and that compositional differences exist between the major plasma lipoprotein classes of normal and resistant rabbits even during the ingestion of low-cholesterol diet. The results indicate that at least a part of the difference in the cholesterolemic responses between the two rabbit groups is due to an enhanced LDL uptake by the mononuclear cells, and presumably by other somatic cells of the resistant group.     

Effect of dietary cholesterol and alloxan-diabetes on tissue cholesterol and apolipoprotein E mRNA levels in the rabbit

Alloxan-diabetic rabbits develop hypercholesterolemia and hypertriglyceridemia in response to cholesterol feeding. To determine whether alterations in apolipoprotein composition of plasma lipoproteins were due to changes in apolipoprotein gene expression, we measured the steady state apoE mRNA levels in several tissues from both control and diabetic rabbits. Control rabbits were fed either chow or chow plus 1.5% cholesterol (chow-fed or cholesterol-fed groups) and diabetic rabbits were fed either chow or chow plus 0.5% cholesterol for dietary periods of 5, 21, and 42 days. The tissues examined were liver, small intestine, brain, adrenals, and aorta. ApoE mRNA levels were measured by Northern and dot blot analysis with a human apoE cDNA probe. In control rabbits fed either chow or cholesterol diets for up to 42 days, the steady state apoE mRNA levels remained relatively constant in all of the tissues examined. In contrast, in alloxan-diabetic rabbits fed a 0.5% cholesterol diet, apoE mRNA was reduced in liver, brain, and adrenals (46 +/- 19%, 56 +/- 5%, and 39 +/- 18% of chow-fed control, respectively), but showed little change in the aorta (91 +/- 22% of chow-fed control). Despite a similar increase in plasma cholesterol, the cholesterol content of the liver and adrenals of cholesterol-fed diabetic rabbits were 20% and 50%, respectively, of that of the liver and adrenals in cholesterol-fed control rabbits. The result that apoE mRNA levels and tissue cholesterol content are altered in the diabetic cholesterol-fed rabbit suggests that insulin deficiency in the rabbit may influence apoE gene expression and tissue cholesterol homeostasis.     

Dietary cholesterol absorption, and sterol and bile acid excretion in hypercholesterolemia-resistant white rabbits

The New Zealand white (NZW) rabbit fed a 0.1% cholesterol-enriched diet (CD) typically responds (normoresponsive, NR) by quickly developing hypercholesterolemia. To study the underlying mechanisms responsible for the widespread phenomenon of inter-individual variability of response to dietary cholesterol, a unique hypercholesterolemia-resistant (RT) rabbit model was developed. These animals were utilized to investigate selected potential mechanisms that might enable the RT animal to compensate for dietary cholesterol overload. When rabbits were fed the low-cholesterol stock diet, there was no significant difference in the plasma cholesterol concentrations of the NR and the RT animals. However, a significant rise was observed in the NR rabbits within 1 month of their being placed on the cholesterol-enriched diet; the plasma cholesterol concentration of the RT animals was not affected. During consumption of the cholesterol diet the cholesterol absorption rate was somewhat greater in the NR rabbits (P less than 0.05), whereas intestinal transit times and the fecal excretion of neutral steroids were substantially the same in both groups. In contrast, the fecal bile acid excretion of the RT animals was more than twice as great (P less than 0.0001) as that of the NR animals. We conclude that the response to dietary cholesterol is a heritable trait in these rabbits and that, although less dietary cholesterol was absorbed by the RT animals, it appears that a major mechanism controlling plasma cholesterol levels involves the rate of conversion of cholesterol to bile acids and their subsequent excretion.     

Effect of chylomicron remnants on cholesterol metabolism in cultured rabbit hepatocytes: production of very low density lipoproteins and bile acids

Primary cultures of rabbit hepatocytes were used to investigate the effect of purified (B-100 free) chylomicron remnants (CR) on lipid and bile acid metabolism. ApoB-100-containing lipoproteins were removed from the CR-enriched plasma fraction by affinity column chromatography on Sepharose 4B conjugated with anti-apoB-100 monoclonal antibodies. CR were shown to stimulate the accumulation of neutral lipids in hepatocytes in a dose-response manner. After 24-hour preincubation of rabbit hepatocytes with 50 micrograms protein/ml CR the cellular neutral lipid content increased: 1.9-4-fold for triglycerides, 1.5-3.7-fold for free cholesterol and 1.5-2.5-fold for esterified cholesterol. This accumulation was accompanied by a decreasing incorporation of [14C] acetate into cholesterol (80-90%) and triglycerides (70-80%). At the same time the incorporation of [14]oleate into triglycerides increased by 50-65%. The inhibited biosynthesis of fatty acids might account for this effect. No effect of CR on cholesterol esterification by [14C]oleate was observed. CR increased the amount of triglycerides and free cholesterol secreted in very low density lipoproteins (VLDL). The secretion of taurocholic acid was decreased. These data confirm our hypothesis that dietary cholesterol is preferentially secreted by hepatocytes within VLDL but is not accumulated as cholesterol esters or oxidized to bile acids.     

Zinc supplementation inhibits lipid peroxidation and the development of atherosclerosis in rabbits fed a high cholesterol diet

Developing atherosclerotic lesions in hypercholesterolemic rabbits are depleted in zinc, while iron accumulates. This study examined the influence of zinc supplementation on the development of atherosclerosis and used isotope dilution gas chromatography-mass spectrometry techniques to measure biomarkers of oxidative lipid damage in atherosclerotic rabbit aorta. Our previous method for F(2)-isoprostane measurement was adapted to include the quantitation of cholesterol oxidation products in the same sample. Two groups of New Zealand white rabbits were fed a high cholesterol (1% w/w) diet and one group was also supplemented with zinc (1 g/kg) for 8 weeks. Controls were fed a normal diet. Zinc supplementation did not significantly alter the increase in total plasma cholesterol levels observed in animals fed high cholesterol. However, in cholesterol-fed animals zinc supplementation significantly reduced the accumulation of total cholesterol levels in aorta which was accompanied by a significant reduction in average aortic lesion cross-sectional areas of the animals. Elevated levels of cholesterol oxidation products (5,6-alpha and beta cholesterol epoxides, 7beta-hydroxycholesterol, 7-ketocholesterol) in aorta and total F(2)-isoprostanes in plasma and aorta of rabbits fed a cholesterol diet were significantly decreased by zinc supplementation. Our data indicate that zinc has an antiatherogenic effect, possibly due to a reduction in iron-catalyzed free radical reactions.     

The effect of thymosin fraction 5 on lipid peroxidation in rabbits fed a high-cholesterol diet

Plasma and erythrocyte lipid levels and susceptibility of erythrocytes to lipid peroxidation were determined in rabbits fed diet containing 2% (w/w) cholesterol, for 3 months. Hypercholesterolemic rabbits had high plasma and erythrocyte lipid peroxide levels as compared to control rabbits. After high-cholesterol diet, the rabbits in the experimental group were divided into two groups. The first group was fed a normal diet for 21 days and the second group was given normal diet plus thymosin F5 injections every other day for the same period. At the end of this period, plasma and erythrocyte lipid peroxide levels were significantly decreased in the group injected with thymosin F5.     

Dissociation between cholesterol secretion and plasma lipid transfer activity in rabbits

Human and rabbit plasma contains a lipid transfer protein that transfers cholesteryl esters and triglycerides among the plasma lipoproteins and may also have a role in the movement of lipids into and out of cells. Little is known about the regulation of the activity of the lipid transfer protein, but in the rabbit, hypercholesterolemia is associated with increased plasma lipid transfer activity (LTA). Perfused rabbit livers secrete LTA, and hepatic cholesterol secretion is increased in rabbits with diet-induced hypercholesterolemia. Thus, experiments were performed with rabbits to determine if LTA is regulated by a concerted hepatic secretion of lipoprotein protein cholesterol and LTA. Rabbits were fed chow or chow plus coconut oil (14% wt/wt), and plasma lipids, LTA, and the rate of secretion of cholesterol into plasma were determined. Coconut oil feeding increased plasma cholesterol by 68%, LTA by 42%, and hepatic cholesterol secretion by 69%. Mevinolin (75 mg/day), an inhibitor of cholesterol biosynthesis, lowered LTA and plasma cholesterol without affecting the rate of secretion of cholesterol into plasma. These studies provide further evidence that, in the rabbit, plasma cholesterol and LTA are closely related, and the association is not likely to be caused by a concerted hepatic secretion of cholesterol and LTA.     

The Influence of Fluoride Ions upon Selected Enzymes of Protein Metabolism in Blood Plasma of Rabbits with Hypercholesterolemia

Three-month studies were performed on 18 adult rabbits of New Zealand breed divided into three groups, with six animals in each: a control group on standard diet, a cholesterol group receiving 500 mg of cholesterol/100 g of feed per rabbit per 24 h (CH group), and a cholesterol + fluorine group (CH + F group) receiving 500 mg of cholesterol/100 g of feed per rabbit per 24 h and 3 mg of F(-)/kg of body weight per 24 h. The conducted studies proved that cholesterol in the applied dosage (500 mg cholesterol per rabbit per 24 h) has an atherogenic action. Fluoride ions administered together with a 500-mg cholesterol atherogenic diet inhibit the atheromatosic changes in the aorta. The concentration of plasma cholesterol was elevated in both study groups when compared to the control group but decreased in the CH + F group when compare to the CH group. The influence of fluoride ions has been examined upon the activity of alanine aminotransferase, aspartate aminotransferase, and glutamate dehydrogenase (GLDH) in the plasma in the liver of rabbits in the course of experimental hypercholesterolemia. Increase in the activity of study enzymes has been observed in the blood plasma, which may be due to damage occurring to hepatocytes of the animals examined (a statistically significant increase in the activity of GLDH in the plasma). In the liver, the inhibition of activity for all examined enzymes has been observed in the group of rabbits with hypercholesterolemia, which testifies the disturbances in protein metabolism in examined animals. The addition of sodium fluoride to the diet rich in cholesterol results in "removing the block" on those activities, which increase. We suppose that the permeability of the hepatocyte membrane was elevated, so the activities of examined enzymes increased in the plasma ("escape" to plasma). On the one hand, fluoride ions result in probable lesion of hepatocytes membranes; on the other hand, they inhibit the atheromatosic changes in the aorta.     

Anti-atherogenic effect of citrus flavonoids, naringin and naringenin, associated with hepatic ACAT and aortic VCAM-1 and MCP-1 in high cholesterol-fed rabbits

The anti-atherogenic effects of the citrus flavonoids, naringin and naringenin, were evaluated in high cholesterol-fed rabbits. At 3 months of age, 30 male New Zealand White (NZW) rabbits were divided into three groups (n = 10 per group). The rabbits were fed a 1% cholesterol diet alone (control group) or a diet supplemented with either 0.1% naringin or 0.05% naringenin for 8 weeks. The plasma lipoprotein levels, total cholesterol, triglyceride, and high-density lipoprotein showed no significant differences in the control and experimental groups. Hepatic acyl-CoA:cholesterol acyltransferase (ACAT) activity was slightly low in naringin (5.0%)- and naringenin (15.0%)-fed rabbits, compared to control group. The aortic fatty streak areas were significantly lower in both the naringin (19.2 +/- 5.6%)- and naringenin (18.1 +/- 6.5%)-supplemented groups than in the control group (60.4 +/- 14.0%). The expression levels of vascular cell adhesion molecule-1 (VCAM-1) and monocyte chemotactic protein-1 (MCP-1), by semiquantitative RT-PCR analysis of the thoracic aorta, were significantly lower in the flavonoids supplemented groups than in the control group. These results suggest that the anti-atherogenic effect of the citrus flavonoids, naringin and naringenin, is involved with a decreased hepatic ACAT activity and with the downregulation of VCAM-1 and MCP-1 gene expression.     

Secretion of cholesteryl-ester-rich lipoproteins by the perfused livers of rabbits fed a wheat-starch-casein diet

Rabbits fed a cholesterol-free semi-synthetic wheat-starch-casein diet had a high plasma cholesterol concentration; most of the cholesterol was associated with low-density lipoproteins (LDL). Chemical analyses of plasma lipoproteins revealed that very-low-density lipoproteins (VLDL), intermediate lipoproteins and LDL from casein-fed rabbits contained more cholesteryl ester than that of lipoproteins isolated from chow-fed animals. The fatty acid composition of cholesteryl esters of plasma lipoproteins showed that there were higher contents of oleic acid than linoleic acids in lipoproteins from casein-fed rabbits. Lipoproteins isolated from liver perfusates of casein-fed rabbits had higher cholesteryl oleate content than lipoproteins from chow-fed rabbit liver perfusates. There was a marked increase in secretion of apolipoproteins from perfused livers of casein-fed rabbits. We conclude that the high levels of plasma cholesterol in casein-fed rabbits are of hepatic origin and that one of the hypercholesterolemic actions of dietary casein in rabbits is the induction of hepatic synthesis and secretion of cholesteryl-ester-rich lipoproteins.     

Effect of baikal skullcap root (Scutellaria baicalensis radix) on cholesterol level and meat quality in rabbits fed a cholesterol rich diet

The aim of this study was to evaluate the effect of the Baikal skullcap root (Scutellaria baicalensis radix) on the cholesterol level and chemical composition of the hind leg muscles of rabbits. Thirty two White New Zealand rabbits were assigned to four groups. Group C consisted of control animals which were fed a basal mixture for rabbits. Group CH received the same basal diet with a 1% (w/w) pure cholesterol supplement. Group CH+SR received the basal diet with two supplements: 1% (w/w) pure cholesterol and 9% (w/w) skullcap root. Group SR received the basal diet with a 9% (w/w) skullcap root supplement. After 6 weeks rabbits were slaughtered and, total cholesterol as well as dry matter, protein, fat, ash and pH24 were determined in samples of hind leg muscles. Using a Baikal skullcap root with hypercholesterolemic diet (group CH+SR) caused significant reduction (P < or = 0.05) in total cholesterol level in comparison with hypercholesterolemic diet (CH group). The addition of Baikal skullcap root to the food of rabbits significantly increased the muscle protein content (P < or = 0.05) in comparison with C and CH groups. Moreover, supplementation with Baikal skullcap root (CH+SR) decreased about 15.6% (P < or = 0.05) fat level in comparison to CH group. No significant effects were seen in dry matter content, ash, and pH24 value of hind leg muscles of experimental rabbits     

A model for demonstration of reversal of impairment of endothelium-dependent relaxation in the cholesterol-fed rabbit.

This investigation was undertaken to determine whether it was possible to restore endothelium-dependent relaxation (EDR) in the cholesterol-fed rabbit model of atherosclerosis following discontinuation of the cholesterol. New Zealand white rabbits, approximately 8 weeks of age, were randomized into (i) control group (9 animals fed a standard rabbit diet) and (ii) experimental group (27 animals: fed the same diet supplemented with 2.5% cholesterol). The experimental animals were restored to the standard diet after 3 weeks. EDR to acetylcholine (-9.0 to -5.0 log mol/L) was examined in the experimental animals at 3, 7, and 15 weeks after commencement of the study (n = 9 at each stage) and the nine control animals examined after 7 weeks. At the end of 7 weeks, EDR to acetylcholine (-6.0 log mol/L) was significantly (p less than 0.05) impaired in the experimental group (34.3 +/- 3.8%) compared with that in the control group (79.8 +/- 3.0%). The loss of EDR was not apparent in the experimental group at 3 weeks (relaxation: 81.7 +/- 4.7%). At the end of 15 weeks, the EDR was significantly restored in the experimental group (relaxation: 63.6 +/- 5.1%). These findings demonstrate that it is possible to reverse the loss of EDR that occurs with cholesterol feeding in the rabbit by limiting the period of exposure to a high cholesterol diet.     

Dietary supplementation with Pluronic L-81 modifies hepatic secretion of very low density lipoproteins in the rat

Supplementation of high fat/cholesterol-enriched diets with polyoxypropylene-polyoxyethylene copolymers containing 90% hydrophobic constituents has been found to impair enteric secretion of chylomicrons, lower plasma levels of very low density (VLDL) and low density (LDL) lipoprotein cholesterol and prevent diet-induced hypercholesterolemia and atherosclerosis. These agents are known to be absorbed from the gastrointestinal tract and excreted in bile. In order to determine whether dietary supplementation with this group of hydrophobic poloxalenes influences hepatic secretion of triglyceride-rich lipoproteins, groups of rats were maintained for 21-34 days on either standard chow, semisynthetic diet containing 10.0% safflower oil/1.0% cholesterol, or each of the above diets supplemented with the hydrophobic poloxalene Pluronic L-81. At the end of the feeding period, newly secreted hepatic VLDL were isolated from 2-hr recirculating liver perfusates, quantitated, and characterized. Compared to perfusions in chow-fed rats, perfusion experiments in rats fed the high fat/cholesterol-enriched semisynthetic diet revealed a 3.1-fold increased net hepatic VLDL secretion rate; enrichment of secretory VLDL in cholesteryl esters and in C18:2 core lipid fatty acids; and a shift in the size distribution of secretory VLDL towards larger particles. When the 0.5% Pluronic L-81 was included in the high fat/cholesterol-enriched semisynthetic diet, the net hepatic VLDL secretion rate fell significantly and the physicochemical properties of secretory VLDL in these rats were found to resemble those of chow-fed animals. Supplementation of the chow diet with L-81 resulted in a significant fall in the net hepatic VLDL secretion rate from that observed in rats fed chow alone. Compared to rats fed chow alone, perfusate VLDL from rats fed each of the other experimental diets contained markedly lower amounts of both apoB molecular weight variants, as analyzed by gradient gel electrophoresis and densitometric gel scanning. Since previous studies have demonstrated that VLDL are the major cholesterol transport lipoproteins following fat/cholesterol feeding; a precursor-product relationship exists between fat/cholesterol-induced hepatic VLDL and plasma VLDL; such particles are capable of delivering cholesterol to the arterial wall; and dietary supplementation with hydrophobic poloxalenes prevents both the increase in plasma VLDL-cholesterol and diet-induced atherosclerosis, it is possible that dietary supplementation with hydrophobic poloxalenes may influence the atherogenic process through direct and/or indirect effects on hepatic VLDL transport.     

Reduction of oxidative stress and apoptosis in hyperlipidemic rabbits by ellagic acid

Oxidative stress is one of the major risk factors for coronary artery disease. Ellagic acid is a phenolic compound present in fruits and nuts, and has been found to have antioxidative property. Twenty-four New Zealand white (NZW) rabbits were assigned randomly into four dietary groups. The normal group was fed regular rabbit chow, and the cholesterol group was fed a high fat and cholesterol diet. The ellagic acid (E) group and probucol group were fed the same diet as the cholesterol group plus the addition of 1% (w/w diet) ellagic acid and probucol, respectively. Oxidative stress [as measured by plasma lipids, oxygen free radicals and thiobarbituric acid reactive substances (TBARS)] increased in the cholesterol group compared with the normal group; however, it decreased in the probucol and E groups compared with the cholesterol group. Forty-five percent of the intimal surface of the thoracic aorta was covered with atherosclerotic lesions in the cholesterol group, but only 2-3% was covered in the E and probucol groups. The aortic level of 8-(OH)dG and the expression of caspase-8, caspase-9 and Fas ligand were also suppressed after ellagic acid supplement. These results indicated that ellagic acid could prevent atherosclerosis via suppression of oxidative stress and apoptosis in hyperlipidemic rabbits.     

Intimal smooth muscle cells up-regulate beta-very low density lipoprotein-mediated cholesterol accumulation by enhancing beta-very low density lipoprotein uptake and decreasing cholesterol efflux

To clarify the mechanism of smooth muscle cell (SMC)-derived foam cell formation, we investigated beta-very low density lipoprotein (beta-VLDL) cholesterol metabolism in vascular medial SMCs (M-SMCs) from normal rabbits compared with intimal SMCs (I-SMCs) from normal rabbits fed a high-cholesterol diet and LDL receptor-deficient rabbits. For both types of I-SMCs, uptake of [3H]cholesteryl oleate labeled beta-VLDL increased 1.6 times and release of [3H]cholesterol decreased 40% compared with M-SMCs. M-SMCs took up part of the beta-VLDL through the LDL receptor but I-SMCs did not. mRNAs for the VLDL receptor and the LDL receptor relative with 11 ligand binding repeats were expressed at similar levels in all SMCs. M-SMCs expressed more LDL receptor-related protein than I-SMCs. Ligand blotting analysis revealed greater 125I-beta-VLDL binding to a 700-kDa protein in I-SMCs compared with M-SMCs. I-SMCs had higher activities of acid cholesterol esterase and acyl-CoA:cholesterol acyltransferase, and lower activity of neutral cholesterol esterase than M-SMCs in both the absence and the presence of beta-VLDL. These results indicate that I-SMCs accumulate more cholesteryl ester than M-SMCs by taking up more beta-VLDL and by effluxing less cholesterol.     

Effects of dietary cholesterol and fatty acids on plasma cholesterol level and hepatic lipoprotein metabolism

The effects of dietary cholesterol and fatty acids on the plasma cholesterol level and rates of very low density lipoprotein (VLDL) cholesterol secretion and low density lipoprotein (LDL) transport through LDL receptors in the liver of the hamster were investigated. Increases of plasma VLDL- and LDL-cholesterol levels and VLDL-cholesterol secretion from hepatocytes were observed in animals fed a diet enriched with 0.1% cholesterol for 2 weeks in comparison with animals fed a control diet. The addition of dietary palmitic acid accelerated the effect of dietary cholesterol on plasma VLDL- and LDL-cholesterol levels and VLDL-cholesterol secretion from hepatocytes. Dietary linoleic acid accelerated the effect of dietary cholesterol on VLDL-cholesterol secretion from hepatocytes and diminished the effect on the plasma LDL-cholesterol level. Hepatic LDL receptor activity was considerably suppressed by a control diet containing 0.05% cholesterol and a further small suppression was induced by a diet enriched with 0.1% cholesterol with or without 5% palmitic acid. However, dietary linoleic acid diminished the effect of dietary cholesterol on the suppression of hepatic LDL receptor activity. These results suggest that dietary palmitic acid augments the effect of dietary cholesterol in elevating the plasma LDL-cholesterol level through acceleration of VLDL-cholesterol secretion from the liver, and that dietary linoleic acid diminishes the effect of dietary cholesterol in elevating the plasma LDL-cholesterol level by preventing the suppression of hepatic LDL receptor activity induced by cholesterol.     

Turnover of cholesterol-4-14-C and cholic acid-24-14-C by rabbits fed a diet containing lactose

Rabbits fed 0.35% of cholesterol in diets containing either 29.35% of lactose or sucrose were studied for 14 weeks. The rabbits fed lactose had higher plasma and liver cholesterol concentrations than those fed sucrose. The half-life of cholesterol was 19.0 days and 35.0 days for rabbits fed sucrose and lactose, respectively. The half-life, pool size, and daily production of deoxycholic acid were 9.7 days, 1.29 g, and 74.1 mg for rabbits fed sucrose; and 14.2 days, 1.40 g, and 49.1 mg, for those fed lactose. Cholesterol was the major neutral sterol in the feces of the rabbits fed lactose, whereas coprostanol (5 Beta-cholestan-3 Beta-ol) dominated the corresponding fraction in those fed sucrose. The fecal steroid composition did not vary between day and night collections. No sterol esters were detected in the feces. Urinary elimination of radioactivity was less than 10% of that injected. The "lactose effect" seems to be due to enhanced retention of steroids, the mechanism of which has not been elucidated.     

Effects of the calcium channel blocker amlodipine on serum and aortic cholesterol,lipid peroxidation,antioxidant status and aortic histology in cholesterol-fed rabbits

Reactive oxygen metabolites and oxidized fatty acids are proinflammatory and are involved in the pathophysiology of atherosclerosis. Amlodipine, a unique third-generation dihydropyridine-type calcium channel blocker, seems to exert atheroprotective effects through its antioxidant properties related to its chemical structure and independent of its calcium channel-blocking effect. In this study, the interactions of amlodipine with major cellular antioxidants were investigated in order to elucidate the mechanisms underlying its atheroprotective effects. New Zealand white male rabbits were fed regular chow (group 1), chow with 1% cholesterol (group 2), regular chow plus 5 mg/kg/day amlodipine per os (group 3) and 1% cholesterol plus amlodipine (group 4) for 8 weeks. Total cholesterol, malondialdehyde (MDA) and vitamin E concentrations and catalase and superoxide dismutase (SOD) activities were determined in blood drawn before and after the experimental period. Aortic tissue was examined for atherosclerotic changes and aortic total cholesterol, MDA, catalase and SOD were determined. At the end of the 8-week treatment period, serum total cholesterol and plasma MDA were elevated in groups 2 and 4. In group 2, serum vitamin E and plasma SOD diminished (p < 0.05) and catalase increased (p < 0.05). In group 4, SOD activity increased at the end of treatment. MDA levels were lower and plasma SOD activities were higher in group 4 than in group 2. Aortic tissue investigations revealed higher total cholesterol and MDA concentrations and catalase activities in group 2 than in group 4, and the highest tissue SOD activity was recorded in group 4 (p < 0.05 for all comparisons). Morphological examination of aortic tissues exhibited endothelial disarrangement and lipid deposition in group 2. Histopathological alterations related to atherogenesis were less in group 4 than in group 2. Amlodipine seems to exert atheroprotective effects by reducing aortic cholesterol accumulation and blood and aortic lipid peroxidation, enhancing SOD activity both in blood and aortic tissue and suppressing the consumption of vitamin E. On the other hand, the suppression of catalase activity in blood and the aorta interferes with the drug's well-known antioxidant effects.