High-cholesterol Feeding Research Articles

Anti-hyperliposis effect of maitake fruit body (Grifola frondosa). I.

Experimental rat models (5-week-old Sprague-Dawley rats) with hyperlipemia were prepared by feeding high-cholesterol feed containing sodium cholate and casein as a protein source. Dried maitake (Grifola frondosa) powder was mixed with the basic high-cholesterol feed and the serum lipids were periodically measured. Values of cholesterol, triglyceride and phospholipid in serum of rats in the maitake-feed group were suppressed by 0.3-0.8 times those in animals fed the basic feed, the latter values being close to those in rats given normal feed. The value of high density lipoprotein (HDL)-cholesterol in serum which is generally reduced by the ingestion of high-cholesterol feed remained the level it was at the beginning of the experiment. Weights of extirpated liver and epididymal fat-pads were significantly less (0.6-0.7 times) than those in the basic feed group, indicating that maitake inhibits lipid accumulation in the body. Liver lipids were also measured and the values were found to be decreased by maitake administration as true of serum lipid, suggesting maitake has an anti-liver lipid activity. Measurement of the amount of total cholesterol and bile acid in feces showed, the ratio of cholesterol-excretion had increased 1.8 times and bile acid-excretion 3 fold by maitake treatment. From these results, it is believed that maitake helps to improve the lipid metabolism as it inhibits both liver lipid and serum lipid which are increased by the ingestion of high-fat feed.

Membrane cholesterol alters gallbladder muscle contractility in prairie dogs.

The cause and effect relationship between membrane cholesterol and gallbladder muscle contractility was examined by altering membrane cholesterol to phospholipid mole ratio using cholesterol-rich or cholesterol-free liposomes. Gallbladder single muscle cells, from prairie dogs that were fed either a regular or high-cholesterol (1.2%) diet, were isolated enzymatically with collagenase. Plasma membranes of gallbladder muscle were purified in sucrose gradient. Cholesterol was measured using the cholesterol oxidase method. Phospholipids were measured with the method of G.R. Bartlett (J. Biol. Chem. 234: 466-468, 1959). The results of this experiment are 1) after high-cholesterol feeding, cholesterol contents and cholesterol/ phospholipid mole ratio in plasma membranes of gallbladder muscle increased 90%, and muscle cell contraction in response to cholecystokinin octapeptide decreased 58%; 2) similar changes were observed when normal gallbladder muscle cells were incubated with cholesterol-rich liposomes for 2 h; and 3) the changes induced either in vivo or in vitro were reversed when muscle cells were subsequently incubated with cholesterol-free liposomes for 2-6 h. We conclude that gallbladder muscle may incorporate excess cholesterol into its plasma membrane when exposed to a cholesterol-rich environment, that excess membrane cholesterol impairs muscle contractility, and that these changes appear to be reversible.

食品成分および生体異物によるコレステロール代謝制御に関する研究

Dietary protein, xenobiotics or excess amino acids affect cholesterol metabolism. Whey protein exhibited a greater hypocholesterolemic effect in comparison with casein or soybean protein. The effect of soy protein peptic hydrolyzate or β-lactoglobulin tryptic hydrolyzate in suppressing the increase in the serum cholesterol level exceeded that of soy protein. In the case of high cholesterol feeding, dietary proteins affected serum cholesterol levels and inhibited cholesterol absorption through changes of micellar cholesterol solubility in the intestine, accompanied by an increase of fecal steroid excretion. Dietary peptides derived from β-lactoglobulin or soy protein inhibited cholesterol absorption in CaCo-2 cells. Dietary proteins affect the nature of bile acid micelles in the intestine, confirming observations by freeze-fracture transmission electron microscopy. Dietary proteins regulates the expression of the hepatic apolipoprotein gene. Dietary excess tyrosine or xenobiotics caused hypercholesterolemia characterized by an increase of both HDLcholesterol and LDL+VLDL-cholesterol. The stimulated synthesis of cholesterol in the liver is the main reason for this. The causal interrelationship between the hypercholesterolemia induced by dietary xenobiotics and the secretion of catecholamines or thyroid hormones was observed. These results indicate that the changes in cholesterol metabolism induced by dietary proteins, xenobiotics or excess tyrosine are expressed through intestinal and hepatic events.

Cocaine and the porcine coronary microcirculation: Effects of chronic cocaine exposure and hypercholesterolemia

To examine the acute effect of cocaine on the coronary microcirculation and whether chronic cocaine administration with or without a concomitant high-cholesterol diet affects beta-adrenoceptor and endothelial functions in the coronary microcirculation. Prospective experimental study. Laboratory and animal research facility. Yorkshire pigs. Pigs were fed a high (2%)-cholesterol diet or a regular diet for 3 months. Animals in both groups received cocaine chronically (7 mg/kg/day, IM). Control animals were fed a regular diet. Responses of the porcine coronary arterioles (90 to 190 microns in diameter) were examined in vitro in a pressurized (40 mmHg) no-flow state using a video-imaging apparatus. Acute application of cocaine caused a significant contraction with a mean maximal diameter decrease of 14% +/- 5%, which was markedly reduced by muscarinic blockade but not significantly affected by alpha 1-adrenergic blockade. Lidocaine or procainamide had no vasoconstrictor effect. Chronic exposure of animals to cocaine diminished contractile responses to cocaine and reduced relaxation responses to the nonselective beta-adrenergic receptor agonist isoproterenol. Phenylephrine caused a minimal (< 4%) contraction of vessels in all groups. Chronic cocaine administration with concomitant high-cholesterol feeding attenuated endothelium-dependent relaxations to serotonin, whereas endothelium-dependent relaxations to bradykinin were unaffected. Endothelium-independent relaxations to sodium nitroprusside were similar in all groups. These results suggest that cocaine can exert a direct vasoconstrictor effect on the porcine coronary microcirculation via a muscarinic mechanism. Chronic exposure to cocaine significantly decreases beta-adrenoceptor-mediated relaxation and blunts endothelium-dependent relaxation to a small degree.

Characterization of the morphological and functional alterations in rabbit subclavian artery subjected to balloon angioplasty

A number of experimental models for the study of the pathogenesis of the restenotic process have been developed, although many fail to correlate the time courses of both functional and morphological alterations following balloon injury. Our aim was to develop a rabbit model of balloon injury, which studied both of these alterations in detail. Male New Zealand White rabbits (12 weeks old) were fed a high-cholesterol diet for 4 weeks, after which they were subjected to balloon injury of the left subclavian artery. After surgery the animals were returned to a normal diet and sacrificed 2, 7, 15 or 30 days after angioplasty. Two further groups of animals were sacrificed either after 4 weeks of high-cholesterol feeding (no angioplasty) or 2 days after a sham angioplasty operation. Angioplasty-induced changes in vasoconstrictor [to 5-hydroxytryptamine (5-HT) and KCl] and endothelium-dependent (ACh and calcimycin) and endothelium-independent (sin-1) vasodilator responses were assessed in isolated vessel rings. Morphological analysis of the size and composition of neointima was also made at each timepoint. Hypercholesterolaemia reduced the responsiveness of the subclavian arteries to the endothelium-dependent vasodilators carbachol and calcimycin; however, this responsiveness was restored after 7 days of a normal diet. The response to carbachol remained depressed in angioplastied arteries until 30 days after angioplasty, whereas recovery of relaxation to calcimycin was unaffected by angioplasty. Responses to 5-HT, KCl and sin-1 were unchanged by either hypercholesterolaemia or angioplasty. Morphological studies demonstrated the development of neointima in all rabbits after 7 days, reaching a maximum size after 15 days. All neointima stained for a smooth muscle actin. Accumulation of macrophages appeared in the media after 7 days and was present in the neointima after 15 days, and subsequently declined. Proliferating smooth-muscle cells were evident in the media 2 days after angioplasty, and in the neointima fro 7 days onwards. In the rabbit subclavian artery, we have developed a model that describes fully the temporal development and characteristics of an intimal cellular response and functional changes following balloon injury.

Beta-Adrenoceptors in endothelium of rabbit coronary artery and alteration in atherosclerosis.

The existence of beta-adrenoceptor (beta-AR) in endothelium of rabbit coronary artery and its alteration in atherosclerosis (AS) were determined by relaxation experiments in isolated preparations and in situ hybridization with a digoxigenin-labelled beta 2-AR cDNA probe. The concentration-relaxing response curves for isoproterenol (ISO) and norepinephrine (NE) in the presence of phentolamine were shifted to the right, and the maximal relaxations were reduced by removing the endothelium. Nitric oxide synthase inhibitor L-NG-nitro-arginine reduced the maximal relaxation induced by ISO, while the cyclooxygenase inhibitor indomethacin showed no effect on relaxation. In situ hybridization showed that mRNA for beta-AR was detected not only in smooth muscles, but also in endothelial cells. Coronary artery AS was created by high cholesterol feeding and was confirmed histologically under light microscopy. The relaxation response to acetylcholine (ACh) was abolished or significantly diminished in AS preparations. The relaxation responses to ISO or NE, however, were potentiated in AS arteries, especially in those which showed diminished (but not abolished) ACh response. The relaxation induced by sodium nitroprusside was reduced significantly in the AS arteries. Those results suggest that beta-AR are present in endothelium of rabbit coronary artery, and that endothelium beta-AR-mediated vasorelaxation is potentiated in AS.

Changes in adrenal gland and liver polyunsaturated fatty acid biosynthesis in hypercholesterolemic rats

The effect of 2% (w/w) cholesterol supplementation of an otherwise balanced diet on polyunsaturated-fatty-acid metabolism was studied in the liver and adrenal microsomes and in cells isolated from the adrenal glands of rats. Dietary cholesterol feeding enhanced Δ9 desaturation activity and decreased Δ6 and Δ5 desaturation activity in adrenal microsomes. The acyl-CoA synthetase activity with long-chain fatty-acid substrates [18:0, 18:2(n-6), 18:3(n-3) and 20:3(n-6) decreased both in liver and adrenal microsomes of the rats fed with cholesterol. The total fatty-acid composition of the plasma and the liver microsomes of the cholesterolfed rats agreed with the desaturase activities. No parallel effect between desaturase activities and fatty acid composition was obtained in adrenal microsomes. The high cholesterol feeding futhermore increased the 1,6-diphenyl-1, 3,5-hexatriene steadystate fluorescence anisotropy in the liver and adrenal microsomes. Adrenal cells isolated from cholesterol-fed rats showed a marked disminution in arachidonic-acid biosynthesis as compared to the controls. However, the elongation of 20:4(n-6) to docosatetraenoic acid (n-6) in adrenal gland cells was not different between two groups. These experiments demostrated that dietary cholesterol altered the uptake and the metabolism of polyunsaturated fatty acids in the adrenal gland and liver.

Response of cholesterol synthesis to cholesterol feeding in men with different apolipoprotein E genotypes

To investigate the influence of dietary cholesterol level and apolipoprotein (apo) E polymorphism on cholesterol synthesis, seven apo E2/ - and six apo E4/ - normolipidemic subjects consumed self-selected diets containing low cholesterol ([LC] 250 mg/d) and high cholesterol ([HC] 800 mg/d) levels for approximately 20 days. On day 20, subjects were given 0.7 g deuterium oxide (D 2O)/kg body water followed by maintenance doses. Cholesterol synthesis was measured as the uptake rate of D into plasma free cholesterol over 24 hours. Serum total cholesterol levels were higher ( P < .05) in the apo E4/ - versus apo E2/ - group over both dietary periods. No influence of dietary cholesterol content on serum levels was observed, nor was there an effect of apo E genotype or dietary cholesterol level on cholesterogenesis. However, a genotype-independent association was observed between both cholesterogenesis ( P < .001) and the increase in cholesterogenesis ( P = .05) with the change in serum total cholesterol level subsequent to high-cholesterol feeding. These findings suggest that (1) apo E genotype is not associated with cholesterol synthesis rate in subjects on self-selected diets, and (2) hyporesponders to a dietary cholesterol challenge display higher synthetic rates than hyperresponders. The observation of lower cholesterol synthesis in individuals with the largest increases in serum cholesterol level after a dietary cholesterol challenge suggests a passive rather than dominant role of cholesterol synthesis in regulating serum levels.

Amiprilose in the prevention of restenosis after coronary intervention in a swine model

Amiprilose hydrochloride is a synthetic carbohydrate with anti-inflammatory and antiproliferative properties. This study tested the potential benefit of amiprilose in preventing coronary artery restenosis in a swine model. The swine restenosis model was prepared using Hanford miniature swine made atherosclerotic with coronary abrasion, high-fat and high-cholesterol feeding, and intracoronary stenting. Eighteen animals were randomized to receive amiprilose, 100 mg/kg body weight orally twice per day (n = 9), or no amiprilose (n = 9) beginning 5 days before stenting and continuing through 4 weeks until sacrifice. Presacrifice quantitative coronary angiography and postsacrifice histologic examination revealed the degree of intimal proliferation. Coronary angiography revealed no difference in percentage-diameter stenosis between the amiprilose and control groups (left anterior descending artery [LAD], 46% +/- 10% vs 44% +/- 17%; circumflex artery [CFX], 43% +/- 21% vs 42% +/- 15%; right coronary artery [RCA], 37% +/- 11% vs 34% +/- 9%; P = not significant [NS]), respectively, or in change in lumen diameter from poststenting to presacrifice (LAD, -1.0 +/- 0.4 mm vs -1.1 +/- 0.7 mm; CFX, -1.2 +/- 0.8 mm vs -1.0 +/- 0.7 mm; RCA, -1.1 +/- 0.4 mm vs -1.0 +/- 0.4 mm; P = NS). Morphometric histologic analysis likewise showed no difference in percentage-area stenosis (LAD, 55% +/- 14% vs 55% +/- 15%; CFX, 53% +/- 15% vs 54% +/- 12%; RCA, 39% +/- 17% vs 39% +/- 20%; P = NS) or in maximal intimal thickness. Amiprilose hydrochloride did not prevent coronary intimal proliferation in this swine model of restenosis.

Plasma lipoprotein metabolism in transgenic mice overexpressing apolipoprotein E. Accelerated clearance of lipoproteins containing apolipoprotein B.

We have reported that transgenic mice overexpressing rat apo E shows marked reduction of plasma cholesterol and triglyceride levels due to the disappearance of VLDL and LDL. In this study, we investigated the metabolism of plasma lipoproteins in transgenic mice. After intravenous injection, the rates of clearance of 125I-VLDL and 125I-LDL were 3.0- and 2.4-fold greater in transgenic mice than in controls, respectively. Furthermore, clearance of chylomicron remnants estimated by oral retinyl palmitate-loading test was markedly enhanced in transgenic mice. The hepatic expression of LDL receptors by immunoblot analysis was similar in both groups. These data suggest that elimination of lipoproteins containing apo B was due to enhanced clearance of these lipoproteins enriched with apo E through hepatic LDL receptors. When fed a high cholesterol diet, controls showed twofold elevation of plasma cholesterol levels with marked increases in VLDL and LDL cholesterol on gel filtration chromatography. In contrast, cholesterol-fed transgenic mice showed resistance against these increases. High cholesterol feeding decreased the activity of hepatic LDL receptors and had no effect on enhancement of chylomicron remnant clearance in transgenic mice. Thus, overexpression of apo E facilitates metabolism of lipoproteins containing apo B presumably primarily via the LDL receptor pathway and possibly through an interaction with the chylomicron remnant receptor.

Heterogeneity in smooth muscle cell population accumulating in the neointimas and the media of poststenotic dilatation of the rabbit carotid artery

Rabbit smooth muscles contain at least three types of myosin heavy chain (MHC) isoforms; SM1, SM2 and SMemb (NMHC-B), the expression of which is developmentally regulated. We have recently reported that smooth muscles with the embryonic phenotype accumulate in the neointimas produced by endothelial denudation or high-cholesterol feeding. In this study, we examined MHC isoform expression in the neointimas and the media of poststenotic dilatation of the rabbit carotid artery, and determined the phenotype of the smooth muscle cell in the dilated segment. We report here that neointimal cells in the dilated segment are smooth muscle cells with the embryonic phenotype as previously reported in our ballooning-injury study. The medial smooth muscles, however, are composed of heterogeneous population of smooth muscles which differ in stage of differentiation as determined by the MHC isoform expression. These results indicate that MHC isoforms are useful molecular markers to identify abnormally proliferating smooth muscles in diseased arteries and to understand the process of atherogenesis occurring following vascular injury.

Recognition sites on rat liver cells for oxidatively modified beta-very low density lipoproteins.

The in vivo fate of beta-very low density lipoproteins (beta-VLDLs) was investigated after Cu(2+)-mediated oxidative modification (Ox-beta-VLDL). Ox-beta-VLDL may be physiologically relevant under conditions of defective VLDL removal by the liver (type III hyperlipoproteinemia) or overloading of the remnant receptor (high cholesterol feeding). On oxidation of beta-VLDL, the kinetics of its removal from the blood and uptake by the liver are unchanged. However, in contrast to beta-VLDL, which is recognized by the remnant receptor of parenchymal cells, liver uptake of Ox-beta-VLDL is mediated mainly by Kupffer cells (65% of liver-associated radioactivity). In vitro competition studies show that the cell association and degradation of iodine-125-labeled Ox-beta-VLDL by both liver endothelial and Kupffer cells are only marginally competed for by acetylated LDL (10-20%), while an efficient blockade is noted with Ox-beta-VLDL, oxidized low density lipoproteins, or polyinosinic acid (80-90%). The capacity of Kupffer cells to associate with and degrade 125I-Ox-beta-VLDL appears to be twofold higher than for endothelial cells. It is concluded that on oxidation of beta-VLDL, the recognition system responsible for the uptake of beta-VLDL from the blood circulation is shifted from the remnant receptor to a specific oxidized-lipoprotein receptor. The efficiency of the scavenger activity on Kupffer cells will then form the protection system against the prolonged circulation of these atherogenic lipoproteins in the blood.

Effects of cocaine on epicardial coronary artery reactivity in miniature swine after endothelial injury and high cholesterol feeding. In vivo and in vitro analysis.

The purpose of this study was to determine the effects of cocaine on vasoreactivity in the swine model. Eight miniature pigs underwent regional endothelial denudation of the left anterior descending coronary artery and were then fed a high cholesterol diet. Cross-sectional area (CSA) of coronary arteries was measured by quantitative angiography. Before denudation, intravenous cocaine (1, 3, and 10 mg/kg) decreased CSA of epicardial vessels by 19-44%. At 3 mo after the denudation, the percent reduction in CSA of the denuded vessels induced by the 10 mg/kg dose was significantly augmented compared to nondenuded vessels (59 +/- 5% vs. 48 +/- 4%, P less than 0.05). Under in vitro conditions where isometric force of isolated ring segments was measured, methoxamine (an alpha 1 agonist) or BHT-920 (an alpha 2 agonist) produced similar degrees of contraction of denuded and control vessels; however, cocaine in concentrations up to 3 x 10(-3) M did not produce contraction. These responses were unaffected by removal of the endothelium. Histologically, myointimal thickening was noted at the denuded site. The present study demonstrates an enhanced vasoreactivity of atherosclerotic coronary arteries to cocaine in vivo, the mechanism of which appears to be mediated by endogenous vasoactive substances rather than by a direct action of cocaine on vascular smooth muscle.

Development of macroangiopathy in sand rats ( Psammomys obesus), an animal model of non-insulin-dependent diabetes mellitus: Effect of gliclazide

The risk of developing macroangiopathy associated with diabetes led us to study in sand rats the long-term consequences of non-insulin-dependent diabetes on the development of arterial lesions promoted by feeding a high-cholesterol diet. Gliclazide, an agent whose preventive effect has previously been suggested in other experimental models of atheroma, was also investigated in these diabetic and hypercholesterolemic animals. Sand rats were fed a natural diet (ND group), a standard laboratory feed (StD group), or a high-cholesterol feed (HCD group) for 15 months. Biologic parameters were monitored throughout the period of the study, and histologic and histochemical examinations were conducted when the animals were killed (month 15). One StD group and one HCD group were treated with gliclazide from month 3 to month 15. The StD group developed a syndrome of obesity, hyperglycemia, hyperinsulinemia, and triglyceridemia. The high cholesterol feed further increased hypercholesterolemia. These biologic abnormalities were accompanied by arterial lesions (thickening of the intima, deposition of glycosaminoglycans). Foam cells were seen in the intima, and microthrombi were present in the lumen of the arteries of animals in the HCD group. Long-term gliclazide medication at doses that normalized serum glucose levels also reduced the obesity, hyperinsulinemia, lipid disorders, and it prevented or retarded the appearance of arterial lesions.

Actin and myosin isoforms in gallbladder smooth muscle following cholesterol feeding in prairie dogs

Gallbladder smooth muscle contractility decreases after high-cholesterol feeding in prairie dogs. This decrease is not associated with alterations in the total amounts of the contractile proteins actin and myosin. The present study was designed to determine if cholesterol feeding results in alterations in the isoforms of actin and/or myosin heavy chain in gallbladder smooth muscle. Control prairie dogs were fed a trace-cholesterol diet and test animals were fed a high (1.2 %)-cholesterol diet for 8 days. Although the proportion of β-actin was unchanged, the proportion of α-actin in the gallbladder was less in the animals fed the high-cholesterol diet (32.6% ± 1.5% in the control animals and 24.6% ± 0.4% in the diet animals). On the other hand, the proportion of γ-actin was significantly greater in the cholesterol-fed animals. There were no significant differences in the proportions of the myosin heavy-chain isoforms between the two groups. Also, there was no change in the volume fraction of smooth muscle in the gallbladders from the two groups. Thus, cholesterol feeding induces a shift in actin isoforms at the same time that there is a decrease in contractility. Whether the altered pattern of actin isoforms is related to the functional changes remains to be determined.

Morphology of the prairie dog gallbladder: normal characteristics and changes during early lithogenesis.

Studies were undertaken to describe the normal structure of the prairie dog gallbladder and adjacent cystic duct, and then to determine sequential changes that occurred as abnormalities in bile composition developed during high cholesterol feeding. Control animals were fed a diet with trace cholesterol, while experimental animals were fed a diet enriched with 1.2% cholesterol for 1, 2, 3, or 4 weeks. Light microscopy and scanning and transmission electron microscopy were used to characterize morphologic changes at each time interval. Biliary lipid composition was altered in all experimental groups, evidenced by significant decreases in bile-acid-to-cholesterol ratios. Cholesterol crystals appeared in experimental bile at 1 and 2 weeks, while stones formed at 3 and 4 weeks. The cystic duct and neck of the gallbladder occasionally displayed goblet cells. Little mucus was demonstrable in principal cells of the gallbladder, but much more in those lining the cystic duct. After 2 weeks of lithogenic diet, there was an increase in mucus content and secretion from all areas, as well as an influx of polymorphonuclear and mononuclear leukocytes. Accumulation of plasma cells in the lamina propria was an especially prominent feature of experimental tissues. These results suggest that 1) there is regional heterogeneity in the mucus content of the gallbladder and cystic duct of the prairie dog, and 2) both regions respond to lithogenesis with mucus hypersecretion and acute and chronic inflammatory changes prior to the appearance of cholesterol gallstones.

Impaired endothelium-dependent relaxation to aggregating platelets and related vasoactive substances in porcine coronary arteries in hypercholesterolemia and atherosclerosis.

Vasoconstrictor responses are augmented in porcine coronary arteries in hypercholesterolemia and atherosclerosis, leading to an occurrence of coronary vasospasm in the latter condition. The role of the endothelium in the vascular hyperreactivity in hypercholesterolemic and atherosclerotic coronary arteries was examined, particularly in response to aggregating and related vasoactive substances. Male Yorkshire pigs underwent balloon endothelial denudation of the left anterior descending coronary artery (LAD) and 2% high-cholesterol feeding for 10 weeks. Electron microscopic examination demonstrated a full lining of endothelial cells in the LAD and the left circumflex coronary artery (LCX). Endothelium-dependent responses were examined in vitro. In cholesterol-fed animals, endothelium-dependent relaxations to aggregating platelets, serotonin, ADP, bradykinin, thrombin, and the calcium ionophore A23187 were depressed in LAD (atherosclerosis), while the relaxations to aggregating platelets, serotonin and ADP were depressed in LCX (hypercholesterolemia). Serotonin-induced contractions were endothelium-dependently augmented in atherosclerotic LAD; the endothelium-dependent component of the contractions was inhibited by blockers of cyclooxygenase. Bioassay studies demonstrated a depressed release of endothelium-derived relaxing factor(s) from the atherosclerotic LAD in response to serotonin. These experiments indicate that the endothelium-dependent relaxations to aggregating platelets and related vasoactive substances are severely impaired in atherosclerosis and moderately impaired in hypercholesterolemia. Since coronary atherosclerosis was induced by a combination of balloon endothelial injury (and regeneration) and high-cholesterol feeding in this study, the combined effects of those factors must account for the severely impaired responses in atherosclerosis. The depressed release of the endothelium-derived relaxing factor(s) and the concomitant release of vasoconstrictor product(s) of cyclooxygenase appear to be responsible for the impaired relaxations.

Dietary cod-liver oil improves endothelium-dependent responses in hypercholesterolemic and atherosclerotic porcine coronary arteries.

This study examined the effects of dietary supplementation with cod-liver oil on impaired endothelium-dependent relaxations in hypercholesterolemia and in atherosclerosis in porcine coronary arteries. Sixteen male Yorkshire pigs underwent balloon endothelium removal of the left coronary arteries and were fed a 2% high-cholesterol diet for 10 weeks, with or without dietary supplementation of cod-liver oil (30 ml/day) (oil-fed and cholesterol-fed groups, respectively). This model allowed the simultaneous examination of the effects of dietary cod-liver oil on vascular reactivity in hypercholesterolemia alone (right coronary artery) and in atherosclerosis (left coronary artery). After 10 weeks of feeding, the dietary treatment with cod-liver oil caused an increase in plasma levels of eicosapentaenoic acid and a decrease in the plasma levels of arachidonic acid, whereas the treatment had no significant effect on the increases in plasma lipid levels induced by the high-cholesterol feeding. Morphometric analysis showed significant inhibition of coronary atherosclerosis by the treatment. Endothelium-dependent responses were examined in vitro in ring preparations and in bioassay experiments. Endothelium-dependent relaxations to bradykinin, serotonin, and adenosine 5'-diphosphate were larger in both right and left coronary arteries from oil-fed than from cholesterol-fed animals. Aggregating platelets from cholesterol-fed and oil-fed pigs induced comparable, larger endothelium-dependent relaxations in rings from oil-fed than from cholesterol-fed pigs. The contractions induced by serotonin or aggregating platelets were significantly inhibited in rings with endothelium from oil-fed pigs, whereas they were comparable in rings without endothelium in both groups. Relaxations to sodium nitroprusside and contractions to potassium chloride or serotonin were comparable in rings without endothelium in both groups. The bioassay experiments revealed that the release of endothelium-derived relaxing factor in response to bradykinin and the relaxations of vascular smooth muscle to the endothelial factor were greater after the fish-oil diet. These results indicate that dietary supplementation of cod-liver oil delays the impairment of endothelium-dependent relaxations in hypercholesterolemia and in atherosclerosis, partly because of an improved release of endothelium-derived relaxing factor and partly because of an improved relaxation of coronary smooth muscle to the factor.

Plasma lipid transfer activity in rabbits: effects of dietary hyperlipidemias

Studies were performed in the rabbit to investigate the relationship between plasma lipids and the cholesteryl ester/triglyceride transfer activity of lipoprotein-deficient plasma ( d > 1.21). The time courses for diet-induced changes in plasma lipids and the lipid (cholesteryl ester/triglyceride) transfer activity of lipoprotein-deficient plasma (LTA) were determined in rabbits fed a variety of hyperlipidemic diets. LTA was not altered within 36 h after a single high-cholesterol/oil meal despite a near doubling of the concentration of plasma cholesterol. With high cholesterol and/or high-fat feeding, LTA increased and reached new steady state levels within about 10 days with little additional change for up to 87 days even when plasma cholesterol continued to increase. For all diets, the greatest increments in LTA occurred about 5 days after initiation of experimental feeding. A low-cholesterol (0.05–0.2%, w/w) diet and a cholesterol-free, high-coconut oil diet (14%, w/w) were associated with comparable increases in both plasma cholesterol and LTA. A marked, concomitant increase in plasma triglycerides was not associated with a further increase in LTA in hypercholesterolemic rabbits. These data indicate that in the rabbit LTA increases in a parabolic manner with moderate and gross, diet-induced increases in plasma cholesterol, and the time courses for the diet-induced changes in LTA are similar for a variety of hyperlipidemic diets.

Calcium-induced contraction and contractile protein content of gallbladder smooth muscle after high-cholesterol feeding of prairie dogs

Feeding a high-cholesterol diet to prairie dogs causes a reduction in contractile responses of gallbladder smooth muscle from these animals. In this study, the influence of cholesterol feeding on the contractile response to calcium and on the concentration of the contractile proteins actin and myosin was determined. Strips of gallbladder smooth muscle, at their optimal length for tension development, were stimulated maximally with carbachol. Then the muscle cell membranes were made permeable and the strips were exposed to a maximally effective concentration of calcium. Strips from cholesterolfed animals developed less stress than those from control animals under all conditions. The concentration of actin and myosin was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. There were no differences in the concentrations of either protein between the cholesterol-fed and control animals. Our results indicate that the decreased contractile response seen in muscle from cholesterol-fed animals is not due to alterations in membrane excitation, excitation-contraction coupling, or in total contractile proteins.