Period Of Cholesterol Feeding Research Articles

Impact of Short-Term Administration of High-Density Lipoproteins and Atorvastatin on Atherosclerosis in Rabbits

This study investigates effects of short-term administration of high-density lipoproteins (HDL) and a statin on atherosclerosis in cholesterol-fed rabbits. Effects of HDL apolipoprotein and phospholipid composition have also been investigated. Aortic atherosclerosis was established over 17 weeks in 46 rabbits by balloon denudation and cholesterol feeding. During the past 5 days of the cholesterol-feeding period, animals received: (1) no treatment; (2) oral atorvastatin 5 mg/kg on each of the 5 days; or (3) infusions of HDL (8 mg/kg apolipoprotein A-I) on days 1 and 3 of the treatment phase. After euthanization, lesion size and composition were assessed by histological and immunohistochemical analysis. HDL (but not atorvastatin) reduced lesion size by 36% (P<0.05). The ratio of smooth muscle cells to macrophages in the lesions increased 2.6-fold in animals infused with HDL (P<0.05) and 4-fold in those receiving atorvastatin (P<0.01). HDL and atorvastatin reduced matrix metalloproteinase (MMP)-9 expression by 42% (P<0.05) and 45% (P<0.03), respectively. HDL increased thrombomodulin expression 2-fold (P<0.03). The beneficial effects on lesion area and plaque cellular composition were influenced by HDL phospholipid and apolipoprotein composition. Infusing small amounts of HDL rapidly reduces lesion size and is comparable to atorvastatin in promoting a stable plaque phenotype.

Membrane Cholesterol and the Formation of Cholesterol Domains in the Pathogenesis of Cardiovascular Disease

AbstractAt least three types of cholesterol‐rich membrane domains have been described in biological membranes including cholesterol rafts, membrane caveolae and crystalline cholesterol domains,. While clear biological functions have been ascribed to both rafts and caveolae, little attention has been directed to the biological consequences of cholesterol enrichment of cell membranes and the formation of cholesterol domains. Elevated blood cholesterol levels have been shown to result in the enrichment of the cell plasma membrane with cholesterol in arterial smooth muscle cells (SMC), endothelial cells (EC) and cardiac myocytes. In the early period of cholesterol feeding (within days), the cell membrane enriches with cholesterol and membrane viscosity and membrane bilayer width increase. This latter effect severely alters membrane protein function, and recent data indicates that this induces the modulation of vascular cells (SMC and EC) to the atherosclerotic phenotype. In cardiac myocytes these membrane modifications appear to induce alterations in gene expression patterns that lead to the development of a heart failure phenotype. In addition, as the cholesterol content increases, phase separation of cholesterol occurs resulting in the formation of immiscible cholesterol domains within the membrane. These domains likely initiate nucleation of cholesterol crystals which would explain the origin of “cholesterol clefts” in atherosclerotic lesions. Taken together, these membrane alterations secondary to cholesterol enrichment constitute a “membrane lesion” which contribute to the very early pathogenic events underlying major human diseases including coronary artery disease, stroke and heart failure.

Local elastic modulus of atherosclerotic lesions of rabbit thoracic aortas measured by pipette aspiration method

Changes in mechanical properties of arteries during atherogenesis remain controversial. One of the reasons could be that they have been evaluated with parameters measured in a whole vessel, although the lesions are localized. The local elastic modulus of atherosclerotic lesions was measured by the pipette aspiration method in thoracic aortas of rabbits fed a cholesterol diet for 8, 16, 24 and 28 weeks. The global elastic modulus of the whole aorta was measured by the pressure–diameter test. The local modulus decreased from that of the normal tissue in 8 weeks and then increased during the cholesterol feeding period. The global modulus did not change until 24 weeks and increased by 28 weeks. Histological observation revealed that the initial soft lesion was mainly composed of foam cells, and the stiffening accompanied first the appearance of smooth muscle cells in the top layer of the hyperplastic intima and then calcification in its bottom layer. The global elastic modulus did not change until marked calcification occurred in the tissue. These results suggest that change in mechanical properties of atherosclerotic lesion is not simple and has a close correlation with its histology. Assessment of local mechanical properties is important for studying mechanical properties of atherosclerotic arteries.

Effects of cholesterol diets on vascular function and atherogenesis in rabbits.

Vascular endothelial dysfunction is an important early event in atherogenesis. To evaluate the effects of different levels of cholesterol-containing diets on vascular function and atherogenesis, 17 New Zealand White male rabbits were randomized into four groups: Control with noncholesterol, 10-week 0.5% (0.5C-10) or 1% cholesterol (1C-10), and 14-week 0.5% cholesterol (0.5C-14) feedings. After 10 or 14 weeks, the aortas were harvested for studies of vascular endothelial function and percentage surface lipid lesions. The 0.5% and 1% cholesterol feedings resulted in the same degree of hypercholesterolemia independent of the level and period of cholesterol feeding. There was a decreased trend in vascular endothelial-dependent relaxation to acetylcholine in cholesterol-fed rabbits. Fourteen-week cholesterol feeding induced the least vascular dilation at a concentration of 10-7 M acetylcholine (-38 +/- 3%, -23 +/- 4%, -23 +/- 2%, and -15 +/- 5% in control, 0.5C-10, 1C-10, and 0.5C-14 groups, respectively, P = 0.003). More cumulative exposure of arterial walls to cholesterol induced more surface lipid lesions in the aorta (r = 0.877, P < 0.001). There was a negative relationship between aortic lesions and vasodilation (r = -0.557, P = 0.020 for calcium ionophore; r = -0.463, P = 0.062 for acetylcholine). We conclude that the 0.5% and 1% cholesterol feedings induce similar degrees of hypercholesterolemia. However, aortic lipid lesions and vascular reactivity are dependent on cumulative exposure to cholesterol rather than serum cholesterol level only. Furthermore, decreased vascular endothelial relaxation in cholesterol-fed rabbits was related to lipid plaques in the aorta.

Monocyte chemotactic protein-1 gene and protein expression in atherogenesis of hypercholesterolemic rabbits

Monocyte adherence to the endothelium and subsequent migration into the subendothelial space are important early events in atherogenesis. Monocyte chemotactic protein-1 (MCP-1) has been shown to be highly expressed in both human atheroma and advanced atherosclerotic lesions of experimental animals. To establish the temporal correlation between MCP-1 expression and plaque development, we examined the expression of MCP-1 during atherogenesis of hypercholesterolemic rabbits using Northern blot analysis, in situ hybridization, and immunohistochemistry. New Zealand White rabbits were fed with 2% cholesterol-containing diet for 1 day, 3 days, 1 week, 3 weeks or 6 weeks. The plasma levels of total cholesterol were significantly increased 3 days after cholesterol feeding and continued to increase during the entire cholesterol-feeding period. Northern blot analysis showed that MCP-1 mRNA levels remained unchanged following cholesterol feeding for up to 1 week, were higher than control levels at 3-week and increased even higher at 6-week. In situ hybridization showed that after 3 weeks of cholesterol feeding, MCP-1 mRNA expression was up-regulated in newly-formed fatty streaks and parts of tunica media in the presence or absence of fatty streaks. At 6-week, pronounced MCP-1 mRNA expression was detected with similar distribution. In contrast, MCP-1 mRNA was detected only in a few endothelial cells and adventitia in control and experimental groups feeding cholesterol up to 1-week. Immunostaining of serial sections indicated that MCP-1 was expressed by macrophages and smooth muscle cells in rabbits fed with cholesterol for 3 or 6 weeks. No MCP-1 was detected in intima or media in all other groups. These results show that a lag period exists between serum cholesterol increase and upregulation of MCP-1 expression, suggesting that cholesterol modifications (e.g. oxidation) are required to stimulate MCP-1 expression. In addition, MCP-1 expressed by both macrophages and smooth muscle cells during the initial stages of atherosclerosis is likely to contribute to the development of fatty streaks in hypercholesterolemic rabbits.

Changes in distribution of glycosaminoglycans during the progression of cholesterol induced atherosclerosis in Japanese quail

The temporal and spatial distribution and relative concentration of the proteoglycan glycosaminoglycan component were studied during the progression of atherosclerosis in the systemic arteries of Japanese quail selected for cholesterol induced atherosclerosis (CIA). The CIA quail were placed on either control or 0.5% added cholesterol diets at 3 months of age. The major systemic arteries (dorsal aorta, right and left brachiocephalic) were collected at 1- or 2-week intervals over the 10-week period of cholesterol feeding. In the cholesterol fed quail, alcian blue staining of the dorsal aorta showed elevations of glycosaminoglycans in regions of the artery with atherosclerotic plaque, beginning at the 6-week time point. By biochemical analysis, increases in glycosaminoglycan relative concentration was detected at the 10-week time point. In addition to the change in glycosaminoglycan relative concentration and distribution, the cholesterol fed animals also formed foam cells characteristic of atherosclerotic plaques. Therefore, the conclusion reached was that the CIA line of Japanese quail is a valid animal model for the study of alterations in proteoglycan metabolism in atherosclerotic plaques induced by hypercholesterolemia.

Inhibition of the protective effect of estrogen by progesterone in experimental atherosclerosis

The aim of the present study was to determine the effect of progesterone on the action of estrogen in the development of atherosclerosis. A total of 48 female New Zealand white (NZW) rabbits were ovariectomized. The animals were separated into 6 groups of 8 animals each and received subsequently a 0.5% cholesterol diet for 12 weeks. During this cholesterol feeding period, either estradiol (1 mg/kg body weight (BW)/week), progesterone (25 mg/kg BW/week), or combined estradiol/progesterone (in above dosages) was administered intramuscularly in each group ( n = 8 each) of ovariectomized rabbits. One additional group of 8 animals received a combined estrogen/ progesterone regimen, but with progesterone at one third of the above mentioned dosage. In another 8 rabbits, progesterone was reduced to one ninth of the maximum dosage above, whereas estrogen was kept the same, at 1 mg/kg BW/week. Eight ovariectomized animals served as the control group and received no hormone treatment. After 12 weeks, the animals were sacrificed and the proximal aortic arch was removed for further histological examination. An inhibitory effect of estrogen on intimal thickening was found, in comparison to the control group (intimal area: 0.7 ± 0.5 mm 2 vs. 3.7 ± 2.5 mm 2, P < 0.01), whereas progesterone alone did not show a significant effect on intimal plaque size (intimal area: 4.0 ± 2.3 mm 2). In combination with progesterone (high dose), estrogen was not able to reduce intimal atherosclerosis (intimal area: 3.4 ± 2.4 mm 2). However, the beneficial effect of estrogen was not affected by progesterone, when this was reduced respectively to one third (intimal area: 0.8 ± 0.7 mm 2), or to one ninth of the highest dosage (intimal area: 0.6 ± 0.4 mm 2). Interestingly, these differences in atherosclerotic plaque development were observed without significant changes in plasma cholesterol concentrations by the administered hormones. In conclusion, progesterone was dose-dependently able to completely inhibit the beneficial effect of estrogen in experimental atherosclerosis, suggesting that progesterone exerts a direct inhibitory effect on the athero-protective action of estrogen. In the context of recently published data, the present work confirms the importance of the ‘non-lipid-mediated’, anti-atherosclerotic effect of estrogen,probably due to an interaction with sex hormone receptors in vascular smooth muscle cells (VSMC).

Replacement of dietary saturated fat with monounsaturated fat: effect on atherogenesis in cholesterol-fed rabbits clamped at the same plasma cholesterol level

The aim was to compare the effect on atherogenesis of dietary monounsaturated and saturated fatty acids in cholesterol-clamped rabbits. To obtain an average plasma cholesterol concentration of 20 mmol/l in each rabbit during the 13-week cholesterol-feeding period, dietary cholesterol was adjusted weekly. The amount of fat fed daily was 10 g per rabbit in Expts A (n 23), C (n 36), and D (n 58) and 5 g per rabbit in Expt B (n 24). The source of monounsaturated fatty acids was olive oil in all four experiments. The source of saturated fatty acids was butter in Expt A, lard in Expt B, coconut oil in Expt C, and butter or lard in Expt D. Generally, olive oil-fed groups received more cholesterol and tended to have more cholesterol in VLDL and less in LDL compared with groups receiving saturated fat. Analysis of variance of the combined results of all four experiments showed that, in comparison with saturated fat, olive oil lowered aortic cholesterol by 13 (-9-30, 95% confidence interval) % in the aortic arch, and by 10 (-10-26) % in the thoracic aorta, which was not significant. In the comparison with olive oil, no differences in effects on aortic cholesterol content were detected between butter, lard and coconut oil. These findings do not support the view that replacement of dietary saturated fat with olive oil has a major impact on the development of atherosclerosis in addition to that accounted for by changes in plasma cholesterol levels.

Effect of isradipine on the formation and regression of fatty streaks in cholesterol fed rabbits

The aim was to determine whether the antiatherogenic effect of the calcium channel blocker isradipine on fatty streak formation was dependent upon a temporal relationship between cholesterol feeding and administration of the drug. The study was done in New Zealand White rabbits fed a diet supplemented with cholesterol (2.5% w/w) for three weeks. Such a regimen results in loss of endothelium dependent relaxation and accumulation of cholesterol in the aorta four weeks later. The calcium antagonist isradipine was given in a dose of 0.25 mg.kg-1.d-1 at specified periods during the study to seven subgroups of animals: (1) standard diet + 2.5% cholesterol for three weeks; (2) standard diet + 2.5% cholesterol for three weeks followed by standard diet for four weeks; (3) standard diet + 2.5% cholesterol for three weeks followed by standard diet for 12 weeks; (4) standard diet + 2.5% cholesterol+isradipine for three weeks followed by standard diet alone for four weeks; (5) standard diet + 2.5% cholesterol for three weeks followed by standard diet for four weeks with isradipine given throughout the seven weeks; (6) standard diet + 2.5% cholesterol for three weeks followed by standard diet for four weeks with isradipine given during the final four weeks only; (7) standard diet + 2.5% cholesterol for three weeks followed by standard diet for 12 weeks with isradipine given during the final eight weeks. Aortic tissue was removed for measurement of cholesterol content, endothelium dependent relaxation to acetylcholine and the calcium ionophore A23187, and relaxant responses to sodium nitrite. Serum was collected for measurement of cholesterol and triglyceride concentration. When isradipine was given either during cholesterol feeding and continued for four weeks following it (subgroup 5) or during the four weeks following cholesterol feeding (subgroup 6), loss of endothelium dependent relaxation and the accumulation of cholesterol in the aorta was prevented. However, administration of isradipine during the period of cholesterol feeding alone (subgroup 4) was without effect. Also, administration of isradipine after lesions of fatty acid streak type were established appeared to have a favourable effect on removal of cholesterol from the aorta. Isradipine protects against the development of fatty streaks in rabbits fed a diet supplemented with 2.5% cholesterol. Administration of this drug after fatty streaks are formed also promotes their resolution.

Bile acid excretion and cholesterol 7 alpha-hydroxylase expression in hypercholesterolemia-resistant rabbits

We have developed a partially inbred substrain of New Zealand white rabbits (CRT/mlo) that are resistant to the hypercholesterolemia that accompanies cholesterol feeding to normal rabbits. The plasma cholesterol concentration of normal rabbits increases dramatically from about 30 mg/dl to > 300 mg/dl after they are fed a 0.1% cholesterol-enriched diet for 3-4 months. Cholesterol-fed CRT/mlo animals, however, maintain a cholesterol level of about 30 mg/dl during the entire cholesterol feeding period. In addition to the low plasma cholesterol level, measurements of cellular cholesterol indicate that the hepatic cholesterol content of the cholesterol-fed resistant rabbit remains markedly lower than it does in normal animals fed the same diet. The only mechanism for removal of significant quantities of cholesterol carbon from the body is via the fecal excretion of cholesterol, neutral sterol metabolites, and bile acids. In comparison to the basal, low-cholesterol diet, we observed that cholesterol-fed resistant rabbits had increased excretion of lithocholic acid, while excretion of this bile acid by cholesterol-fed normal rabbit remained similar to basal diet levels. Deoxycholic acid excretion, the other main bile acid excreted in the feces of rabbits, was decreased in response to cholesterol challenge in animals with either resistant or normal phenotypes, but the decrease was significantly less in the resistant rabbits. Thus, the resistant rabbits excreted relatively more lithocholic and deoxycholic acid than did the cholesterol-fed normal rabbit. The difference in bile acid excretion was also manifest by a higher than normal level of cholesterol 7 alpha-hydroxylase activity and cholesterol 7 alpha-hydroxylase mRNA in the livers from resistant versus normal rabbits. As cholesterol 7 alpha-hydroxylase is the putative rate-limiting step of bile acid synthesis, we believe that the increased excretion of bile acids by resistant animals is due, at least in part, to increased levels of cholesterol 7 alpha-hydroxylase expression.

実験的家兎動脈硬化症における中枢神経組織内カルシウム, 燐, マンガン, マグネシウム沈着とelastaseの金属沈着予防作用について

The aims of this study were shed light on the evaluation of calcium (Ca), phosphorus (P), manganese (Mn), and magnesium (Mg) in central nervous system (CNS), liver, and kidney of rabbits with atherosclerosis experimentally induced by a cholesterol-rich diet. We also investigated the protective effect of exogenous elastase on deposition of these metals in the CNS and soft tissues.Twenty five male rabbits, weighing 2, 000g, were divided into equal six groups. The experimental atherosclerosis was performed by the modified procedure of Kritchevsky et al. Group A was fed a standard diet for three months. Also for three months, Group B was fed a standard diet that was 1.5% cholesterol-rich, and Group C had a 1.5% cholesterol-rich diet plus daily intraperitoneal administrations of elastase 450EL.U/kg. Other groups were fed a standard diet (Group D), a 0.67 cholesterol-rich diet (Group E) and a 0.67% cholesterol-rich diet plus daily intraperitoneal administration of elastase 450 EL.U/Kg (Group F) for six months. After feeding rabbits with the above regimens for three to six months, the rabbits fed with cholesterol-rich diet (Groups B, C, E and F) were shown to have atherosclerosis using biochemical and histological techniques. The amelioration of atherosclerotic lesion in each tissue induced by the cholesterol-rich diets was confirmed with intraperitoneal administration of elastase.Ca, P, and Mn contents in the frontal lobe, pons, cerebellum, spinal cord, liver, and kidney of each rabbit were determined by the well-established neutron activation analysis method, and the Mg content was obtained by inductively coupled plasma emission spectrometry. Deposits of Ca, P, Mn, and Mg in the CNS were remarkable in rabbits fed with cholesterol-rich diets for 6 months compared to those in rabbits fed with 1.5% cholesterol-rich diets for 3 months, metal deposition in CNS being dependent on the length of the cholesterol feeding period. In rabbits with a 0.67% cholesterol-rich diet, the level of Ca, P, Mn, and Mg in CNS tended to decrease, and in part, significantly reduced by administration of exogenous elastase. It appears likely that rabbits with atherosclerosis have higher concentrations of Ca, P, Mn, and Mg in their CNSs, and that these metals are removed from the CNS by the action of elastase.

Treatment of young rats with cholestyramine or a hypercholesterolemic diet does not influence the response of serum cholesterol to dietary cholesterol in later life

Groups of 10 female Wistar rats (aged 4 weeks) were fed for 29 days either a low-cholesterol commercial diet, a commercial diet containing 2% (w/w) cholesterol, 0.5% cholate and 5% olive oil or a diet containing 2% cholestyramine. The rats were then fed the low-cholesterol commercial diet for the next 91 days and the high-cholesterol diet for another 29 days. There was no significant difference between the groups in the increase of cholesterol in serum and liver during the last period of cholesterol feeding. A fourth group of 10 animals was fed the diet containing cholesterol and cholate during the entire experimental period of 149 days. By the end of the experiment serum cholesterol in these animals was lower and liver cholesterol was higher than in the 3 groups fed the high-cholesterol diet during days 120–149 of the experiment. This study does not present evidence for imprinting effects of early diet manipulation on the later cholesterolemic response to a high cholesterol diet.

動脈平滑筋細胞の膜リン脂質に関する研究

We already reported the effects of hyperlipidemic rabbit serum on cultured smooth muscle cells and various organelle membrane phospholipids. This findings suggest the possibility that cell proliferation by attack of hyperlipidemic serum might be resistance to develop atherosclerosis. In the present study, we have observed the changes of membrane phospholipids on experimental hypercholesteremic rabbits.Fifteen male New Zealand white rabbits were fed with diet containing 1.5% cholesterol and were divided into three groups by cholesterol feeding period. And, control group (five male New Zealand white rabbits) was fed with standard rabbit's diet.Cells of intima-media were obtained from the thoracic aorta according to method described by Chamley et al. Lipids were extracted by Folch's method. Technique of thin layer chromatography was applied to determine the composition of various phospholipids of the membranes.The results are as follows.1) Hyperlipidemia was increased according to the period of cholesterol feeding.2) In distribution of various serum phospholipids, Sphingomyelin (SPH) was most increased and Lysophosphatidyl choline (LPC) was increased, but Phosphatidyl choline (PC) and Phosphatidyl ethanolamine (PE) were decreased. This tendency significantly increased according to the period of cholesterol feeding.3) In the cells of intima-media obtained from the thoracic aorta, CE and TG increased and FC, PL and FA decreased in the cholesterol feeding groups as compaired with those in the controls. This tendency significantly increased according to the period of cholesterol feeding.4) In the composition of phospholipids in cells of aortic intima-media, SPH increased, LPC and PC also increased, but PE, Phosphatidyl inositol (PI) decreased in the control group.5) Contrary, in atherosclerotic rabbits which were fed with diet containing 1.5% cholesterol for one month, SPH decreased and Phosphatidic acids (PA), PE increased.6) From above mentioned results, it is concluded that in early period of atherosclerosis, cells of aortic intima-media might play protective reaction against to the development of atherosclerosis, since cell membrane seems to increase biological activities from the aspect of change in the phospholipid composition caused by the cholesterol feeding.

Hypertension-accelerated atherogenesis in cholesterol-fed rabbits

Entry of 125I-labelled low density lipoprotein ([ 125I]LDL) into the aortic intima was studied over 6 hours in normotensive and hypertensive rabbits fed a 1% cholesterol diet for 9 and 4 weeks respectively. Studies were also made in hypertensive and normotensive cholesterol-fed rabbits in which blood pressure was reduced acutely with parenteral hydralazine. In all groups the entry of [ 125I]LDL was greatest in the aortic arch and significantly less in both the descending thoracic and abdominal regions. Lipoprotein entry into the aorta of cholesterol-fed rabbits was increased some 10-fold over the corresponding value previously found in rabbits fed a normal diet [1]. This increase was due to increased vascular permeability as well as to increased plasma LDL concentration. The hypertensive cholesterol-fed rabbits did not show significantly greater entry of [ 125I] LDL than the normotensive cholesterol-fed rabbits. Comparison of the rate of LDL entry over 6 hours and the quantity of cholesterol accumulated in the aortic segments over the period of cholesterol feeding indicated that lipoprotein fractions other than LDL must contribute significant amounts of cholesterol to the developing lesion. The finding that LDL entry paralleled accumulation during cholesterol feeding, together with the finding that acute reversal of hypertension did not reduce the entry of [ 125I]LDL suggest that mechanisms other than increased filtration of plasma low density lipoprotein contribute significantly to the accelerated development of atherosclerosis in hypertension.

ON THE BILE ACID AND NEUTRAL FECAL STEROID EXCRETION IN MAN AND RABBITS FOLLOWING CHOLESTEROL FEEDING. BILE ACIDS AND STEROIDS 150.

AbstractThe effect of cholesterol feeding on bile acid turnover and neutral fecal steroid excretion was studied in rabbits and human subjects. In rabbits the addition of 1% cholesterol to a low fat pellet diet (on the average 700 mg of cholesterol per day) caused a marked increase of the serum cholesterol level but a reduction of the turnover and the fecal elimination of deoxycholic acid. On the subsequent feeding of a semisynthetic cholesterol free diet, the serum cholesterol level decreased in spite of a further reduction of the fecal bile acid excretion. When human subjects received a diet containing egg yolk lipids, which provided 1.4 g cholesterol per day, the serum cholesterol level increased moderately over the control values, but there were no consistent effects on either the biliary bile acid composition or on the turnover of cholic acid. The amount of cholesterol excreted as neutral fecal steroids during the cholesterol feeding period corresponded on the average to 80 and 77% of the amount of cholesterol given to rabbits and human subjects respectively. Cholesterol and the plant sterols β‐sitosterol and methylcholesterol were metabolized into neutral compounds that were the same in rabbit and in human feces. Rabbit feces contained proportionally more 5α‐sterols than human feces.

Transfer of labelled cholesterol across the aortic intimal surface of normal and cholesterol-fed cockerels

Summary Citrate blood from normal and cholesterol-fed birds was incubated with [4- 14 C]-cholesterol and then reinjected to the donor birds, which were killed 10 min, 1, 2, 4, 5 or 24 h later. Plasma elimination curves for the labelled cholesterol were consistent with the concept that, at the time of injection, about 75% of the label in plasma was part of plasma lipoproteins. The thoracic aorta was split into two layers of approximately equal thickness. These layers were studied for the uptake of labelled cholesterol. In some experiments free and esterified cholesterol were separated. The uptake of label by the inner layer was used in calculations of the rate of transfer of plasma total cholesterol across the intimal surface. In normal birds a value of 0.10 µg/cm 2 /h was obtained. In cholesterol-fed birds an average value of 0.23 µg/cm 2 /h was calculated for the period of cholesterol feeding. At the time of experimentation the rate was calculated at 0.40 µg/cm 2 /h. A co-variation was present between the rate of transfer of plasma cholesterol across the intimal surface and the aortic intima-media cholesterol concentration in 25 birds ( P P

THE ACID MUCOPOLYSACCHARIDE CONTENT OF THE PLASMA OF CHOLESTEROL-FED CHICKENS.

Chickens fed a high‐protein, high‐cholesterol diet develop, in addition to hypercholesterolæmia and hyperlipæmia, a high level of plasma metachromasia. This is related to the cholesterol content of the plasma and not to age or period of cholesterol feeding. After the removal of chylomicra the plasma has a greatly lengthened recalcification time pointing to the presence of a heparin‐like substance.

Inhibition of experimental hypercholesterolemia and atherogenesis by 4-amino pteroylglutamic acid (aminopterin).

Rabbits pretreated with Aminopterin (4-amino pteroylglutamic acid) for 4 weeks were fed an atherogenic diet for 8 weeks, during which Aminopterin injections also were continued. The atherogenic diet consisted of a stock diet with 3/4 per cent cholesterol added. As a result of some manipulation of the Aminopterin dosage during the period before cholesterol feeding was begun, some of the Aminopterin-treated animals lost weight from overdosage, and 7 of the original 20 died. The surviving animals upon reduction of dosage made good weight gains, comparable to the controls, during the cholesterol feeding period. When sacrificed after 8 weeks of cholesterol feeding, the control animals, 21 in number, all had grossly demonstrable 1+ to 4+ atheromatosis of the aorta. Of the 13 surviving Aminopterin-treated animals, 9 had no atheromatosis or doubtful deposits of minimal extent. Only 4 had definite atheromatosis comparable in extent to the controls. Serum cholesterol levels were 30 to 50 per cent lower in the treated animals than in the controls.

Deposition and fate of cholesterol in ocular aortic implant and in the aorta in situ.

Aortic implants were placed in the anterior eye chamber of 30 rabbits subsequently fed excess cholesterol and cottonseed oil. After 3 months of such feeding, seven of these animals were sacrificed, and their implants and also segments of their own aorta were analyzed for cholesterol. Two more groups of these rabbits were sacrificed 2 and 3 months, respectively, after their return to a cholesterol-free diet. It was observed that the aortic implant gained almost twice as much cholesterol as the host's own aorta at the end of the cholesterol feeding period. This difference became even greater in animals that were sacrificed 2 months after cessation of excess cholesterol feeding, but still hypercholesteremic. However, the ocular implants of rabbits examined 3 months after cessation of cholesterol feeding were observed to have lost almost all of their cholesterol, whereas the animal's own aorta continued to exhibit an unchanged excess of cholesterol. The findings suggest that the ocular aortic implant differs markedly from the aorta in situ in regard to its penetration and retention of cholesterol.

Reduction of excess cholesterol in the rabbit aorta by inhibition of endogenous cholesterol synthesis.

Hepatic cholesterol synthesis in rabbits, as measured by the incorporation of C(14)-labelled acetate, was inhibited by addition of non-toxic amounts of vanadyl sulfate (0.05 per cent VOSO(4).2H(2)O) to the diet. This diet reduced excess aortic cholesterol in cholesterol prefed rabbits when fed during the 6 weeks immediately following a 4 week period of cholesterol feeding.