Effects of dietary cholesterol and voluntary exercise on histopathology,plasma and hepatic lipids of the male rat

Summary To avoid the stress of imposed activity, male weanling rats were allowed to exercise voluntarily in individual activity wheels. The exercising animals, which were compared to sedentary controls, ran over 26 km/wk (over 2 miles/day). Half of the animals in each group were fed a 10% coconut oil diet; the other half were fed the same diet with 1% added cholesterol.Plasma cholesterol was monitored throughout the 23-week regime. Consistently lower plasma cholesterol values were shown by the exercising animals during the first weeks of the study, the differences being statistically significant at the end of the 8th week. Dietary cholesterol sharply elevated plasma cholesterol, which reached a peak at the 5th week, then declined to basal levels by the 10th week.Both neutral glycerides and cholesterol levels of the livers were elevated considerably by the addition of cholesterol to the diet. Exercising, however, had a lowering effect on both liver cholesterol and neutral glycerides. The weights of the hearts of the exercising rats were increased, while those of the other organs selected were unchanged.Histologic examination of sections of livers showed fat infiltration of hepatic cells varying in severity, depending on the diet. Greater damage to liver cells was noted when cholesterol was added to the basal diet. Fat infiltration was lessened considerably in exercising rats on the basal diet; exercising partially overcame the effects of added cholesterol.This work was supported in part by Grant-In-Aid from The Nutrition Foundation, Inc.; State of Washington Initiative 171 Fund and USPHS Research Grant HD-03475 from the National Institutes of Health.     

Hepatic lipids of dogs fed on arteriosclerosis-inducing diet

Lipid composition of liver in dogs was investigated after feeding them either an arteriosclerosis-inducing diet which contained 16% hydrogenated coconut oil and 5% cholesterol, the same diet but without cholesterol supplement, or meat-chow. Animals fed the last diet did not develop vascular lesions and were regarded as controls. The composition and concentration of free fatty acid and phospholipid fractions of hepatic lipids from dogs fed either experimental diet for 4 months were similar but differed from controls. However, cholesteryl oleate, total cholesteryl ester and triglyceride concentrations were significantly higher in liver of the group with cholesterol supplement than in the group without cholesterol added to their diet. In addition, the cholesterol supplemented diet fed for 12–16 months caused greater hepatic lipid changes than those induced by the same diet in 4 months.Unlike adipose tissue, kidney, or myocardial and skeletal muscle, hepatic cholesterol esters showed a profound difference between the four month feedings of cholesterol supplemented and cholesterol free diets. These findings suggest that the liver may play a predominant regulatory role in the onset of diet-induced hyperlipemia and that exogenous cholesterol enhances the effects seen by feeding saturated medium chain fatty acids without cholesterol.Lipid changes observed in mitochondrial and microsomal fractions generally were similar, and also like those observed in lipid extracts of whole liver.     

Cell cholesterol esters and high-density lipoprotein plasma levels during liver hyperplasia in choline-fed male and female rats

Sexual dimorphism exists in the response of rats to lead nitrate, liver hyperplasia occuring earlier and being more pronounced in males. Excess dietary choline in females shifted the growth pattern towards that of males. To determine whether phosphatidylcholine-induced growth modulations could be related to a derangement of cholesterol metabolism, liver accumulation of cholesterol esters and plasma lipoprotein patterns were investigated. In males, lead-induced liver hyperplasia was associated with increased total cholesterol hepatic content, accumulated cholesterol esters and reduced concentration of plasma High Density Lipoprotein (HDL) cholesterol. Females were less responsive to the liver mitogenic signal of lead nitrate; there was no elevation of cholesterol content nor any marked accumulation of cholesterol esters. This is consistent with the lack of change in the plasma levels of HDL cholesterol. Continuous choline feeding displaced the liver cholesterol ester pattern and plasma HDL cholesterol levels in females, and in parallel that of DNA synthesis, towards those of males. Choline was not observed to have any effect in males. These results suggest that the derangement of phosphatidylcholine metabolism induces growth-related changes in cholesterol turnover; they are consistent with the proposal that the intracellular content of cholesterol esters may have a role in regulating liver growth rates.     

The effects of graded dietary levels of cholesterol and cholic acid on plasma and hepatic lipids and histopathology of the young male rat

Summary Young male rats were maintained on a basal diet containing 20% coconut oil with cholesterol added at 0, 0.25, 1 or 4% and cholic acid at 0, 0.25 or 0.5% weight. Determinations were made of plasma cholesterol and neutral glyceride levels throughout the regimen. After 10 weeks, the rats were killed and their livers, hearts, testes and adrenal glands were weighed. Histologic preparations were made from sections of livers, hearts and aortae. Analyses were made of liver lipids.A decrease in food intake with concomitant lessening in body weight gain occurred when both cholesterol and cholic acid were added to the diet; simultaneously relative liver and adrenal weights were increased. A definite interaction was observed between the dietary cholesterol and cholic acid as evidenced by a considerable elevation in plasma cholesterol levels which showed a peak of 67–110% above the initial values at the 3rd week. No consistent alteration was seen in plasma neutral glyceride values. Both hepatic cholesterol levels and relative liver weights were increased as a result of feeding cholesterol and cholic acid. Liver cells sustained severe injury from fat infiltration. Myocardial cells, which were little affected from added cholesterol, became somewhat vaeuolated with areas of fiber degeneration when cholic acid was in the diet.Supported in part by Grant-in-Aid from The Nutrition Foundation, Inc.; State of Washington Initiative 171 Funds and USPHS Research Grant HD-02519 from the National Institutes of Health.     

Effect of exercise on Hepatic cholesterof of rats fed diets high in saturated or unsaturated fats

Summary Rats have been fed diets containing 24.2% coconut or corn oil or an equal mixture of each for 14–18 weeks. Half of the animals in each dietary group were exercised by running in motor-driven work wheels throughout the entire experimental period. During the final 10–14 weeks, these exercised animals ran continuously for 60 min at 1.0 mph or faster each day. Comparisons between sedentary groups revealed that hepatic cholesterol and excretion of digitonin precipitated sterols in the feces increased (P < 0.01) as the per cent of unsaturated fat (corn oil) in the ingested food increased. In contrast, total liver lipid decreased (P < 0.01) as the consumption of corn oil increased. No change in plasma cholesterol occurred in the sedentary rats in response to the three diets. Hepatic cholesterol of the exercised groups was significantly less (P < 0.05–P < 0.01) than that of their respective control groups (same diet). However, the group fed the corn oil diet had a significantly higher (P < 0.01) liver cholesterol after exercise than did the exercised group fed the coconut oil diet. Liver lipid was reduced (P < 0.01) by exercise in the corn oil and mixed corn-coconut oil fed groups. Plasma cholesterol and sterol excretion were unchanged by the exercise program.This investigation supported by Research Grant HE 08262 from the National Heart Institute, National Institutes of Health, U.S. Public Health Service.     

Food intake,body composition and blood lipids following treadmill exercise in male and female rats

Body weight gain, food intake, body composition and blood lipids of male and female Osborne Mendel rats were compared on the same exercise treadmill program. To mimic their nocturnal habits, rats were exercised daily at the beginning of the 12 hour dark cycle and food intake was measured for both light and dark cycles. After a 10 day treadmill adaptation period, the duration of exercise was successively increased over a 12 day period until 60 min/day at 21.3 meters/min was reached. Relative to their respective controls, exercised male rats showed a reduction in body weight and light cycle food intake while female runners showed no change in body weight or food intake. Exercise resulted in a decrease in percent body fat in both males and females while only male runners increased percent protein. Both males and females reduced serum triglycerides while serum cholesterol was reduced only in the males. The short term exercise program produced highly significant changes in the males while the females were more resistant to the same exercise regimen.     

Anti-hypercholesterolemic Effect of Melatonin in Rats

The effects on plasma lipids of daily intraperitoneal injections of 4mg of melatonin (N-acetyl-5-methoxytrypt-amine) for 10 27 day periods were examined biochemically and morphologically in rats fed regular and high-cholesterol (1% cholesterol, 0.5% cholic acid) diets. Melatonin administration had no significant effect on plasma lipids and lipoproteins in the rats on a normal diet but blunted the effects of a high-cholesterol diet on these parameters. No effects of melatonin on lipase activity were noted. Melatonin also diminished the fatty infiltration in the liver of animals on the high-cholesterol diet. The high-cholesterol diet produced major increases in VLDL and LDL cholesterol and protein content, and decreases in HDL cholesterol and protein. Melatonin decreased the extent of this plasma lipoprotein increase, although it did not completely prevent the phenomenon. Therefore, the effect is thought to be quantitative and not quantitative in nature. Acta Pathol Jpn 39: 613-618, 1989.     

Impact of exercise on blood lipids and lipoproteins

Abnormal blood lipids are a significant cardiovascular health risk. Drug therapy and diet continue to be standard management strategies. However, considerable evidence supports physical activity and exercise as having a positive impact on abnormal lipids and such are often recommended as adjunctive interventions. The purpose of this review is to clarify the mechanisms by which exercise facilitates favorable changes in levels of blood lipids and lipoproteins. Studies relative to the effects of exercise on blood lipid levels are notable: The impact of exercise on high-density lipoproteins (HDL-C) is best studied and specify effects of intensity and amount of exercise as well as a genetic influence. Exercise also exerts an effect on HDL-C maturation and composition, cholesterol efflux, and cholesterol delivery to receptors (reverse cholesterol transport). Positive effects of exercise are also seen with blood triglycerides (TG), but little specific effect is seen on low-density lipoprotein cholesterol (LDL-C) and total cholesterol (TC). Abundant evidence supports the benefits of exercise on levels of certain blood lipids (namely HDL-C and TG). Although standard management of abnormal blood lipids is drug therapy and diet, it seems prudent to incorporate aerobic exercise as an important component of a healthy lifestyle. In certain individuals, drug therapy may be decreased in dosage or perhaps discontinued in the patient who is "exercise trained," especially if there is associated weight loss.     

Creatine kinase isoenzyme profiles after exercise in the rat: sex-linked differences in leakage of CK-MM

Changes in creatine kinase (CK) activity and CK isoenzyme profiles in plasma after exercise were studied in rats in order to establish the source of the exercise-induced rise in CK activity. Male and female rats ran on a treadmill for 2 h and blood samples, taken before and after exercise, were assayed for total CK, CK isoenzymes and aminoaspartate transaminase (AST) activity. These enzymes were also assayed in homogenates of liver and several muscles. We found that the isoenzyme composition of liver, plasma and muscle did not differ between the sexes. However, the exercise-induced CK and AST responses did differ: CK and AST increased after exercise in males (101% and 15% resp.), but much less in females (47% and 1%). Although the isoenzyme profiles in rest did not differ, significant differences were observed after running: in males CK-MM inereased with 678%, but females only showed a 114% increase. In contrast, CK-BB showed a small increase that was about the same for both sexes (males 41%, females 35%). We conclude that both males and females show a small and similar increase in CK-BB activity after exercise, and that a large release of CK-MM from skeletal muscle, observed only in males, accounts for sex-linked differences reported earlier.     

Plasma lipid and lipoprotein levels in obese post-menopausal women: effects of a short-term low-protein diet and exercise

Obesity is associated with an increased prevalence of cardiovascular and cerebrovascular disease, probably mediated by the induction of an atherogenic lipid profile. Since few data are available concerning plasma lipid levels and the effects of short-term dieting on these parameters in obese postmenopausal women, we studied plasma lipid and lipoprotein levels in such women and also the effects on these levels of a short-term hypocaloric low-fat diet combined with a moderately intense physical exercise programme. Plasma triglycerides and low-density-lipoprotein cholesterol (LDL-C) levels were significantly higher, whereas high-density-lipoprotein cholesterol (HDL-C) and apoprotein A1 (ApoA1) levels, as well as the HDL-C/LDL-C and ApoA1/ApoB ratios, were significantly lower in moderately to severely obese women (Body Mass Index greater than 30, n = 26) than in non-obese post-menopausal controls. A short-term (4 week) protein-sparing modified fast diet, providing 400 calories (1675 J), resulted in a mean weight loss of 7.7 +/- 2.8 (S.D.) kg. While plasma cholesterol, LDL-C and ApoB levels decreased by approximately 25% and reached the levels recorded in normal controls, ApoA2 decreased by 20%. HDL-C and HDL2-C levels remained unchanged and as a consequence the HDL-C/LDL-C and the ApoA1/Apob ratios increased, indicating a shift towards a less atherogenic lipid profile. No correlation was observed between weight loss and changes in lipid or lipoprotein levels. It was concluded that a hypocaloric, low-fat diet combined with our physical exercise programme, resulted in the normalization of plasma lipids within 4 weeks.     

Sex-difference in the age related change of cholesterol metabolism in rats

In Sprague-Dawley rats at the ages of 5 weeks (young) and 9 months (adult), the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase in age-matched animals was significantly higher in females than in males. The magnitude of the age-related decrease in the reductase activity was also greater in female rats. When rats were fed a cholesterol-enriched (1%) diet for 30 h as cholesterol challenge, the reduction of reductase activity depended more on sex than on age. The activity of cholesterol 7 alpha-hydroxylase was also higher in female than in male rats and it apparently remained unchanged with age in female rats while it decreased in male rats. With a cholesterol-enriched diet, the hydroxylase exhibited a significant age- and sex-dependent difference and it increased only in young males and adult females. In male rats, the concentration of hepatic cholesterol was significantly higher in adult than in young rats while it was comparable in female rats. The increase in hepatic cholesterol with dietary cholesterol was observed only in male adult rats. A significant age-related difference was observed in the concentration of serum cholesterol. The results suggest an existence of sex-dependent compensatory mechanism for maintenance of hepatic cholesterol homeostasis with age.     

Effect of treadmill exercise on food intake and body weight in lean and obese rats

Body weight and food intake of lean and obese, male and female Osborne-Mendel rats following treadmill exercise were compared. Rats were assigned, separately by sex, to one of three diet groups; Group 1 was fed a low fat (10%) diet throughout the study, Group 2 was fed a high fat (55%) diet for 16 weeks and then switched to the low fat diet 1 week prior to exercise, and Group 3 was fed the high fat diet throughout the study. To control for differences in work output between the leanest and heaviest animals, exercise intensity was adjusted across groups such that all exercised rats had equivalent energy expenditure. After a 3 day training period, the exercise was successively increased over 8 days until a work output of 374.9J was reached. Relative to their respective controls, obese exercised males showed a reduction in body weight but no change in food intake. In contrast, exercised females showed no change in body weight or food intake, regardless of dietary condition.     

Alterations in hepatocytes of mice fed a gallstone-inducing diet: Occurrence of nuclear and cytoplasmic lipids

Mice fed a high cholesterol-cholic acid (lithogenic) diet for one year develop fatty livers in addition to gallstones. Light and electron micrographs demonstrate large amounts of lipids in liver parenchymal cells, often to the exclusion of most other cytoplasmic organelles. In addition, some hepatocytes exhibit nuclear lipid pseudo- and true inclusions. Other prominent features of hepatocytes after lithogenic diet include segregation of nucleolar granular and fibrillar material. Accumulation of considerable collagen in extracellular spaces is also noted. Observations suggest changes induced by the cholesterol diet are comparable to cytologic alterations seen in spontaneous and drug induced hepatic tumors, as well as to more general “fatty metamorphosis” of the liver.     

Alterations in hepatocytes of mice fed a gallstone-inducing diet: occurrence of nuclear and cytoplasmic lipids.

Mice fed a high cholesterol-cholic acid (lithogenic) diet for one year develop fatty livers in addition to gallstones. Light and electron micrographs demonstrate large amounts of lipids in liver parenchymal cells, often to the exclusion of most other cytoplasmic organelles. In addition, some hepatocytes exhibit nuclear lipid pseudo- and true inclusions. Other prominent features of hepatocytes after lithogenic diet include segregation of nucleolar granular and fibrillar material. Accumulation of considerable collagen in extracellular spaces is also noted. Observations suggest changes induced by the cholesterol diet are comparable to cytologic alterations seen in spontaneous and drug induced hepatic tumors, as well as to more general "fatty metamorphosis" of the liver.     

Anti-hypercholesterolemic effect of melatonin in rats

The effects on plasma lipids of daily intraperitoneal injections of 4 mg of melatonin (N-acetyl-5-methoxytryptamine) for 10-27-day periods were examined biochemically and morphologically in rats fed regular and high-cholesterol (1% cholesterol, 0.5% cholic acid) diets. Melatonin administration had no significant effect on plasma lipids and lipoproteins in the rats on a normal diet but blunted the effects of a high-cholesterol diet on these parameters. No effects of melatonin on lipase activity were noted. Melatonin also diminished the fatty infiltration in the liver of animals on the high-cholesterol diet. The high-cholesterol diet produced major increases in VLDL and LDL cholesterol and protein content, and decreases in HDL cholesterol and protein. Melatonin decreased the extent of this plasma lipoprotein increase, although it did not completely prevent the phenomenon. Therefore, the effect is thought to be quantitative and not qualititative in nature.     

Diet, plasma lipoproteins and experimental atherosclerosis in baboons (Papio sp.)

Diet-induced hyperlipidaemia in baboons is similar to that inhumans. As in humans, the ratio between low density lipoprotein(LDL) and high density lipoprotein (HDL) cholesterol is a majordeterminant of atherosclerosis. Baboons, like humans and othernon-human primates, vary in their lipaemic responses to dietarylipids. By selective breeding based on variability in plasmaand lipoprotein cholesterol response to diet, lines of baboonswith high and low responses of various lipoproteins have beendeveloped. Genetic analyses suggest that lipoprotein patternsin responses to dietary cholesterol and fat are heritable. Metabolicand molecular studies of high and low LDL and HDL cholesterolresponses to dietary lipids have suggested that different mechanismsregulate plasma LDL cholesterol on the chow and on the highcholesterol-high fat (HCHF) diet. On the chow diet, plasma LDLcholesterol levels are positively associated with cholesterolabsorption and negatively associated with hepatic LDL receptorlevels and, thus, cholesterol absorption and LDL receptors seemto regulate plasma LDL cholesterol levels. However, when theanimals consume a human-like fat- and cholesterol-enriched diet,plasma LDL cholesterol levels are not associated with eithercholesterol absorption or hepatic LDL receptor mRNA levels,but are negatively associated with plasma 27-hydroxycholesterolconcentrations, hepatic sterol 27-hydroxylase activity, andmRNA levels. Hepatic sterol 27-hydroxylase activity and mRNAlevels are induced by dietary cholesterol and fat in low respondingbaboons more than in high responding baboons. Thus, the abilityto induce sterol 27-hydroxylase determines the LDL cholesterolresponse in baboons. High HDL response baboons often have highlevels of HDL₁ in their plasma. Our studies suggest that theN-terminal fragment of apo C-I with 38 amino acids and a molecularweight of 4 kDa acts as a cholesteryl ester transfer inhibitorpeptide in high HDL₁ baboons. The inhibitor peptide associateswith apo A-1 in HDL to produce a modified apo A-1 protein witha molecular weight of 31 kDa. The inhibitor peptide is a geneproduct and the presence of this peptide produces an antiatherogenichigh HDL₁ phenotype.     

Administration of dehydroepiandrosterone enanthate to oophorectomized women - effects on sex hormones and lipid metabolism

Eight bilaterally oophorectomized women were given a depot injection of 200 mg DHEA-enanthate to study the effect on endocrine and lipid metabolism.

A decrease in sex-hormone binding globulin (SHBG) and an increase in androstenedione was found 14 and 30 days after the injection. No changes could be detected in LH, FSH, oestrone, oestradiol or oestriol. Testosterone showed a tendency towards an increase. As compared to pre-treatment values, plasma lipids were unaltered after 30 days. A decrease in high density lipoproteins (HDL), cholesterol and in very low density lipoproteins (VLDL), free cholesterol, total cholesterol and phospholipids were seen in the lipid composition of the lipoproteins on day 30. These findings are in agreement with previous data reported after the administration of drugs with androgen-like effects. The relative fatty acid composition of plasma lecithin revealed only minor changes while the fatty acid composition of cholesterol esters indicated a decreased portion of essential fatty acids. These results suggest, in agreement with previous studies, an impaired endogenous cholesterol formation in the liver. The results from the analysis of the fatty acid composition of lecithin and cholesterol esters might indicate a decreased percentage of exogenous (dietary) cholesterol ester in plasma.     

Ultrastructure of hepatic cholesterol crystals in the hypercholesterolemic - diabetic rat

The cellular morphology of lipid accumulation in the liver was examined in normal rats fed a diet containing cholesterol and cholic acid, and streptozotocin-diabetic rats fed the same diet. The cholesterol-fed non diabetic rats displayed moderate hypercholesterolemia (average cholesterol 317 mg/dl) whereas the cholesterol-fed diabetic rats exhibited severe hypercholesterolemia (cholesterol greater than 1300 mg/dl). Ultrastructural studies were performed on hepatic tissues following in situ fixation and water soluble embedment, which were used to reduce lipid extraction and minimize structural distortions. Although both groups exhibited hepatocyte lipid droplets, the accumulation was markedly accentuated in the diabetic animals. The Kupffer cells of the diabetic animals contained cytosolic lipid crystals that were membrane delimited and showed lattice ordering 3.9 +/- 2.2 nm periodicity. These findings suggest that cholesteryl ester crystals of the cholesteric phase, similar to those found in atherosclerotic lesions, may form in other cellular foci exposed to abnormally high plasma lipid levels.     

Coenzyme A and hyperlipoproteinaemias

Coenzyme A (CoA) exerts a favourable effect in lowering plasma lipids in patients with primary hyperlipoproteinaemias of phenotype IV (hypertriglyceridaemia) and of phenotype IIb (combined hyperlipidaemia). The mechanism by which CoA influences plasma lipids may be associated with the well-known role of this coenzyme in the catalysis of acylation reactions and in the control of lipid metabolism. The administration of CoA in animals fed on hyperlipidaemic diets reduces plasma lipid levels and causes a reduction of the hepatic concentrations of triglycerides and/or lipids. Mitochondria and peroxisomes isolated from liver of rats fed on a hyperlipidaemic diet and treated with CoA present an increased oxidation of palmitate. These results suggest that the primary effect of CoA is to increase fatty-acid oxidation in the liver that results in a decrease in endogenous synthesis of triglycerides as well as a reduced formation of VLDL and probably of cholesterol. The stimulation of fatty-acid oxidation in extrahepatic tissues may be also responsible for an increased catabolism of VLDL.     

N-nitrosodiethylamine-induced toxicity in relation to oxidative stress and development of atherosclerosis in hypercholesterolemic diet-fed rabbits

N-nitrosodiethylamine (NDEA) is an important carcinogenic nitrosamine frequently present in human environment, besides being a part of the human food chain by virtue of its reported presence in various foodstuffs and beverages. This study was planned to investigate the toxicity of NDEA in relation to the development of atherosclerosis in experimental rabbits. Oral administration of NDEA at 50 mg per day along with hypercholesterolemic diet to rabbits resulted in significant increase in osmotic fragility of erythrocytes as well as increased in vitro lipid peroxidation (LPO) of erythrocytes. The plasma total lipids, cholesterol and glycerides continued to increase during the feeding of hypercholesterolemic diet with or without NDEA. However, after the cessation of hypercholesterolemic diet, decrease in the lipid fractions was relatively less in the experimental group receiving NDEA. Administration of NDEA in the hypercholesterolemic diet did not affect the total lipid content in the liver, although it marginally increased the hepatic cholesterol levels. Histopathological changes in different tissues (heart, aorta and liver) were relatively more severe in experimental rabbits receiving NDEA treatment as compared to the control ones. Our study therefore indicates that oral administration of NDEA results in increased LPO of blood and decreased lipid clearance, which may in turn result in increased degree of atherosclerosis.