Comparative hypocholesterolemic effects of six dietary oils in cholesterol-fed rats after long-term feeding

Rats (8 wk of age) fed a conventional diet were shifted to diets containing 10% Oenothera biennis Linn oil (OBLO, linoleic acid +γ-linolenic acid) from a wild plant, evening primrose oil (EPO, linoleic acid +γ-linolenic acid) from a cultivated plant, bio-γ-linolenic acid oil from mold (BIO, palmitic acid+oleic acid+linoleic acid+γ-linolenic acid), safflower oil (linoleic acid), palm oil (PLO, palmitic acid+oleic acid+linoleic acid), or soybean oil (linoleic acid+α-linolenic acid) with 0.5% cholesterol for 13 wk. Though there were no significant differences in the food intake among the groups, the body weight gain of the OBLO group was significantly lower than that of other groups except for the BIO and PLO groups, and that of the EPO and SPO groups were the highest among the groups. The liver weight of the OBLO group was significantly lower than that of other groups, and that of the PLO group was the highest among the groups. The serum total cholesterol and very low density lipoprotein (VLDL)+intermediate density lipoprotein (IDL)+low density lipoprotein (LDL) cholesterol concentrations of the OBLO and EPO groups were consistently lower than those in the other groups. However, those of the BIO group were higher than those in the OBLO and EPO groups. The liver cholesterol concentration of the PLO group was the highest among all groups except for the EPO group. The fecal neutral sterol and bile acid extraction of the BIO group tended to increase compared to other groups. The results of this study demonstrate that OBLO and EPO inhibit the increasing of serum total cholesterol and VLDL+IDL+LDL-cholesterol concentrations in the presence of excess cholesterol in the diet compared with the other dietary oils.     

Effects of diets enriched in n−6 or n−3 fatty acids on cholesterol metabolism in older rats chronically fed a cholesterol-enriched diet

Hypocholesterolemic effects in older animals after long-term feeding are unknown. Therefore, aged rats (24 wk of age) fed a conventional diet were shifted to diets containing 10% perilla oil [PEO; oleic acid+linoleic acid+α-linolenic acid; n−6/n−3, 0.3; polyunsaturated fatty acid/saturated fatty acid (P/S), 9.6], borage oil [oleic acid+linoleic acid+α-linolenic acid; n−6/n−3, 15.1; P/S, 5.3], evening primrose oil (FPO; linoleic acid+γ-linolenic acid; P/S, 10.5), mixed oil (MIO; oleic acid+linoleic acid+γ-linolenic acid+α-linolenic acid; n−6/n−3, 1.7; P/S, 6.7), or palm oil (PLO; palmitic acid+oleic acid+linoleic acid; n−6/n−3, 25.3; P/S, 0.2) with 0.5% cholesterol for 15 wk in this experiment. There were no significant differences in the food intake and body weight gain among the groups. The liver weight in the PEO (n−6/n−3, 0.3) group was significantly higher than those of other groups in aged rats. The serum total cholesterol and very low density lipoprotein (VLDL) +intermediate density lipoprotein (IDL)+low density lipoprotein (LDL)-cholesterol concentrations of the PLO (25.3) group were consistently higher than those in the other groups. The serum high density lipoprotein cholesterol concentrations of the PEO (0.3) and EPO groups were significantly lower than in the other groups at the end of the 15-wk feeding period. The liver cholesterol concentration of the PLO (25.3) group was significantly higher than those of other groups. There were no significant differences in the hepatic LDL receptor mRNA level among the groups. Hepatic apolipoprotein (apo) B mRNA levels were not affected by the experimental conditions. The fecal neutral steroid excretion of the PLO (25.3) group tended to be low compared to the other groups. The results of this study demonstrate that both n\t-6 fatty acid and n\t-3 fatty acids such as \gg-linolenic acid and \ga-linolenic acid inhibit the increase of serum total cholesterol and VLDL+IDL+LDL-cholesterol concentrations of aged rats in the presence of excess cholesterol in the diet compared with dietary saturated fatty acid.     

Comparative hypocholesterolemic effects of six vegetable oils in cholesterol-fed rat

The hypocholesterolemic efficacies of various polyunsaturated fatty acids were compared in rats given cholesterol-enriched diets.Oenothera biennis Linn oil (OBLO, linoleic +γ-linolenic), sunflower oil (linoleic), palm oil (PLO, oleic+linoleic), soybean oil (linoleic+α-linolenic), high-oleic safflower oil (oleic+linoleic), or mixed oil (linoleic+α-linolenic) was added to the diet at 200 g/kg (20% groups). OBLO was also added at 100 g/kg diet (10% group). The serum total and very low density lipoprotein+intermediate lipoprotein+low density lipoprotein cholesterol concentrations of the 10 and 20% OBLO groups were consistently lower than those in the other groups. The liver cholesterol concentration in the PLO group was lower in all groups. The liver cholesterol concentrations in the 10 and 20% OBLO groups were also lower than in the other groups. There were no significant differences in the fecal neutral sterol and bile acid extraction among groups.     

Effects of dietary linseed oil and marine oil on lipid peroxidation in monkey liverin vivo andin vitro

Diets rich in linoleic acid (CO) from corn oil, or in linoleic acid and either α-linolenic acid (LO) based on linseed oil or n−3 fatty acids (MO) from menhaden oil were fed to male and female Cynomolgus monkeys for 15 wk. In the liver a 40% reduction of α-tocopherol occurred in the MO group relative to the CO and LO groups followed by increased formation of lipofuscinin vivo. A four-fold increase of α-tocopherol in the MO diet (MO+E) brought the level in the liver to that found with CO and LO. The increased peroxidation in the MO group in the liver phospholipids was associated with the replacement of 60% of the n−6 fatty acids by n−3 fatty acids from menhaden oil. Similar fatty acid profiles were found in groups fed MO and MO+E, respectively. Compared to the CO fed group, feeding α-linolenic acid only resulted in a slight incorporation of n−3 fatty acids in the liver membranes mainly due to a direct incorporation of α-linolenic acid. However, in monkeys fed menhaden oil more than 30% of the total fatty acids in the liver phospholipids were n−3 fatty acids. The various diets did not influence the activity of liver catalase (EC 1.11.1.6) nor superoxide dismutase (EC 1.15.1.1), but glutathione-peroxidase activity (EC 1.11.1.9) was higher in monkeys fed the MO diet. The catalase activity in females was 20% higher than in males. In anin vitro assay, liver microsomes from monkeys fed the MO diet or the MO diet supplemented with tocopherol produced similar amounts of thiobarbituric acid reactive substances and at a much higher rate than microsomes from the CO and LO groups. It appeared that α-tocopherol did not protect long-chain n−3 C₂₀ and C₂₂ fatty acids as well as n−6 fattya acids against peroxidation. The present data showed that monkeys were not fully able to compensate for increased peroxidative stress but a four-fold supplement of vitamin E to the diets reduced the oxidation.     

The effect of dietary supplementation of cholesterol and its subsequent withdrawal on the liver lipids and serum lipoproteins of chickens

Two groups of male chickens were fed either a control diet (group N) containing a standard poultry ration admixed with 10% corn oil or a cholesterol diet (group C) in which the control diet was supplemented with 1% cholesterol. After 6 weeks on the diets, a negligible amount of very low density lipoprotein (VLDL) was found in the serum from control animals. On the other hand, the serum VLDL from the cholesterol-fed birds was the predominant lipoprotein and carried 72% of the total serum lipids. Surprisingly this lipoprotein from cholesterol-fed animals was very low in triglycrides (6%) and high in total cholesterol (77%). While the level of serum low density liporotein was unaffected by the ingestion of cholesterol, the concentration of total lipids and phospholipids in the high density lipoprotein decreased in cholesterol-fed animals. The greatest change in liver lipids from animals fed cholesterol was found in the cholesterol esters, whereas the unesterified cholesterol, triglyceride and phospholipid varied slightly or remained constant. In normal animals the distribution of cholesterol between the liver and the serum was about equal, whereas in the cholesterol-fed birds the liver accounted for 80% of the cholesterol found in the liver-serum pool. In order to determine how the hypercholesterolemic bird responds to the withdrawal of cholesterol from the ration, a diet-exchange experiment was conducted. In this study the birds that were originally fed the cholesterol diets (group C) for 6 weeks were placed on the control diet (group CN) and the birds fed the control diet (group N) for 6 weeks were given the cholesterol diet (group NC). At periodic intervals, 1, 3, 7 and 14 days following the change of diets, 3–5 animals from each group were sacrificed, and analyses performed on their serum lipoproteins and liver lipids. Within one day after the diet substitution, there was a 31-fold increase and a 46% decrease, respectively, in the serum VLDL concentration in groups NC and CN as compared with their corresponding steady state values (groups N and group C, respectively). The liver cholesterol increased 4-fold and decreased 40%, respectively, in the two groups NC and CN as compared with the values obtained before the diet substitution. It is suggested that the concentration of cholesterol in the liver is the principal factor controlling cholesterol metabolism in chickens fed a hypercholesterolemic diet. This represents a portion of a Ph.D. thesis submitted by A.W. Kruski to the University of Illinois in February 1971.     

Dietary effect of gamma-linolenic acid on the lipid profile of rat fed erucic acid rich oil

This study evaluated the effects of dietary supplementation of gamma-Linolenic acid (18:3n-6, GLA) on the lipid profile of serum and other tissues of rats fed erucic acid (C22:1) rich oil like mustard oil. The rats were fed diet containing 20% mustard oil as erucic acid rich oil and 20% groundnut oil as dietary fat. These groups were kept as reference groups. Another group fed diet containing 20% fat to which evening primrose oil as a source of GLA was blended with mustard oil and groundnut oil at 5% level. The feeding experiment was done for 4 weeks. In another set mustard oil fed group was kept as control while the experimental group was fed evening primrose oil as a source of GLA blended with mustard oil at 2.5% level. The feeding experiment was carried out for 12 weeks. The other dietary components remained same for all the groups. After the scheduled feeding period, it was found that there was no significant change in weight gain, food intake and food efficiency ratio. It was found that dietary GLA resulted in significant decrease in serum triglyceride (TG) and very low density lipoprotein (VLDL) cholesterol and significant increase in high density lipoprotein (HDL) cholesterol in serum in the experimental group. In liver total cholesterol (TC) is significantly higher and in heart and liver TG is significantly lower in GLA fed group.     

Rice bran oil and hypocholesterolemia in rats

Rats fed rice bran oil at 10% level for a period of eight weeks showed significantly lower levels of total cholesterol, low density lipoprotein and very low density lipoprotein cholesterol, both on cholesterol-containing and cholesterol-free diets. High density lipoprotein cholesterol was increased but triglyceride showed a decrease that was not statistically significant. Liver cholesterol and liver triglycerides were also reduced. Fecal excretion of neutral sterols and bile acids was increased after ingestion of rice bran oil.     

Enzyme-resistant fractions of beans lowered serum cholesterol and increased sterol excretions and hepatic mRNA levels in rats

Feeding rats beans with resistant starch reduces their serum cholesterol concentration; however, the mechanism by which this occurs is not fully understood. We examined the effects of enzyme-resistant fractions of adzuki (Vigna angularis) and tebou (Phaseolus vulgaris, var.) beans on serum cholesterol and hepatic mRNA in rats. Rats were fed a cholesterol-free diet with 50 g of cellulose powder (CP)/kg, 50 g of an enzyme-resistant fraction of adzuki starch (AS)/kg, or 50 g of an enzyme-resistant fraction of tebou starch (TS)/kg diet for 4 wk. There were no significant differences in body weight, liver weight, and cecum contents among the groups, nor was there a significant difference in food intake among the groups. The levels of serum total cholesterol, VLDL + intermediate density lipoprotein + LDL-cholesterol, and HDL cholesterol in the AS and TS groups were significantly (P<0.05) lower than in the CP group throughout the feeding period. Total hepatic cholesterol in the CP group was significantly (P<0.05) lower than in the AS and TS groups, fecal cholesterol excretion in the TS group was significantly (P<0.05) greater than in the CP and AS groups, and the fecal total bile acid concentrations in the AS and TS groups were significantly (P<0.05) higher than in the CP group. Cecal acetate, propionate, and n-butyrate concentrations in the AS and TS groups were significantly (P<0.05) higher than in the CP group. The level of hepatic scavenger receptor class B1 (SR-B1) mRNA in the TS group was significantly (P<0.05) higher than in the CP group, and the levels of hepatic cholesterol 7α-hydroxylase mRNA in the AS and TS groups were significantly (P<0.05) higher than in the CP group. These results suggest that AS and TS have a serum cholesterol-lowering function due to the enhanced levels of hepatic SR-B1 and cholesterol 7α-hydroxylase mRNA.     

Effects of dietary lipids on daunomycin-induced nephropathy in mice: comparison between cod liver oil and soybean oil

Although it is well known that dietary lipids affect the course of glomerulonephritis in rats and humans, the precise mechanisms involved have not been fully elucidated. The aim of this study was to investigate the effects of different types of dietary lipids (fish oil and vegetable oil) on daunomycin (DM)-induced nephropathy in mice fed on soybean oil (SO) or cod liver oil (CLO). Urinary protein excretion, serum albumin, creatinine, total cholesterol, and TG were measured, and glomerular histological changes were evaluated. Antioxidant enzymes were also measured, along with the levels of lipid peroxide, GSH, thromboxane (Tx) B_2′ and 6-keto prostaglandin F_1α in renal cortical tissue. Dietary CLO significantly reduced urinary albumin excretion and ameliorated the histological changes induced by DM. The increase of tissue lipid peroxide levels seen in SO-fed mice was suppressed in CLO-fed mice, whereas CLO-fed mice showed higher GSH levels than SO-fed mice throughout the experiment. In addition, renal tissue GSH peroxidase activity was significantly higher at 72 h after DM injection in CLO-DM mice than in SO-DM mice. Both renal cortical TxB₂ and 6-keto PGF_1α levels were significantly lower in CLO-DM mice than in SO-DM mice. These results suggest that inhibition of oxidative damage by dietary CLO played an important role in the prevention of DM nephropathy in this mouse model. The effect of CLO was closely associated with the inhibition of Tx synthesis.     

Lipid metabolism and tissue composition in Atlantic salmon (Salmo salar L.)—Effects of capelin oil, palm oil, and oleic acid-enriched sunflower oil as dietary lipid sources

Triplicate groups of Atlantic salmon (Salmo salar L.) were fed four diets containing different oils as the sole lipid source, i.e., capelin oil, oleic acid-enriched sunflower oil, a 1∶1 (w/w) mixture of capelin oil and oleic acid-enriched sunflower oil, and palm oil (PO). The β-oxidation capacity, protein utilization, digestibility of dietary fatty acids and fatty acid composition of lipoproteins, plasma, liver, belly flap, red and white muscle were measured. Further, the lipid class and protein levels in the lipoproteins were analyzed. The different dietary fatty acid compositions did not significantly affect protein utilization or β-oxidation capacity in red muscle. The levels of total cholesterol, triacylglycerols, and protein in very low density lipoprotein (VLDL), low density lipoprotein (LDL), high density lipoprotein (HDL), and plasma were not significantly affected by the dietary fatty acids. VLDL, LDL, and HDL fatty acid compositions were decreasingly affected by dietary fatty acid composition. Dietary fatty acid composition significantly affected both the relative fatty acid composition and the amount of fatty acids (mg fatty acid per g tissue, wet weight) in belly flap, liver, red and white muscle. Apparent digestibility of the fatty acids measured by adding yttrium oxide as inert marker, was significantly lower in fish fed the PO diet compared to the other three diets.     

Hypercholesterolemia and triglyceride secretion rates in monkeys fed different dietary fats

The influence of hypercholesterolemia on the triglyceride secretion rate was studied in both squirrel and cebus monkeys fed coconut oil, corn oil, or safflower oil. The triglyceride secretion rate (TGSR) was determined in vivo following the administration of Triton WR1339, which blocks the clearance of very low density lipoprotein (VLDL). Thus, the increase observed in circulating triglyceride after Triton administration presumably reflects hepatic triglyceride (VLDL) secretion in the fasted state. The VLDL-TGSR was lowest in hypercholesterolemic monkeys and highest in those fed unsaturated fat diets and having a low serum cholesterol. In all instances, TGSR was inversely correlated with the plasma cholesterol concentration. While a definitive explanation for these observations must await further investigation, the possibility that circulating low density lipoprotein (LDL) acts to feed back on VLDL secretion is discussed. The decreased TGSR associated with the diet-induced cholesterolemia also implies clearance of VLDL is impaired under these conditions.     

Serum lipids in spontaneously hypertensive rats and sprague-dawley rats fed menhaden oil

Dietary n-3 fatty acids, abundant in fish oil, exert a variety of effects that attenuate cardiovascular disease. In this study, we assessed the effect of fish oil (menhaden oil) on the serum lipid profile in hypertensive and normotensive rats. Spontaneously hypertensive rats (SHR) or Sprague-Dawley rats (SD) were fed either standard powdered diet (L-485), or L-485+5% menhaden oil (MO) or L-485+5% corn oil (CO) from weaning through eight months of age. Systolic blood pressure (BP) was periodically determined on SHR. Serum lipid profiles were performed at eight months on sample taken from the exposed hearts of anesthetized, fasted rats. SHR, compared with SD (diets combined) had significantly lower triaclyglycerols (TG), higher cholesterol (CHOL), higher high density lipoprotein cholesterol (HDL CHOL), higher low density lipoprotein cholesterol (LDL CHOL), and a higher LDL:HDL ratio. Comparison among diets (strains combined) revealed that rats fed MO had the lowest values for TG, CHOL, LDL and LDL:HDL; HDL did no vary with diet. SHR were less responsive to diet-induced changes than were SD; no decrease in TG, LDL or LDL:HDL was observed in SHR, nor was degree of hypertension altered in SHR by the MO or CO diet. In summary, MO is more effective than CO in shifting the lipid profile of rats toward one that is less atherogenic. However, the SD rat is more susceptible to diet-induced lipid modification than is the SHR.     

l-Carnitine effects on chemical composition of plasma lipoproteins of rabbits fed with normal and high cholesterol diets

l-Carnitine plays an important role in the mitochondrial uptake of long-chain fatty acids in mammals. It has recently been shown that this compound has a marked hypo-cholesterolemic effect when used in conjunction with lipid-rich diets. The aim of this study was to investigate the effects of l-carnitine on the fatty acid composition of plasma lipoproteins in rabbits fed with different diets. Four different groups were investigated: group I (standard diet), group II (standard diet supplemented with l-carnitine at 80 mg/kg), group III (standard diet supplemented with 0.5% cholesterol), and group IV (standard diet supplemented with 0.5% cholesterol plus l-carnitine at 80 mg/kg). The feeding period was 126 d. Total plasma cholesterol was indistinguishable in groups I and II, but increased nearly 40-fold in group III. This increment was reduced by 50% in group IV. Correspondingly, total cholesterol content in lipoprotein fractions [very low density lipoprotein (VLDL), low density lipoprotein (LDL), high density lipoprotein (HDL) separated by agarose gel chromatography was the same for groups I and II, while for animals fed a cholesterol-rich diet (III) total cholesterol in VLDL+LDL increased nearly 100-fold when compared with groups I and II but, again, the increment was reduced by 50% in group IV. In contrast, total cholesterol in HDL increased only fivefold for both groups III and IV when compared with groups I and II, indicating no effects of l-carnitine on this parameter. The reduction of total cholesterol in VLDL+LDL particles in animals fed a cholesterol-rich diet plus l-carnitine was associated with a marked decrease in the ratio of cholesteryl ester to free cholesterol and a dramatic increase in their phospholipid content; opposite effects were observed for HDL. l-Carnitine induced a marked decrease in the saturated to unsaturated C₁₆+C₁₈ fatty acid ratio in cholesteryl esters associated with VLDL and LDL from animals fed with both normal and cholesterol-rich diets. The opposite effect (a large increase in the saturated to unsaturated fatty acid ratio) was observed for both cholesteryl esters and phospholipids associated with HDL in animals fed with both diets. The results suggested that the hypocholesterolemic effects of l-carnitine could be associated with increased systemic breakdown of cholesteryl esters, a probable increase in reverse cholesterol transport, and the stabilization of a phospholipid-based structure of VLDL+LDL particles.     

Dietary squalene increases tissue sterols and fecal bile acids in the rat

Feeding 1% squalene increased markedly the concentrations of squalene and methyl sterols in each serum lipoprotein class, intestinal mucosa, liver and also in adipose tissue. It also increased cholesterol concentration of the liver and serum VLDL, and esterified cholesterol in serum LDL as well as fecal bile acids. The results suggest that absorbed dietary squalene contributes to some extent to the squalene content of adipose tissue, effectively increases the overall cholesterol synthesis and enhances cholesterol elimination preferentially as fecal bile acids.     

Oxidative susceptibility of low density lipoprotein from rabbits fed atherogenic diets containing coconut,palm, or soybean oils

The oxidative susceptibilities of low density lipoproteins (LDL) isolated from rabbits fed high-fat atherogenic diets containing coconut, palm, or soybean oils were investigated. New Zealand white rabbits were fed atherogenic semisynthetic diets containing 0.5% cholesterol and either (i) 13% coconut oil and 2% corn oil (CNO), (ii) 15% refined, bleached, and deodorized palm olein (RBDPO), (iii) 15% crude palm olein (CPO), (iv) 15% soybean oil (SO), or (v) 15% refined, bleached, and deodorized palm olein without cholesterol supplementation [RBDPO(wc)], for a period of twelve weeks. Total fatty acid compositions of the plasma and LDL were found to be modulated (but not too drastically) by the nature of the dietary fats. Cholesterol supplementation significantly increased the plasma level of vitamin E and effectively altered the plasma composition of long-chain fatty acids in favor of increasing oleic acid. Oxidative susceptibilities of LDL samples were determined by Cu²⁺-catalyzed oxidation which provide the lag times and lag-phase slopes. The plasma LDL from all palm oil diets [RBDPO, CPO, and RBDPO(wc)] were shown to be equally resistant to the oxidation, and the LDL from SO-fed rabbits were most susceptible, followed by the LDL from the CNO-fed rabbits. These results reflect a relationship between the oxidative susceptibility of LDL due to a combination of the levels of polyun-saturated fatty acids and vitamin E. Based on a paper presented at the PORIM International Palm Oil Congress (PIPOC) held in Kuala Lumpur, Malaysia, 1993.     

Response of plasma lipids to dietary cholesterol and wine polyphenols in rats fed polyunsaturated fat diets

This experiment was designed to evaluate the effects of dietary red wine phenolic compounds (WP) and cholesterol on lipid oxidation and transport in rats. For 5 wk, weanling rats were fed polyunsaturated fat diets (n−6/n−3=6.4) supplemented or not supplemented with either 3 g/kg diet of cholesterol, 5 g/kg diet of WP, or both. The concentrations of triacylglycerols (TAG, P<0.01) and cholesterol (P<0.0002) were reduced in fasting plasma of rats fed cholesterol despite the cholesterol enrichment of very low density lipoprotein + low density lipoprotein (VLDL+LDL). The response was due to the much lower plasma concentration of high density lipoprotein (HDL) (−35%, P<0.0001). In contrast, TAG and cholesteryl ester (CE) accumulated in liver (+120 and +450%, respectively, P<0.0001). However, the cholesterol content of liver microsomes was not affected. Dietary cholesterol altered the distribution of fatty acids mainly by reducing the ratio of arachidonic acid to linoleic acid (P<0.0001) in plasma VLDL+LDL (−35%) and HDL (−42%) and in liver TAG (−42%), CE (−78%), and phospholipids (−28%). Dietary WP had little or no effect on these variables. On the other hand, dietary cholesterol lowered the α-tocopherol concentration in VLDL+LDL (−40%, P<0.003) and in microsomes (−60%, P<0.0001). In contrast, dietary WP increased the concentration in microsomes (+21%, P<0.0001), but had no effect on the concentration in VLDL+LDL. Cholesterol feeding decreased (P<0.006) whereas WP feeding increased (P<0.0001) the resistance of VLDL+LDL to copper-induced oxidation. The production of conjugated dienes after 25 h of oxidation ranged between 650 (WP without cholesterol) and 2,560 (cholesterol without WP) μmol/g VLDL+LDL protein. These findings show that dietary WP were absorbed at sufficient levels to contribute to the protection of polyunsaturated fatty acids in plasma and membranes. They could also reduce the consumption of α-tocopherol and endogenous antioxidants. The responses suggest that, in humans, these substances may be beneficial by reducing the deleterious effects of a dietary overload of cholesterol.     

Eicosanoid synthesis in 7,12-dimethylbenz(a)anthracene-induced mammary carcinomas in Sprague-Dawley rats fed primrose oil,menhaden oil or corn oil diet

The comparative effects of high-fat diets (20%, w/w) on eicosanoid synthesis during mammary tumor promotion in 7,12-dimethylbenz(a)anthracene (DMBA)-induced rats were studied using diets containing 20% primrose oil (PO), 20% menhaden oil (MO) or 20% corn oil (CO). Sprague-Dawley rats fed the PO or MO diet had 21% or 24% fewer adenocarcinomas, respectively, than rats fed the CO diet. Histologically (i.e., mitotic figures, inflammatory cell infiltration and necrosis), the CO-fed rats exhibited the highest frequency of changes within tumors. Plasma fatty acid composition was significantly altered by diet, reflecting the composition of the oils which were being fed. Only the plasma of PO-fed rats contained detectable levels of gamma-linolenic acid (GLA). Arachidonic acid (AA) levels were significantly higher (p<0.05) in PO-fed than in CO- or MO-fed rats. MO-fed rats had significantly higher levels of plasma palmitic acid, while palmitoleic, eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids were detected only in MO-fed rats. As expected, linoleic acid (LA) and AA levels were lower (p<0.05) in the MO-fed rats than in PO- or CO-fed groups. The plasma of the CO-fed rats contained significantly higher levels of oleic acid. Eicosanoid synthesis in mammary carcinomas of rats fed the 20%-fat diets was 2–10 times higher than in mammary fat pads of control rats. The synthesis of PGE₁ and LTB₄ was significantly (p<0.05) higher in PO-fed rats than in CO-fed or MO-fed rats, although PGE values were significantly (p<0.05) higher in CO-fed rats than in Mo or PO groups. The synthesis of eicosanoids in both mammary fat pads and mammary carcinomas of MO-fed rats was lower (p<0.05) than in tissues of rats fed either CO or PO diets due to less AA precursor being fed and/or to competition between n−6 and n−3 fatty acids for cyclooxygenase and lipoxygenase. The ratios of monoenoic to dienoic eicosanoids in both mammary fat pads and mammary carcinomas were higher in the PO group than in the MO or CO groups. These results suggest that inclusion of GLA (PO feeding) or EPA and DHA (MO feeding) in the diet may decrease malignancy by altering eicosanoid profiles.     

Vitamin E inhibits fish oil-induced hyperlipidemia and tissue lipid peroxidation in hamsters

Previous research has linked hyperlipidemia with increased serum concentrations of lipid peroxidation products; however, a specific association between diet-induced oxidative stress and hyperlipidemia has not been studied. In the present study, the relationship between tissue lipid peroxidation and hyperlipidemia induced by ingestion of fish oil was examined. In Experiment 1, male Golden Syrian hamsters were fed semipurified diets composed of 1.6 wt% safflower oil plus 15.0 wt% of either butterfat (BF), safflower oil (SAFF), or high-cholesterol menhaden oil [MHO(H-CHOL)] semipurified diets for 27 d. The cholesterol contents of the diets were adjusted to 0.088%. The MHO(H-CHOL)-fed hamsters exhibited higher serum concentrations of total cholesterol, triglycerides, apolipoprotein B, and lipid peroxides when compared to the BF and SAFF diet groups. In a further study (Experiment 2), hamsters were fed for 27 d three dietary treatments: (i) MHO(H-CHOL) with no vitamin E content; (ii) a low-cholesterol menhaden oil containing high concentrations of vitamin E (2.5 mg tocopherol/g oil or dietary concentrations of 375 mg/kg) [MHO(L-CHOL)+E]; and (iii) the MHO(L-CHOL+E) with added cholesterol (595 mg/kg) [MHO(L-CHOL)+CHOL+E] to match the cholesterol content of the MHO(H-CHOL). The MHO(L-CHOL)+E and MHO(L-CHOL)+CHOL+E diet groups showed lower concentrations of serum cholesterol, triglycerides, and hepatic lipid peroxides than the MHO(H-CHOL)-treated group. Moreover, in contrast to the hypercholesterolemia caused by the MHO(H-CHOL) feeding, the MHO(L-CHOL)+E and MHO(L-CHOL)+CHOL+ E diets did not show a serum cholesterol-elevating action. This study supports the hypothesis that oxidative stress in the Syrian hamster could play a causal role in dietary-induced hyperlipidemia which can be inhibited by high vitamin E intake.     

Dietary saturated fat level alters the competition between α-linolenic and linoleic acid

Male weanling rats were fed semi-synthetic diets high in saturated fat (beef tallow) vs high in linoleic acid (safflower oil) with or without high levels of α-linolenic acid (linseed oil) for a period of 28 days. The effect of feeding these diets on cholesterol content and fatty acid composition of serum and liver lipids was examined. Feeding linseed oil with beef tallow or safflower oil had no significant effect on serum levels of cholesterol. Serum cholesterol concentration was higher in animals fed the safflower oil diet than in animals fed the beef tallow diet without linseed oil. Feeding linseed oil lowered the cholesterol content in liver tissue for all dietary treatments tested. Consumption of linseed oil reduced the arachidonic acid content with concomitant increase in linoleic acid in serum and liver lipid fractions only when fed in combination with beef tallow, but not when fed with safflower oil. Similarly, ω3 fatty acids (18∶3ω3, 20∶5ω3, 22∶5ω3, 22∶6ω3) replaced ω6 fatty acids (20∶4ω6, 22∶4ω6) in serum and liver lipid fractions to a greater extent when linseed oil was fed with beef tallow than with safflower oil. The results suggest that the dietary ratio of linoleic acid to saturated fatty acids or of 18∶3ω3 to 18∶2ω6 may be important to determine the cholesterol and arachidonic acid lowering effect of dietary α-linolenic acid.     

Comparative study of the blood pressure effects of four different vegetable fats on young,spontaneously hypertensive rats

Following the suckling period, four groups of male four-week-old spontaneously hypertensive rats (SHR) were fed semisynthetic diets with 14% (by weight) of either sunflower seed oil [46% 18∶2(n−6); linoleic acid (LA)-rich], linseed oil [62.5% 18∶3(n−3)+12.9% 18∶2(n−6); α-linolenic acid (LNA)-rich], evening primrose oil [9.2% 18∶3(n−6)+71% 18∶2(n−6); γ-linolenic acid (LNA)-rich] or hydrogenated palm kernel fat [1.5% 18∶2(n−6); polyunsaturated fatty acid (PUFA)-deficient], respectively, up to an age of 18 wk. All diets enriched with PUFA provoked an attenuation of hypertension development. The effect was lowest in the LA-rich group and highest in the γ-LNA-rich group. Differences in fatty acid composition of renal phospholipids between groups reflect the fatty acids present in the respective dietary fats. Renomedullary production of PGF_2α was significantly reduced in α-LNA-rich and slightly diminished in γ-LNA-rich fed rats. Aortic formation of 6-keto-PGF_1α and TXB₂ was increased in animals fed the γ-LNA-rich diet. Thus, the attenuation of hypertension development cannot be explained only by changes in prostanoid formation. Other mechanisms possibly involved should be pursued.