Butter-enriched diets reduce arterial prostacyclin production in rats

What is the role of alpha-linolenic acid for mammals?

This review examines the data pertaining to an important and often underrated EFA, alpha-linolenic acid (ALA). It examines its sources, metabolism, and biological effects in various population studies, in vitro, animal, and human intervention studies. The main role of ALA was assumed to be as a precursor to the longer-chain n-3 PUFA, EPA and DHA, and particularly for supplying DHA for neural tissue. This paper reveals that the major metabolic route of ALA metabolism is beta-oxidation. Furthermore, ALA accumulates in specific sites in the body of mammals (carcass, adipose, and skin), and only a small proportion of the fed ALA is converted to DHA. There is some evidence that ALA may be involved with skin and fur function. There is continuing debate regarding whether ALA has actions of its own in relation to the cardiovascular system and neural function. Cardiovascular disease and cancer are two of the major burdens of disease in the 21st century, and emerging evidence suggests that diets containing ALA are associated with reductions in total deaths and sudden cardiac death. There may be aspects of the action and, more importantly, the metabolism of ALA that need to be elucidated, and these will help us understand the biological effects of this compound better. Additionally, we must not forget that ALA is part of the whole diet and should be seen in this context, not in isolation.

The anhydrous milk fat, ghee, lowers serum prostaglandins and secretion of leukotrienes by rat peritoneal macrophages

Ghee, the anhydrous milk fat, is one of the most important sources of dietary fat in India. Male Wistar rats were fed diets containing 2.5, 5.0 and 10 wt% ghee for a period of 8 weeks. The diets were made isocaloric with groundnut oil. The results showed that serum thromboxane levels decreased by 27-35%, and 6-keto-prostaglandin F1alpha by 23-37% when ghee was incorporated at level of 10% in the diet. Prostaglandin E2 levels in serum and secretion of leukotrienes B4, C4 and D4 by peritoneal macrophages activated with calcium ionophore decreased when increased amounts of ghee from 2.5 to 10% were included in the diet. Arachidonic acid levels in macrophage phospholipids decreased when incremental amounts of ghee were fed to rats. These studies indicate that ghee in the diet not only lowers the prostaglandin levels in serum but also decreases the secretion of leukotrienes by macrophages.

Administration of a small amount of lard enhances intimal thickening in the balloon catheter injury model without affecting serum lipids

Effects of fatty acids on intimal thickening induced by a balloon catheter injury model were investigated by feeding rabbits a small amount of either lard [L] or fish oil [F]. Serum lipids of these groups were not different from those of basal diet-fed rabbits [controls] after 4 weeks of feeding. Serum saturated fatty acids such as 14:0, 16:0, and 18.0 were significantly greater in the L-fed rabbits compared with controls, but those of the aorta were not significantly different. Fatty acid composition of the F-fed rabbits was only different from that of the controls in that n-3 fatty acids slightly increased. The mean and maximum intimal thickening 2 weeks after ballooning, carried out 2 weeks after feeding, were significantly higher in the carotid arteries of the L-fed rabbits than in the controls. The intimal thickening of the F-fed rabbits did not significantly differ from that of the controls. These results suggest that lard promotes the formation of the smooth muscle cell dominant type of arteriosclerosis without affecting serum lipid levels.

Platelet and aorta arachidonic and eicosapentaenoic acid levels and in vitro eicosanoid production in rats fed high-fat diets

There is a significant interest in the interrelationship between long-chain n-3 and n-6 fatty acids due to their ability to modulate eicosanoid production. In general, the intake of arachidonic acid (AA) results in enhanced eicosanoid production, whereas n-3 polyunsaturated fatty acids (PUFA) decrease the production of eicosanoids from AA. The purpose of this study was to investigate whether the effects of dietary AA on eicosanoid production in the rat were correlated with the AA and EPA levels in platelets and aorta (eicosanoid-producing tissues). Four groups of male Sprague-Dawley rats were fed a high-fat diet enriched with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (approximately 100 mg/day of EPA + DHA) for 24 d. During the last 10 d, the four groups were orally supplemented with 0, 30, 60, and 90 mg/day of ethyl arachidonate. A further group of rats was fed a control diet (without long-chain n-3 PUFA) for 24 d. In vitro aorta prostacyclin (PGI2) production, serum thromboxane A2 (TxA2) production and plasma, and platelet and aorta phospholipid (PL) fatty acids were measured. Enriching the diet with n-3 PUFA resulted in significant reductions in tissue AA levels and an increase in the n-3 PUFA, particularly EPA. On this diet, the AA to EPA ratio was 1:1 in platelet PL, and it was 2:1 in the aorta PL. There were significant decreases in the in vitro PGI2 and TxA2 production compared with the control animals. The inclusion of AA in the diet resulted in marked increases in AA levels in the platelet and aorta PL with corresponding decreases in EPA. The lowest dose of AA (30 mg/rat) reversed the effects of 100 mg/day of n-3 PUFA on AA levels in platelet and aortic PL and on in vitro aorta PGI2 and serum TxA2 production. The dietary AA caused a differential (twofold) increase in TxA2 relative to PGI2 for all three levels of AA supplementation. There were greater changes in the levels of AA and/or EPA in platelet PL compared with the aorta PL, which might have accounted for the differential effects of these PUFA on thromboxane production compared with PGI2 production in this study.

n-3 fatty acids reduce in vitro thromboxane production while having little effect on in vitro prostacyclin production in the rat

Male Sprague-Dawley rats were fed diets with 50% of the energy from fat over a 20-day period. The fats used were hydrogenated beef-fat (HBF), or HBF supplemented with ethyl arachidonate A, safflower oil (SO), or a mixture of SO and linseed oil (LO). For comparative purposes, another group of animals was fed a diet providing 50% of the energy as butter-fat. In vitro aortic prostacyclin (PGI2) and serum thromboxane (TXA2) levels (from clotting blood) were determined by radioimmunoassay of 6-keto PGF1 alpha and TXB2, respectively. The HBF diet had similar AA levels relative to the butter-fed rats but significantly reduced tissue levels of eicosapentaenoic acid (EPA) and this was associated with an increased production of serum TXB2. Supplementing the HBF diet with AA increased tissue levels of AA while maintaining low levels of n-3 fatty acids. These changes were accompanied by significant increases of both TXB2 and 6-keto-PGF1 alpha. LO supplementation to the HBF diet (with constant SO) led to elevated levels of EPA and relatively constant AA levels and this was associated with reduced production of TXB2. These results highlight the responsiveness of TXA2 to n-3 fatty acids in contrast to PGI2 which was more influenced by the level of AA in the tissue phospholipids in the rat.

The effect of linoleic, arachidonic and eicosapentaenoic acid supplementation on prostacyclin production in rats

We examined the effect of dietary supplementation of linoleic acid (LA), arachidonic acid (AA) or eicosapentaenoic acid (EPA) to rats fed a diet low in linoleic acid on in vitro and in vivo production of prostacyclin. Male Sprague Dawley rats were fed a high-fat diet (50% energy as fat, 1.5% linoleic acid) for two weeks. Three of the groups were then supplemented orally with either 90 mg/d of LA, AA or EPA, all as the ethyl esters, for a further two weeks while remaining on the high-fat diet. Forty-eight hour urine samples were collected at the end of the second and fourth weeks. In vivo prostacyclin production was determined by a stable isotope dilution, gas chromatography/mass spectrometry assay for the major urinary metabolite of prostacyclins (2,3-dinor-6-keto-PGF1 alpha or PGI2-M and delta 17-2,3-dinor-6-keto-PGF1 alpha or PGI3-M). In vitro prostacyclin production was determined by radioimmunoassay of the stable metabolite (6-keto-PGF 1 alpha) following incubation of arterial tissue. Oral supplementation with AA resulted in a rise in plasma and aorta 20:4n-6, and increased in vitro prostacyclin and urinary PGI2-M production. EPA supplementation resulted in a rise in plasma and aorta 20:5n-3 and 22:5n-3, and a decline in plasma 20:4n-6, but not in the aorta. In the EPA-supplemented group, the in vitro prostacyclin and the urinary PGI3-M increased, but urinary PGI2-M decreased. The increase in in vitro prostacyclin production in the EPA-supplemented rats was unexpected and without obvious explanation.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of dietary fat level and quality on plasma lipoprotein lipids and plasma fatty acids in normocholesterolemic subjects

This study examined the effect on the plasma lipids and plasma phospholipid and cholesteryl ester fatty acids of changing froma typical western diet to a very low fat (VLF) vegetarian diet containing one egg/day. The effect of the addition of saturated, monounsaturated or polyunsaturated fat (PUFA) to the VLF diet was also examined. Three groups of 10 subjects (6 women, 4 men) were fed the VLF diet (10% energy as fat) for two weeks, and then in the next two weeks the dietary fat in each group was increased by 10% energy/week using butter, olive oil or safflower oil. The fat replaced dietary carbohydrate. The VLF diet reduced both the low density lipoprotein (LDL)- and high density lipoprotein (HDL)-cholesterol levels; addition of the monounsaturated fats and PUFA increased the HDL-cholesterol levels, whereas butter increased the cholesterol levels in both the LDL- and HDL-fractions. The VLF diet led to significant reductions in the proportion of linoleic acid (18:2 omega 6) and eicosapentaenoic acid (20:5 omega 3) and to increases in palmitoleic (16:1), eicosatrienoic (20:3 omega 6) and arachidonic acids (20:4 omega 6) in both phospholipids and cholesteryl esters. Addition of butter reversed the changes seen on the VLF diet, with the exception of 16:1, which remained elevated. Addition of olive oil resulted in a significant rise in the proportion of 18:1 and significant decreases in all omega 3 PUFA except 22:6 compared with the usual diet. The addition of safflower oil resulted in significant increases in 18:2 and 20:4 omega 6 and significant decreases in 18:1, 20:5 omega 3 and 22:5 omega 3. These results indicate that the reduction of saturated fat content of the diet (< 6% dietary energy), either by reducing the total fat content of the diet or by exchanging saturated fat with unsaturated fat, reduced the total plasma cholesterol levels by approximately 12% in normocholesterolemic subjects. Although the VLF vegetarian diet reduced both LDL- and HDL-cholesterol levels, the long-term effects of VLF diets are unlikely to be deleterious since populations which habitually consume these diets have low rates of coronary heart disease. The addition of safflower oil or olive oil to a VLF diet produced favorable changes in the lipoprotein lipid profile compared with the addition of butter. The VLF diets and diets rich in butter, olive oil or safflower oil had different effects on the 20 carbon eicosanoid precursor fatty acids in the plasma.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of the effects of diets rich in stearic acid versus myristic acid and lauric acid on platelet fatty acids and excretion of thromboxane A2 and PGI2 metabolites in healthy young men

The present study compared the effects of diets rich in stearic acid (C18:0) versus one high in lauric and myristic acid (C12:0, C14:0) on platelet phospholipid fatty acid levels and concentrations of urinary thromboxane B2 (TXB2) and 6-keto-PGF1 alpha, which are stable metabolites of thromboxane A2 (TXA2) and PGI2 and indicators of cardiovascular hemostasis. A diet high in dairy butter (B) was the source of C12:0 and C14:0; C18:0 was provided by diets high in cocoa butter (CB), milk chocolate (CHOC) or CB+B in a 4:1 ratio (MIX). A randomized, crossover double-blind experimental design was used. Experimental subjects (n = 15) consumed each diet for 26 days, with a 1-month washout period between each experimental period. Urine and blood were collected from each subject at the beginning and end of each dietary period. Urinary TXB2 and 6-keto-PGF1 alpha were analyzed by radioimmunoassay (RIA). There were no effects of diet on the 24-hour excretion of either metabolite or on the ratio of 6-keto-PGF1 alpha/TXB2, even though there were significant changes in the eicosanoid precursor, arachidonic acid (C20:4n-6), in platelet phospholipids. C20:4n-6 levels increased (44.8% +/- 1.0% to 47.1% +/- 1.3%; P < .05) in the phosphatidylethanolamine phospholipid subclass in subjects on the B diet and decreased in the phosphatidylcholine subclass on the CB diet (16.5% +/- 1.0% to 14.2% +/- 1.1%; P < .05) compared with baseline values.(ABSTRACT TRUNCATED AT 250 WORDS)

Arachidonic acid supplementation dose-dependently reverses the effects of a butter-enriched diet in rats

Male Sprague Dawley rats were fed a butter-enriched diet (50% fat) for 2 weeks which was supplemented orally with 9, 18, 36, or 72 mg/day of ethyl arachidonate for a further 2 weeks. The control group of animals were fed a 5% fat diet for 4 weeks. Aortic prostacyclin (PGI2) production, platelet aggregation and thromboxane A2 (TXA2) production and plasma and aortic phospholipid (PL) fatty acids were measured. 50% butter-feeding resulted in a significant reduction in aortic PGI2 production and collagen-induced platelet aggregation and TXA2 production. These changes were accompanied by a reduction in plasma and aortic PL arachidonic acid levels and an increase in eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), 5,8,11-eicosatrienoic acid (ETA) and dihomo-gamma-linolenic acid (DGLA). These changes in prostanoid production, platelet aggregation and PL fatty acid composition were dose-dependently reversed by the daily oral administration of ethyl arachidonate (9, 18, 36, or 72 mg). The threshold dose being as little as 9 mg of ethyl arachidonate/rat/day for reversal of PL fatty acid composition, collagen-induced platelet aggregation and TXA2 production, and 18 mg of ethyl arachidonate/rat/day for reversal of aortic PGI2 production. Full reversal was seen generally with 36 or 72 mg of ethyl arachidonate/rat/day. The data highlight the responsiveness of tissue eicosanoid production to small quantities (ppm) of dietary eicosanoid precursors.

A high-fat diet worsens metabolic control in streptozotocin-treated rats by increasing hepatic glucose production

The aim of this study was to determine the mechanism by which a high-fat diet exacerbates the diabetes produced by a low dose of streptozotocin (STZ). The glucose clamp technique was used to determine hepatic glucose production (HGP) and the disappearance rate (Rd) of glucose, basally and during insulin infusions of 1.0 and 3.0 mU/kg/min in control of STZ-treated rats fed either a low-fat or high-fat diet. Fasting plasma glucose in the high fat-STZ (HFS) group was significantly higher than in any of the other groups: low fat-STZ (LFS), high-fat controls (HFC), or low-fat controls (LFC) (18.1 +/- 1.6 v 8.1 +/- 0.8 mmol/L, P less than .001; 6.0 +/- 0.2 mmol/L, P less than .001; 5.4 +/- 0.1 mmol/L, P less than .001, respectively). Basal HGP was markedly higher in the HFS group compared with each of the other three groups (98.8 +/- 5.9 v 61.4 +/- 3.7, P less than .001; 42.9 +/- 1.6, P less than .001; 39.6 +/- 1.3 mumol/kg/min, P less than .001; HFS v LFS, HFC, and LFC, respectively). Following insulin infusion, no differences were observed in HGP between the LFC and LFS groups at either insulin dose. However, HGP was not suppressed to control levels in either of the high-fat diet groups, and this defect was more marked in the HFS group. It is concluded that a high-fat diet exacerbates mild STZ diabetes primarily by increasing HGP.

The effects of saturated fatty acids on endothelial cells

The present study reports on the effects of myristic(14:0), palmitic(16:0) and stearic(18:0) acids separately and combined with linoleic(18:2n-6), arachidonic(20:4n-6) and eicosapentaenoic(20:5n-3) acids on cultured human endothelial cell monolayers(ECM). The cell viability determined by trypan blue exclusion study, the release of lactate dehydrogenase(LDH) and 6-keto-PGF1 alpha into the medium from ECM incubated with albumin bound fatty acids(FA) were measured. The cell viability was reduced and the release of LDH from ECM was enhanced by 18:0(0.2mM, ratio 1, 2 and 4) and 16:0(0.4mM, ratio 2), but not by 14:0, or the unsaturated FA. The reduced cell viability induced by 18:0 was completely inhibited by polyunsaturated FA, 18:2n-6, 20:4n-6 and 20:5n-3. The release of 6-keto-PGF1 alpha was increased by 18:0, but not by 14:0 and 16:0. All three saturated FA potentiated 6-keto-PGF1 alpha production induced by 20:4n-6. Combined with 18:2n-6 or 20:5n-3, they also stimulated 6-keto-PGF1 alpha production. This study indicates that the three main dietary SFA, 18:0, 16:0 and 14:0 do not have the same effects on ECM. The damaging effect on endothelial cells induced by 18:0 and 16:0 may be of significance for the thrombogenic effects related to these saturated fatty acids.

Coronary heart disease: seven dietary factors

The dietary factors believed to be linked with the incidence of coronary heart disease are reviewed in the light of evidence with regard to their functional role, either in protection or in promotion. Detailed analysis of the evidence shows that the relations are more complex than the current lipid hypothesis suggests. It is proposed that, in particular, the polyunsaturated/saturated ratio as a measure of the propensity of the diet to influence the incidence of coronary heart disease should be replaced by indices of atherogenicity and thrombogenicity.

Reductions in serum thromboxane, prostacyclin, and leukotriene B4 levels in swine fed a fish oil supplement to an atherogenic diet

We have reported previously that fish oil rich in omega-3 fatty acids added to a butter-cholesterol atherogenic diet for swine resulted in marked retardation of the atherosclerotic process which many regard as largely an inflammatory response to injury by excessive lipids in the intima. In this report on the same swine we present serum levels of several eicosanoids derived from arachidonic acid via the cyclooxygenase and lipoxygenase pathways. The study involves six swine fed a high fat, high cholesterol diet (BT group) for 4 months, six swine fed the same diet but with 30 ml/day fish oil added (BT + FO), and five swine fed a low fat, low cholesterol mash diet (MA). The serum eicosanoids were measured by radioimmunoassay. Thromboxane B2 levels (ng/dl: means +/- SEM) were 543 +/- 49 for MA, 231 +/- 12 for BT, and 105 +/- 20 for BT + FO, and all differences were statistically highly significant, 6-Keto PGF1 alpha (a relatively stable prostacyclin metabolite) levels were 249 +/- 31 for MA, 184 +/- 12 for BT, and 101 +/- 10 for BT + FO, and all differences were significant. Leukotriene B4 levels at 4 months were 151 +/- 25 for MA, 112 +/- 11 for BT, and 84 +/- 11 for BT + FO. BT + FO was significantly different from both MA and BT, but BT was not significantly different from MA. Leukotriene C4 levels were not significantly different among the three groups. Of special interest was the effect of the BT diet without the FO additive in reducing several eicosanoid levels compared to MA values. The affected eicosanoid levels were reduced still further by the fish oil additive, indicating its ability to inhibit both the cyclooxygenase and the lipoxygenase pathways. The relation of the fish oil-induced inhibition to the observed retardation of atherogenesis is not as yet clear but there are several theoretical possibilities, including reduction in recruitment of monocytes and in proliferation of smooth muscle cells.

Effects of dietary fats on prostanoid production and aortic and plasma fatty acid composition in rats

Male Sprague-Dawley rats were fed diets with 10%, 30%, or 50% of energy derived from fat for two weeks. The fats used were beef tallow, olive oil, peanut oil and butter. Aortic prostacyclin (PGI2) production, platelet aggregation and thromboxane A2 (TXA2) production and plasma and aortic phospholipid (PL) content were measured. Butter- and beef tallow-feeding reduced aortic PGI2 production and collagen-induced TXA2 production in a dose-dependent manner as the level of fat in the diet increased. Neither olive oil nor peanut oil had any effect on aortic PGI2 production or collagen-induced TXA2 production. Butter-feeding also resulted in a decrease in collagen-induced platelet aggregation; however, none of the other fats had any effect on collagen-induced platelet aggregation. The observed decreases in aortic PGI2 and collagen-induced TXA2 production were paralleled by similar decreases in aortic and plasma PL arachidonic acid content and an increase in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Only the most saturated fats, butter and beef tallow, had significant inhibitory effects on prostanoid production and platelet aggregation.

Arachidonic acid and linoleic acid supplementation increase prostanoid production in rats fed a butter-enriched diet

Male Sprague Dawley rats were fed a butter-enriched diet (50% fat) for 2 weeks and then supplemented orally with either 90 mg of ethyl arachidonate or ethyl linoleate daily for 2 weeks. For comparative reasons, one group of animals was fed standard laboratory rat chow for 4 weeks. Aortic prostacyclin (PGI2) production, platelet aggregation and thromboxane A2 (TXA2) production and plasma and aortic phospholipid (PL) fatty acids were measured. When compared to butter-fed rats, aortic PGI2 production, collagen-induced platelet aggregation and TXA2 production were significantly increased in rats supplemented with ethyl arachidonate to levels similar to those seen in chow-fed rats. Ethyl linoleate supplementation also tended to increase aortic PGI2 production, collagen-induced platelet aggregation and TXA2, but not to the same extent. These changes were accompanied by increases in the level of arachidonic acid and linoleic acid in aortic and plasma PL and a decrease in the level of eicosapentaenoic acid (EPA) and docsahexaenoic acid (DHA). These data indicate that supplementation with small doses of preformed arachidonic acid was more effective than supplementation with its precursor, linoleic acid, in reversing the effects on prostanoid production and phospholipid fatty acid composition in rats fed diets enriched with butter.

Absorption and transport of fat in mammals with emphasis on n-3 polyunsaturated fatty acids

The current state of knowledge concerning the absorption and transport of dietary fat with emphasis on long-chain polyunsaturated n-3 fatty acids in mammals is reviewed. It is apparent that long-chain polyunsaturated n-3 fatty acids, either as free acids or as part of triglycerides, are readily absorbed in the gut and transported by the circulatory system. Indeed, it would appear that long-chain polyunsaturated n-3 fatty acids are digested, absorbed and transported similarly to other long-chain fatty acids with only minor variations, although there is much that is still not understood about these processes. The main unresolved issues in the area of the absorption and transport of long-chain polyunsaturated n-3 fatty acids appear to be: 1) If they, when located in the 2-position of triglycerides, have unique metabolic pathways; and 2) whether the unnatural forms, i.e., methyl or ethyl ester derivatives, are suitable vehicles for administration as dietary supplements. The effect in man of dietary, long-chain polyunsaturated n-3 fatty acids on blood serum lipid and lipoprotein levels, particularly the low density lipoproteins, remains controversial, except for the well-documented reduction in serum triglyceride levels. Also, there is uncertainty regarding their distribution and metabolism in tissues. Finally, if the consumption of long-chain polyunsaturated n-3 fatty acids has beneficial health consequences, what is the appropriate therapeutic dose? In view of these important, unresolved issues and uncertainties, it would seem prudent to direct additional research toward a better understanding of the overall process by which fat is digested, absorbed and transported.

Effects of dietary butter enrichment on the fatty acid distribution of phospholipid fractions isolated from rat platelets and aortae

Rats were maintained for 2 weeks on a low-fat basal diet (5% energy) and a diet from which 50% of the energy was derived from butter. Lipids were extracted from aortae and platelets and the fatty acid profiles of individual phospholipids were examined. Similar responses to dietary butter enrichment occurred in PI, PS, PE and PC fractions from either tissue: 20:4(n - 6) and all other n - 6 series longer-chain polyunsaturated fatty acids except 20:3(n - 6) decreased in percentage; all n - 3 series polyunsaturated fatty acids increased, including 20:5(n - 3) and 22:6(n - 3); n - 9 series polyunsaturated fatty acids, derived from 18:1(n - 9), increased. Despite the considerable redistribution of polyunsaturated fatty acids, the percentages of total polyunsaturated fatty acids in each phospholipid were, in every case, independent of diet. None of the changes were localized in a particular phospholipid fraction. Quantitation of fatty acids using heptadecanoic acid as an internal standard revealed that the concentrations of 20:4(n - 6) in platelet and aortic PE and PC was higher than in PI fractions. Therefore, in terms of substrate amount, it appears that PC and PE as well as PI have the potential to provide endogenous 20:4(n - 6) for oxygenation to the prostanoids thromboxane A2 and prostacyclin I2.