Study of diet and drug interactions on prostanoid metabolism

To study the extent to which combinations of different dietary lipids stimulate or inhibit prostanoid synthesis groups of 12 rats were fed diets containing 10% (w/w) of either safflower oil, hydrogenated coconut oil/safflower oil, cod liver oil/safflower oil or cod liver oil/linseed oil for a period of four weeks. All diets, with the exception of the safflower oil feed, contained similar levels of linoleic acid. Two further groups of rats placed on the cod liver oil diets were injected with indomethacin (4 mg/kg, i.p.) every three days to establish the completeness of dietary prostaglandin (PG) inhibition. In spite of a 20 fold difference in dietary linoleic acid content, the safflower oil group had similar PG generating capacities to the saturated fat control group, suggesting tight metabolic control of PGs and their precursors. Although there were prostanoid variations in tissue responses, both of the cod liver oil diets substantially reduced generation of aortic, whole blood and renal prostanoids, and decreased urinary PG excretion. The degree of inhibition of renal PGs was substantially greater in the cod liver oil/linseed oil group, with prostaglandin levels being 35% lower than those observed in the cod liver oil/safflower oil fed animals suggesting that linolenic acid and the marine oil fatty acids act synergistically to inhibit formation of 2-series prostaglandins. Concurrent administration of omega-3 fatty acids and indomethacin reduced PG levels further than those obtainable by diet alone, demonstrating that the diets did not result in maximal inhibition. Awareness of these various effects is important for both physiological or clinical studies in which dietary manipulations are used as a means of modifying prostanoid synthesis.     

Dietary fish oils reduce plasma levels of platelet activating factor precursor (lyso-PAF) in rats

The object of this study was to develop an assay for platelet activating factor (PAF) in rat plasma, and to utilise this to determine the effects of dietary fish oil on PAF in normotensive and spontaneously hypertensive rats. Measurement of platelet activating factor in blood plasma has proved difficult because of its rapid hydrolysis in vivo to lyso PAF. We describe here a method based on the prior acetylation of lyso PAF extracted from plasma to PAF before bioassay using 14C-serotonin labelled platelets. The active material found in acetylated plasma extracts was characterized as PAF by its chromatographic mobility, the action of phospholipases A2, C and D and by cross-desensitization studies with rabbit platelets. Rats fed dietary fish oil ('max EPA') had significantly decreased plasma lyso-PAF levels compared to control animals fed hydrogenated coconut oil (HCO). Serum thromboxane B2 (TXB2) levels were also significantly lower in animals fed the 'max EPA' diet. Spontaneously hypertensive rats (SHR) had significantly lower plasma lyso-PAF levels than their normotensive Wistar Kyoto (WKY) controls maintained on the same diets. It is proposed that dietary alterations in PAF synthesis may influence platelet behaviour in addition to the well described effects of dietary fish oil on the proaggregatory prostanoid TXA2. Rat strain differences in lyso-PAF synthesis occur, but are unlikely to be related to the maintenance of hypertension in SHR.     

Modification of upper gastrointestinal prostaglandin synthesis by dietary fatty acids

The effects of dietary iols on gastric, duodenal mucosa and liver were investigated ina rat model. Unsaturated fatty acid profles and in vitro prostaglandin (PG) synthesis (PGE₂, PGF_2α, 6-oxo-PGF_1α and thromboxane B₂). were measured after 14 days of dietary oil supplements.There were no significant differences in prostanoid synthesis between rats fed coconut oil (high saturated fat content) and standard diet. After fish oil supplement, tissue eicosapentaenoic acid and docosahexaenoic acid levels were higher, arachidonic acid levels were lower, and prostanoid synthesis was reduced in both stomach and duodenum. After corn oil and evening primrose oil, linoleic acid levels were variaby increased, bt there were no significant differences in arachidonic acid or prostanoid synthesis. Dihomogamma-linolenic acid levels were slightly increased after evening primrose oil.Dietary incorporation of fatty acids into gastroduodenal tissue is not uniform. When incorporated, fatty acids can modify prostaglandin synthesis.     

Isoproterenol-induced mortality and cardiac lipids of aspirin-pretreated rats with various fat intakes

The effect of altering cardiac concentrations of precursors and inhibitors of prostaglandin synthesis by varying fat intake was determined in rats injected with the cardiotoxic drug isoproterenol, following pretreatment with aspirin or potassium phosphate buffer solution. Prior to injection, four groups of rats were fed either a low-fat diet (3.7 energy percent coconut oil 3.7 energy percent safflower oil) or a high-fat diet (3.7 energy percent safflower oil-36.4 energy percent coconut oil mixture or 40.1 energy percent safflower oil.) Mortality as well as fatty acid composition of cardiac lipids changed in response to altered kinds and amounts of fats. Mortality and cardiac C20:4/C22:6 ratio were lowered by feeding 3.7 energy percent coconut oil, and increased by feeding 40.1 energy percent safflower oil. Aspirin reduced mortality in rats fed 40.1 energy percent safflower oil, but not in rats fed other diets. Results suggest that dietary manipulations which increase tissue content of polyunsaturated fatty acids of the n-6 type relative to those of the n-3 type may increase sensitivity to isoproterenol, and that effectiveness of aspirin in reducing isoproterenol-induced mortality depends upon the n-6/n-3 ratio of cardiac fatty acids.     

Reduction in plasma cholesterol and increase in biliary cholesterol by a diet rich in n-3 fatty acids in the rat

Cholesterol and lipoprotein metabolism were investigated in a group of rats fed a fish oil-supplemented diet, a rich source of n-3 fatty acids. For comparison purposes, other groups of rats were fed either safflower oil (n-6 fatty acids) or coconut oil (saturated fatty acids). Diets were isocaloric and contained identical amounts of cholesterol. Rats fed fish oils for 2 weeks showed a 35% lower plasma cholesterol level than rats fed safflower oil, who in turn showed a 14% lower plasma cholesterol level than those fed coconut oil. The fall in plasma cholesterol level with fish oils was associated with significant falls in low density and high density lipoprotein cholesterol levels, but with no significant change in the ratio of low density to high density lipoprotein cholesterol. The fatty acid compositions of plasma, hepatic, and biliary lipids showed relative enrichment with n-3 fatty acids, reflecting the composition of the diet. The fish oil diet increased the basal secretion rate of cholesterol into bile, but the bile acid secretion rate remained unchanged. It is suggested that n-3 fatty acids reduce the plasma cholesterol level in rats by increasing the transfer of cholesterol into bile.     

Superiority of dietary safflower oil over olive oil in lowering serum cholesterol and increasing hepatic mRnas for the LDL receptor and cholesterol 7alpha-hydroxylase in exogenously hypercholesterolemic (exHC) rats

The exogenously hypercholesterolemic (ExHC) rat is a strain segregated from SD rats with a high response to dietary cholesterol. To understand the underlying mechanism(s) for this hypercholesterolemia, the interactive effects of dietary fatty acid and the susceptibility of rats to dietary cholesterol on the serum cholesterol concentration and hepatic mRNA abundance of the low-density lipoprotein (LDL) receptor, cholesterol 7alpha-hydroxylase (7alpha-hydroxylase) and 3-hydroxyl-3methylglutaryl (HMG) CoA reductase were examined. Both strains were fed on a diet supplemented with 10% each of olive, safflower or coconut oil with or without the addition of 1% cholesterol for one week. The ExHC rats fed on olive, safflower and coconut oil in combination with cholesterol respectively resulted in a 3.5-, 2.0- and 2.1-fold higher serum cholesterol concentration than that in the animals fed on the corresponding dietary fats without any supplementation of cholesterol (p < 0.01 by dietary cholesterol or type of fat). The dietary cholesterol dependent-elevation of serum cholesterol in the SD rats was less than 1.5-fold (p<0.01) and there was no dietary fat effect. The ExHC rats fed on the safflower oil-containing diet supplemented with cholesterol resulted in a higher mRNA abundance of the LDL receptor and 7alpha-hydroxylase than in the corresponding fat-fed rats without cholesterol (p<0.05). There was no dietary cholesterol-dependent change of mRNA abundance in either strain fed on olive or coconut oil, except for a decreased abundance of HMG CoA reductase mRNA in the olive oil-fed ExHC rats and coconut oil-fed Sprague-Dawley (SD) rats (p<0.05). These results indicate that the hepatic mRNA abundance of the LDL receptor and of 7alpha-hydroxylase depended on the dietary combination of cholesterol and a fatty acid and suggest that a linoleic acid-rich diet may alleviate exogenous hypercholesterolemia by activating the process involved in the hepatic uptake and biliary excretion of serum cholesterol.     

Effects of dietary saturated, N-6 and N-3 polyunsaturated fats on blood pressure and prostaglandins outflow from perfused mesenteric vascular bed in rats

Effects of the dietary administration of saturated fat and of n-6 and n-3 polyunsaturates on blood pressure, prostaglandin metabolism in small vessels, tissue fatty acid distribution and urinary PGE2 excretion were compared. Rats were divided into three groups. Diets contained 10% hydrogenated coconut oil (HCO), 10% safflower oil (SFO) or 10% cod liver oil (CLO) added to a basic fat free diet for 10 weeks. Systolic blood pressure was increased in the CLO group animals. Urinary PGE2 excretion was decreased in the HCO and CLO groups as compared to that in the SFO group animals. PGE2, 6-keto-PGF1 alpha and thromboxane (Tx) B2 outflow from isolated perfused mesenteric arterial beds were extremely decreased in the CLO group animals, and to a lesser extent in the HCO group as compared to the SFO animals. In the tissue phospholipid, 20:3n-9/20:4n-6 ratios were increased in the HCO group indicating essential fatty acid deficiency, and n-6 and n-3 polyunsaturates were elevated in the SFO and the CLO group animals respectively. Arachidonic acid concentration was highest in the SFO group, while there was no significant differences between the HCO and the CLO group. These results suggest that dietary fatty acid manipulation affects urinary PGE2 excretion and PGI2, PGE2 and TxA2 synthesis in mesenteric arterial beds and also changes the tissue fatty acid distribution. Furthermore, n-3 polyunsaturates caused an extreme reduction of 2-series PGs synthesis in small resistance vessels.     

The prostaglandin outflow from perfused mesenteric vasculature of rats fed different fats

The effects of dietary n-6 polyunsaturated fatty acids and replacement with saturated fat or fish oil on the prostaglandin outflow from perfused mesenteric vasculature in rats were studied. Seventy-two weanling male rats were fed ad libitum a semi-synthetic diet supplemented with 10% by weight of oil, composed wholly of n-6 fatty acid-rich evening primrose oil, or replaced partly or completely (25, 50, 75 or 100%) by n-6 fatty acid-deficient fish oil or hydrogenated coconut oil for 8 weeks. The outflows of 6-keto-PGF1 alpha, thromboxane B2, and prostaglandin E from the perfused mesenteric vasculature were measured at 60 min-time point after starting the perfusion. In general, the release of prostanoids from the mesenteric vasculature was significantly reduced in rats fed a diet in which evening primrose oil was partly or completely replaced by either hydrogenated coconut or fish oil. This was probably due to the insufficient conversion of linoleic acid to arachidonic acid. The extent of reduction was greater in fish oil-fed than in hydrogenated coconut oil-fed rats, while the levels of arachidonic acid in aortic phospholipids were similar between these two groups. This result implies that the greater reduction of prostaglandin synthesis in rats fed fish oil was due to the inhibitory effect of eicosapentaenoic and docosahexaenoic acids in fish oil on the conversion of arachidonate to eicosanoids.     

Effect of n-6 and n-3 dietary fatty acids on phospholipid composition of plasma, platelets and aorta in the rat

Female Wistar rats were fed with diets containing as dietary lipids 10% of hydrogenated coconut oil, grape-seed oil, olive oil, linseed oil and fish oil, respectively, for a period of 60 days. At the end of dietary treatment plasma, platelets and aorta phospholipids were extracted and fatty acid spectra determined. Plasma and platelet phospholipids showed the largest diet dependent changes. Anyway in aorta samples too, phospholipids showed marked increase in oleic (olive oil group) linoleic (grape-seed oil group) and alpha linoleic (linseed oil group) acids percentage. Conversely decreased amounts of arachidonic acid were detected in rats fed with diets containing linseed and fish oils. In these samples eicosapentenoic acid partly replaced arachidonic one.     

Dietary n-3 fatty acids,curcumin and capsaicin lower the release of lysosomal enzymes and eicosanoids in rat peritoneal macrophages

Male Wistar rats (12 rats/group) were fed a diet containing 8 wt % coconut oil or groundnut oil or cod-liver oil for a total period of 8 weeks. The diets were also supplemented with 2 wt % groundnut oil for providing essential fatty acids. During the last 2 weeks, 6 rats form each group were additionally given curcumin (30 mg/kg body wt/day) or capsaicin (5 mg/kg body wt/day) in 1 ml groundnut oil. The peritoneal macrophages from rats fed cod-liver oil diet secreted lower levels of lysosomal enzymes collagenase, elastase and hyaluronidase as compared to those from rats fed coconut oil or groundnut oil diets. Curcumin and capsaicin significantly lowered the secretion of these lysosomal enzymes from macrophages in animals given coconut oil or groundnut oil diet. Macrophages from rats fed cod-liver oil secreted lower amounts of prostaglandin E₂, 6-keto PGF_1a, leukotrienes B₄and C₄and also incorporated lesser amounts of [^3H]-arachidonic acid as compared to those given coconut oil or groundnut oil diets. Curcumin and capsaicin lowered the secretion of these eicosanoids and decreased the incorporation of [³H]-arachidonic acid in macrophage lipids. However curcumin and capsaicin significantly increased the secretion of 6-keto PGF_1ain all the groups of animals. These studies indicated that dietary cod-liver oil (rich in n-3 fatty acids), and spice principles curcumin and capsaicin can lower the secretory functions of macrophages in a beneficial manner.     

Effects of dietary linoleic acid on blood pressure and renal function in subtotally nephrectomized rats

The effect of a high linoleic acid diet on blood pressure, renal function, and urinary prostaglandin excretion was studied in rats with decreased renal mass. Subtotally nephrectomized (5/6 nephrectomy) male rats received either a 15% linoleic acid (high linoleic acid, HLA) diet containing 20% safflower oil or a 0.28% linoleic acid (low linoleic acid, LLA) diet containing 20% coconut oil. Sham-operated rats were also placed on either HLA or LLA diet. The subtotal nephrectomized rats developed similar degrees of hypertension during the first 3 weeks after subtotal nephrectomy. However, 4 weeks after subtotal nephrectomy, the rats on HLA diet had significantly lower blood pressure than the rats on LLA diet [HLA 152 +/- 3 (mean +/- SE) mm Hg versus LLA 171 +/- 3 mm Hg]. This difference persisted until termination of the experiment at 7 weeks after subtotal nephrectomy (HLA 159 +/- 7 mm Hg versus LLA 192 +/- 6 mm Hg). The GFR measured 7 weeks after subtotal nephrectomy was significantly lower in both of the subtotally nephrectomized groups. However, the HLA subtotal nephrectomized rats had significantly higher GFR than the LLA-treated rats (HLA 0.23 +/- 0.05 ml/min 100 g versus LLA 0.12 +/- 0.02 ml/min/100 g, P less than 0.05). There was no difference in the GFR or blood pressure in the sham-operated rats treated with HLA or LLA diet. PGE2 excretion was lower in the two groups of subnephrectomized rats, but there was no difference between the HLA and LLA treated rats. Urinary 6-ketoPGF1 alpha was not decreased by subtotal nephrectomy and there was no difference between the dietary groups. However, TXB2 excretion was higher in the groups with subtotal nephrectomy, but there was no difference between the two dietary groups. In conclusion, the HLA diet attenuates the rise in blood pressure after subtotal nephrectomy in the rat and preserves renal function. There was no difference in urinary excretion of PGE2, 6-keto-PFG1 alpha, or thromboxane B2 between the two dietary groups.     

Effects of dietary saturated, n-6 and n-3 polyunsaturated fats on blood pressure and prostaglandins outflow from perfused mesenteric vascular bed in rats

Effects of the dietary administration of saturated fat and of n-6 and n-3 polyunsaturates on blood pressure, prostaglandin metabolism in small vessels, tissue fatty acid distribution and urinary PGE₂ excretion were compared. Rats were divided into three groups. Diets contained 10% hydrogenated cocunut oil (HCO), 10% safflower oil (SFO) or 10% cod liver oil (CLO) added to a basic fat free diet for 10 weeks. Systolic blood pressure was increased in the CLO group animals. Urinary PGE₂ excretion was decreased in the HCO and CLO groups as compared to that in the SFO group animals. PGE₂, 6-keto-PGF₁ and thromboxane (Tx) B₂ outflow from isolated perfused mesenteric arterial beds were extremely decreased in the CLO group animals, and to a lesser extent in the HCO group as compared to the SFO animals. In the tissue phospholipid, 20:3n−9/20:4n−6 ratios were increased in the HCO group indicating essential fatty acid deficiency, and n-6 and n-3 polyunsaturates were elevated in the SFO and the CLO group animals respectively. Arachidonic acid concentration was highest in the SFO group, while there was no significant differences between the HCO and the CLO group. These results suggest that dietary fatty acid manipulation effects urinary PGE₂ excretion and PGI₂, PGE₂ and TxA₂ synthesis in mesenteric arterial beds and also changes the tissue fatty acid distribution. Furthermore, n-3 polyunsaturates caused an extreme reduction of 2-series PGs synthesis in small resistance vessels.     

Steroid balance and tissue cholesterol accumulation in germfree and conventional rats fed diets containing saturated and polyunsaturated fats

Steroid balance studies were conducted on 24 conventional and 12 germfree male rats, 90-120 days old, fed diets containing either 20% safflower or 20% coconut oil. Both germfree and conventional rats fed the safflower oil diets had significantly lower serum cholesterol levels and significantly higher liver cholesterol levels than did the rats fed coconut oil. No significant differences in total fecal neutral sterols, coprostanol, Delta(7)-cholestenol, or total fecal bile acid excretion were seen between dietary groups of rats of either status. There was no evidence of qualitative differences in fecal bile acid excretion as a function of diet. The increased liver cholesterol was in the ester form, with cholesteryl linoleate the largest single component. There was no significant difference in the cholesterol content of the skin, muscle, adipose tissue, or gastrointestinal tract. The significance of a large increase in liver cholesteryl ester, lowered serum cholesterol, and no change in steroid excretion is discussed.     

Fish oil reduces cholesterol and arachidonic acid content more efficiently in rats fed diets containing low linoleic acid to saturated fatty acid ratios

Rats were fed diets containing a high level of saturated fatty acids (hydrogenated beef tallow) versus a high level of linoleic acid (safflower oil) at both low and high levels of fish oil containing 7.5% (w/w) eicosapentaenoic and 2.5% (w/w) docosahexaenoic acids for a period of 28 days. The effect of feeding these diets on the cholesterol content and fatty acid composition of serum and liver lipids was examined. Feeding diets high in fish oil with safflower oil decreased the cholesterol content of rat serum, whereas feeding fish oil had no significant effect on the cholesterol content of serum when fed in combination with saturated fatty acids. The serum cholesterol level was higher in animals fed safflower oil compared to animals fed saturated fat without fish oil. Consumption of fish oil lowered the cholesterol content of liver tissue regardless of the dietary fat fed. Feeding diets containing fish oil reduced the arachidonic acid content of rat serum and liver lipid fractions, the decrease being more pronounced when fish oil was fed in combination with hydrogenated beef tallow than with safflower oil. These results suggest that dietary n-3 fatty acids of fish oil interact with dietary linoleic acid and saturated fatty acids differently to modulate enzymes of cholesterol and fatty acid metabolism.     

Influence of an increased intake of linoleic acid on the incorporation of dietary (n-3) fatty acids in phospholipids and on prostanoid synthesis in rat tissues.

We investigated whether the amount of dietary linoleic acid (LA) (as corn oil) influences the incorporation of dietary eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) in tissue phospholipids and the prostanoid biosynthesis. Rats were fed four different levels of corn oil (at a total dietary fat level of either 2.5%, 5%, 10% or 20%); at each corn oil level, two groups of rats were supplemented with either EPA and DHA (200 mg/day) during 6 weeks, and compared with a group receiving oleic acid. The phospholipid fatty acid composition of liver, kidney and aorta showed, as expected, that the incorporation of EPA was highly suppressed by increasing the content of dietary linoleic acid in the diets. On the other hand, DHA was almost unaffected by the amounts of (n - 6) fatty acids in the diets. These results indicate that EPA levels but not DHA levels in tissue phospholipids were influenced by the competing dietary (n - 6) fatty acids. The tissue arachidonate content was similar under the various dietary linoleic acid conditions, but feeding EPA or DHA lowers the AA content. Moreover, the amount of dietary linoleic acid did not significantly influence the prostaglandin E2 (PGE2) production in stimulated aortic rings. However, PGE2 synthesis was significantly decreased in the groups treated with either EPA or DHA. Thromboxane B2 levels in serum followed a similar pattern. It is suggested that an increase of dietary (n - 3) PUFAs is more efficient to reduce (n - 6) eicosanoid formation than a decrease of dietary (n - 6) fatty acids.     

Effect of dietary alpha-linolenic acid on the activity and gene expression of hepatic fatty acid oxidation enzymes

The activities of hepatic fatty acid oxidation enzymes in rats fed linseed and perilla oils rich in alpha-linolenic acid (alpha-18:3) were compared with those in the animals fed safflower oil rich in linoleic acid (18:2) and saturated fats (coconut or palm oil). Mitochondrial and peroxisomal palmitoyl-CoA (16:0-CoA) oxidation rates in the liver homogenates were significantly higher in rats fed linseed and perilla oils than in those fed saturated fats and safflower oil. The fatty oxidation rates increased as dietary levels of alpha-18:3 increased. Dietary alpha-18:3 also increased the activity of fatty acid oxidation enzymes except for 3-hydroxyacyl-CoA dehydrogenase. Unexpectedly, dietary alpha-18:3 caused great reduction in the activity of 3-hydroxyacyl-CoA dehydrogenase measured with short- and medium-chain substrates but not with long-chain substrate. Dietary alpha-18:3 significantly increased the mRNA levels of hepatic fatty acid oxidation enzymes including carnitine palmitoyltransferase I and II, mitochondrial trifunctional protein, acyl-CoA oxidase, peroxisomal bifunctional protein, mitochondrial and peroxisomal 3-ketoacyl-CoA thiolases, 2, 4-dienoyl-CoA reductase and delta3, delta2-enoyl-CoA isomerase. Fish oil rich in very long-chain n-3 fatty acids caused similar changes in hepatic fatty acid oxidation. Regarding the substrate specificity of beta-oxidation pathway, mitochondrial and peroxisomal beta-oxidation rate of alpha-18:3-CoA, relative to 16:0- and 18:2-CoAs, was higher irrespective of the substrate/albumin ratios in the assay mixture or dietary fat sources. The substrate specificity of carnitine palmitoyltransferase I appeared to be responsible for the differential mitochondrial oxidation rates of these acyl-CoA substrates. Dietary fats rich in alpha-18:3-CoA relative to safflower oil did not affect the hepatic activity of fatty acid synthase and glucose 6-phosphate dehydrogenase. It was suggested that both substrate specificities and alterations in the activities of the enzymes in beta-oxidation pathway play a significant role in the regulation of the serum lipid concentrations in rats fed alpha-18:3.     

Interactions of saturated, n-6 and n-3 polyunsaturated fatty acids to modulate arachidonic acid metabolism

Anti-thrombotic effects of omega-3 (n-3) fatty acids are believed to be due to their ability to reduce arachidonic acid levels. Therefore, weanling rats were fed n-3 acids in the form of linseed oil (18:3n-3) or fish oil (containing 20:5n-3 and 22:6n-3) in diets containing high levels of either saturated fatty acids (hydrogenated beef tallow) or high levels of linoleic acid (safflower oil) for 4 weeks. The effect of diet on the rate-limiting enzyme of arachidonic acid biosynthesis (delta 6-desaturase) and on the lipid composition of hepatic microsomal membrane was determined. Both linseed oil- or fish oil-containing diets inhibited conversion of linoleic acid to gamma-linolenic acid. Inhibition was greater with fish oil than with linseed oil, only when fed with saturated fat. delta 6-Desaturase activity was not affected when n-3 fatty acids were fed with high levels of n-6 fatty acids. Arachidonic acid content of serum lipids and hepatic microsomal phospholipids was lower when n-3 fatty acids were fed in combination with beef tallow but not when fed with safflower oil. Similarly, n-3 fatty acids (18:3n-3, 20:5n-3, 22:5n-3, and 22:6n-3) accumulated to a greater extent when n-3 fatty acids were fed with beef tallow than with safflower oil. These observations indicate that the efficacy of n-3 fatty acids in reducing arachidonic acid level is dependent on the linoleic acid to saturated fatty acid ratio of the diet consumed.     

Recycling of docosahexaenoic acid in rat retinas during n-3 fatty acid deficiency.

About 50% of the fatty acids in retinal rod outer segments is docosahexaenoic acid [22:6(n-3)], a member of the linolenic acid [18:3(n-3)] family of essential fatty acids. Dietary deprivation of n-3 fatty acids leads to only modest changes in 22:6(n-3) levels in the retina. We investigated the mechanism(s) by which the retina conserves 22:6(n-3) during n-3 fatty acid deficiency. Weanling rats were fed diets containing 10% (wt/wt) hydrogenated coconut oil (no n-3 or n-6 fatty acids), linseed oil (high n-3, low n-6), or safflower oil (high n-6, less than 0.1% n-3) for 15 weeks. The turnover of phospholipid molecular species and the turnover and recycling of 22:6(n-3) in phospholipids of the rod outer segment membranes were examined after the intravitreal injection of [2-3H]glycerol and [4,5-3H]22:6(n-3), respectively. Animals were killed on selected days, and rod outer segment membranes, liver, and plasma were taken for lipid analyses. The half-lives (days) of individual phospholipid molecular species and total phospholipid 22:6(n-3) were calculated from the slopes of the regression lines of log specific activity versus time. There were no differences in the turnover rates of phospholipid molecular species among the three dietary groups, as determined by the disappearance of labeled glycerol. Thus, 22:6(n-3) is not conserved through a reduction in phospholipid turnover in rod outer segments. However, the half-life of [4,5-3H]22:6(n-3) in the linseed oil group (19 days) was significantly less than in the coconut oil (54 days) and safflower oil (not measurable) groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Activities of liver microsomal fatty acid desaturases in zinc-deficient rats force-fed diets with a coconut oil/safflower oil mixture of linseed oil

The present study was conducted to investigate the effect of zinc deficiency on fatty acid desaturation in rats fed two different types of dietary fat, a mixture of coconut oil and safflower oil (7∶1, w/w, “coconut oil diet”) or linseed oil (“linseed oil diet”). In order to ensure an adequate food intake, all rats were force-fed by gastric tube. Zinc deficiency caused statistical significant reducion of Δ9-desaturase activity in liver microsomes of rats fed coconut oil diet and tendencial reduction (p<0.15) in rats fed linseed oil diet compared with control rats fed diets with the same type of fat. In agreement with this effect, zinc deficiency in the rats fed both types of dietary fat increased the ratio between total saturated and total monounsaturated fatty in liver phospholipids and liver microsomes. Zinc deficient rats on the coconut oil diet had unchanged Δ6-desaturase activity with linoleic acid as substrate and lowered activity with α-linolenic acid as substrate. In contrast, zinc deficient rats on the linseed oil diet had increased Δ6-desaturase activity with linoleic acid as substrate and unchanged activity with α-linolenic acid. Because linoleic acid is the main substrate for Δ6-desaturase in the rats fed coconut oil diet, and α-linolenic acid is the main substrate in the rats fed linseed oil diet, it is concluded that in vivo Δ6-desaturation was not changed by zinc deficiency in the rats fed both types of dietary fat. Activity of Δ5-desaturase was also not changed by zinc deficiency in the rats fed both dietary fats. Levels of fatty acids in liver phospholipids and microsomes derived by Δ4-, Δ5-, and Δ6-desaturation were not consistently changed by zinc deficiency in the rats fed both types of dietary fat. Thus, the enzyme studies and also fatty acid composition data of liver phospholipids and microsomes indicate that zinc deficiency does not considerably disturb desaturation of linoleic and α-linolenic acid. Therefore, it is suggested that similarities between deficiencies of zinc and essential fatty acids described in literature are not due to disturbed desaturation of linoleic acid in zinc deficiency. The present study also indicates that zinc deficiency enhances incorporation of eicosapentaenoic acid into phosphatidylcholine of rats fed diets with large amounts ofn-3 polyunsaturated fatty acids.     

Effects of dietary polyunsaturated fatty acid on platelet aggregation in rats

In the present study, we changed the fatty acid profile in blood and platelet membranes by dietary manipulation, and examined the effect on platelet aggregation in rats. Fifty-five rats were divided into five groups and fed for 56 days with 1% cholesterol and different types of fatty acid-rich diets: basal, lard, lard + fish oil, soybean oil, and soybean oil + fish oil. a decrease in serum arachidonic acid (20:4, omega-6, AA) and an increase in serum eicosapentaenoic acid (20:5, omega-3, EPA) were found in all experimental dietary groups fed with refined fish oil. Similar changes in the polyunsaturated fatty acids were also found in the platelet membrane phospholipids. Platelet aggregation, quantitated by the slope and height of the aggregation curve induced by different concentrations of ADP in a platelet aggregometer, was inhibited in all groups fed with refined fish oil. This inhibition of platelet aggregation may be related to an increase in the ratio of EPA and AA in the platelet membrane phospholipids after dietary manipulation. The differences in the platelet aggregation and thromboxane B2 (TXB2) concentration between the lard and the lard + fish oil groups were more profound than that between the soybean oil and the soybean oil + fish oil group. However, the malondialdehyde (MDA) concentration revealed no significant differences between the five groups.