Effect of very long chain fatty acids on peroxisomal β-oxidation in primary rat hepatocyte cultures

Previous studies have demonstrated that certain high fat diets can induce peroxisomal fatty acid β-oxidation in rodent liver and that this may be due to their content oftrans 22∶1 fatty acids. In this study we have examined the effects ofcis andtrans 22∶1 fatty acids (erucic and brassidic) and oleic acid (18∶1) on palmitoyl-CoA oxidation, carnitine acetyltransferase and carnitine palmitoyltransferase activities in primary rat hepatocyte cultures. Brassidic and erucic acid and, to a lesser extent, oleic acid were cytotoxic to rat hepatocytes. However, at a concentration of 0.1 mM, brassidic acid produced small increases in palmitoyl-CoA oxidation and carnitine acetyltransferase activities in hepatocytes cultured 70 hr. Treatment of cells with 0.1 and 0.3 mM of either erucic or oleic acid had no effect on any of the enzymes measured.     

Erucic Acid is Differentially Taken up and Metabolized in Rat Liver and Heart

Because X-linked adrenoleukodystrophy is treated using erucic acid (22:1n-9), we assessed its metabolism in rat liver and heart following infusion of [14-¹⁴C]22:1n-9 (170 Ci/kg) under steady-state-like conditions. In liver, 2.3-fold more tracer was taken up as compared to heart, accounted entirely by increased incorporation into the organic fraction (4.2-fold). The amount of tracer entering the aqueous fraction, which represents β-oxidation, was not different between groups; however a significantly elevated proportion of tracer was in the heart aqueous fraction. In both tissues, 76% of the radioactivity found in the organic fraction was esterified in neutral lipids, while only about 10% was found esterified into phospholipids. In liver, 56% of lipid radioactivity was found in cholesteryl esters, whereas in heart 64% was found in triacylglycerols. Because 22:1n-9 can be chain shortened, we assessed tracer metabolism using phenacyl fatty acid derivatives esterified from saponified esterified neutral lipid (triacylglycerol/cholesteryl ester) and phospholipid fractions. In heart esterified neutral lipids, 75% of tracer was recovered as 22:1n-9 and only 10% as oleic acid (18:1n-9), while in liver only 25% of the tracer was recovered as 22:1n-9, while 50% was found as stearic acid (18:0) and 10% as 18:1n-9. In liver and heart phospholipids, the tracer was distributed amongst the n-9 fatty acid family. Thus, 22:1n-9 under went tissue selective metabolism, with conversion to 18:0 the dominant pathway in the liver presumably for export in the neutral lipids, while in heart it was found primarily as 22:1n-9 in neutral lipids and used for β-oxidation.     

Preparation and characterization of prostanoyl carnitine

A method is described for the preparation of prostanoyl carnitine from prostanoic acid and L-carnitine. The crystalline compound exhibits an IR spectrum and chemical reactivity characteristic of long chain acyl carnitine esters and undergoes β-oxidation in rat liver mitochondria in the absence of exogenous carnitine and ATP. This suggests that it may be an intermediate in the transport of prostanoic acid across the mitochondrial membrane. The data supply additional evidence that prostaglandin-like substances are converted to the carnitine ester prior to transport in the mitochondrion.     

Total and peroxisomal oxidation of various saturated and unsaturated fatty acids in rat liver,heart and m. quadriceps

Rates of total and peroxisomal fatty acid oxidation were estimated from the production of¹⁴C-labeled CO₂ and acid-soluble products from differently labeled [¹⁴C]fatty acids, in the absence and presence of antimycinrotenone, in homogenates of liver, heart and m. quadriceps. Total and peroxisomal oxidation rates of palmitic, oleic and linoleic acid were 3–4 times higher than those of arachidonic and adrenic acid which had higher oxidation rates than those of lignoceric and erucic acid. The peroxisomal contribution to the oxidation of the last fatty acids was similar to or higher than that of palmitic acid. For all fatty acids tested in these tissues, the mitochondrial contribution to β-oxidation was higher than the peroxisomal contribution. Production of¹⁴CO₂ and¹⁴C-labeled, acid-soluble metabolites from [13-¹⁴]arachidonic acid indicated that polyunsaturated fatty acids can be chain-shortened beyond their double bonds in m. quadriceps and heart as well as in liver. Although 2,4-dienoyl-CoA reductase requires NADPH, addition of this coenzyme did not influence arachidonic acid oxidation. Arachidonic acid oxidation was inhibited by palmitic acid in mitochondria and peroxisomes, but arachidonic acid had only a slight effect on palmitic acid oxidation.     

Influence of partially hydrogenated vegetable and marine oils on lipid metabolism in rat liver and heart

Partially hydrogenated marine oils containing 18∶1-, 20∶1- and 22∶1-isomers and partially hydrogenated peanut oil containing 18∶1-isomers were fed as 24–28 wt % of the diet with or without supplement of linoleic acid. Reference groups were fed peanut, soybean, or rapeseed oils with low or high erucic acid content. Dietary monoene isomers reduced the conversion of linoleic acid into arachidonic acid and the deposition of the latter in liver and heart phosphatidylcholine. This effect was more pronounced for the partially hydrogenated marine oils than for the partially hydrogenated peanut oil. The content oftrans fatty acids in liver phospholipids was similar in groups fed partially hydrogenated fats. The distribution of various phospholipids in heart and liver was unaffected by the dietary fat. The decrease in deposition of arachidonic acid in rats fed partially hydrogenated marine oils was shown in vitro to be a consequence of lower Δ6-desaturase activity rather than an increase in the peroxisomal β-oxidation of arachidonic acid. The lower amounts of arachidonic acid deposited may be a result of competition in the Δ6-desaturation not only from the C22-and C20-monoenoic fatty acids originally present in the partially hydrogenated marine oil, but also from C18- and C16-monoenes produced by peroxisomal β-oxidation of the long-chain fatty acids. Part of this work was presented at the ISF-AOCS Congress, New York City, 1980.     

The nutritive value of refined rapeseed oils: A review

Recent findings on the nutritive value of rapeseed oil (RSO) with high erucic acid content have been compared to those of canbra oil (CO), an oil extracted from newly bred Canadian rapeseed with no erucic acid. Erucic acid in diets retards animal growth even if food consumption is not altered. Growth performances of CO are as good as olive or peanut oil. The unbalanced ratio of palmitic acid to monoethylenic acids of CO does not affect rat growth rate. Because of its glyceride structure and high content of erucic acid, RSO has a lower digestibility (81%) than CO (96%) in the rat. Unabsorbed erucic acid is not preferentially excreted as calcium soaps. Interesterification of RSO which converts 31.7% of the erucic chains to the 2 position improves digestibility of erucic acid. 2-Monoerucin is more efficiently absorbed than the free acid. In vivo metabolic conversion of erucic to oleic acid has been proved in the rat. β-oxidation of injected 14-¹⁴C labeled erucic acid proceeded at the same rate as oleic acid but the over-all yield of the reaction was lower. Fatty acid composition of tissues in animals fed RSO or CO is influenced on one hand by erucic and gadoleic (C_20∶1) acids of RSO, and on the other hand by the unbalanced ratio of palmitic-monoethylenic acids and the linolenic acid content of both oils. Nonnegligible amounts of erucic acid are deposited in the body fats of rats, chickens, turkeys, lambs and found in the milk of female rats fed RSO. Almost no erucic acid is incorporated in liver and testicles in the rat and it is not recovered in chicken egg yolk. The effect of RSO on rat reproduction has been re-examined. Dietary lipid and vitamin levels are of great importance in the results obtained. RSO induces myocarditis in several animal species. Similar lesions, although less frequent and severe, have been observed also with CO in the rat. Some authors have reported that erucic acid of RSO was responsible for the effect on heart muscle. Common fatty acid patterns to both RSO and CO have to be further investigated to explain the persisting effect of CO. One of 9 papers presented at the Symposium, “Cruciferous Oil-seeds,” ISF-AOCS World Congress, Chicago, September 1970.     

Effects of rapeseed oil on fatty acid oxidation and lipid levels in rat heart and liver

The comparative rates of oxidation of erucic and oleic acids and of their CoA esters were studied in heart and liver mitochondria of rats fed a standard diet or semisynthetic diets containing 25% of the calories as either rapeseed oil (46.6% erucic and 10.4% eicosenoic acid) or olive oil, for a period of 5 months. The long exposure to the diet containing 25% rapeseed oil did not alter the oxidative activity of mitochondria and did not induce morphological changes in the heart. It is confirmed that erucic acid is oxidized in mitochondria at lower rates than other long chain fatty acids and that its activation as CoA derivative may be one of the rate limiting steps of the overall oxidation process. Total lipids and triglycerides do not significantly change in the heart whereas they increase in the liver of rats fed the diet containing rapeseed oil.     

Tetradecylthioacetic Acid Increases Hepatic Mitochondrial β-Oxidation and Alters Fatty Acid Composition in a Mouse Model of Chronic Inflammation

The administration of tetradecylthioacetic acid (TTA), a hypolipidemic and anti-inflammatory modified bioactive fatty acid, has in several experiments based on high fat diets been shown to improve lipid transport and utilization. It was suggested that increased mitochondrial and peroxisomal fatty acid oxidation in the liver of Wistar rats results in reduced plasma triacylglycerol (TAG) levels. Here we assessed the potential of TTA to prevent tumor necrosis factor (TNF) α-induced lipid modifications in human TNFα (hTNFα) transgenic mice. These mice are characterized by reduced β-oxidation and changed fatty acid composition in the liver. The effect of dietary treatment with TTA on persistent, low-grade hTNFα overexpression in mice showed a beneficial effect through decreasing TAG plasma concentrations and positively affecting saturated and monounsaturated fatty acid proportions in the liver, leading to an increased anti-inflammatory fatty acid index in this group. We also observed an increase of mitochondrial β-oxidation in the livers of TTA treated mice. Concomitantly, there were enhanced plasma levels of carnitine, acetyl carnitine, propionyl carnitine, and octanoyl carnitine, no changed levels in trimethyllysine and palmitoyl carnitine, and a decreased level of the precursor for carnitine, called γ-butyrobetaine. Nevertheless, TTA administration led to increased hepatic TAG levels that warrant further investigations to ascertain that TTA may be a promising candidate for use in the amelioration of inflammatory disorders characterized by changed lipid metabolism due to raised TNFα levels.     

Effect of sesamin on mitochondrial and peroxisomal β-oxidation of arachidonic and eicosapentaenoic acids in rat liver

The effects of dietary sesamin on the hepatic metabolism of arachidonic (AA) and eicosapentaenoic (EPA) acids, were investigated with respect to their β-oxidation and secretion as triacylglycerol (TG). For 2 wk, rats were fed three types of dietary oils: (i) corn oil (control) group; (ii) FPA group: FPA ethyl esters/rapeseed oil=2∶3; (iii) AA group: AA ethyl esters/palm oil/perilla oil=2∶2∶1, with or without 0.5% (w/w) of sesamin. Dietary sesamin significantly increased the activities of hepatic mitochondrial and peroxisomal fatty acid oxidation enzymes (mitochondrial carnitine acyltransferase I, acyl-CoA dehydrogenase, and peroxisomal acyl-CoA oxidase). Dietary FPA increased mitochondrial carnitine acyltransferase I and peroxisomal acyl-CoA oxidase. Dietary AA, however, had an effect on peroxisomal acyl-CoA oxidase only. In whole liver and the TG fraction, EPA and AA concentrations were significantly increased by dietary EPA and AA, respectively, and were decreased by dietary sesamin. In hepatic mitochondria and peroxisomes, EPA concentration was increased by dietary EPA, but AA was not changed by dietary AA. The addition of dietary sesamin to the EPA-supplemented diet significantly decreased the EPA concentration compared to concentrations found with consumption of dietary EPA alone. These results suggest that sesamin increased β-oxidation enzyme activities and reduced hepatic EPA and AA concentrations by degradation. The stimulating effect of sesamin on β-oxidation, however, was more significant in the EPA group than in the AA group. Hepatic AA concentration was altered by the joint effect of sesamin through esterification into TG and the stimulation of β-oxidation.     

On the interrelationship between hepatic carnitine, fatty acid oxidation, and triglyceride biosynthesis in nephrosis

The nephrotic syndrome is associated with disturbances in plasma lipid pattern and metabolism. However, the reason for these perturbations is poorly understood. In the present study, we have investigated hepatic triglyceride metabolism in puromycin aminonucleoside-induced nephrotic syndrome in rats. Nephrotic rats displayed a 70% increase in hepatic triglyceride levels compared to controls (16.9±1.6 vs. 9.8±0.6 μmol/g liver; means±SEM, P<0.01). The capacity for hepatic mitochondrial β-oxidation of fatty acids was substantially elevated (80%). This was associated with a rise in the liver content of the fatty acid carrier carnitine (1.24±0.06 vs. 0.85±0.07 μmol/g dry weight, P<0.05). A positive correlation between the levels of acetylcarnitine and acetyl-CoA was found in normal as well as in nephrotic rats, implying that carnitine plays an important role as an acetyl group acceptor in the liver under normo- and hyperlipidemic conditions. Changes in carnitine levels seem to be tightly coupled to the rate of fatty acid oxidation. There was a significant elevation in the activity of phosphatidate phosphohydrolase (E.C. 3.1.3.4) in liver microsomes from nephrotic rats (1.07±0.09 vs. 0.81±0.04 nmol/min·mg protein, P<0.02). Hepatic very low density lipoprotein (VLDL)-triglyceride secretion rate was 18% higher in nephrotic rats than in controls. The results demonstrate a deranged hepatic triglyceride metabolism in nephrosis, with an increased hepatic triglyceride biosynthesis, a sizable accumulation of hepatic triglycerides, and only a modest increase in VLDL triglyceride secretion. In addition, mitochondrial β-oxidation of fatty acids was enhanced, associated with an increased availability of carnitine.     

On the effect of peroxisomal β-oxidation and carnitine palmitoyltransferase activity by eicosapentaenoic acid in liver and heart from rats

Repeated administration of highly purified eicosapentaenoic acid (as ethyl ester) resulted in a decrease in plasma triglycerides and high density lipoprotein (HDL) cholesterol. This was accompanied by a stimulation in the activities of carnitine palmitoyltransferase, fatty acyl-CoA oxidase and peroxisomal β-oxidation in the liver. The results suggest that the triglyceride-lowering effect observed with eicosapentaenoic acid may be due to a reduced supply of fatty acids for hepatic triglyceride synthesis because of increased fatty acid oxidation. Eicosapentaenoic acid feeding marginally affected the triglyceride content of heart and mitochondrial and peroxisomal enzyme activities.     

Eicosapentaenoic acid,but not oleic acid,stimulates β-oxidation in adipocytes

The beneficial roles of dietary fish oil in lowering serum TAG levels in animals and humans have been attributed in part to the high content of two n−3 polyunsaturated very long-chain FA, EPA, and DHA. Recent studies show that EPA induces mitochondrial β-oxidation in hepatocytes, which might contribute to the systemic lipid-lowering effect. Whether EPA affects FA storage or oxidation in adipocytes is not clear. To investigate this possibility, 3T3-L1 adipocytes incubated with EPA (100 μM) for 24 h were assayed for β-oxidation, carnitine palmitoyl transferase 1 (CPT-1) activity, protein, and mRNA expression of CPT-1. For comparison, cells treated with oleic acid, octanoic acid, and clofibrate, a synthetic ligand for peroxisome proliferator-activated receptor α were also analyzed. Mitochondria were isolated by differential centrifugation, and the mitochondrial membrane acyl chain composition was measured by GLC. EPA increased the oxidation of endogenous FA but did not inhibit lipogenesis. Oleic acid and clofibrate did not affect FA oxidation or lipogenesis, whereas octanoic acid suppressed the oxidation of endogenous FA and inhibited lipogenesis. Increased β-oxidation by EPA was associated with increased CPT-1 activity but without changes in its mRNA and protein expression. EPA treatment increased the percentage of this FA in the mitochondrial membrane lipids. We suggest that EPA increased the activity of CPT-1 and β-oxidation in adipocytes by altering the structure or dynamics of the mitochondrial membranes.     

Long-term effects of high-fat diets on peroxisomal β-oxidation in male and female rats

In weanling male rats a 4-fold increase of heart triacylglycerols was observed after three days on a high-fat diet containing partially hydrogenated fish oil (PHFO). In female rats this increase was only about 50%. No significant differences were observed between female and male rats in the fatty acid composition of the accumulated lipids. The initial level of peroxisomal β-oxidation activity was similar in male and female rats in both liver and heart. After three weeks of receiving high-fat diets, the rats showed a marked increase in peroxisomal β-oxidation activity with PHFO in the diet and less with soybean oil (SO), confirming previous studies with male rats. Catalase activity was similarly affected in hearts of both sexes. In male rats the levels of peroxisomal β-oxidation observed after three weeks of feeding on the high-fat diets were found to be maintained, both in liver and heart, during a feeding period of three months. The response to high-fat diets in females, however, seems to be further accentuated after three months of feeding, resulting in a capacity of peroxisomal β-oxidation in liver of about three times that of the male rats when calculated on a total body-weight basis.     

Pitavastatin ameliorates severe hepatic steatosis in aromatase-deficient (Ar−/−) mice

Tamoxifen is a potent antagonist of estrogen, and hepatic steatosis is a frequent complication in adjuvant tamoxifen for breast cancer. Impaired hepatic FA β-oxidation in peroxisomes, microsomes, and mitochondria results in progression of massive hepatic steatosis in estrogen deficiency. This impairment, although latent, is potentially serious: About 3% of the general population in the United States is now suffering from nonalcoholic steatohepatitis associated with obesity and hyperlipidemia. Therefore, in the present study we tried to restore impaired hepatic FA β-oxidation by administering a novel statin, pitavastatin, to aromatase-deficient (Ar−/−) mice defective in intrinsic estrogen synthesis. Northern blot analysis of Ar−/− mice liver revealed a significant restoration of mRNA expression of essential enzymes involved in FA β-oxidation such as very long fatty acyl-CoA synthetase in peroxisome, peroxisomal fatty acyl-CoA oxidase, and medium-chain acyl-CoA dehydrogenase. Severe hepatic steatosis observed in Ar−/− mice substantially regressed. Consistent findings were obtained in the in vitro assays of FA β-oxidation activity. These findings demonstrate that pitavastatin is capable of restoring impaired FA β-oxidation in vivo via the peroxisome proliferator-activated receptor-α-mediated signaling pathway and is potent enough to ameliorate severe hepatic steatosis in mice deficient in intrinsic estrogen.     

Acetyl carnitine formation in rat heart

The comparative incorporation of acetate into long chain fatty acids and acetyl carnitine by cell-free preparations of rat heart has been investigated. Whereas the addition of 1 mM carnitine stimulated (45%) fatty acid synthesis by liver preparations in citrate-containing media, fatty acid synthesis from acetate in rat heart homogenates under the same incubation conditions was markedly depressed. This depression by carnitine of acetate incorporation into long chain fatty acids in 105,000 × g soluble fractions of heart was associated with increased acetyl carnitine formation. Thus in heart tissue acetyl CoA is effectively shuttled into acetyl carnitine and is unavailable for synthesis of fatty acids. These data are in agreement with results obtained earlier in studies with perfused rat heart. A similar conversion of added acetyl CoA to the carntine derivative occurred when labeled malonyl CoA was used as fatty acid precursor, again resulting in reduced fatty acid synthesis. It was shown by direct measurement that acetyl carnitine formation in the absence of carnitine was greatest in heart mitochondria and least in microsomes. In the presence of carnitine, acetyl carnitine formation was increased in all subcellular fractions, with the greatest change again occurring with mitochondria.     

The effect of clofibrate on heart and plasma lipids in rats fed a diet containing rapeseed oil

The effect of clofibrate on heart and plasma lipids in rats fed a diet containing 30% of the calories as peanut oil (PO) or rapeseed oil (RSO) (42.7% erucic acid and 0.5% eicosenoic acid) was studied. A decrease of erucic acid content to one-third and concomitant increase in the content of 18∶1, 16∶1 and 16∶0 fatty acids in plasma triacylglycerols were observed after administration of clofibrate to rats fed the RSO-diet. It is suggested that these changes reflect the increased capacity of the liver to chainshorten very long chain length fatty acids. The extent of lipidosis in the heart of rats fed the RSO-diet was decreased by 50% by clofibrate. However, the concentration of erucic acid in heart triacylglycerols decreased much less (30%) than the concentration of all other fatty acids (50–65%). It is concluded that the clofibrate administration increased the oxidative capacity of the heart mitochondria and that the heart cell does not have an efficient system to handle very long chain length monounsaturated fatty acids as does the liver.     

Activities of liver mitochondrial and peroxisomal fatty acid oxidation enzymes in rats fedtrans fat

The effect oftrans fat on the activities of liver mitochondrial and peroxisomal fatty acid oxidation enzymes was examined in various strains of rats. When Wistar and Sprague-Dawley rats were fed for 30 days diets containing either olive oil or partially hydrogenated corn oil as a source ofcis-ortrans-octadecenoate, respectively, the activities of various enzymes of mitochondrial and peroxisomal β-oxidation measured withcis- andtrans-9-octadecenoic acid as substratese showed little dietary fatdependent change. In Fischer 344 rats, feedingtrans fat for 15 mo increased only moderately various enzymes of β-oxidation except for carnitine acyltransferase. The rate of mitochondrial ketogenesis and the activity of carnitine acyltransferase measured withtrans-9-octadecenoic acid as a substrate were about half those with thecis-counterpart. Peroxisomes oxidizedtrans-9-octadecenoyl-CoA at a rate comparable to thecis-counterpart. It was concluded from this study and previous ones that the difference in the geometry of dietary fatty acid had only a marginal effect in modulating the hepatic fatty acid oxidation system, in spite of marked differences in the metabolic behavior ofcis-andtrans fatty acid in cell-free preparations and perfused liver.     

Mitochondrial hydroxylation of the cyclohexane ring as a result of β-oxidation blockade of a cyclohexyl substituted fatty acid

Among the urinary metabolites of dodecylcyclohexane or cyclohexylacetic acid, the glycine conjugate of 1-hydroxy-cyclohexylacetic acid was identified and its origin studied, using cyclohexylacetic acid as the starting molecule, as it results from β-oxidation of cyclohexyldodecanoic acid produced by terminal oxidation of the alkyl chain of the cycloparaffin. Three hypotheses were tested: (a) hydroxylation by the liver microsomal mixed-function oxidases involved in detoxication mechanisms; (b) hydroxylation by a cyt. P₄₅₀-containing mitochondrial hydroxylase; and (c) β-oxidation blockade after the reaction catalyzed by enoyl-CoA-hydratase. Liver microsomal or mitochondrial fractions were prepared and incubated in the presence of [¹⁴C] cyclohexylacetic acid, glucose-6-phosphate dehydrogenase and a NADPH-producing system. On the other hand, mitochondria were incubated in a suitable respiratory medium with or without cofactors required for ATP production. The reaction products were extracted and analyzed by thin layer radiochromatography and radio gas chromatography. Evidence is given that hydroxylation of cyclohexylacetic acid in position 1 is a mitochondrial step requiring activation in the acyl-CoA form and results from β-oxidation blockade, the cyclohexane ring hindering hydroxyacyl-CoA-dehydrogenase action.     

Restriction of maternal food intake inhibits fatty acid activation in developing rat hearts

We studied the effect of restricting the diet of pregnant and lactating rats on the β-oxidation of fatty acids by the developing heart in suckling pups. Control pregnant rats were fed a stock diet ad libitum. For the experimental group, food was restricted to half of the control intake on the seventh day of pregnancy and continued through lactation. The pups on the restricted diet were significantly smaller than the controls. At postnatal days 5, 14 and 21, the β-oxidation of [1-¹⁴C] palmitate by heart homogenates was determined in the presence of ATP, carnitine and CoA. At day 21, the production of¹⁴CO₂ was 60% lower in the group on the restricted diet. Consequently, the possibility of inhibiting activation or intramitochondrial transport of fatty acids by heart mitochondria was studied in vitro using [1-¹⁴C] palmitate, [1-¹⁴C] palmitoyl CoA and [1-¹⁴C] palmitoyl carnitine. With [1-¹⁴C]-palmitate, the rate of¹⁴CO₂ produced was 2464±317 cpm/mg protein/min for the control and 1682±91 for the restricted diet group. With [1-¹⁴C] palmitoyl CoA and [1-¹⁴C] palmitoyl carnitine, the oxidation rate of the experimental group was similar to control values, showing clearly that the inhibition of oxidation was from a problem with activation. A significant decrease in palmitoyl CoA synthetase activity in the heart homogenates and mitochondria of the diet-restricted pups took place. Presented at the 74th Annual Meeting of the American Oil Chemists' Society, Chicago, Illinois, May 1983. Deceased.     

Changes in fatty acid composition of cardiac mitochondrial phospholipids in rats fed rapeseed oil

Male Wistar rats were fed rapeseed oil containing high or low levels or erucic acid for 20 weeks, and changes in the fatty acid composition of cardiac mitochondrial phospholipids were studied. Treatment with rapeseed oil containing 46.2% erucic acid showed incorporation of 22∶1 (5.6%) into isolated cardiolipin from heart mitochondria. After high or low (3.7%) erucic rapeseed oil feeding, linoleic acid was slightly incorporated into cardiolipin. Moreover, both of these rapeseed oils induced a significant increase of linoleate-arachidonate ratio in phosphatidylethanolamine and phosphatidylcholine. This ratio was also significantly increased in fatty acids esterified to the β-position of these phospholipids. On the basis of such results, we have to consider the role of linolenic acid which is present at a high level in the different rapeseed oils used, as a possible inhibitor of heart microsomal enzymes involved in linoleate arachidonate conversion. Such alterations might account for mitochondrial fragility and myocardial lesions obtained in long term rapeseed oil feeding experiments. ERA-CNRS n^o 070497