Paradoxical conservation of cardiac and renal arachidonate content in essential fatty acid deficiency

Fatty acid abnormalities in cystic fibrosis-the missing link for a cure?

The care for cystic fibrosis (CF) has dramatically changed with the development of modulators, correctors, and potentiators of the CFTR molecule, which lead to improved clinical status of most people with CF (pwCF). The modulators influence phospholipids and ceramides, but not linoleic acid (LA) deficiency, associated with more severe phenotypes of CF. The LA deficiency is associated with upregulation of its transfer to arachidonic acid (AA). The AA release from membranes is increased and associated with increase of pro-inflammatory prostanoids and the characteristic inflammation is present before birth and bacterial infections. Docosahexaenoic acid is often decreased, especially in associated liver disease Some endogenously synthesized fatty acids are increased. Cholesterol and ceramide metabolisms are disturbed. The lipid abnormalities are present at birth, and before feeding in transgenic pigs and ferrets. This review focus on the lipid abnormalities and their associations to clinical symptoms in CF, based on clinical studies and experimental research.

Arachidonic acid and docosahexaenoic acid supplemented to an essential fatty acid-deficient diet alters the response to endotoxin in rats

This study examined fatty acid profiles, triene-tetraene ratios (20:3n9/20:4n6), and nutritional and inflammatory markers in rats fed an essential fatty acid-deficient (EFAD) diet provided as 2% hydrogenated coconut oil (HCO) alone for 2 weeks or with 1.3 mg of arachidonic acid (AA) and 3.3 mg of docosahexaenoic acid (DHA) (AA + DHA) added to achieve 2% fat. Healthy controls were fed an AIN 93M diet (AIN) with 2% soybean oil. The HCO and AA + DHA diets led to significant reductions of linoleic acid, α-linolenic acid, and AA (20:4n6) and increases in Mead acid (20:3n9) in plasma and liver compared with the AIN diet; but the triene-tetraene levels remained well within normal. However, levels of 20:3n9 and 20:4n6 were lower in liver phospholipids in the AA + DHA than in HCO group, suggesting reduced elongation and desaturation in ω-9 and -6 pathways. The AA + DHA group also had significantly lower levels of 18:1n9 and 16:1n7 as well as 18:1n9/18:0 and 16:1n7/16:0 than the HCO group, suggesting inhibition of stearyl-Co A desaturase-1 activity. In response to lipopolysaccharide, the levels of tumor necrosis factor and interleukin-6 were significantly lower with HCO, reflecting reduced inflammation. The AA + DHA group had higher levels of IL-6 and C-reactive protein than the HCO group but significantly lower than the AIN group. However, in response to endotoxin, interleukin-6 was higher with AA + DHA than with AIN. Feeding an EFAD diet reduces baseline inflammation and inflammatory response to endotoxin long before the development of EFAD, and added AA + DHA modifies this response.

Postnatal essential fatty acid deficiency in mice affects lipoproteins, hepatic lipids, fatty acids and mRNA expression

We have previously reported that essential fatty acid deficiency (EFAD) during suckling in mice resulted in an adult lean phenotype and a resistance to diet-induced obesity. We now hypothesized that postnatal EFAD would cause long-term effects on lipid metabolism. C57BL/6 mice were fed an EFAD or a control diet from the 16th day of gestation and throughout lactation. The pups were weaned to standard diet (STD) and at 15 weeks of age given either high fat diet (HFD) or STD. Lipoprotein profiles, hepatic lipids, fatty acids and mRNA expression were analyzed in 3-week-old and 25-week-old offspring. At weaning, the EFAD pups had higher cholesterol levels in both plasma and liver and 6-fold higher concentrations of hepatic cholesterol esters than control pups. Adult EFAD offspring had higher levels of hepatic cholesterol and linoleic acid, but lower levels of dihomo-γ-linolenic acid and Pparg mRNA expression in the liver. In addition, HFD fed EFAD offspring had lower plasma total cholesterol, lower hepatic triglycerides and lower liver weight compared to controls fed HFD. In conclusion, early postnatal EFAD resulted in short-term alterations with increased hepatic cholesterol accumulation and long-term protection against diet-induced liver steatosis and hypercholesterolemia.

Maternal arachidonic acid supplementation improves neurodevelopment in young adult offspring from rat dams with and without diabetes

Maternal diabetes may compromise infant arachidonic acid (AA) status and development. This study tested if maternal AA supplementation improves neurodevelopment in adult offspring. Rat dams were randomized into 6 groups: Saline-Placebo, streptozotocin-induced diabetes with glucose controlled at <13mmol/L, or poorly controlled at 13-20mmol/L using insulin; and fed either a Control or AA (0.5% fat) diet throughout reproduction. Weaned-offspring were fed regular chow to 12 weeks of age. Testing included exploratory behavior, rota rod and water maze (WM). Poorly controlled offspring showed longer (p≤0.018) escape-latency on testing-day 1 WM but not thereafter (p>0.05). Maternal glucose concentration positively correlated with (p=0.006) male offspring testing-day 1 WM latency. The AA-diet offspring performed better in WM and rota rod (p≤0.032) and showed higher exploratory behavior (p=0.008) than Control-diet offspring. These data suggest maternal hyperglycemia has longstanding consequences to initial stages of learning in the offspring. Maternal AA supplementation and training positively influence learning outcomes.

Early development of essential fatty acid deficiency in rats: fat-free vs. hydrogenated coconut oil diet

This study examined the effects of feeding an essential fatty acid deficient (EFAD) diet either without fat or with added hydrogenated coconut oil (HCO) on fatty acid profiles in rats. Both diets induced equivalent biochemical evidence of EFAD reflected by the triene/tetraene ratio in plasma phospholipids within 2 weeks. However, the HCO diet led to larger increases of 16:1n7 and 18:1n9 in muscle but smaller increases in fat tissue and plasma triglycerides than the fat-free diet, suggesting greater increases in hepatic de novo lipogenesis with the latter. In addition, the HCO diet led to larger decreases of some 18:3n3 metabolites, particularly 22:6n3, in muscle, fat and brain tissues than the fat-free diet, presumably related to lesser stimulation of elongation and desaturation. Thus, these secondary effects of an EFAD diet on fatty acid metabolism can be modified by the saturated fat in the diet while the primary impact of both diets on development of EFAD is unaffected.

Comparative fatty acid profiles of wild and farmed tropical freshwater fish rohu (Labeo rohita)

The proximate composition of the whole body and the fatty acid composition of the liver, muscle, eye and brain of wild and cultured rohu (Labeo rohita) were analyzed. The cultured species was found to have significantly (P < 0.05) higher lipid contents than its wild counterpart. The saturated (SFA) and monounsaturated (MUFA) fatty acid contents were significantly higher in the cultured species, whereas the n-6 and n-3 polyunsaturated fatty acid (PUFA) levels were higher in the wild species. Fatty acids C16:0 and C18:1 n-9 were the principal fatty acids of the SFAs and MUFAs, respectively, identified in the analyses. Docosahexaenoic acid, eicosapentaenoic acid, and arachidonic acid were the predominant PUFAs in both groups, and all three were found to be present at significantly (P < 0.05) higher levels in the wild species. Erucic acid (C22:1 n-9), which was the predominant fatty acid (30.76%) in the feed, was detected only at low levels in muscle (0.30%), liver (1.04%) and eye (1.28%) of cultured fish tissue.

Fatty acid composition of liver, adipose tissue, spleen, and heart of mice fed diets containing t10, c12-, and c9, t11-conjugated linoleic acid

Conjugated linoleic acid (CLA) isomers have unique effects on tissue lipids. Here we investigated the influence of individual CLA isomers on the lipid weight and fatty acid composition of lipid metabolizing (i.e. liver and retroperitoneal adipose) and lipid sensitive (i.e. spleen and heart) tissues. Female mice (8 week old; n=6/group) were fed either a control or one of the two CLA isomer supplemented (0.5%) diets for 8 weeks. The cis-9, trans-11-CLA diet reduced the 18:1n-9 wt% by 20-50% in liver, adipose tissue, and spleen, reduced the spleen n-3 polyunsaturated fatty acid (PUFA) by 90%, and increased the n-6 PUFA wt% by 20-50% in all tissues except heart. The trans-10, cis-12-CLA reduced both the n-6 and n-3 PUFA wt% in liver (>50%), reduced the heart n-3 PUFA wt% by 25%, and increased the wt% of spleen n-3 PUFA by 700%. The functional consequences of such changes in tissue fatty acid composition need to be investigated.

Biochemical, functional, and histochemical effects of essential fatty acid deficiency in rat kidney

The present study was designed to examine the effects of EFA deficiency (EFAD) on biochemical, functional, and structural aspects of the kidney in growing and adult rats fed a normal or EFAD diet for 9 wk after weaning. Food and fluid intake (F1), urine volume, and Na+ and K+ excretions were measured weekly from weeks 4 to 8 by placing the rats in individual metabolic cages for 24 h. At week 9, Li+ and a 5% water load, respectively, were administered at 14 and 1.5 h prior to glomerular and proximal tubular function studies, as assessed by 3-h creatinine (C(Cr)) and Li+ (C(Li+)) clearances. Hematocrit and urine volume; serum and urine [Cr], [Li+], [Na+], and [K+]; and renal FA distribution were also measured. Data [corrected to 100 g/body weight (bw) and presented as means +/- SEM] were significant, at P< or = 0.05. Despite a similar ingestion of solids from weeks 4 to 7 (weeks 7 to 10 of life), the rats on the EFAD diet showed a decreased body weight from week 5. From weeks 4 to 8, Fl and urine volume were similar for both groups, but the Fl increased at week 6 in the EFAD group; 24-h Na+ and K+ excretions were similar at all weeks, except for an increase in the EFAD group for both ions at week 7. In the EFAD group, CCr and CLi+ decreased by 27 and 56.3%, respectively (385.7 +/- 33.4 vs. 280 +/- 21.1, and 21.0 +/- 2.1 vs. 9.2 +/- 1.1 microL/min/100 g; n = 9 vs. 10), the latter result suggesting increased proximal reabsorption. The 3-h Na+ and K+ excretions were similar, but the Li+ decreased (0.78 +/- 0.06 x 10(-2) vs. 0.32 +/- 0.03 x 10(-2) microeq/min/100 g) in the EFAD group, giving additional support to the suggestion. Renal structure was normal and similar for both groups, but the EFAD group showed a more prominent proximal tubule brush border, together with heavier periodic acid-Schiff staining in all specimens from weeks 5 to 9. In the EFAD group, FA of the n-9 and n-7 series were higher, but most of the n-6 series were lower as a percentage of total lipids in the medulla and cortex. Medullary levels of 20:4n-6 were maintained, 22:4n-6 declined twice, arachidonic acid was maintained, and 20:5n-3 was lower. The EFAD diet affected glomerular function, proximal tubular structure and function, and FA distribution in the rat kidney.

Effects of essential fatty acid deficiency on periodontal tissue adaptation to spontaneous tooth migration

Essential fatty acids (EFAs) play a significant role in bone metabolism. Herein we studied the adaptation of alveolar bone to physiologic tooth drift in young rats deprived of essential fatty acids from birth. Reductions in femur size and trabecular bone volume reflected body growth impairment. Along the alveolar wall, osteoclastic resorption and bone formation were depressed, disrupting the adaptive deformation of the tooth socket to ongoing migration. As a result, the periodontal ligament narrowed considerably, and further adaptation was achieved through root resorption. Essential fatty acid deficiency (EFAD), did not affect precursor recruitment or differentiation in the periodontal ligament (PDL), but caused redistribution of nonspecific-esterase (NSE)-positive osteoclast precursors and tartrate-resistant acid phosphatase (TRAP)-positive pre-osteoclasts between the bone compartment (which was depleted) and the root compartment (which was enriched). EFAD had also a marked effect on the PDL vasculature; the number of vessels was reduced, whereas their size was markedly increased. As a whole, our results show that EFAD disturbs alveolar bone adaptation to drift, but that a reaction (detrimental to root integrity) prevents root collision with the bone surface, thereby preserving the PDL as a source of precursor cells for bone and cementum homeostasis. Moreover, our results confirm that although alveolar bone resorption is arachidonic acid-dependent, the factors activating root resorption are different.

Differential utilization of hepatic and myocardial fatty acids during forced molt of laying hens

Feed was totally withdrawn from laying hens (n = 30, Hy-Line Brown, 608 d of age, 2.04 +/- 0.07 kg of mean BW) to induce molting. Ten birds were slaughtered on d 0 and 12, and the hepatic and myocardial triacylglycerol (TAG) and phospholipid (PL) fatty acid composition, as well as the tissue malondialdehyde (MDA) and reduced glutathione (GSH) concentrations were determined. The liver TAG and PL contents decreased by 24.3 and 16.1%, respectively, whereas the myocardial TAG content increased by 12%, and the PL decreased by 22%. Liver TAG fraction has been found to selectively retain arachidonic and docosahexanoic acids. Hepatic PL fatty acids were markedly affected by fasting; these changes reflected an altered PL metabolism, primarily degradation. Liver TAG compensated for the absence of dietary fatty acids, because we found practically no qualitative alteration in myocardial TAG. The lipid peroxide status, as measured with MDA content was, accordingly, increased in the liver tissue only. In the myocardial PL fatty acids, preferred conservation of arachidonic acid was shown, and it was hypothesized that energy deprivation of cardiomyocytes strongly improved PL degradation in fasting laying hens and influenced PL homeostasis. Generally the physiological recovery from forced molting associated with fasting is complete; however, the use of total feed withdrawal methods should be reevaluated.

Essential fatty acid deficiency affects the fatty acid composition of the rat small intestinal and colonic mucosa differently

The intestinal mucosal fatty acid (FA) composition was investigated in Sprague-Dawley rats after 7 and 23 weeks on an isocaloric diet with qualitatively different essential fatty acid (EFA) composition. For comparison, serum and red blood cell (RBC) membranes were investigated in parallel. The molar percentage of most FAs differed significantly between serum and RBC membranes both in controls and rats fed an EFA deficient (EFAD) diet. The influence of the EFA diet was similar on serum and RBC membrane phospholipids except for arachidonic acid (AA) which was more markedly decreased in serum than in RBC membranes. The FA composition was similar in ileal and colonic mucosa, markedly differing from the jejunal mucosa, in which the AA concentration was lower (13.0+/-0.8 versus 16.8+/-0.5 and 15. 7+/-2.8 mol%) and the linoleic acid (LA) concentration higher (34. 0+/-1.6 versus 17.8+/-1.3 and 15.5+/-2.8 mol%, respectively). The EFAD diet induced a more than five-fold decrease in the jejunal and ileal concentration of LA from 33.9+/-1.6 to 6.0+/-1.5 mol% and 17. 8+/-1.3 to 2.1+/-0.7 mol%, respectively. AA decreased more in the ileal and colonic mucosa than in the jejunum. The changes in the FA composition of the intestinal compartments after EFAD diet were different from that in serum and RBC membranes, and did not further change after 23 weeks compared to 7 weeks after introduction of the diet. The study shows that dietary influences are tissue specific and serum or RBC membranes do not mirror local changes in any of the different intestinal segments.

Effects of altering dietary fatty acid composition on prostaglandin synthesis and fertility

Several studies over the past 20 years have demonstrated that subjects on diets composed of substances with high levels of n-3 polyunsaturated fatty acids (PUFAs) (e.g. fish) have a decreased incidence of heart disease. On this basis, a recent report from the Department of Health has advised UK consumers to decrease the proportion of saturated as opposed to unsaturated fats in their diet and to increase the ratio of n-3 to n-6 PUFAs. This could be achieved by altering the amounts of these constituents in milk and meat. n-3 Fatty acids can most easily be added to animal feed as either fish oil or linseed oil and can be increased in the blood and milk of ruminants following protection to avoid hydrogenation in the rumen. In western countries the ratio of consumption of n-6 to n-3 PUFAs is greater than 10 and current evidence tends to suggest that a ratio nearer 5 would be more desirable and compatible with cardiovascular well being. As fertility in the UK dairy herd is already poor, it is important to establish whether alterations in dietary n-3 and n-6 PUFAs affects herd fertility before widespread changes in animal diets are recommended. Therefore, this review considers the role played by PUFAs and eicosanoids in fertility, with particular reference to the implications for farm livestock production. The evidence reviewed shows that alteration of the concentration and ratio of n-6 and n-3 PUFAs in feeds can influence prostaglandin synthesis/metabolism in a number of mammalian systems. The changed patterns of prostaglandin synthesis can as a consequence, affect the diverse functions (e.g. hormone secretion) that are normally mediated via prostaglandins. Similarly, changes in prostaglandin synthesis effected through manipulation of PUFAs has a major bearing on fertility (as PGs affect many reproductive parameters, e.g. ovulation). Several studies in cattle and other mammals, show that feeding or infusing different types of fat with varying PUFA content to females can alter: the number and size of ovarian follicles, the ovulation rate, progesterone production by the corpus luteum, the timing of luteolysis and gestational length. In the male most recent work has focussed on sperm production and experiments in fowl have demonstrated clear effects of dietary PUFAs on both the sperm membrane phospholipid composition and on fertilizing ability.

Addition of triglycerides with arachidonic acid or docosahexaenoic acid to infant formula has tissue- and lipid class-specific effects on fatty acids and hepatic desaturase activities in formula-fed piglets

The effects of including triglycerides with arachidonic [20:4(n-6)] or docosahexaenoic acid [22:6(n-3)] in formula on plasma chylomicron, LDL and HDL, liver, heart, kidney and brain (n-6) and (n-3) fatty acids were investigated in formula-fed piglets. Piglets were fed formula with (in % total fatty acids) 20% 18:2(n-6) and 2% 18:3(n-3) without or with 0.8% 20:4(n-6) or 0.3% 22:6(n-3) from birth to 18 d. The effects of adding 20:4(n-6) or 22:6(n-3) to the formula differed among different tissues and lipids, with the brain showing resistance to change. Piglets fed formula with 20:4(n-6) had significantly higher plasma, heart and kidney phospholipid and triglyceride, and liver triglyceride 20:4(n-6), but lower plasma and tissue phospholipid 18:2(n-6) than piglets fed formula without 20:4(n-6). Supplementation with 22:6(n-3), in contrast, had no effect on plasma or tissue 18:2(n-6). Higher 22:6(n-3) in liver phospholipid (30-92% greater) and triglyceride (200% greater) in piglets fed formula with 22:6(n-3) rather than without 22:6(n-3) was accompanied by lower 20:4(n-6) in liver phosphatidylethanolamine (mean +/- SEM, 8.6 +/- 0.4 and 10.5 +/- 0.4% fatty acids, respectively), but higher 20:4(n-6) in triglyceride (5.2 +/- 0.4 and 11.5 +/- 0.5%, respectively), and higher liver, heart and kidney phospholipid 20:5(n-3). These results indicate competitive interaction between dietary 20:4(n-6) and tissue 18:2(n-6), and between dietary 20:4(n-6) and tissue 20:5(n-3), rather than 22:6(n-3). The results also show that even at low intakes, dietary 22:6(n-3) or 20:4(n-6) supplementation alters the tissue phospholipid 20:4(n-6) to 20:5(n-3) balance. Studies on the physiologic effects of dietary 20:4(n-6) and 22:6(n-3) supplementation should consider the different sensitivity among tissues to dietary fatty acids.

The effect of essential fatty acid deficiency on the fatty acid composition of different salivary glands and saliva in rats

The main purpose was to compare the changes in fatty acid composition of lipids induced by essential fatty acid (EFA) deficiency in the rat submandibular, parotid and sublingual glands. Three groups of rats were fed for 28 weeks (1 week gestation, 3 weeks lactation and 24 weeks thereafter) diets containing 7% hydrogenated coconut oil (HCO) (EFA-deficient in both n-6 and n-3), 7% soybean oil (SBO) (control) and 7% safflower oil (SFO) (deficient in n-3). Rats were killed and salivary glands were dissected out. Lipids were extracted and the fatty acid composition of total lipids and phospholipids was determined by gas chromatography-mass spectrometry. The fatty-acid compositional changes indicative of an EFA deficiency, such as decreases in the levels of 18:2 n-6, along with an accumulation of 20:3 n-9, were generally observed in all the salivary glands of rats fed 7% HCO diet. In the submandibular glands, the proportions of 16:1, 18:1 n-9 and 18:1 n-7 were also higher in the HCO-fed group than in the other two groups. There were some differences in the fatty acid composition of the three glands. Total lipids of parotid gland had higher levels of 12:0 and 18:1 n-9 as compared to the other two glands. The levels of 18:0, 20:3 n-9, 20:3 n-6 and 20:4 n-6 were, however, lower in the parotid gland as compared with the other glands. In total phospholipids of rats fed SBO- and SFO-containing diets, the sublingual gland had lower levels of 18:2 n-6 and higher levels of 20:4 n-6 than the parotid or the submandibular. These differences in fatty acid composition may be related to possible differences in chain elongation/desaturation. The changes in fatty acid composition were also reflected in total lipids of plasma, liver and whole saliva of rats fed the various diets. A number of fatty acids were identified in saliva by gas chromatography-mass spectrometry.

Effects of essential fatty acid deficiency on prostaglandin E2 production and cell-mediated immunity in a mouse model of leprosy

Results from animal and in vitro studies suggest that essential fatty acid (EFA) deficiency enhances cell-mediated immunity by reducing production of prostaglandins with immunosuppressive actions. However, direct experimental evidence that EFA deficiency enhances T-lymphocyte function in vivo has not been obtained. In this study, athymic (nu/nu) mice were infected in the footpads with Mycobacterium leprae and fed a linoleic acid-free diet. These mice, and infected nu/nu mice on control diets, were given an adoptive transfer of M. leprae-primed, T-cell-enriched lymphocytes. After 2 weeks, M. leprae bacilli were harvested from the recipient mice and bacterial viability was determined by the BACTEC system. M. leprae recovered from recipient mice fed control diets displayed little reduction in metabolic activity. In contrast, M. leprae from recipient mice fed the EFA-deficient (EFAD) diet exhibited markedly reduced viability. In vitro, donor cells from M. leprae-primed mice secreted elevated levels of gamma interferon upon exposure to the bacilli. These cells also exhibited an enhanced proliferative response, which was reduced by exogenous prostaglandin E2 (PGE2). In addition, M. leprae-infected granuloma macrophages (Mphi) from EFAD recipient nu/nu mice secreted significantly less PGE2 than granuloma Mphi from mice on control diets. These data suggest that enhanced levels of Mphi-generated PGE2, induced by M. leprae or its constituents, could act as an endogenous negative modulator of the immune response occurring in the microenvironment of the lepromatous granuloma.

Oxygenation of 5,8,11-eicosatrienoic acid by prostaglandin H synthase-2 of ovine placental cotyledons: isolation of 13-hydroxy-5,8,11-eicosatrienoic and 11-hydroxy-5,8,12-eicosatrienoic acids

Prostaglandin H synthase-1 of ram vesicular glands metabolises 5,8,11-eicosatrienoic (Mead) acid to 13R-hydroxy-5,8,11-eicosatrienoic and to 11R-hydroxy-5,8,12-eicosatrienoic in a 5:1 ratio. We wanted to determine the metabolism of this fatty acid by prostaglandin H synthase-2. Western blot showed that microsomes of sheep and rabbit placental cotyledons contained prostaglandin H synthase-2, while prostaglandin H synthase-1 could not be detected. Microsomes of sheep cotyledons metabolised [1-14C]5,8,11-eicosatrienoic acid to many polar metabolites and diclofenac (0.05 mM) inhibited the biosynthesis. The two major metabolites were identified as 13-hydroxy-5,8,11-eicosatrienoic and 11-hydroxy-5,8,12-eicosatrienoic acids. They were formed in a ratio of 3:2, which was not changed by aspirin (2 mM). 5,8,11-Eicosatrienoic acid is likely oxygenated by removal of the pro-S hydrogen at C-13 and insertion of molecular oxygen at either C-13 or C-11, which is followed by reduction of the peroxy derivatives to 13-hydroxy-5,8,11-eicosatrienoic and 11-hydroxy-5,8,12-eicosatrienoic acids, respectively. Prostaglandin H synthase-1 and -2 oxygenate 5,8,11-eicosatrienoic acid only slowly compared with arachidonic acid.

Differential effects of 1,25-(OH)2D3 on acyl hydrolase and cyclooxygenase activities in interleukin 1 beta-stimulated human synovial fibroblast cultures

Effects of proinflammatory cytokines on synovial fibroblasts are considered to play a role in the accumulation of prostaglandin E2 (PGE2) in the inflamed joint in rheumatoid arthritis. We have previously shown that interleukin 1 beta (IL-1 beta) induces PGE2 production in synovial fibroblast cultures and that this effect is suppressed by the active metabolite of vitamin D3, 1,25-(OH)2D3. To study the mechanism of the inhibitory action of 1,25-(OH)2D3, its effect on acyl hydrolase (arachidonic acid (AA) release) and cyclooxygenase (COX) activities were investigated. Our findings indicate that IL-1 beta caused an increase in AA release and COX activity and that in the presence of 1,25-(OH)2D3 AA release, but not COX activity, is suppressed. In comparison, dexamethasone, which also inhibits IL-1 beta induction of PGE2, had inhibitory effects on both parameters.

Metabolism of orally fed [3H]-eicosapentaenoic and [14C]-arachidonic acid in essential fatty acid-deficient rats

The metabolism of individual polyunsaturated fatty acids (PUFA) may be influenced differently by nutritional status and nutritional intake. In normal rats, radioactive arachidonic acid (20:4(n-6), is preferentially retained in tissue phospholipids compared to linoleic (18:2(n-6), or eicosapentaenoic acid (20:5(n-3). This study compares the fate of 20:4(n-6) and 20:5(n-3) acids in essential fatty acid-deficient (EFAD) rats. [3H]-20:5 and [14C]-20:4 were fed in a fish oil emulsion to EFAD rats. Tissue lipids were analysed for radioactivity at 1, 2 and 4 h. The conversion of [3H]-20:5 to docosapentaenoic acid (22:5) and docosahexaenoic acid (22:6) was examined using high performance liquid chromatography (HPLC). The recovery of 3H in small intestine was lower than that of 14C (26 vs. 36% after 4 h, p < 0.001), but was higher in the liver (26 of 3H vs. 22% of 14C, p < 0.01), kidneys (1.5 vs. 1.2%, p < 0.001) and colon (0.3 vs. 0.2%, p = 0.01). The percentages of 3H and 14C in phospholipids were investigated in intestine and liver, and were higher in EFAD rats than in normal rats, particularly for phosphatidylethanolamine (PE). The proportions of [3H]-20:5 transformed to 22:5 and 22:6 did not exceed 7% in the intestine and 10% in the liver. In conclusion, the metabolism of dietary fatty acids 20:4 and 20:5 differed less than in normal rats, mainly due to the preferential retention of both fatty acids in phospholipids.

Changes in arachidonic acid metabolism and the aggregation of polymorphonuclear leukocytes in rats with streptozotocin-induced diabetes

Changes in lipid composition were examined in peritoneal polymorphonuclear leukocytes (PMNL) from rats with streptozotocin-induced diabetes. The largest changes associated with the lipids in PMNL prepared from rats with insulin-dependent diabetes mellitus were found in the composition of fatty acids of phospholipids although no consistent changes were noted in the amounts of phospholipids in individual classes. The relative amount of arachidonic acid was significantly reduced and that of linoleic acid was significantly increased in PMNL from diabetic rats. The extent of A23187-stimulated release of arachidonic acid from CGP and IGP in PMNL from diabetic rats was much smaller than that from normal PMNL. Moreover, there were decreases in the production of free arachidonic acid and its metabolites, such as LTB4 and 5-HETE by A23187-stimulated PMNL from diabetic rats as compared to PMNL from normal rats. Aggregation of PMNL provoked by A23187 was significantly suppressed in PMNL from diabetic rats. However, addition of free arachidonic acid or LTB4 to normal PMNL and to those from diabetic rats resulted in aggregation to similar extents, a result that supports a role for enhanced availability of endogenous arachidonic acid in the induction of the aggregation of PMNL from diabetic rats. The present results suggest that diabetes-associated changes in arachidonic acid metabolism might play a critical role in the modulation of aggregation of PMNL.

Ratios of linoleic acid to alpha-linolenic acid in formulas for term infants

Commercial infant formulas with a ratio of linoleic acid (LA) to alpha-linolenic acid (ALA) of 10:1 or higher are nutritionally inadequate; the tissue levels of docosahexaenoic acid (DHA) are lower and the visual function indices are reduced in infants who are fed these formulas. All the evidence points to using LA:ALA ratios of less than 8:1, but there has been only one study in infants that used formulas with reduced LA:ALA ratios, and only biochemical indices were monitored. There is a need for both short-term studies to establish the ratios of LA to ALA that will make possible the accumulation of DHA to levels close to those in breast-fed infants and long-term trials to determine the effects of such fat blends on growth and development.

A comparison of the specific activities of linoleate and arachidonate in liver, heart and kidney phospholipids after feeding rats ethyl linoleate-9,10,12,13-d4

In order to determine how dietary linoleate is metabolized, rats were maintained on a chemically defined diet containing 1.6% ethyl linoleate. After 5 weeks the linoleate was replaced by an equal amount of ethyl 9,10,12,13-d4-linoleate. The animals were killed 3 days later and the molar percentage of d4-linoleate and d4-arachidonate were quantified in liver, heart and kidney phospholipids. In liver, 54 and 22.8 mol% respectively of the esterified linoleate and arachidonate was deuteriated. The lower specific activity of arachidonate versus linoleate suggests that desaturation of linoleate, by a 6-desaturase, is not only rate limiting for synthesis of arachidonate but that the amount of newly synthesized arachidonate is insufficient by itself to maintain steady state levels of esterified arachidonate. The molar fraction of deuteriated linoleate in heart and kidney phospholipids was respectively 35 and 37.4%. These values are lower than for liver phospholipids but it appears there is adequate dietary linoleate available in these tissues for the synthesis of arachidonate. However, of the esterified arachidonate in heart and kidney phospholipids only 4.2 and 8.6 mol% respectively was deuteriated. Our results suggest that arachidonate is made in liver and transported to heart and kidney.

Prostaglandin E2 production in submandibular salivary glands of rats in essential fatty acid deficiency

Three groups of rats were fed an essential fatty acid (EFA)-deficient diet (EFAD), marginally EFA-deficient diet (MEFAD) or a control diet. Arachidonic acid levels in total phospholipids and the ex-vivo production of prostaglandin E2 (PGE2) in the presence of calcium ionophore were measured at 5 and 9 weeks in the submandibular salivary glands (SMSG). The arachidonic acid levels were significantly different among the 3 groups of rats fed the respective diets for 9 weeks. Ex-vivo PGE2 production was significantly decreased in the EFAD group but not in the MEFAD group as compared to the control group. The changes in fatty acid composition, arachidonic acid levels and ex-vivo production of PGE2 were reversed after 5 weeks of feeding the control diet to the EFAD or the MEFAD rats. Since arachidonic acid and PGE2 are involved in signal transduction pathways in the SMSG, an EFA deficiency is likely to modify these pathways.

Essential fatty acid deficiency in the pig: effects on eicosanoid basal levels and in vitro synthesis by the small intestine

The influence of nutritional essential fatty acid (EFA) deficiency on arachidonate metabolism by porcine small intestine has been studied. Great care was exercised in the manipulation of the jejunal wall to avoid artefactual metabolism of arachidonate. Thus, jejunal wall was frozen in liquid nitrogen after organ removal and washing, and subsequently lyophilized. This lyophilized tissue was used as starting material for all experiments, including organic solvent extractions (for basal level determinations) and reconstitution in aqueous buffer (for neosynthesis experiments). Feeding pigs with a low linoleate diet for 12 weeks resulted in a 36% diminution in the % of arachidonate in jejunal phospholipids. Basal levels of 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha), thromboxane B2 (TXB2), PGF2 alpha, PGE2, PGD2 and leukotriene B4 (LTB4) were not altered in the EFA-deficient state. However, we observed a significant lowering of the synthesis of each of these eicosanoids (except LTB4) by the EFA-deficient jejunum during brief (15s) in vitro neosynthesis experiments. The origin of arachidonate as a substrate of PG endoperoxide synthase, also named PGH synthase or cyclooxygenase (Cox) in these neosynthesis experiments is probably a non-esterified fatty acid pool since, (1) neosynthesis was not inhibited by the phospholipase A2 (PLA2) inhibitor parabromophenacylbromide, and (2) substantial amounts of arachidonic acid were found in the jejunum, frozen or lyophilized. Cox activity of the lyophilized jejunum and Cox content of liver and intestine microsomes were not modified in the EFA-deficient state.(ABSTRACT TRUNCATED AT 250 WORDS)

Delta 5 desaturase activity in rat kidney microsomes

Rat kidney microsomal fraction is able to catalyze the enzymatic desaturation of eicosatrienoic acid (20:3n-6) to arachidonic acid (20:4n-6) by the delta 5 desaturase pathway, in the presence of reduced nicotinamide adenine dinucleotide (NADH), adenosinetriphosphate (ATP) and coenzyme A (CoA). The substrate of the reaction [1-14C]eicosa-8,11,14-trienoic acid (20:3n-6), was separated from the product [1-14C]eicosa-5,8,11,14-tetraenoic acid (20:4n-6) by reverse phase high-pressure liquid chromatography (RP-HPLC). These fatty acids were individually collected by monitoring the eluent at 205 nm and their radioactivity was measured by liquid scintillation counting. The delta 5 desaturase activity in kidney microsomes increased linearly with the substrate concentration up to 20 microM. Enzymatic activity was sensitive to pH with the maximum at 7.0 and was proportional with incubation time up to 10 min. The apparent Km and Vmax of delta 5 desaturase were 56 microM and 60 pmoles.min-1.mg-1 microsomal protein, respectively. Neither the cytosolic renal fraction nor the cytosolic liver fraction enhanced the delta 5 desaturase activity. Contrary to a report but in accordance to others, the present results suggest that rat kidneys can synthesize arachidonic acid at least to satisfy partially their needs for eicosanoid production.

Increments of dietary linoleate raise liver arachidonate, but markedly reduce heart n-6 and n-3 fatty acids in the rat

Four diets containing 20% of energy (en%) as fat and with linoleic acid contents of 1.9, 3.1, 7.7 and 10.1 en%, respectively, were fed to one-month-old male rats for three months. The fatty acid profiles and the levels of the major n-6 and n-3 fatty acids in the lipids of plasma, liver, heart and kidney were measured. We found that with increasing concentrations of 18:2n-6 in the diet, linoleic acid rose in plasma and in all organs, but long-chain n-6 and n-3 fatty acids responded differently. In liver, arachidonic acid increased and n-3 fatty acids were not significantly affected; in heart, both arachidonic and docosahexaenoic acids were progressively reduced; and in kidney, there was no change of n-6 and n-3. The results indicate that incremental changes in dietary linoleate affect the levels of polyunsaturated fatty acids in liver and extrahepatic organs differently.

Arachidonic acid channelling in the phospholipid fractions and subcellular compartments of cultured myocardial cells

Arachidonic acid (AA) channeling in cultured heart cells was studied following pulse labelling for 1 h. AA was shown to be esterified immediately and equally distributed between the neutral lipids and phospholipids. A rapid constant flow to various phospholipid classes occurred thereafter, while the AA oxidation was only between 12%. The subcellular distribution of AA was studied by nitrogen cavitation followed by fractionation on 6.7% percoll in sucrose-EDTA. After 1 h pulse labeling and 2 h post-pulse incubation, most of the radioactivity was found in the sarcolemmal fraction with a much smaller amount in the mitochondrial fraction.

Reduction by clofibric acid of serum arachidonic acid in rats. Effect on the acyl composition of renal phospholipids

Alterations induced by p-chlorophenoxyisobutyric acid (clofibric acid) in the composition of phosphatidylcholine and cholesterol esters in serum and their influence on the composition of phosphatidylcholine in the kidney were studied. Rats of different ages responded differently to the drug in terms of the levels of arachidonic acid (20:4) and linoleic acid (18:2) in the phosphatidylcholine and cholesterol esters in the serum. Administration of clofibric acid to 26-week-old rats for 2 weeks caused a marked decreased in the relative level of 20:4 in phosphatidylcholine and cholesterol esters in serum, whereas similar treatment of 6-week-old rats resulted in a reduction of 18:2 and, to a lesser extent, of 20:4 in serum lipids. The decrease in phosphatidylcholine that contained 20:4 in the serum of old rats was mainly due to a decrease in the concentration of stearoyl-arachidonoyl (18:0-20:4) species. The decrease in cholesterol arachidonate in serum caused by the treatment of old rats with clofibric acid seemed to be due to a reduction in the relative level of serum phosphatidylcholine containing 20:4. The marked reduction in serum lipids that contained 20:4 caused a decrease in the relative level of 20:4 in renal phospholipids, in particular, a decrease in the proportion of palmitoyl-arachidonoyl (16:0-20:4) and 18:0-20:4 phosphatidylcholine.

Effect of dietary fats on some membrane-bound enzyme activities, membrane lipid composition and fatty acid profiles of rat heart sarcolemma

The effect of various dietary fats on membrane lipid composition, fatty acid profiles and membrane-bound enzyme activities of rat cardiac sarcolemma was assessed. Four groups of male weanling Charles Foster Young rats were fed diets containing 20% of groundnut, coconut, safflower or mustard oil for 16 weeks. Cardiac sarcolemma was prepared from each group and the activities of Na+, K(+)-ATPase, 5'-nucleotidase, Ca(2+)-ATPase and acetylcholinesterase were examined. ATPase activities were similar in all groups except the one fed coconut oil, which had the highest activities. Acetylcholinesterase activity was also similar in all the groups, however, it was significantly higher in the group fed mustard oil. No significant changes were observed among the groups in 5'-nucleotidase activity, in the cholesterol-to-phospholipid molar ratio and in sialic acid content. The coconut, safflower and mustard oil diets significantly increased cholesterol and phospholipid contents and the lipid-to-protein ratio of cardiac sarcolemma as compared to feeding the groundnut oil diet. The fatty acid composition of membrane lipids was quite different among the various groups, reflecting the type of dietary fat given. The total unsaturated-to-saturated fatty acid ratio was not different among the various groups; however, the levels of some major fatty acids such as palmitic (16:0), oleic (18:1) and linoleic (18:2) acids were significantly different. Cardiac sarcolemma of the group fed safflower oil had the highest polyunsaturated fatty acid content. The results suggest that dietary fats induce changes not only in the fatty acid composition of the component lipids but also in the activities of sarcolemmal enzymes involved in the regulation of cardiac function.

Essential fatty acids are not required for wound healing

Rats with essential fatty acid deficiency (EFAD) exhibit mild body growth retardation, diminished leukocyte influx in certain models of inflammation, and skin lesions characterized by ulceration, thinning and decreased pigmentation. In the present study we examined the role of EFAD in cutaneous wound healing, a process in which the inflammatory response and the macrophage play a central role. We reproduced the EFAD condition in Lewis rats (n = 35), and examined its effects in wound healing using the paired rat surgical incision model. Rats were compared with weight-matched controls, receiving standard chow diet. Skin samples harvested at days 5, 7, 14 and 21 post-wounding were evaluated for tensiometry and histology. EFAD rats exhibited all the characteristics of this condition, and the typical alteration of liver lipids. Skin samples harvested at different days post-wounding did not show difference in maximal breaking strength when compared to weight-matched controls. Histological evaluation of skin samples showed no difference in the cellular inflammatory infiltration in either EFAD rats or in weight-matched controls. Immunohistochemical studies revealed no difference in the influx of macrophages in the different groups of rats. Fatty acid supplementation of EFAD rats (n = 7), successfully reversed the EFAD state as assessed by the macroscopic skin and liver changes and liver fatty acid content, without modifying either tensile strength or cellular inflammatory infiltration. Our results suggest that EFAD does not alter the normal course of the cutaneous wound repair in rats, despite all the cutaneous alterations produced by this condition. We conclude that essential fatty acids (EFAs) are not essential for cutaneous wound repair.

Effect of an essential fatty acid deficiency on the phospholipid composition in anterior pituitary membranes

The effects of an essential fatty acid deficient diet were investigated on the phospholipid fatty acids of several membrane fractions of the rat anterior pituitary, the secretion of which is known to be partly dependent on the membrane phospholipidic constituents. In standard dietary conditions, arachidonic acid (20:4n-6) and its elongation product, adrenic acid (22:4n-6), were the two main polyunsaturated fatty acids in all fractions studied. In rats deprived of EFA for 6 weeks after weaning, the levels of both 20:4n-6 and 22:4n-6 were not changed in microsomal + plasma membrane and nuclear fractions, whereas they were decreased in heavy mitochondrial and light mitochondrial fractions. The present data suggest a mechanism of compensation between membrane fractions which may preferentially preserve 20:4n-6 and 22:4n-6 in discrete membrane fractions.

Apparent relative retention of the phosphatidylethanolamine molecular species 18:0-20:5(n-3), 16:0-22:6(n-3) and the sum 16:0-20:4(n-6) plus 16:0-20:3(n-9) in the liver microsomes of pig on an essential fatty acid deficient diet

Attempts at a better understanding of the cell membrane organization and functioning need to assess the physical properties which partly depend (i) on the positional distribution of the fatty acids in the membrane phospholipids (PLs) and (ii) on the way by which the PL molecular species are affected by exogenous fatty acids. To do that, the effects of essential (polyunsaturated) fatty acid (EFA) deficiency and enrichment were studied in the liver microsomes of piglets feeding on either an EFA-deficient diet or an EFA-enriched diet containing hydrogenated coconut oil or a mixture of soya + corn oils, respectively. After derivatization, the diacylated forms of choline and ethanolamine PLs were analyzed using a combination of chromatographic techniques and fast-atom bombardment-mass spectrometry. The dinitrobenzoyl-diacylglycerol derivatives corresponding to the molecular species of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were identified. It appears that three factors brought about a marked apparent relative retention: the nature of (i) the base of the polar head, (ii) fatty acids at the sn-1 position and (iii) fatty acids at the sn-2 position. The highest apparent relative retentions were displayed by the 18:0-20:5(n-3)-PE and 16:0-22:6(n-3)-PE. It is noteworthy that the behavior of 20:3 n-9--which is synthesized during the EFA-deficient diet by the same bioconversion system as 20:4 n-6--was very similar to that of 20:4 n-6 during the formation of PC and PE molecular species and that the molecular species of PE containing 20:4(n-6) and 20:3(n-9), gathered together as metabolical homologues, were also apparently retained, particularly in association with 16:0. Present observations are consistent with some others showing retention or preferential distribution of EFA in PE and suggest that specific acyltransferase(s), ethanolamine phosphotransferase and methyltransferase would be mainly involved for PE and PC formation in liver endoplasmic reticulum. Fast-atom bombardment-mass spectrometry of intact phospholipids enables us to show that there is no very long chain dipolyunsaturated phospholipid in liver endoplasmic reticulum.

The fatty acid chain elongation system of mammalian endoplasmic reticulum

Much has been learned about FACES of the endoplasmic reticulum since its discovery in the early 1960s. FACES consists of four component reactions, requires the fatty acid to be activated in the form of a CoA derivative, utilizes reducing equivalents in the form of NADH or NADPH, is induced by a fat-free diet, resides on the cytoplasmic surface of the endoplasmic reticulum, appears to function in concert with the desaturase system and appears to exist in multiple forms (either multiple condensing enzymes connected to a single pathway or multiple pathways). FACES has been found in all tissues investigated, namely, liver, brain, kidney, lung, adrenals, retina, testis, small intestine, blood cells (lymphocytes and neutrophils) and fibroblasts, with one exception--the heart has no measurable activity. Yet, much more needs to be learned. The critical, inducible and rate-limiting condensing enzyme has resisted solubilization and purification; the purification of the other components has met with limited success. We know nothing about the site of synthesis of each component of FACES. How is each component enzyme integrated into the endoplasmic reticulum membrane? Is there a single mRNA directing synthesis of all four components or are there four separate mRNAs? How are elongation and desaturation coordinated? What is (are) the physiological regulator(s) of FACES--ADP, AMP, IP3, G-proteins, phosphorylation, CoA, Ca2+, cAMP, none of these? The molecular biology of FACES is only in the fetal stage of development. We are only scratching the surface--it is an undiscovered country.

Antigen-presenting cells in essential fatty acid-deficient murine epidermis: keratinocytes bearing class II (Ia) antigens may potentiate the accessory cell function of Langerhans cells

Essential fatty acid deficiency (EFAD) is a useful model for studying the role of (n-6) fatty acid metabolism in normal physiology. Because cutaneous manifestations are among the earliest signs of EFAD and because abnormalities in the distribution and function of tissue macrophages have been documented in EFAD rodents, we studied the distribution and function of Class II MHC (Ia) antigen-bearing cells in EFAD C57B1/6 mouse epidermis. Immunofluorescence studies revealed 1.9-9.6 (mean +/- SEM = 5.2 +/- 2.6) times more class II MHC (Ia) antigen-bearing epidermal cells in suspensions prepared from EFAD as compared to normal skin. Analysis of epidermal sheets demonstrated similar numbers of dendritic Ia+ and NLDC145+ cells in EFAD and normal epidermis, however. This discrepancy occurred because some keratinocytes in EFAD epidermal sheets expressed class II MHC (Ia) antigens, whereas keratinocytes in normal mouse epidermis did not. Two-color flow cytometry confirmed that all Ia+ cells in normal epidermis are Langerhans (Ia+ NLDC145+) cells, whereas Ia+ cells in EFAD epidermis are comprised of Langerhans cells and a subpopulation of keratinocytes (Ia+ NLDC145-). Similar levels of Ia antigens were expressed on EFAD and normal Langerhans cells. EFAD and normal epidermal cells were also compared in several in vitro assays of accessory cell function. Epidermal cells prepared from EFAD C57B1/6 mice present the protein antigen DNP-Ova to primed helper T cells more effectively than epidermal cells prepared from normal animals. EFAD epidermal cells are also more potent stimulators of T cells in primary and secondary allogeneic mixed lymphocyte-epidermal cell reactions than normal epidermal cells. The functional differences between EFAD and normal epidermal cells do not appear to result from increased cytokine release or decreased prostaglandin production by EFAD epidermal cells. In view of these findings and the observation that the antigen-presenting cell activity of EFAD epidermal cells correlates with the number of Ia+ keratinocytes in epidermal cell preparations, Ia+ keratinocytes (in the presence of Langerhans cells) may potentiate cutaneous immune responses in vitro and perhaps in vivo as well. These results also suggest that (n-6) fatty acids or metabolites of (n-6) fatty acids are involved in regulating the expression of class II MHC (Ia) antigens by keratinocytes in vivo.

Do rat kidney cortex microsomes possess the enzymatic machinery to desaturate and chain elongate fatty acyl-CoA derivatives?

Rat kidney cortex microsomal preparations were unable to catalyze delta 9, delta 6 and delta 5 desaturation of stearoyl-coenzyme A (CoA), linoleoyl-CoA and dihomo-gamma-linolenoyl-CoA, respectively. The kidney cortex microsomal fraction, however, did catalyze the malonyl-CoA dependent fatty acyl-CoA elongation. The biochemical properties of palmitoyl-CoA elongation were studied as a function of protein concentration, time, reduced nicotinamide adenine dinucleotide phosphate (NADPH), malonyl-CoA and substrate concentrations; of the substrates investigated, delta 6,9,12-18:3 was the most active. Unlike what was observed in the hepatic system, a high-carbohydrate, fat-free diet did not induce kidney fatty acid chain elongation. All intermediate kidney cortex microsomal reactions, i.e., beta-ketoacyl-CoA reductase, beta-hydroxyacyl-CoA dehydrase and trans-2-enoyl-CoA reductase activities, were significantly higher (greater than one order of magnitude) than the condensing enzyme activity, suggesting that the rate-limiting step in total elongation is the initial condensation reaction. Contrary to other reports, the results suggest that the kidney cannot synthesize arachidonic acid needed for eicosanoid production.

Metabolites of cis,trans, and trans,cis isomers of linoleic acid in mice and incorporation into tissue lipids

Metabolism of octadecadienoic acid isomers in weanling mice was studied by feeding fat-free diets supplemented with 2% by weight of cis-9,trans-12-octadecadienoic acid (c,t-18:2-d0), tetradeuterated trans-9,cis-12-octadecadienoic acid (t,c-18:2-d4) or dideuterated cis-9,cis-12-octadecadienoic acid (c,c-18:2-d2). Rates for conversion of c,t-18:2-d0 and c,c-18:2-d2 to c,t-20:4-d0 and c,c-20:4-d2 were identical and both were 5-times higher than conversion of t,c-18:2-d4 to t,c-20:4-d4. Accumulation of t,c-18:2-d4 in liver lipids was 2-4-times higher than for c,t-18:2-d0 or c,c-18:2-d2. The t,c-18:2 diet significantly increased with the 20:3(n-9) and total lipid concentrations in liver but not in heart, plasma or brain. The 20:3(n-9)/20:4(n-6) ratio in the liver lipids was 2-4-times higher for t,c-18:2-d4 than c,c-18:2-d2 fed mice. The position of the trans bond had a marked influence on the distribution of the various intermediate desaturation and elongation products. Intermediate metabolite data for the liver lipids indicated t,c-18:2-d4 was preferentially converted to 5c,11c,14t-20:3 ('dead end' product) rather than to t,c-20:4. Concentration of the 18:3(n-6) metabolite of c,t-18:2-d0 was about 10-times greater than the 18:3(n-6) metabolite of c,c-18:2-d2. Conversely, the concentration of the normal 20:3(n-6) metabolite from c,c-18:2-d2 was 4-times higher than the 20:3(n-6) metabolite of c,t-18:2-d0. Compared to the c,c-18:2 diet, the t,c- and c,t-18:2 diets significantly increased the total n-3, but not the total n-6 fatty acid content of heart lipids. These results illustrate that the position of the trans double-bond influences a variety of enzyme activities and the isomers differ in their physiological effects.