Effect of eicosatetraynoic acid on liver and plasma lipids

Groups of rats were fed a fat-free diet supplemented with 0.5% safflower oil (control) or the control diet containing 0.5% of 5,8,11,14-eicosatetraynoic acid (TYA). Blood was collected weekly and plasma lipids analyzed. After 4 weeks, the animals were killed and the liver lipids were analyzed in detail. The acetylenic fatty acid perturbed plasma neutral lipid and phospholipid class concentrations and reduced growth rates. Liver triglyceride concentrations were reduced dramatically in the TYA fed animals, suggesting interference with complex lipid synthesis. Plasma and liver triglycerides were shifted to higher molecular weight species suggesting that TYA affected fatty acid metabolism. The phospholipids showed an accumulation of 18∶2 and a fall in 20∶4 percentages indicating an inhibition in the conversion of linoleate to arachidonate. All major lipid classes exhibited an increase in 18∶1 levels. Analysis of the octadecenoate positional isomers indicated the proportion of oleate increased substantually in all lipid classes whereas vaccenate proportions had fallen dramatically. All of the data collectively suggest that TYA inhibits the elongation of unsaturated fatty acids. A group of rats bearing hepatoma 7288CTC were also fed the TYA diet. Host liver lipids were affected by TYA similar to normal TYA fed animals, but the effects on hepatoma lipids were marginal.     

Relationship between mouse liver Δ9 desaturase activity and plasma lipids

This study was undertaken to investigate the total plasma fatty acid composition and the relationship between plasma triacylglycerol (TG) levels and liver Δ9 desaturase activity in mice fed n−3 and/or n−6 fatty acid or hydrogenated coconut oil (HCO) (maximum 25 mg/g) supplemented diets. Generally, plasma TG levels and Δ9 desaturase activity were inversely correlated with the ratio of the sum of long chain n−3 fatty acids to 18∶2n−6 and to the ratio of the sum of long chain n−3 fatty acids to 18∶n−3, but they were positively correlated with the ratio of products and substrates (18∶1/18∶0) of the enzyme in plasma total lipids. The n−3 fatty acid (mainly 20∶5n−3) enriched diet, when compared to the HCO diet at 21 d, caused a significant reduction in plasma TG levels but not in Δ9 desaturase activity. However, a marked reduction in plasma TG content (50–60%) and Δ9 desaturase activity (55–70%) was observed when both 20∶5n−3 and 18∶3n−6 were supplemented in the diet. The plasma TG levels and Δ9 desaturase activity rose again when the animals were fed the HCO diet or chow. The results suggest that low dose supplementation of a mixture of n−3 (mainly 20∶5n−3) and n−6 (18∶3n−6) fatty acids modified both plasma TG content and liver Δ9 desaturase activity, in parallel.     

近交系小鼠H-2基因与接种乙型肝炎疫苗后无(弱)应答的相关性分析

目的分析近交系小鼠H-2基因与接种乙型肝炎疫苗后无(弱)应答的相关性,建立免疫无应答小鼠动物模型,从基因水平和细胞因子水平研究免疫无应答的遗传机制,为乙肝疫苗的研制及人类免疫无应答的研究提供理论依据。方法采用微量细胞毒法检测不同近交系小鼠(DBA/1、BALB/c、NIH、SJL、C57BL/6、C57BL/10)的H-2单倍型;PCR法检测小鼠的H-2A和H-2E基因。用3种重组乙型肝炎疫苗(酿酒酵母、汉逊酵母、CHO细胞)和治疗性乙型肝炎疫苗(乙克)分别免疫6种不同品系近交系小鼠,采用ELISA法检测抗体水平,流式细胞术检测小鼠CD4~+、CD8~+、CD19~+T细胞和Treg细胞免疫前后的变化。结果不同近交系小鼠有不同的H-2单倍型。除封闭群小鼠NIH外,近交系小鼠SJL在A基因区内有两条200和500 bp的区带,其余均为1条区带;不同品系小鼠在H-2E基因区段均无异常表现。C57BL/10小鼠对乙肝疫苗表现为免疫无(弱)应答。结论 C57BL/10小鼠可作为免疫无应答实验动物模型,进行乙肝疫苗免疫无(弱)应答的相关性研究。建议在进行疫苗效力检测时先检测所用小鼠的H-2基因型,根据小鼠H-2基因的单倍型与免疫反应的相关性筛选实验用小鼠。     

The effects of fat-free,saturated and polyunsaturated fat diets on rat liver and plasma lipids

The liver and plasma lipids and fatty acid composition of rats fed synthetic diets of differing fat type and content were studied. All animals were starved for 48 hr and then refed a high carbohydrate, fat-free diet for 48 hr. They were then divided into three groups and fed for an additional 48 hrs the following: group 1, the fat-free diet; group 2, a diet containing 44% of calories from corn oil; and group 3, a diet containing 44% calories from completely hydrogenated soybean oil. The total lipid concentration of the liver in the animals on the fat-free diet was elevated at 72 and 96 hr. The addition of either saturated or unsaturated fat in the diet at 48 hr prevented this accumulation. The total phospholipid and cholesterol concentrations of the liver were relatively uninfluenced by any diet in this study. Plasma total fatty acid concentration was elevated at 72 hr in the animals on a fat-free diet compared to those fed the stock diet, starved for 48 hr or fed the fat-containing diets. By 96 hr, however plasma fatty acid concentrations in all groups were similar to those in animals fed only the stock diet. The release of de novo synthesized fatty acids into plasma from the liver was strongly inhibited by dietary fat, either saturated or polyunsaturated. With the fat-free diet there was a significant increase in the saturated and monounsaturated fatty acids in both liver and plasma. The addition of corn oil to the diet facilitated a reversion of the fatty acid composition in liver and plasma to that found in the animals fed the stock diet ad libitum, but saturated fat did not. No effect of diet on the fatty acid composition of the red cells was observed during the course of this study. Exogenous saturated fatty acids, although similar chemically to the fatty acids synthesized by the liver, may have physiological actions that differ from endogenously synthesized fat.     

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

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

Rapid analysis of fatty acids in plasma lipids

A rapid and convenient procedure for the quantitative determination of the fatty acid composition of plasma lipids is described. Human plasma was applied directly to the preadsorbent zones of thin-layer silica gel plates with added antioxidant, internal standards and carriers. The thin-layer chromatography (TLC) plates were partially developed with methanol followed by chloroform/methanol (1∶1, v/v), and then they were fully developed in hexane/diethyl ether/acetic acid (80∶20∶1, v/v/v) to separate the major classes of lipids. Silica gel from regions containing the separated lipids was scraped into screw-capped tubes and treated with boron trifluoride-methanol prior to gas chromatography. The method of direct application to TLC plates gave yields and compositions of fatty acids very similar to the method of applying extracted plasma lipids. This relatively simple method is suitable for analyzing the fatty acids in plasma lipids from a 50 microliter finger-tip blood samples from an individual, and it may be useful in wide-scale screening of different individuals to estimate the relative amounts of ingested polyunsaturated fatty acids. Pfizer Biomedical Research Awardee.     

Genetic variability of human plasma and erythrocyte lipids

Genetic variation of fasting plasma lipids, lipoproteins and erythrocyte membrane lipids was studied in 67 sets of like-sexed twins and 3 sets of triplets. All of the plasma lipids were more variable in dizygotic twins than monozygotic twins with the exception of phosphatidyl ethanolamine, but only cholesteryl esters, lecithin, phosphatidyl inositol and β-lipoprotein showed significant genetic variation. In contrast, no significant genetic variability was found in any of the erythrocyte membrane lipids and erythrocyte phosphatidyl ethanolamine had significantly greater variation in monozygotic twins. Two sets of twins had an extra lipoprotein band (slow α1); in one family the variant appeared to be segregating as a dominant trait. Presented in part at the ISF-AOCS World Congress, Chicago, September 1970.     

Intake of different eicosapentaenoic acid-containing lipids and fatty acid pattern of plasma lipids in the rats

The ethyl ester of eicosapentaenoic acid (EPA) is the only pure EPA-containing lipid available in bulk for oral administration. However, there is doubt as to whether EPA ethyl ester can efficiently increase the plasma levels of EPA in comparison with the ability of other kinds of EPA-containing lipids to do so. Therefore, two other kinds of EPA-containing lipids were prepared to study the efficiency of oral administration of those lipids for increasing the EPA content in plasma phospholipids and cholesteryl esters. EPA-containing lipids which were investigated were [A], 1,2,3-trieicosapentaenoyl-glycerol, [B] 2-eicosapentaenoyl-phosphatidylcholine and [C] ethyl ester of EPA. An adjusted amount of lipids [A], [B] and [C] was administered to rats through a gastric tube for 4 days (the first experiment) or for 10 days (the second experiment), and the fatty acid composition of plasma phospholipids and cholesteryl esters was determined. In the first experiment, there were no significant differences in the efficiency for increasing EPA levels in either phospholipids or cholesteryl esters among the lipids. In the second experiment, the EPA levels of both plasma phospholipids and cholesteryl esters of rats administered ethyl ester of EPA were significantly higher than those of rats administered 2-eicosapentaenoyl-phosphatidylcholine. The EPA levels of the rats administered 1,2,3-trieicosapentaenoylglycerol were between the levels of the two groups mentioned above, but the differences in the EPA levels were not significant. Although an ethyl ester-type molecule is not a naturally occurring lipid, ethyl ester of EPA is equal to 1,2,3-trieicosapentaenoyl-glycerol and appears to be superior to 2-eicosapentaenoyl-phosphatidylcholine as to the efficiency for increasing EPA levels in total plasma phospholipids and plasma cholesteryl esters.     

1,2-Propanediol-induced changes in plasma and tissue lipids of rats

Oral administration of 1,2-propanediol to rats in a daily dose of 1 ml of 28.4% aqueous solution per 100 g body weight for 30 days caused a significant decrease in the total lipids, fatty acids, phospholipids, and triglycerides of plasma, liver, and heart, The cholesterol content in plasma decreased while that in the tissues increased significantly. The accumulation of cholesterol in tissues tends to discourage long term use of 1,2-propanediol even by the oral route.     

Red blood cell lipids and the plasma membrane

The red-blood cell occupies a unique position both in the historical development of membrane theory and current experimentation on membrane properties. The cell is readily accessible and has been studied in many animal species and disease conditions. Differences in composition, structure, and properties have been described, and a num-ber of highly specific cell types are now available for investigation. Several techniques are used to study the mem-brane of the intact cell. The membrane surface may be labeled in specific areas by the selective exchange of lipids such as cholesterol. Exchange studies provide information about lipid-lipid and lipid-protein interactions in the intact structure-Membrane lipids are hydrolyzed by phospho-lipases, and enzymatic activity is modified by the action of penetrating hemolytic agents. Perme-ability is readily measured by hemolysis and correlated with chemical structure, partition coefficient, and biological activity of different metabolites and drugs. The red cells of Vitamin B-deficient animals are particularly susceptible to hyperoxia. Hemolysis in these cells is correlated with alterations in membrane structure through the formation of lipid peroxides. Gorter and Grendel first used monolayers pre-pared from red-cell lipids to show that sufficient lipid was present in the membrane to form a bimolecular layer. Lipids extracts from the red cells of different animal species and disease states have been used in recent monolayer studies. The surface properties of these lipids and their purified neutral lipid and phospholipid fractions yield ad-ditional information about lipid-lipid interactions which may exist in the membrane. Enzyme hy-drolysis and penetration studies indicate that lipids in monolayers and membranes have similar properties.     

Abnormal plasma lipids of patients withRetinitis pigmentosa

Retinitis pigmentosa (RP) is a hereditary retinal degeneration of unknown etiology, resulting in progressive night blindness, loss of peripheral vision, abnormal retinal pigmentation and reduced electroretinographic response. Docosahexaenoic acid (22∶6ω3) is found in high concentration in the rod outer segment membranes of the retina. Previous reports of low 22∶6ω3 in blood lipids or phospholipids in RP patients prompted us to evaluate the complete fatty acid (FA) profiles of plasma phospholipids (PL), cholesteryl esters, triglycerides (TG) and nonesterified fatty acids (NEFA) in ten patients with RP. In the PL fraction, we found significantly depressed levels of 22∶6ω3, 22∶5ω3, total ω3, 22∶5ω6, 22∶4ω6 and total ω6 polyunsaturated FA (PUFA), and elevated total saturated acids. Plasma TG showed normal levels of PUFA, normal total saturated FA and total monounsaturated FA. The NEFA fraction showed significant elevation in total saturated FA with depressed total ω6 PUFA. Evidence is accumulating that RP is associated with abnormal PUFA and lipid metabolism. Based in part on a paper presented at the Third International Congress on Essential Fatty Acids and Eicosanoids, Adelaide, Australia, March 1992.     

Major clofibrate effects on liver and plasma lipids are independent of changes in polyunsaturated fatty acid composition induced by dietary fat

The effects of clofibrate on the content and composition of liver and plasma lipids were studied in mice fed for 4 wk on diets enriched in n−6 or n−3 polyunsaturated fatty acids (PUFA) from sunflower oil (SO) or fish oil (FO), respectively; both oils were fed at 9% of the diet (dry weight basis). Only FO was hypolipidemic. Both oil regimes led to slightly increased concentrations of phospholipids (PL) and triacylglycerols (TG) in liver as compared with a standard chow diet containing 2% fat. Clofibrate promoted hypolipidemia only in animals fed SO. Its main effect was to enlarge the liver, such growth increasing the amounts of major glycerophospholipids while depleting the TG. SO and FO consumption changed the proportion of n−6 or n−3 PUFA in liver and plasma lipids in opposite ways. After clofibrate action, the PUFA of liver PL were preserved better than in the absence of oil supplementation. However, most of the drug-induced changes (e.g., increased 18∶1n−9 and 20∶3n−6, decreased 22∶6/20∶5 ratios) occurred inrrespective of lipids being rich in n−6 or n−3 PUFA. The concentration of sphingomyelin (SM), a minor liver lipid that virtually lacks PUFA, increased with the dietary oils, decreased with clofibrate, and changed its fatty acid composition in both situations. Thus. oil-increased SM had more 22∶0 and 24∶0 than clofibrate-decreased SM, which was significantly richer in 22∶1 and 24∶1.     

Low-density lipoprotein turnover in inbred strains of rabbits hypo- or hyperresponsive to dietary cholesterol

In two inbred strains of rabbits with high or low response of plasma cholesterol to dietary cholesterol, low density lipoprotein (LDL) apolipoprotein (apoLDL) kinetics were determined with the use of a heterologous tracer isolated from a Watanabe heritable hyperlipidemic (WHHL) rabbit. On a diet without added cholesterol, the total clearance of apoLDL (which equals apoLDL production) did not differ significantly between rabbits of both strains. After the feeding of a diet containing 0.1% cholesterol for six weeks, plasma LDL cholesterol, plasma apoLDL and liver cholesterol concentrations rose significantly in the hyperresponsive but not in the hyporesponsive rabbits. Cholesterol feeding depressed the total fractional catabolic rate (FCR) of apoLDL in the hyper- but not in the hyporesponsive rabbits; this was attributed to a decrease of receptor-dependent FCR while receptor-independent FCR was similar in the two strains. On the diet containing cholesterol, the receptor-mediated absolute catabolic rate (ACR) of apoLDL did not differ between hyper- and hyporesponsive rabbits but receptor-independent ACR of apoLDL was higher in hyperresponders. It is concluded that the higher plasma apoLDL levels in hyperresponsive rabbits fed the 0.1% cholesterol diet are caused by a higher production of apoLDL and not by a lower flux of apoLDL through the receptor-mediated pathway.     

Changes in host animal plasma lipids during hepatoma growth

The concentrations of the major neutral lipid and phospholipid classes in the plasma of rats bearing hepatoma 7288CTC were determined at various times after transplantation. The fatty acid composition of each lipid class was also analyzed quantitatively as tumor growth progressed. Generally, most lipid classes exhibited a slight decrease between the third and sixth day after transplantation, returned to near normal levels by the 15th day, increased dramatically and peaked between the 24th and 27th days before plummeting sharply. At peak concentrations, triglycerides were increased 5 times the normal levels, whereas cholesterol, cholesteryl esters and phosphatidylcholines were increased 3-fold. The percentage of hexadecenoates decreased in all lipid classes as tumor growth progressed and generally, stearate levels increased. In addition to monounsaturated fatty acids, lysophosphatidylcholines and phosphatidylcholines showed relatively large decreases in the percentages of polyunsaturated fatty acids with increased tumor growth. These results indicate that hepatoma 7288CTC can cause perturbation of host animal plasma lipids in the early stages of growth which precedes the massive hyperlipidemia. The interpretation of these results suggests that the early changes in plasma lipids may result from alterations in the normal lipid metabolism of the host, and the hyperlipidemia that develops later may result from the mobilization of lipids to compensate for the altered metabolism. This paper was given by M. Matocha as an Honored Student Award presentation at the AOCS meeting, San Francisco, CA, April 29–May 31, 1979. This work has been submitted in partial fulfillment of the requirement for the M.S. degree.     

Genetic variations in serum lipid levels of inbred mice and response to hypercholesterolemic diet

The serum lipid contents of a number of inbred and congenic strains of mice were measured. There were interstrain variations in each of the lipid fractions in mice fed a normal diet. Male and female C3H mice had the highest total cholesterol level; AKR mice showed the lowest values. Serum phospholipids were correlated well with cholesterolemia. The greatest variations between strains were in the triglyceride levels. There also was significant variation in the high density lipoprotein cholesterol serum levels (from 73–88% of the total cholesterol). The response to a hypercholesterolemic diet (1% cholesterol) was tested in seven inbred strains. All strains showed changes in serum cholesterol and in the proportions of the lipoproteins fractions. There was a large increase in the low density lipoprotein+very low density lipoprotein fractions. Feeding the diet revealed marked interstrain differences in the responses of the serum cholesterol and electrophoretic lipoprotein profiles. The C57BL/6 and B10.D2 strains were hyperresponders to the hypercholesterolemic diet with 71% and 63% of their serum cholesterol in the low density lipoprotein plus very low density lipoprotein fractions, respectively.     

Hydrocarbons and alcohols of basking shark and pig liver lipids

Four samples of the unsaponifiables of basking shark liver oil were adsorbed on alumina and eluted to yield Fractions 1–5, inclusive. Analyses by temperature programmed GC and by silica gel chromatography showed hydrocarbons in the first four fractions with squalene increasing to Fraction 3 and the pristane level being highest in Fraction 1. Aside from pristane and squalene, other hydrocarbons occurred at levels of 420–750 mg% in the oils on a weight basis, of which about 60% constituted a series of n-paraffins (relative carbon number range: 15.0–38.0) together with smaller amounts of at least one branched chain saturated group. Unsaturated hydrocarbons eluted mainly after squalene. The oils contained up to 460 mg% sterol and 78–270 mg% alcohols of C₁₀ to C₃₀, the ratio of saturated to unsaturated members being about 1.6. The composition of the unsaponifiable lipids of pig liver was quite different from that of the marine oils. It contained 10.6% sterol in addition to 400 mg% alcohols, the latter consisting of 81.8% saturated components (C₁₂ to C₃₁; ratio of saturated: unsaturated members, 4.4). The hydrocarbons comprised 450–700 mg% of the unsaponifiable mixture and squalene, paraffins and additional unsaturated components occurred at levels of 20.6, 24.4 and 11.9 mg%, respectively. The saturated hydrocarbons were high in normal homologs of relative carbon number range, 15 to 36; pristane could not be detected.     

Effect of biliary obstruction on canine plasma and biliary lipids

The common bile duct was obstructed in 17 dogs. Reciprocal changes were noted for the plasma and biliary lipid concentrations of each after obstruction. As the plasma lecithin and free cholesterol concentrations increased, the biliary lipid concentrations declined. After biliary obstruction the reflux of biliary lecithin into the plasma of these animals was demonstrated with both labeled and unlabeled lecithin. The plasma lipid abnormalities seen after acute biliary obstruction were closely simulated by the reflux of lecithin alone from the biliary tree. The isolated reflux of biliary tract taurocholate produced a distinct lowering of plasma phospholipid and cholesterol concentrations, quite different from the plasma lipid alteration noted with acute biliary obstruction. Similar to observations in human obstruction, some of the plasma lipid was in mesophase form after these animals were obstructed.     

Long-chain polyunsaturated fatty acids in plasma lipids of obese children

Fatty acid composition of plasma phospholipids (PL), triglycerides (TG), and sterol esters (STE) was determined by high-resolution capillary gas-liquid chromatography in 22 obese children (age: 13.7±1.4 y, body weight relative to normal weight for height: 170±24%, mean ±SD) and compared with data obtained in 25 age-matched healthy controls. There were no differences in the levels of linoleic acid (LA, C_18∶2n-6) in any of the plasma fractions from the obese children and the controls. Obese children exhibited significantly higher values of arachidonic acid (AA, C_20∶4n-6) than controls both in PL (12.6 [2.4] vs. 8.3 [1.4], % wt/wt, [median (interquartile range)],P<0.001) and STE (7.3 [1.8] vs. 6.0 [1.1],P<0.05). Similarly, obese children showed higher values than controls for dihomo-γ-linolenic acid (DHGLA, C_20∶3n-6) in PL (4.0 [0.5] vs. 3.0 [0.6],P<0.001), TG (0.4 [0.1] vs. 0.2 [0.1],P<0.001), and STE (0.9 [0.1] vs. 0.7 [0.1],P<0.01), and for γ-linolenic acid (C_18∶3n-6) in STE (1.1 [0.2] vs. 0.8 [0.2],P<0.001). The AA/LA ratios were higher in obese children than in controls in PL (0.68 [0.16] vs. 0.42 [0.09],P<0.0005) and STE (0.16 [0.04] vs. 0.12 [0.02],P<0.05), whereas the AA/DHGLA ratios were lower in TG of obese children than in controls (3.40 [0.64] vs. 5.10 [1.75],P<0.005). Plasma glucose concentrations were inversely related to AA in TG (r=0.53,P<0.05), and plasma TG concentrations were inversely related to AA in PL and STE (r=−0.49,P<0.05 andr=−0.48,P<0.05) and to the AA/DHGLA ratios in PL (r=−0.57,P<0.01),TG (r=−0.56,P<0.01) and STE (r=−0.56,P<0.01). We conclude that the significantly higher values of n-6 long-chain polyunsaturated fatty acids (LCP) in plasma lipids of obese children than in age-matched controls may be caused by an enhanced activity of Δ6-desaturation, and we speculate that elevated fasting immunoreactive insulin seen in obese children (19.4±8.0 μU/mL) may stimulate synthesis of n-6 LCP fatty acids.     

Distribution of deuterium-labeledcis-andtrans-12-octadecenoic acids in human plasma and lipoprotein lipids

Triglycerides containingcis- andtrans-12-octadecenoic acid (12c-18∶1 and 12t-18∶1) andcis-9-octadecenoic acid (9c-18∶1) labeled with deuterium were fed to 2 young adult male subjects. These fatty isomers each contained a different number of deuterium labels, which allowed mass spectrometric analysis to distinguish among them after they were fed as a mixture. This approach results in a direct comparison of the absorption and distribution of these 3 monoenoic acids into blood plasma and lipoprotein lipids. Plasma lipid data indicated that all phospholipid fractions selectively incorporate 12c-18∶1 and 12t-18∶1 in preference to 9c-18∶1. Discrimination against 12c-18∶1 and 12t-18∶1 compared to 9c-18∶1 was found in the plasma neutral lipids, with a strong discrimination against 12t-18∶1 incorporation into the cholesteryl ester fraction. Considerable reduction in the percentage of linoleic and arachidonic acid was observed when 12–18∶1 isomers were incorporated in plasma triglyceride, phosphatidylcholine and sphingomyelin samples. Chylomicron lipid analyses indicated that all isomers were well absorbed. Variation was observed in the relative distribution of 12c-18∶1, 12t-18∶1 and 9c-18∶1 between the very low density, low density and high density lipoprotein lipid classes. No desaturation of 12c-18∶1 to linoleic acid was detected.