Incorporation of dietarycis andtrans octadecenoate isomers in the lipid classes of various rat tissues

The percentage distribution of the geometrical and positional isomers in the hexadecenoates and octadecenoates isolated from triglycerides, phosphatidylcholines, and phosphatidylethanolamines of brain, heart, kidney, liver, lung, muscle, spleen, and adipose tissues from rats maintained four weeks on a semipurified diet supplemented with 15% partially hydrogenated safflower fatty acids, has been determined. Except for brain, octadecenoate percentages were increased in each of the lipid classes of all the tissues by the dietary fat. Although the diet did not contain detectable hexadecenoates, the 16∶1 fraction from the lipid classes of all the tissues was composed of 10–70% of thetrans isomers, indicating chain shortening of the dietary octadecenotes. Distribution ofcis andtrans positional isomers in triglyceride hexadecenoates was approximately the same in all tissues. Relatively high percentages of the Δ9, Δ10, and Δ11 isomers were observed, but the Δ8 was the predominatingtrans hexadecenoate isomer, indicating preferential chain shortening of thetrans δ10 octadecenoate.Trans octadecenoates were found in all tissues, but concentrations were dependent on tissue and lipid class. The distribution of thecis andtrans octadecenoate isomers was similar in all the tissue triglycerides, with the distribution of thetrans isomers resembling the diet. In contrast, the percentage distribution of thetrans octadecenoates in the phospholipid classes differed dramatically from the diet, and the distribution was dependent on both the tissue and lipid class. The Δ12, Δ13, and Δ14trans octadiet, suggesting an accumulation of these isomers. Although thecis Δ10 octadecenoate was a significant dietary component, this isomer was not incorporated significantly into any lipid class of any tissue. The metabolic fate of this isomer remains unknown.     

Effect of methyl 2-hexadecynoate on hepatic fatty acid metabolism

Normal and hepatoma bearing rats were fed a low level of methyl 2-hexadecynoate in a low fat diet for one month. The effect of the acetylenic acid on lipid metabolism as derived from mass analysis of lipid classes, fatty acids and positional monoene isomers isolated from the major lipid classes of liver and hepatoma has been assessed. Methyl 2-hexadecynoate caused a 25% decrease in body weight and the appearance of essential fatty acid deficiency symptoms within one week. Non-tumor-bearing animals contained a seven-fold increase in all neutral lipid classes, except cholesterol, while host animals did not contain fatty livers. The apparent protective effect of the host animal by the hepatoma also resulted in only marginal changes in the fatty acid and positional monoene isomers from host liver and hepatoma lipids. In contrast to host liver and hepatoma, methyl 2-hexadecynoate caused a massive accumulation of palmitate and hexadecenoates with a concomitant decrease in stearate and octadecenoates in most of the lipid classes from non-tumor-bearing animals. These changes were accompanied by a shift from the higher molecular weight triglycerides to lower molecular weights corresponding to carbon number 48. The high concentrations of hexadecenoates consisted predominantly of the Δ9 isomer. Despite the high concentrations ofcis Δ9 hexadecenoate, precursor ofcis Δ11 octadecenoate (vaccenate), total vaccenate levels of the five major lipid classes were lower than control values. All of these data strongly suggest that long-chain 2-ynoic acids inhibit elongation of saturated and monoene fatty acids.     

Geometrical and positional isomer content of the monounsaturated fatty acids from various rat tissues

The percentage distribution of the geometrical and positional isomers in the hexadecenoates and octadecenoates isolated from triglycerides, phosphatidylch olines, and phosphatidylethanolamines of brain, heart, kidney, liver, lung, muscle, spleen, and adipose tissues from normal rats maintained on a laboratory diet has been determined. All of the octadecenoates and most of the hexadecenoates from the lipid classes of all the tissues consisted of more than 95%cis isomers. Generally, palmitoleic was the predominant hexadecenoate, but many of the tissue phospholipids contained relatively high percentages of the Δ6 and Δ7 isomers. Oleate and vaccenate were the predominant octadecenoates in all tissues. Except for brain and adipose tissues, the oleate to vaccenate ratios differed for each lipid class, as well as between most tissues. In contrast to the monoenes of the phospholipids, the triglyceride monoenes exhibited the same approximate: percentage composition; percentage of geometrical isomers; and percentage distribution of hexadecenoate and octadecenoate positional isomers. These data add to our basic information about the percentage distribution of geometrical and positional isomers of naturally occurring unsaturated fatty acids in the major lipid classes of various normal tissues. Some new concepts were advanced as possible explanations to some of the observed positional isomer distributions.     

Double bond position affects metabolism ofcis-octadecenoates

The metabolic fate ofcis-positional isomers of octadecenoates has been compared to that of naturally occurring oleic acid (cis-Δ9). Radioactive mixtures of tritium-labeled positional octadecenoate isomer and oleic acid-10-¹⁴C were administered to laying hens, and their eggs were analyzed for the isotopic ratios (³H/¹⁴C) incorporated into total egg lipid, triglycerides, and phospholipids. Variations in the isotopic ratios indicated the comparative metabolic utilization ofcis-positional isomers Δ8 through Δ12. Incorporation into egg lipid fractions is as follows: triglycerides: Δ9>Δ8, Δ9>Δ10, Δ9>Δ11, Δ9>12; phospholipid: Δ9>Δ8, Δ9>Δ10, Δ9<Δ11, Δ9<Δ12. Presented at the AOCS meeting in Cincinnati, September 28–October 1, 1975.     

Identification of noveltrans isomers of 20∶5n−3 in liver lipids of rats fed a heated oil

Trans polyunsaturated n−3 fatty acids are formed as a result of the heat treatment of vegetable oils. It was demonstrated previously that the 18∶3 Δ9cis, 12cis, 15trans containing acis Δ9 ethylenic bond was converted to a geometrical isomer of 20∶5n−3, the 20∶5 Δ5cis, 8cis, 11cis, 14cis, 17trans. In the present study, we have identified two new isomers of eicosapentaenoic acid, the Δ11 monotrans and the Δ11, 17 ditrans isomers in liver of rats fed a heated oil. These are formed as a result of the conversion of two of the main isomers of linolenic acid which are present in refined and frying oils, the 18∶3 Δ9trans, 12cis, 15cis and the 18∶3 Δ9trans, 12cis, 15trans.     

Effect of different acids with Δ9,12-dienoic structures on Δ9 desaturation activity in rat liver microsomes

The effect of oral administration, for 24 or 48 hr, of different octadeca fatty acids containing a 9,12-dienoic structure on the fatty acid composition and Δ9 desaturation activity of liver microsomes of rat fed a fat-free diet was studied. The ethyl esters of linoelaidic and γ-linolenic acids, the methyl ester of linoleic acid and free columbinic acid were administered to rats maintained on a fat-free diet. The supplementation of the fat-free diet with linoelaidate produced no relevant changes in the fatty acid composition pattern of liver microsomes and did not modify the percentage of conversion of palmitic to palmitoleic acid. The addition of linoleate or γ-linolenate to the fat-free diet returned liver microsome Δ9 desaturation activity toward the control and partially restored the liver microsome fatty acid spectrum found in the fat-free diet. Columbinic acid (5-trans-9-cis,12-cis-18∶3), which cannot be transformed into arachidonic acid, also decreased the Δ9 desaturation activity enhanced by the fat-free diet and evoked changes in the microsomal fatty acid composition similar to those produced by the ω6 fatty acids. These results suggest that the modulation of Δ9 desaturase activity evoked by dietary administration of unsaturated acids of ω6 series would depend on thecis double bond configuration of these acids.     

Distribution of hexadecenoic,octadecenoic and octadecadienoic acid isomers in human tissue lipids

Thetrans 16∶1, 18∶1 and 18∶2 fatty acid composition of various human organ lipids was studied to determine if isomers accumulated in specific tissues. “Trans” isomers are defined as those fatty acids containing one or moretrans double bonds. Adipose, kidney, brain, heart and liver tissue lipids were analyzed. Gas chromatography with a 100-SP2560 capillary column was used to characterize the various positional and/or geometrical isomers. The distribution ofrans 16∶1 and 18∶1 isomers ranged from 0.3% in the brain to 4.0% in adipose tissue, whiletrans 18∶2 isomers ranged from 0.0% in the brain to 0.4% in adipose tissue. Notrans 18∶3 isomers were detected. Positional isomer ratios forcis 16∶1 (Δ9 vs Δ7) andcis 18∶1 (Δ11 vs Δ9) were also determined. Since these ratios are reproducible from one individual to the next, they might be useful for diagnosis of human metabolic disorders.     

Desaturation of isomericcis 18∶1 acids

The desaturation of positionalcis 18∶1 isomers (Δ4 through Δ11) was studied, using essential fatty acid deficient rat liver microsomes. Thecis Δ4, Δ5, Δ6 and Δ7 isomers were not desaturated. Thecis Δ10 and Δ11 isomers were desaturated at a very low rate. The maximum desaturation was obtained for Δ8 and Δ9 isomers. Thecis Δ8 and Δ11 isomers were desaturated by Δ5 desaturase; thecis Δ9 isomer was desaturated by Δ6 desaturase; and thecis Δ10 isomer was desaturated to Δ7,10 and 5,10–18∶2 acids.     

Lipids of the pawpaw fruit: Asimina triloba

The fatty acid composition and structure of pawpaw fruit (Asimina triloba) triglycerides were examined and found to contain fatty acids ranging from C₆ to C₂₀. Octanoate represented 20% of the fatty acids while other medium-chain fatty acids were present in low amounts. Analysis of the intact triglycerides by high-temperature gas-liquid chromatography gave an unusual three-cycle carbon number distribution. Analysis of triglyceride fractions separated according to degree of unsaturation suggested that one octanoate was paired with diglyceride species containing long-chain fatty acids. Determination of the double-bond positions of monoene fatty acids revealed cis Δ9 and cis Δ11 hexadecenoate and cis Δ9, cis Δ11, and cis Δ13 octadecenoate isomers were present in significant quantities. Octanoate and positional monoene fatty acid isomers were found only in the fruit lipids and not in the seed lipids. Phenacyl esters of fatty acids were found to be useful derivatives for structure determination using multiple types of analyses.     

Study of individual trans- and cis-16∶1 isomers in cow, goat, and ewe cheese fats by gas-liquid chromatography with emphasis on the trans-Δ3 isomer

Low-temperature gas-liquid chromatography (GLC) was applied to study the distribution profiles of isomeric trans-and cis-hexadecenoic acids in ruminant (cow, goat, and ewe) milk fat after their fractionation by argentation thin-layer chromatography (Ag-TLC). The fat was extracted from cheeses (12 samples of each species), the most common foods made with goat and ewe milks. The predominant trans-16∶1 isomer is palmitelaidic acid (the Δ9 isomer), but it does not exceed one-third of the total group, which itself represents 0.17% (cow), 0.16% (goat), and 0.26% (ewe) of the total fatty acids. The trans-Δ3 16∶1 isomer, which is reported for the first time in ruminant lipids and which likely comes from the animals' feed, is present at a level of ca. 10% of the trans-16∶1 acid group. Otherwise, all isomers with their ethylenic bond between positions Δ4 and Δ14 are observed in the three species studied, roughly showing the same relative distribution pattern. Quantitatively, the trans-16∶1 isomers only represent ca. 5% of the sum of the trans-16∶1 plus trans-18∶1 isomers, and they appear of little importance in comparison. It is inferred from this and recent studies that some previously reported data that were established for consumption assessments dealt in fact mainly with iso-17∶0 acid, which was confused with (and added to) trans-Δ9 (palmitelaidic) acid; consequently, these results were large overestimates. Regarding the cis-16∶1 acids, the Δ9 isomer is the prominent constituent as expected, but the second-most important isomer is the Δ13 isomer. It does not appear that trans-16∶1 isomers are from ruminant milk fats of great nutritional importance as compared with trans-18∶1 isomeric acids. As for trans-18∶1 isomers, the combination Ag-TLC/GLC is a necessary procedure to quantitate trans-16∶1 acids accurately and reliably. Ag-TLC allows removal of interfering branched 17∶0 acids and cis-16∶1 acids, and low-temperature GLC permits an accurate measurement of all individual isomers most of which with baseline resolution.     

<Emphasis Type="Italic">Trans</Emphasis>-18∶1 isomers in rat milk fat as effective biomarkers for the determination of individual isomeric <Emphasis Type="Italic">trans</Emphasis>-18∶1 acids in the dams' diet

Female rats were fed a diet containing by weight 10% partially hydrogenated sunflower oil, 2% sunflower oil, and 1% rapeseed oil during gestation and lactation. The trans-18∶1 isomer profile of the fat supplement was (in % of total trans 18∶1 acids in the fat supplement): Δ4, 0.5; Δ5, 1.0;Δ6–Δ8, 18∶0; Δ9 (elaidic), 13.5; Δ10, 22.2;Δ11 (vaccenic), 16.0; Δ12, 11.3; Δ13–Δ14, 12.8; Δ15, 2.5; and Δ16, 2.2 (total trans 18∶1 acids in the fat supplement: 40.6%). The cis 18∶1 isomer profile was (in % of total cis-18∶1 isomers):Δ6, Δ8, 2.1; Δ9 (oleics), 70.9; Δ10, 6.1; Δ11, 8.3; Δ12, 4.0; Δ13, 2.8; Δ14, 4.6, and Δ15, 1.2 (total cis-18∶1 acids in the fat supplement: 32.6%). Suckling rats from four litters were sacrificed at day 17 or 18 after birth, and their stomach content (milk) was analyzed. The trans-18∶1 isomer profile of milk was (relative proportions, in % of total): Δ4, 0.3; Δ5, 1.1; Δ6–Δ8, 16.8; Δ9, 15.3; Δ10, 22.0; Δ11, 16.7; Δ12, 11.8; Δ13–14, 11.8; Δ15, 2.5, and Δ16, 1.9 (total trans 18∶1 acids in milk: %). That of cis-18∶1 isomers was (proportions in % relative to total cis-18∶1 isomers): Δ6–Δ8, 4.7; Δ9, 72.5; Δ10, 4.0; Δ11, 8.0; Δ12, 7.1; Δ13, 1.9; Δ14, 1.0, and Δ15, 0.7 (total cis-18∶1 acids in milk: %). These results demonstrate that all isomeric acids, independent of the geometry and the position of the ethylenic bond, are incorporated into milk lipids. With regard to trans-18∶1 isomers, the distribution profile in milk is identical to that in the dams' diet, i.e., there is no discrimination against any positional isomer between their ingestiona nd their deposition into milk lipids. As a consequence, this study indicates that the trans-18∶1 isomer profile of milk reflects that in the dams' diet and supports our earlier hypothesis that the profile of trans-18∶1 isomers in milk can be used to deduce the relative contribution of ruminant fats and partially hydrogenated oils in the diet ot the total intake of trans-18∶1 isomers. On the other hand, the cis-18∶1 isomer profile in milk shows significant differences when compared to that in the dams' diet. Surprisingly, there are no major differences for the cis-Δ9 (oleic) and the cis-Δ11 (asclepic) isomers, which can be synthesized by the mother. However, there seems to be a significant positive selectivity for the group cis-Δ6–Δ8, and for the cis-Δ12 isomer, whereas a negative selectivity occurs for the Δ10 and Δ13 to Δ15 cis isomers. Dr. Robert L. Wolff Robert Wolff passed away at the age of 53 on the 10th of November, 2002. His know-how in the field of lipids was recognized internationally. He had the ability to lead his research projects in both the animal and vegetal worlds. His scientific achievement, more than 100 publications to his name in the field of trans fatty acids, made him highly esteemed by his colleagues. He was Conference Master at Bordeaux 1 University (France) up until 2001, at which time he joined the Nutritional Lipid Unit in I.N.R.A., Dijon (France). His mission there was to develop a research program on plasmalogens and their role in brain and muscle function, for which his analytical and biochemical skills were a guarantee of success. Unfortunately, his state of health did not allow him to complete this project. This publication is his final one.     

Activation of long chain fatty acids by subcellular fractions of rat liver: II. Effect of ethylenic bond position on acyl-CoA formation oftrans-octadecenoates

The rates of acyl-CoA biosynthesis of thetrans Δ⁴ to Δ¹⁵ octadecenoates have been studied using rat liver microsomes and mitochondria as the enzyme(s) source. Acyl-CoA formation was lowest when the Δ⁹ isomer was the substrate and increased as the double bond was moved to either end of the fatty acid chain. Maximal activation was observed when the Δ⁶ and Δ¹⁴ trans-octadecenoates were substrates. All-trans retinoate caused differential inhibition in the activation rates of the varioustrans-octadecenoate isomers. In contrast, the activation profile relative to double bond position was not altered by changing the incubation temperature, pH, or buffer or by adding fatty acid free albumin to the incubation medium or by aging the enzyme. These results do not support the suggestion that more than one enzyme activates the varioustrans-octadecenoate positional isomers. Triton X-100 differentially activated acyl-CoA biosynthesis of the various isomers resulting in a uniform rate of activation. Release of the isomers from the detergent micelle is suggested to be rate-limiting under these conditions.     

The effect of conjugated linoleic acid isomers on fatty acid profiles of liver and adipose tissues and their conversion to isomers of 16:2 and 18:3 conjugated fatty acids in rats

Conjugated linoleic acid (CLA) is a collective term that describes different isomers of linoleic acid with conjugated double bonds. Although the main dietary isomer is 9cis,11trans-18∶2, which is present in dairy products and ruminant fat, the biological effects of CLA generally have been studied using mixtures in which the 9cis,11trans- and the 10trans,12cis-18∶2 were present at similar levels. In the present work, we have studied the impact of each isomer (9cis,11trans- and 10trans,12cis-18∶2) given separately in the diet of rats for 6 wk. The 10trans,12cis-18∶2 decreased the triacylglycerol content of the liver (−32%) and increased the 18∶0 content at the expense of 18∶1n−9, suggesting an alteration of the Δ9 desaturase activity, as was already demonstrated in vitro. This was not observed when the 9cis,11trans-18∶2 was given in the diet. Moreover, the 10trans,12cis-18∶2 induced an increase in the C₂₂ polyunsaturated fatty acids in the liver lipids. The 10trans,12cis-18∶2 was mainly metabolized into conjugated 16∶2 and 18∶3, which have been identified. The 9cis,11trans isomer was preferentially metabolized into a conjugated 20∶3 isomer. Thus, the 9cis,11trans- and the 10trans,12cis-CLA isomers are metabolized differently and have distinct effects on the metabolism of polyunsaturated fatty acids in rat liver while altering liver triglyceride levels differentially.     

Occurrence of octadecenoic fatty acid isomers from hydrogenated fats in human tissue lipid classes

The level oftrans-18∶1 isomers in several isolated lipid classes of human liver, heart, red blood cells and plasma was determined. Phospholipids contained substantially fewertrans-18∶1 isomers than triglycerides. The double bond distribution of thecis andtrans octadecenoate fraction of triglycerides and phosphatidylcholines from human liver and heart was determined. Whereas the double bond distribution of the triglycerides correlated closely with the pattern found in dietary hydrogenated vegetable oils, the phosphatidylcholine fraction showed evidence of selective incorporation or metabolism of specifictrans positional isomers. In general, isomers with double bonds near the methyl terminus were present at levels higher than expected from their relative abundance in the diet. Refinements in methodology needed to analyze octadecenoate double bond configuration and location in human tissues are presented.     

Lipid composition of selected margarines

Results of analytical studies on the composition of 10 selected margarines representative of consumeravailable hard and soft types are presented. Paired hard and soft products from the same manufacturer were chosen where possible. All of the margarines were compared on the basis of total fatty acid composition, polyunsaturated to saturated fatty acid ratios, totaltrans and thetrans content of the monoene and diene fractions, location of the double bond in the monoene isomers, per cent conjugation, distribution of the fatty acids at the 2 position of the triglycerides, tocopherol content, and the ratios of α-tocopherol to polyunsaturated fatty acids. As expected the soft margarines contained more polyunsaturated fatty acids than their companion hard types, but all soft margarines did not contain more polyunsaturated fatty acids than all of the hard margarines. The one margarine containing safflower oil had the highest polyunsaturated to saturated ratio. Eight of the ten margarines contained more than 15%trans monoene and nine contained less than 5%trans diene. Positional isomers in the monoene fraction were Δ6 toΔ12 with thecis Δ9 isomer predominating. All of the margarines contained less than 1.9% conjugation. The percentage oftrans monoene at the 2 position was greater for some margarines than that in the total fatty acid. This was attributed to the preferential placement of polyunsaturated fatty acids at the 2 position in the original vegetable oils. The forms of tocopherol found were characteristic of the original vegetable oils. Ratios of α-tocopherol to PUFA varied from 0.1 to 0.5 mg/g. Determination of the relationship of the amount of tocopherol content to either source or hardness is not possible on the basis of our data.     

Analysis of the monoenoic fatty acid distribution in hydrogenated vegetable oils by silver-ion high-performance liquid chromatography

A silver-ion high-performance liquid chromatography column (hexane/acetonitrile as solvent, ultraviolet detection) was used to analyze the fatty acid distribution (as fatty acid methyl esters) of a representative sample of hydrogenated oil. Fractions containingcis- andtrans-18:1 isomers were readily separated. The positional fatty acid isomers were separated by rechromatographing these fractions. The elution order and percent compositions were compared with results obtained by gas chromatography. Of the Δ8 to Δ14trans-18:1 isomers, only the Δ8 and Δ9 pair could not be separated. The Δ8 and Δ9cis-18:1 pair also could not be separated, and the Δ10 isomer was poorly separated from this pair. Area percents were comparable to results obtained by gas chromatography.     

Incorporation oftrans long-chain n−3 polyunsaturated fatty acids in rat brain structures and retina

During heat treatment, polyunsaturated fatty acids and specifically 18∶3n−3 can undergo geometrical isomerization. In rat tissues, 18∶3 Δ9c, 12c, 15t, one of thetrans isomers of linolenic acid, can be desaturated and elongated to givetrans isomers of eicosapentaenoic and docosahexaenoic acids. The present study was undertaken to determine whether such compounds are incorporated into brain structures that are rich in n−3 long-chain polyunsaturated fatty acids. Two fractions enriched intrans isomers of α-linolenic acid were prepared and fed to female adult rats during gestation and lactation. The pups were killed at weaning. Synaptosomes, brain microvessees and retina were shown to contain the highest levels (about 0.5% of total fatty acids) of thetrans isomer of docosahexaenoic acid (22∶6 Δ4c, 7c, 10c, 13c, 16c, 19t). This compound was also observed in myelin and sciatic nerve, but to a lesser extent (0.1% of total fatty acids). However, the ratios of 22∶6trans to 22∶6cis were similar in all the tissues studied. When the diet was deficient in α-linolenic acid, the incorporation oftrans isomers was apparently doubled. However, comparison of the ratios oftrans 18∶3n−3 tocis 18∶3n−3 in the diet revealed that thecis n−3 fatty acids were more easily desaturated and elongated to 22∶6n−3 than the correspondingtrans n−3 fatty acids. An increase in 22∶5n−6 was thus observed, as has previously been described in n−3 fatty acid deficiency. These results encourage further studies to determine whether or not incorporations of suchtrans isomers into tissues may have physiological implications. Presented in part at the 32nd International Conference on the Biochemistry of Lipids, 1991, Granada, Spain. Delta nomenclature (Δ) is used fortrans polyunsaturated fatty acids to specify the position and geometry of ethylenic bonds. Polyunsaturated fatty acids containingtrans double bonds are abbreviated giving the locations of thetrans double bonds only; e.g., 20∶5 Δ17t 20∶5 Δ5c,8c,11c,14c,17t; 22∶5 Δ19t, 22∶5 Δ7c,10c,13c,16c,19t; 22∶6 Δ19t 22∶6 Δ4c,7c,10c,13c,16c,19t.     

Effect of hepatoma on host liver,heart and lung lipids as tumor growth progresses

A large group of rats was transplanted with hepatoma 7288CTC and 4 animals were sacrificed at 3-day intervals for four weeks. Lipid class concentrations, fatty acid class compositions, and the distribution ofcis octadecenoate positional isomers in the major lipid classes were determined for heart, liver and lung at each time period. The hearts of host animals decreased in dry weight as hepatoma growth progressed. At day 30, heart weights were less than two-thirds of initial weights. Lipid class concentrations changed in all three tissues: cholesterol and free fatty acids increased in liver; triglycerides and cholesterol decreased and then increased in heart; and cholesterol, triglycerides and PC decreased in lung as tumor growth progressed. Hexadecenoate percentages exhibited a progressive decrease in all the lipid classes of heart and liver. Although total octadecenoate percentages showed only minor changes, oleate concentrations generally increased and vaccenate levels decreased in heart and liver lipids as tumor growth progressed. Palmitoleate, precursor of vaccenate, exhibited decreased concentrations early that resulted in decreased vaccenate levels. Decreased palmitoleate concentrations suggest inhibition of the Δ9 desaturase system, but normal oleate concentrations complicate this interpretation. Most of the changes in the lipids were detectable 3–6 days after transplantation, indicating the hepatoma affects the lipid metabolism of the host animal early and well in advance of nutritional stresses.     

Dietary fats containing concentrates ofcis ortrans octadecenoates and the patterns of polyunsaturated fatty acids of liver phosphatidylcholine and phosphatidylethanolamine

The effects of the mixedcis- 18∶1 isomers and mixedtrans-18∶1 isomers present in partially hydrogenated soybean oil (PHSO) upon the patterns of polyunsaturated fatty acids (PUFA) in liver phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were studied in rats fed concentrates ofcis- 18∶1 ortrans- 18∶1 isomers isolated as triacylglycerides from PHSO. Thecis- 18∶1 andtrans- 18∶1 concentrates were fed at levels equal to those present in PHSO fed at 17.9% of the diet. All diets contained the required amounts of both linoleic and linolenic acids. Thetrans- 18∶1 concentrate was found to suppress the levels of 20∶4ω6 and 20∶3ω9, and to increase the levels of 18∶2ω6 and 20∶5ω3 in PC and PE. Thecis- 18∶1 concentrate suppressed 20∶4ω6 in PC, 20∶5ω3 in PC and PE, and 18∶2ω6 was more effective than thetrans concentrate in suppressing 22∶6ω3. Thetrans- 18∶1 concentrate was more effective in suppressing 20∶4ω6. Thetrans-18∶ isomers appear to modify PUFA metabolism by inhibition of PUFA synthesis, whereas thecis- 18∶1isomers appear to compete with 2-position fatty acyl transfer and to inhibit ω3 PUFA acylation.     

Trans- and cis-octadecenoic acid isomers in the hump and milk lipids from Camelus dromedarius

The distribution profiles of individual trans- as well as cis-18∶1 isomers from the fat prepared from the hump adipose tissue and the milk from Camelus dromedarius (the single-humped Arabian species) are described. Gas-liquid chromatography on two capillary columns with different polarities and lengths were used for this purpose in combination with argentation thin-layer chromatography. A comparison of the profiles established is made with that of true ruminant fats. In the fats from the dromedarius as well as from true ruminants, the trans-18∶1 isomers have their ethylenic bonds in all positions between Δ4 and Δ16. The prominent trans isomer is the 11–18∶1 (vaccenic) acid in all species, and the complete distribution profiles are quite similar. Concerning the cis isomers, the prominent isomer is oleic acid, followed by cis-vaccenic acid, as in true ruminant fats. Other cis isomers encompass the Δ6–8 and the Δ12 to Δ15 isomers. Camelidae (suborder Tylopoda) and Bovidae (suborder Ruminantia) have evolved independently since the Eocene, that is for approximately 50 million years. Despite this considerable period, and the profound differences in anatomy, morphology, physiology, ecological and dietary habits between the extant species of these suborders, the rumen microflora has continued to synthesize the same trans- and cis-octadecenoic acid isomers, in comparable proportions, at least as deduced from their composition profiles. We conclude that the trans-18∶1 acid profile is not intrinsically species-dependent, but it can be affected by the nature and the proportions of dietary unsaturated fatty acids that themselves depend on the feed, and that may be species-specific.