Incorporation of radioactive polyunsaturated fatty acids into liver and brain of developing rat

The incorporation of radioactivity from orally administered linoleic acid-1-¹⁴C, linolenic acid-1-¹⁴C, arachidonic acid-³Hg, and docosahexaenoic acid-¹⁴C into the liver and brain lipids of suckling rats was studied. In both tissues, 22 hr after dosing, 2 distinct levels of incorporation were observed: a low uptake (from 18∶2-1-¹⁴C and 18∶3-1-¹⁴C) and a high uptake (from 20∶4-³H₈ and 22∶6-¹⁴C). In adult rats, the incorporation of radioactivity into brain lipids from 18∶2-1-¹⁴C and 20∶4-³H was considerably lower than the incorporation into the brains of the young rats. In the livers of the suckling rats, the activity from the 18 carbon acids was associated mostly with the triglyceride fraction, whereas the activity from the 20∶4-³H₈ and 22∶6-¹⁴C was concentrated in the phospholipid fraction. In the brain lipids, the activity from the different fatty acids was associated predominantly with the phospholipids. In the liver and brain phospholipid fatty acids, some of the activity in the 18∶2-1-¹⁴C and 18∶3-1-¹⁴C experiments was associated with 20 and 22 carbon polyunsaturated fatty acids; however, radioactivity from orally administered 20∶4-³H₈ and 22∶6-¹⁴C was incorporated intact into the tissue phospholipid to a much greater extent compared with the incorporation of radioactivity into 20∶4 and 22∶6 in the experiments where 18∶2-1-¹⁴C and 18∶3-1-¹⁴C, respectively, were administered. Possible reasons for these differences are discussed. Rat milk contains a wide spectrum of polyunsaturated fatty acids, including linoleate, linolenate, arachidonate, and docosahexaenoate. During the suckling period in the rat, there is a rapid deposition of 20∶4 and 22∶6 in the brain. The results of the present experiments suggested that dietary 20∶4 and 22∶6 were important sources of brain 20∶4 and 22∶6 in the developing rat.     

Incorporation of polyunsaturated fatty acids into CT-26, a transplantable murine colonic adenocarcinoma

Previous studies in our laboratory have shown that marine oils, with high levels of eicosapentaenoic (EPA, 20∶5n−3) and docosahexaenoic acids (DHA, 22∶6n−3), inhibit the growth of CT-26, a murine colon carcinoma cell line, when implanted into the colons of male BALB/c mice. Anin vitro model was developed to study the incorporation of polyunsaturated fatty acids (PUFA) into CT-26 cells in culture. PUFA-induced changes in the phospholipid fatty acid composition and the affinity with which different fatty acids enter the various phospholipid species and subspecies were examined. We found that supplementation of cultured CT-26 cells with either 50 μM linoleic acid (LIN, 18∶2n−6), arachidonic acid (AA, 20∶4n−6), EPA, or DHA significantly alters the fatty acid composition of CT-26 cells. Incorporation of these fatty acids resulted in decreased levels of monounsaturated fatty acids, while EPA and DHA also resulted in lower levels of AA. While significant elongation of both AA and EPA occurred, LIN remained relatively unmodified. Incorporation of radiolabeled fatty acids into different phospholipid species varied significantly. LIN was incorporated predominantly into phosphatidylcholine and had a much lower affinity for the ethanolamine phospholipids. DHA had a higher affinity for plasmenylethanolamine (1-O-alk-1′-enyl-2-acyl-sn-glycero-3-phosphoethanolamine) than the other fatty acids, while EPA had the highest affinity for phosphatidylethanol-amine (1,2-diacyl-sn-glycero-3-phosphoethanolamine). These results demonstrate that,in vitro, significant differences are seen between the various PUFA in CT-26 cells with respect to metabolism and distribution, and these may help to explain differences observed with respect to their effects on tumor growth and metastasis in the transplantable model.     

The metabolism of polyunsaturated fatty acids in rat sertoli and germinal cells

The metabolism of [1-¹⁴C]linoleic, [1-¹⁴C]arachidonic and [3-¹⁴C]docosa-4,7,10,13,16-pentaenoic acids was investigated after intratesticular injection of the labeled compounds and isolation of rat Sertoli and germinal cells. Following injection of either¹⁴C-linoleate or¹⁴C-arachidonate, the specific activity (sp act) of docosa-4,7,10,13,16-pentaenoic acid of Sertoli cells was greater than that of the germinal cells. The data suggest that the Sertoli cells are more active in the biosynthesis of the 22-carbon pentaene than the germinal cells. Differences between these 2 cell types were also noted in the distribution of the incorporated¹⁴C among the various lipid classes. Following intratesticular injection of¹⁴C-docosapentaenoic acid, a greater proportion of the recovered¹⁴C in Sertoli cells than in germinal cells was present in 20-carbon fatty acids, suggesting a greater activity in Sertoli cells in the metabolism of the pentaene. The major portion of the recovered¹⁴C in both cell types was present in triacylglycerols during early time periods and in phospholipids after 24 hr. The possibility of transfer of biosynthesized docosapentaenoic acid from Sertoli to germinal cells is discussed.     

Incorporation ofcis- andtrans-octadecenoic acids into the membranes of rat liver mitochondria

The incorporation of dietary isomeric fatty acids into the membranes of liver mitochondria was investigated. Three groups of rats were fed diets containing 3% sunflower seed oil plus 15%, 20%, or 25% partially hydrogenated arachis oil. A fourth group was fed 25% partially hydrogenated arachis oil, but no sunflower seed oil. All diets were given for 3, 6, or 10 weeks. After 10 weeks, the content oftrans fatty acids in the lipids of the mitochondrial membranes was 15–19% of the total fatty acids. The composition of thetrans- and thecis-octadecenoic acids in the lipids of the mitochondrial membranes was similar for all groups supplemented with sunflower seed oil (SO), irrespective of time and dietary level of partially hydrogenated arachis oil (HAO). Thecis 18∶1 (n−8), which was a major isomer of the partially hydrogenated arachis oil, was almost excluded from the mitochondrial fatty acids. Likewise, the content oftrans 18∶1 (n−8) was considerably lower in the mitochondrial lipids than in the diet. On the contrary, the content oftrans 18∶1 (n−6) was higher in the mitochondrial lipids than in the diet. In the group fed without sunflower seed oil, isomers of linoleic acid and arachidonic acid were observed in the lipids of mitochondrial membranes. Presented in part at the ISF Congress, Marseille, September 1976.     

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.     

Reactions of conjugated fatty acids. VI. Selenium catalysis,a method for preparing diels-alder adducts from cis,trans-octadecadienoic acid

Summary Adducts of dienophiles and alkali-conjugated safflower fatty acids containing conjugated linoleic acid in thecis,trans form were prepared by heating the reactants in the presence of selenium as a catalyst. The products appeared to be identical to those prepared fromtrans,trans conjugated linoleic acid so that isomerization ofcis-trans totrans,trans acids is eliminated as a separate step. Although yields of pure product were lower than desired because of difficulties in removing selenium, yields of crude adducts ranged from 64–82%. The adducts obtained could be epoxidized with hydrogen peroxide and an ion-exchange resin as catalyst in 80–93% yield or with peracetic acid in 89–98% yield. Presented at the meeting of the American Oil Chemists' Society, Cincinnati. O. September 30–October 2, 1957.     

Metabolism of linolenic acid in developing brain: I. Incorporation of radioactivity from 1-14C linolenic acid into brain fatty acids

Twelve-thirteen day old rats were given 1-¹⁴C linolenic acid by intraperitoneal injection. Fatty acids were isolated from the brains of animals sacrificed at the end of 8 and 48 hr and 15 and 45 days. Eight hr after the tracer, radioactivity was found neither in 18∶3 nor its endproduct, 22∶6, and palmitate was the most highly radioactive component. At longer intervals, 22∶6 seemed to retain much of the radioactivity, whereas palmitate showed a precipitous decline in radioactivity. Initial oxidation of linolenate and sparing of the linolenate complexed with polar lipids are discussed.     

Incorporation and metabolism of fatty acids by cultured dissociated cells from rat cerebrum

Dissociated brain cells in culture incorporate a variety of saturated and unsaturated fatty acids into their cellular lipids. Of the various fatty acids studied, uptake of radioactivity was greatest for stearic acid and decreased progressively with decreasing chain length. Incorporation of radioactivity from linoliec and linolenic acids was more extensive than from oleic acid. Cellular phospholipids and triacylglycerols were labeled preferentially from all fatty acid precursors, with the relative amount of label in phospholipids being greatest when cells were incubated with linolenic acid. Fatty acids underwent desaturation and chain elongation. Changes in the labeling pattern of phospholipid fatty acids in the course of incubation demonstrated precursor-product relationships for laurate (12∶0), myristate (14∶0), palmitate (16∶0), and stearate (18∶0) and for linolenate (18∶3), eicosapentaenoate (20∶5), docosapentaenoate (22∶5), and docosahexaenoate (22∶6). The appearance of label in 22∶5 and 22∶6 paralleled the entrance of label into the ethanolamine phosphoglyceride fraction. Conversion of linoleate (18∶2 ω6) to arachidonate (20∶4 ω6) could be demonstrated but did not proceed via 18∶3 ω6.     

Enzymatic enrichment of C20 cis-5 polyunsaturated fatty acids fromBiota orientalis seed oil

Enrichment ofcis-5 polyunsaturated fatty acids [20:3(5c,11c,14c), 4.3% and 20:4(5c,11c,14c,17c), 11.3%] fromBiota orientalis seed oil was carried out by lipase-catalyzed selective esterification and hydrolysis reactions. Lipases fromRhizomucor miehei (Lipozyme),Candida cylindracea and porcine pancreas were used. Lipozyme-catalyzed esterification ofBiota fatty acids withn-butanol inn-hexane allowed 20:3 and 20:4 (as fatty acids) to be enriched to a maximum level of 52.9%, and in the presence ofC. cylindracea lipase 61.5% enrichment was achieved. Esterification with pancreatic lipase was poor with low levels of enrichment of 20:3 and 20:4 (22%). A multigram scale esterification of the free fatty acids fromBiota seed oil by repeated treatment of the isolated fatty acid fraction withn-butanol inn-hexane in the presence ofC. cylindracea lipase furnished an enrichment yield of 72.5% of a mixture of 20:3 and 20:4 fatty acids. Urea fractionation of the free fatty acids ofBiota oil gave an initial enriched fraction of 20:3 (9.5%) and 20:4 (25.2%) which, upon treatment withC. cylindracea lipase inn-butanol andn-hexane, gave an enriched fraction of 85.3% of 20:3 and 20:4 fatty acids. Partial hydrolysis of the triglycerides ofBiota oil byC. cylindracea lipase in potassium phosphate buffer at 25°C resulted in a 2.8-fold enrichment ofcis-5 polyunsaturated fatty acids (40.8% of 20:3 and 20:4) as contained in the unhydrolyzed acylglycerol fractions.     

Effect of phospholipid n‐3 polyunsaturated fatty acids on rat lipid metabolism

It has been demonstrated that the amount and type of dietary fat are factors involved in the risk of arteriosclerosis and coronary or cerebral artery disease through lipid metabolism. In this study, we investigated the effects of phospholipids (PLs) containing n‐3PUFAs on lipid metabolism in rats. PLs containing n‐3PUFAs were prepared from squid (Todarodes pacificus) mantle muscle. Groups of male Wistar rats were fed AIN93G diet containing soybean oil (SO, 7%), fish oil (1.2%) + SO (5.8%), soybean PLs (1.8%) + SO (5.2%), or PLs containing n‐3PUFAs (1.8%) + SO (5.2%). The following indicators were assayed as indexes of lipid metabolism: TAG and cholesterol in serum and liver, fecal cholesterol, bile‐acid excretion, and liver mRNA expression levels of genes encoding proteins involved in cholesterol homeostasis. Serum and liver TAG contents decreased significantly in the group fed PLs containing n‐3PUFAs as compared to other groups, accompanied by a significant decline in the expression level of sterol regulatory element binding protein‐1c. The decrease in cholesterol content in the group fed PLs containing n‐3PUFAs was due to the increase in fecal cholesterol excretion and the increase of mRNA expression levels of ATP‐binding cassette (ABC) G5 and ABCG8 in liver. Practical applications : PLs containing n‐3PUFAs decreased serum and liver TAG contents compared with that induced by soybean PLs. Further, PLs containing n‐3PUFAs can induce a reduction in serum and liver cholesterol concentrations as well as the triglyceride‐reducing effect of conventional n‐3PUFAs containing TAG. In other words, dietary n‐3PUFAs contained in PLs can prevent life‐style diseases such as hyperlipidemia, arteriosclerosis and coronary, or cerebral artery disease more effectively than TAG containing n‐3PUFAs. Therefore, it is expected that the risk of lifestyle diseases would be decreased if PL containing n‐3PUFAs can be supplied routinely. In this study, PLs containing n‐3PUFAs were prepared from squid mantle muscle. On an industrial scale, such PLs can be produced from various unused resources and waste materials of fisheries. We conclude that highly functional foods could be developed based on the findings of this study, and would be available for health promotion worldwide.     

Enzymatic modification of trilinolein: Incorporation of n-3 polyunsaturated fatty acids

Two immobilized lipases, IM60 fromMucor miehei and SP435 fromCandida antarctica, were used as biocatalysts for the modification of trilinolein with n-3 polyunsaturated fatty acids (PUFA), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), by using their ethyl esters as acyl donors (EEPA and EDHA, respectively). Transesterification (ester-ester interchange) reactions were carried out in organic solvent. The products were analyzed according to their equivalent carbon number and polarity by reverse-phase high-performance liquid chromatography, and the fatty acid profiles were determined by gas-liquid chromatography. Modified triacylglycerol products contained 1 or 2 molecules of n-3 PUFA. With EEPA as the acyl donor, the total EPA product yields with IM60 and SP435 as biocatalysts were 79.6 and 81.4%, respectively. However, with EDHA as the acyl donor and IM60 and SP435 as biocatalysts, the total DHA product yields were 70.5 and 79.7%, respectively. Effects of reaction parameters, such as type of solvent, enzyme load, time course, and molar ratio of substrates on the n-3 PUFA incorporation, were followed with SP435 as the biocatalyst. High yields were obtained, even in the absence of organic solvent. These lipids do hold promise for specialty nutrition and other therapeutic uses.     

Dietary linoleic acid and polyunsaturated fatty acids in rat brain and other organs. Minimal requirements of linoleic acid

Starting three weeks before mating, 12 groups of female rats were fed different amounts of linoleic acid (18∶2n−6). Their male pups were killed when 21-days-old. Varying the dietary 18∶2n−6 content between 150 and 6200 mg/100 g food intake had the following results. Linoleic acid levels remained very low in brain, myelin, synaptosomes, and retina. In contrast, 18∶2n−6 levels increased in sciatic nerve. In heart, linoleic acid levels were high, but were not related to dietary linoleic acid intake. Levels of 18∶2n−6 were significantly increased in liver, lung, kidney, and testicle and were even higher in muscle and adipose tissue. On the other hand, in heart a constant amount of 18∶2n−6 was found at a low level of dietary 18∶2n−6. Constant levels of arachidonic acid (20∶4n−6) were reached at 150 mg/100 g diet in all nerve structures, and at 300 mg/100g diet in testicle and muscle, at 800 mg/100 g diet in kidney, and at 1200 mg/100 g diet in liver, lung, and heart. Constant adrenic acid (22∶4n−6) levels were obtained at 150, 900, and 1200 mg/100 g diet in myelin, sciatic nerve, and brain, respectively. Minimal levels were difficult to determine. In all fractions examined accumulation of docosapentaenoic acid (22∶5n−6) was the most direct and specific consequence of increasing amounts of dietary 18∶2n−6. Tissue eicosapentaenoic acid (20∶5n−3) and 22∶5n−3 levels were relatively independent of dietary 18∶2n−6 intake, except in lung, liver, and kidney. In several organs (muscle, lung, kidney, liver, heart) as well as in myelin, very low levels of dietary linoleic acid led to an increase in 20∶5n−3. Dietary requirements for 18∶2n−6 varied from 150 to 1200 mg/100 g food intake, depending on the organ and the nature of the tissue fatty acid. Therefore, the minimum dietary requirement is estimated to be about 1200 mg/100 g (i.e., the level that ensures stable and constant amounts of arachidonic acid).     

Incorporation ofcis-octadecenoic acids into the rat liver mitochondrial membrane phospholipids and adipose tissue triglycerides

The incorporation of the dietarycis 18∶1 (n−12) andcis 18∶1 (n−10) into liver mitochondrial membrane phospholipids and adipose tissue trigly cerides was studied in 4 groups of rats fed diets containing 10 weight percent (wt%) of fat with the following contents of octadecenoic acids: 50%cis 18∶1(n−12) +9%cis 18∶1 (n−9); 25%cis 18∶1 (n−12)+32%cis 18∶1 (n−9); 50%cis 18∶1 (n−10)+10%cis 18∶1 (n−9); or 54%cis 18∶1 (n−9). Dietary linoleic acid was 3 wt% in all 4 groups. In the mitochondrial membranes, the isomeric octadecenoic acids were primarily incorporated into the 1-position of phosphatidylcholines and phosphatidylethanolamines at the expense of saturated fatty acids. The maximal incorporations observed in the 1-position of phosphatidylethanolamines were 4.8% 18∶1 (n−12) and 8.9% 18∶1 (n−10). No effects on the contents of polyunsaturated fatty acids in the phospholipids were seen. In the adipose tissue, the isomeric octadecenoic acids were incorporated at a level of 13%cis 18∶1 (n−12) or 23%cis 18∶1 (n−10), paralleled by a reduction in the content of oleic acid. Presented in part at the 9th Scandinavian Symposium on Lipids, Visby, Sweden, June 1977.     

Clinical application of C18 and C20 chain length polyunsaturated fatty acids and their biotechnological production in plants

A potential revolution in FA therapies is on the horizon. In recent years, the full magnitude of various FA treatments and their overall importance to health has become increasingly apparent. Fetal and infant nutrition studies have clearly shown that FA status at birth can have life-long health implications affecting eye and brain function, insulin resistance, and blood pressure control. As well, nutrition studies have identified dietary imbalances and deficiencies that have the potential to alter the health of future generations severely and to promote progression of age-related degenerative disorders. Mixtures of naturally occurring FA have shown promise as therapeutic agents for a diverse range of health conditions including atopic eczema, rheumatoid arthritis, cardiovascular disease, and neurological problems. Through the 1990s, the creation of technologies to concentrate and formulate pharmacologically active individual FA components as well as tailored combinations propelled development of this new drug category. However, high production costs and government regulatory encumbrance limited the expansion of this emerging pharmaceutical sector. Fortunately, many countries are now creating regulatory frameworks that are better suited for product evaluation and control of the manufacturing FA products than historical drug models, and hence expansion in this area is now anticipated.     

Incorporation of linolenic-1-C14 acid into eicosapentaenoic and docosahexaenoic acids in fish

Following intraperitoneal injection of methyl linolenate-1-C¹⁴ into kelp bass,Paralablax clathratus, the highly polyunsaturated fatty acids of their body fats were concentrated by low temperature crystallization from acetone, and eicosapentaenoic and docosahexaenoic acids were isolated from the concentrate by reversed-phase chromatography and hydrogenated. The resulting arachidic and behenic acids were degraded stepwise to margaric acid, and the distribution of activity was determined. The results indicate that the injected linolenic acid was converted to eicosapentaenoic acid and the latter incorporated into docosahexaenoic acid. A probable conversion pathway is linolenic acid→6,9,12,15-octadecatetraenoic acid→8,11,14,17-eicosatetraenoic acid→5,8,11,14,17-eicosapentaenoic acid→7,10,13,16,-19-docosapentaenoic acid→4,7,10,13,16,19-docosahexaenoic acid. Supported by a training grant from the National Heart Institute, Bethesda, Md. This paper based partially on work performed under Contract AT(04-1)GEN-12 between the Atomic Energy Commission and the University of California.     

Incorporation of 1-14C-Acetate into C26 fatty acids of the marine spongeMicrociona prolifera

The incorporation of 1-¹⁴C-acetate into the many fatty acids of the marine spongeMicrociona prolifera was investigated. Probable precursors of 26∶2Δ5,9 and 26∶3Δ5,9,19 showed high levels of radioactivity, supporting the following pathways for the biosynthesis of C₂₆ acids: $$\begin{array}{*{20}c} {16:0 \to \to \to 26:0 \to 26:1\Delta 9 \to 26:2\Delta 5,9} \\ {16:1\Delta 9 \to \to \to 26:1\Delta 19 \to } \\ {26:2\Delta 9,19 \to 26:3\Delta 5,9,19} \\ \end{array}$$ Degradation of the unsaturated C₂₆ acids at their double bonds showed that the¹⁴C was concentrated near the carboxyl end of the chain. Hence, chain elongation was the major mechanism for acetate incorporation into these acids.     

Incorporation of conjugated linoleic acid and vaccenic acid into lipids from rat tissues and plasma

The objective of this study was to determine the incorporation of conjugated linoleic acid (CLA) into triacylglycerols (TAG) and phospholipids (PL) of tissues and plasma, and to interpret the role of dietary‐derived vaccenic acid (VA) in increasing the tissue content of CLA (c9,t11) and the influence on the fatty acid profile. We fed five groups of rats semi‐purified diets with varying levels of CLA and VA: control butter with low CLA (c9,t11) and VA; control butter added 5% CLA (c9,t11); control butter added 5% Tonalin [equal amount of CLA (c9,t11) and CLA (t10,c12)]; control butter added 5% VA; butter with high CLA (c9,t11) and VA (H‐CLA), for 3 weeks. The highest incorporation of CLA (c9,t11) was found in adipose tissue, and the lowest was observed in liver. Low intake of CLA (c9,t11) combined with high intake of VA resulted in a higher incorporation of CLA (c9,t11) in tissues due to the conversion of VA to CLA (c9,t11), compared to feeding CLA (c9,t11) without VA. However, in enterocytes, the proportion of CLA (c9,t11) was low after feeding VA, indicating no or only a minor conversion of VA to CLA (c9,t11) in the intestine. The incorporation of CLA (t10,c12) into TAG from plasma and tissues was generally much lower than that of the CLA (c9,t11) isomer, except in the enterocyte TAG, which had similar proportions of the two isomers.     

Competitive inhibitions in the metabolism of polyunsaturated fatty acids studied via the composition of phospholipids,triglycerides and cholesteryl esters of rat tissues

Male rats which had been kept on fat-free diet and which were deficient in essential fatty acids were divided into ten groups. All ten groups received 0.8% of calories of linolenate, and nine received one of three levels of either linoleate, γ-linolenate or arachidonate for a period of six days. The rats were sacrificed, the livers, kidneys and testes were extracted, and the phospholipids, triglycerides and cholesteryl esters were separated by thin-layer chromatography. The fatty acid composition of each was determined by gas-liquid chromatography. The inhibition of the metabolism of linolenic acid by linoleate, γ-linolenate and arachidonate was evidenced in all three lipid classes and in all tissues. The activities in suppressing linolenate metabolism were in the order 20:4 >18:3 >18:2. Presented before the AOCS, Houston, April, 1965.