Synthesis of phospholipids and phospholipid fatty acids by isolated perfused rat lung

Synthesis of phospholipids and phospholipid fatty acids in isolated perfused rat lung was studied. The perfusion fluid was a Krebs-Ringer bicarbonate buffer containing a¹⁴C labeled substrate. It was found that 1-¹⁴C-acetate, 1-¹⁴C-laurate, 1-¹⁴C-palmitate, 1-¹⁴C-stearate, 1-¹⁴C-oleate, or U-¹⁴C-D-glucose was incorporated into tissue lipids in the isolated perfused lung at a rate geeater than that in incubated minced tissue. However, the patterns of the newly synthesized lipids from these two systems were similar. In 1 hr of perfusion, 6.8, 3, 14.5, 7.5, 7, and 2% of the initial¹⁴C-radioactivity of 1-¹⁴C-acetate, 1-¹⁴C-laurate, 1-¹⁴C-palmitate, 1-¹⁴C-stearate, 1-¹⁴C-oleate, and U-¹⁴C-D-glucose, respectively, were incorporated into phospholipids. Phospholipid fatty acids accounted for 95–96% total phospholipids-¹⁴C when¹⁴C-substrates, other than glucose, were used. For glucose, only 20% phospholipids-¹⁴C was in phospholipid fatty acids. More than 80% phospholipid fatty acids-¹⁴C was in palmitic acid when 1-¹⁴C-acetate and U-¹⁴C-D-glucose were used, while 37, 61, 80, and 94% phospholipid fatty acid-¹⁴C from 1-¹⁴C-laurate, 1-¹⁴C-sterate, 1-¹⁴C-oleate, and 1-¹⁴C-palmitate, respectively were recovered in the original form of the fatty acid used. The newly synthesized phospholipid fatty acid (13–24%) from 1-¹⁴C-laurate, 1-¹⁴C-stearate, and 1-¹⁴C-oleate was palmitic, and 10% of phospholipid fatty acid from 1-¹⁴C-stearate was in oleic acid. Hydrolysis by phospholipase A showed that¹⁴C from perfused substrates was esterified to both α and β positions of phospholipids. It was found that positional selectivity of phospholipid fatty acids was determined by chain length, degree of unsaturation, and source of fatty acid.     

Lipid metabolism in plasma,liver, and adipose tissue of rats with experimental chronic nephrotic syndrome

Plasma, liver, and adipose tissue lipid composition and synthesis from [1-¹⁴C] acetate were studied three months following induction of nephrotic syndrome in rats by injection of antiglomerular basement membrane protein. Plasma triglyceride concentrations and specific radioactivities were elevated, and the triglycerides contained increased proportions of oleic acid. Plasma cholesterol and phospholipid concentrations were also increased, but free fatty acid levels were not. Liver triglyceride concentrations were decreased and incorporation of [1-¹⁴] acetate into liver triglycerides was also depressed below that of normal controls. Nephrotic rat liver triglycerides contained a higher proportion of oleic acid and lower arachidonic acid than did controls. Incorporation of [1-¹⁴C] acetate into adipose tissue lipids of the nephrotic rats was increased, and the proportion of palmitic acid was decreased. In the chronic nephrotic rat, the major source of the increased plasma triglycerides may be fatty acids mobilized from adipose tissue stores.     

Metabolism of long-chain fatty acids,alcohols and alkylglycerols in the fish parasiteParatenuisentis ambiguus (Acanthocephala)

Specific differences between the acyl composition of lipids on the helminthParatenuisentis ambiguus and its host eel, as shown previously, prompted us to study the lipid metabolism in this intestinal fish parasite. Adults and larvae ofP. ambiguus were fed various lipid precursors, e.g., fatty acids, long-chain alcohols and 1-O-alkylglycerols, which may occur as common nutrients of intestinal parasites. Incorporation of [1-¹⁴C]palmitic acid into neutral and polar lipids was found to be similar under aerobic and near-anaerobic conditions. In adult parasites maintained in culture medium supplemented with glucose, [1-¹⁴C]palmitic acid was incorporated mainly into triacylglycerols and phosphatidylcholines, whereas [1-¹⁴C]oleic acid was incorporated preferentially into triacylglycerols. In fasted adults, as well as in larvae, [1-¹⁴C]oleic acid was mainly transferred to phosphatidylcholines. Lipolytic activity was detected in adult parasites that had been incubated with radioactive trioleoylglycerol. [1-¹⁴C]Hexadecan-1-ol was oxidized inP. ambiguus at a high rate to labeled palmitic acid, which was incorporated into various lipid classes ofP. ambiguus. Small but significant proportions of radioactivity from hexadecan-1-ol were incorporated into ether glycerolipids of the parasite. A more direct precursor in ether glycerolipid metabolism, i.e.,rac-1-O-[1′-¹⁴C] hexadecylglycerol, was incorporated into alkyl and 1′-alkenyl moieties of choline and etha-nolamine etherglycerophospholipids ofP. ambiguus in high yield. High proportions of labeled diacylglycerols, triacylglycerols and steryl esters were detected in surface lipids as well as lipid extracts of the culture media after incubation ofP. ambiguus with [1-¹⁴C]palmitic or [1-¹⁴C]oleic acids. The results suggest that palmitic acid and oleic acid are incorporated into neutral and polar lipids ofP. ambiguus maintained in glucose medium quite differently with oleic acid showing a strong preference for triacylglycerols. However, the incorporation of palmitic acid in glucose-fed parasites was similar to that of oleic acid in fasted parasites, as well as in larvae. This may be explained by partial fatty acid depletion in fasted worms and rapid cell division in larvae, respectively.     

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.     

Selectivity in incorporation,utilization and retention of oleic and linoleic acids by human skin fibroblasts

Fetal human fibroblasts were grown in culture medium containing 10% fetal bovine serum supplemented with [1-¹⁴C] linoleate or [1-¹⁴C] oleate. At all concentrations of exogenous fatty acids, the incorporation of oleate was greater than that of linoleate. With increased medium fatty acid concentrations, linoleate in triacylglycerol (TAG) could be increased from 13 to 75% of the total incorporated; at each concentration, relatively more linoleate than oleate was in TAG. When the cells were exposed to exogenous oleate/linoleate mixtures, the composition of the mixture determined the extent of incorporation of both fatty acids. When the mixture was primarily linoleate, scarce oleate was used preferentially for phospholipids (PL); no such specificity for scarce linoleate was observed. Addition of exogenous fatty acids resulted in a shift of previously incorporated¹⁴C fatty acids from phospholipid into TAG; retention of oleate in PL was greater than that of linoleate. Incorporation of oleate into phospholipids was also higher than that of linoleate from exogenous fatty acid mixtures which were 80% saturated. It is suggested that normal human fibroblasts have adapted to the low levels of exogenous polyunsaturated fatty acids in culture media by increased use of oleate in phospholipid. Even when the cells aresupplemented with linoleate, the preferential use of oleate in phospholipid groups is retained. Presented in part at the ASBC Meeting, Dallas, april 1979.     

Intravenously injected [1-14C]arachidonic acid targets phospholipids, and [1-14C]palmitic acid targets neutral lipids in hearts of awake rats

The differential uptake and targeting of intravenously infused [1-¹⁴C]palmitic ([1-¹⁴C] 16∶0) and [1-¹⁴C]arachidonic ([1-¹⁴C]20∶4n−6) acids into heart lipid pools were determined in awake adult male rats. The fatty acid tracers were infused (170 μCi/kg) through the femoral vein at a constant rate of 0.4 mL/min over 5 min. At 10 min postinfusion, the rats were killed using pentobarbital. The hearts were rapidly removed, washed free of exogenous blood, and frozen in dry ice. Arterial blood was withdrawn over the course of the experiment to determine plasma radiotracer levels. Lipids were extracted from heart tissue using a two-phase system, and total radioactivity was measured in the nonvolatile aqueous and organic fractions. Both fatty acid tracers had similar plasma curves, but were differentially distributed into heart lipid compartments. The extent of [1-¹⁴C]20∶4n−6 esterification into heart phospholipids, primarily choline glycerophospholipids, was elevated 3.5-fold compared to [1-¹⁴C]16∶0. The unilateral incorporation coefficient, k ^*, which represents tissue radioactivity divided by the integrated plasma radioactivity for heart phospholipid, was sevenfold greater for [1-¹⁴C]20∶4n−6 than for [1-¹⁴C]16∶0. In contrast, [1-¹⁴C]16∶0 was esterified mainly into heart neutral lipids, primarily triacylglycerols (TG), and was also found in the nonvolatile aqueous compartment. Thus, in rat heart, [1-¹⁴C]20∶4n−6 was primarily targeted for esterification into phospholipids, while [1-¹⁴C]16∶0 was targeted for esterification into TG or metabolized into nonvolatile aqueous components.     

Hepatic metabolism of 1-14C octanoic and 1-14C margaric acids

The hepatic metabolism of 1-¹⁴C margaric acid, a 17 carbon long chain saturated fatty acid which is present in the liver in trace amounts, was compared with 1-¹⁴C octanoic acid and 1-¹⁴C palmitic acid to determine if the enhanced oxidation of medium chain fatty acids to CO₂ was dependent on fatty acid chain length or the endogenous pool size of the fatty acid substrate. Despite the fact that endogenous margarate is present in trace amounts, there was no significant difference in the oxidation of margarate and palmitate to CO₂, while the oxidation of octanoate to CO₂ was significantly more rapid. Both margarate and palmitate were more readily incorporated into lipid soluble products in contrast to the low rate of incorporation of octanoate. However, margarate was less readily incorporated into triglyceride, phospholipid and monoglyceride than palmitate. These studies suggest that the chain length rather than hepatic content of the fatty acid determines whether the carboxyl group of equimolar amounts of a 1-¹⁴C-carboxyl labeled fatty acid will be preferentially oxidized to CO₂ or incorporated into tissue lipid in the liver.     

Fatty acid metabolism of the calanoid copepodParacalanus parvus: 2. Palmitate,stearate, oleate and acetate

The de novo biosynthesis of fatty acids in the wild, calanoid copepodParacalanus parvus was studied. The incubation of labeled acetate proved the de novo biosynthesis of saturated and monounsaturated even fatty acids from 14 to 20 carbons and the 22∶1 acid. Saturated and monounsaturated uneven fatty acids from 15 to 21 carbons were also synthesized. The copepod could not synthesize linoleic and α-linolenic acids. By administration of [1-¹⁴C]palmitate, [1-¹⁴C] stearate and [1-¹⁴C]oleate, it was possible to elucidate the general pattern of the de novo biosynthesis of fatty acids in the wildP. parvus.     

Preferential metabolism of linoleic acid by five-day-old barley shoots

The degradation of exogenous radioactively labeled fatty acids by 5-day-old barley shoots was examined. [1-¹⁴C] Linoleic acid was observed to be degraded 7 times faster than [1-¹⁴C] oleic acid and 5 times faster than [1-¹⁴C] palmitic acid. The pathway of degradation was determined by identifying the water-soluble products and determined to be β-oxidation. During a 15 min incubation, the barley shoots took up 0.91 nmol/g fresh wt of linoleic acid, of which 0.16 nmol/g fresh wt was incorporated into glutamic acid, 0.07 nmol/g fresh wt into succinic acid and 0.002 nmol/g fresh wt into carbohydrates. By 30 min, additional TCA cycle intermediates, especially malic acid, were detected. Palmitic acid and oleic acid were broken down to the same products. The rates of uptake and the distribution of label into lipids were determined. The uptake of label by the tissue was similar for all 3 fatty acid substrates. Label from linoleic, oleic and palmitic acids was found to be incorporated into similar lipids, primarily phosphatidylcholine (PC), and the extent of incorporation was comparable. Although all 3 fatty acid substrates were broken down by β-oxidation, the reason for the more rapid degradation of linoleic acid was not established. It does not appear to be related to uptake of substrate or incorporation of label into lipids.     

Influence of medium-chain triglycerides on lipid metabolism in the rat

Lipid metabolism was studied in rats fed diets containing corn oil, coconut oil, or medium-chain triglyceride (MCT), a glyceride mixture containing fatty acids of 8 and 10 carbons in length. The ingestion of MCT-supplemented, cholesterolfree diets depressed plasma and liver total lipids and cholesterol as compared with corn oil-supplemented diets. In rats fed cholesterol-containing diets, plasma cholesterol levels were not influenced by dietary MCT, but liver cholesterol levels were significantly lower than in animals fed corn oil. In vitro cholesterol synthesis from acetate-1-¹⁴C was lower in liver slices of rats that consumed MCT than in similar preparations from corn oil-fed rats. Studies of fatty acid carboxyl labeling from acetate-1-¹⁴C and the conversion of palmitate-1-¹⁴C to C₁₈ acids by liver slices showed that chain-lengthening activity is greater in the liver tissue of rats fed MCT than in the liver of animals fed corn oil. The hepatic fatty acid desaturation mechanisms, evaluated by measuring the conversion of stearate-2-¹⁴C to oleate, was also enhanced by feeding MCT. Adipose tissue of rats fed MCT converts acetate-1-¹⁴C to fatty acids at a much faster rate than does tissue from animals fed corn oil. Evidence is presented to show that the enhanced incorporation of acetate into fatty acids by the adipose tissue of rats fed MCT represents de novo synthesis of fatty acids and not chain-lengthening activity. Data are also presented on the fatty acid composition of plasma, liver, and adipose tissue lipids of rats fed the different fats under study.     

Wirkungsmechanismus langkettiger Monoenfettsäuren im Energiestoffwechsel des Herzens

Mechanism of Long Chain Monoenoic Fatty Acids Acting on the Energy Metabolism of Heart The oxidation of 1-¹⁴C-erucic (C_22:1) and 1-¹⁴C-nervonic (C_24:1) acids was studied in comparison to 1-¹⁴C-palmitic and -oleic acids in isolated rat and pig heart mitochondria. After mitochondrial incubation with the albumin-bound fatty acids only small amounts of ¹⁴CO₂ developed from the oxidation of the long chain monoenoic acids as compared to palmitic or oleic acid. The slow down of the oxidation rate was more pronounced in rat than in pig heart mitochondria. The oxidation of palmitic or oleic acid was not found to be inhibited by the C²⁰–C²⁴-monoenoic acids, whereas palmitic or oleic acid inhibited the oxidation of erucic acid competitively. From present findings an idea may be developed of the interference on fatty acid metabolism in heart muscle by erucic and other long chain monoenoic acids.     

The rare caribbean spongeLeucosolenia canariensis: Phospholipid fatty acids and sterols

The phospholipid fatty acid composition of the Calcarean spongeLeucosolenia canariensis was studied, and no Δ^5,9 fatty acids were detected. These results are in contrast to the phospholipids from sponges belonging to the class Demospongiae where Δ5,9 fatty acids are predominant. Odd branched-chain fatty acids between 17 and 19 carbons accounted for 26% of the total fatty acids ofL. canariensis, while straight-chain fatty acids between 16 and 22 carbons accounted for 61% of the total fatty acid composition. The sterol composition ofL. canariensis is also reported, and only Δ^5,7,22 sterols were observed.     

Hepatic metabolism of 1-14C octanoic and 1-14C palmitic acids

The hepatic metabolism of 1⁻¹⁴C octanoic acid was compared with that of 1⁻¹⁴C palmitic acid in male rats which were fed. After intraportal injection only 1/6 to 1/18 as much octanoic acid as palmitic acid was incorporated into hepatic lipids. In contrast, octanoic acid yielded two to four times as much water-soluble product as did palmitic acid. Similar, but even more impressive, differences between the incorporation of these fatty acids into hepatic lipids were observed in liver slices incubated with¹⁴C octanoate and¹⁴C palmitate. The oxidation of octanoate to CO₂ was more than 10 times as great as that of palmitate. With both substrates, triglycerides comprised almost half the labeled lipid recovered. However octanoate yielded a higher proportion of labeled, unesterified fatty acids and a lower proportion of labeled phospholipid and monoglycerides than did palmitate. Most of the¹⁴C recovered in hepatic lipids after incubation with 1⁻¹⁴C octanoate was found in the carboxyl groups of long-chain fatty acids, suggesting that the latter had been synthesized from 2-carbon fragments formed from the oxidation of octanoate. In contrast, only a small fraction of the palmitate was elongated. The similarities and differences between the metabolism of octanoic and palmitic acid in liver and intestine, and the possible nutritional significance of octanoic acid are discussed.     

Absorption and metabolism of 1-14C-hydroxy octadecadienoate in the rat

The metabolism of 1-¹⁴C-9(13)-hydroxy octadecadienoic acid methyl ester (1-¹⁴C-HAME) by the rat was investigated in vivo and in liver slices. A 1.5 mg dose of 1-¹⁴C-HAME administered by stomach tube was efficiently hydrolyzed and absorbed from the intestinal tract. In comparison with 1-¹⁴C-methyl linoleate (1-¹⁴C-ML), 1-¹⁴C-HMAE was more extensively oxidized to¹⁴CO₂ in vivo and in vitro. After 1-¹⁴C-HAME administration as much as 50% of the radioactivity in the adipose tissue triglycerides was associated with¹⁴C-hydroxy fatty acids. The remaining activity was present in randomly labeled normal fatty acids. No evidence was obtained for the incorporation of¹⁴C-hydroxy acids into liver lipids; most of the radioactivity from 1-¹⁴C-HAME in this organ was recovered in saturated and monoenoic fatty acids. About 10% of the radioactivity 24 hr after 1-¹⁴C-HAME administration was associated with triglyceride trienoic acids, indicating that at least a portion of this acid was dehydrated in the liver. An unidentified polar acid was detected in the urine of the 1-¹⁴C-HAME-treated animals.     

Fatty acid biosynthesis and incorporation into lipid classes in seeds and seed tissues of flax

Fatty acid metabolism in developing flaxseeds was studied by incubating whole seeds or isolated seed tissues in buffered solutions of 1-¹⁴C-acetate, 2-¹⁴C-malonate and¹⁴CO₂. Lipid classes were separated by thin layer chromatography, and fatty acid labeling in phospholipids, diglycerides and triglycerides was determined by combined thin layer and gas liquid chromatographic techniques. Incorporation of¹⁴C from acetate into embryo lipids was very rapid with phospholipids and 1,2-diglycerides becoming highly labeled in treatment times as short as 5 min. Triglycerides were labeled more slowly. Phospholipid radioactivity was largely associated with the phosphatidyl choline fraction. Oleic acid had the highest specific activity of all major fatty acids in short treatment periods. This was followed in decreasing order of activity by palmitic, linoleic, stearic and linolenic acids. As the treatment period was lengthened to 90 min or longer, linoleic and linolenic activities were markedly increased. Use of malonate or CO₂ rather than acetate as the substrate increased the labeling of the saturated acids. Incorporation of¹⁴C from acetate into lipids of endosperm tissues and whole flax seeds was slower than incorporation into embryo lipids. Stearate had the highest specific activity of the fatty acids in endosperm and whole seeds. Presented in part at the AOCS Meeting in New York, October 1968.     

Esterification of palmitic acid in swine aortic homogenates

The incorporation of [1-¹⁴C] palmitic acid into tissue lipids of the medial and intimal layers of swine aortic homogenates was investigated. The homogenates obtained were metabolically active as indicated by their ready incorporation of labeled palmitic acid into phospholipids, diglycerides and triglycerides in the presence of α-glycerophosphate in the incubation medium. Predominantly, labeling of phospholipids and especially of phosphatidylcholine was found when α-glycerophosphate or lysolecithin served as the fatty acid acceptor. Glycerol and monoolein did not serve as fatty acid acceptors. More than 98% of the radioactivity was recovered as the phosphatidylcholine fraction at the level of 0.64 μmoles/ml of lysolecithin in the incubation medium.     

Hydrolysis of biliary phospholipids in the upper small intestine of the chick

Chick endogenous phospholipids were doubly labeled by an intravenous injection of [³²P] phosphate and [1-¹⁴C] oleic acid, and the free fatty acid and phospholipid fraction of gall bladder bile and in contents of upper small intestine were analyzed 4 days later. There was evidence of hydrolysis of biliary phosphatidylcholine to lysophosphatidylcholine in the duodenum and jejunum, but this did not account for the pronounced increase in the¹⁴C radioactivity of the free fatty acids relative to the³²P phospholipid radioactivity between bile and upper intestinal segments. It is suggested that phosphatidylcholine is largely absorbed in the duodenum of the chick while the remainder is progressively hydrolyzed and absorbed.     

Pulmonary surfactant lipid synthesis from ketone bodies,lactate and glucose in newborn rats

The contribution of acetoacetate (AcAc), β-hydroxybutyrate (βOHB), lactate and glucose to pulmonary surfactant lipid synthesis in three-to five-day-old rats was measured. Minced lung tissue was incubated with³H₂O and [3-¹⁴C]AcAc, [3-¹⁴C]βOHB, [U-¹⁴C]lactate or [U-¹⁴C]glucose, and the radioactivity incorporated into surfactant lipids was measured. When expressed as nmol of substrate incorporated/g lung tissue per four hr, lactate was incorporated more rapidly than other substrates into total surfactant lipids and phosphatidylcholine (PC). There was no difference in the rates of incorporation of lactate, AcAc or glucose into disaturated PC (DSPC). Substrates other than glucose were incorporated almost exclusively into fatty acids, whereas 60–80% of glucose incorporated into surfactant phospholipids was found in fatty acids, with the remaining in glyceride-glycerol. When expressed as nmol acetyl units incorporated/g lung tissue per four hr, the rates of AcAc, lactate and glucose incorporation into total surfactant fatty acids were comparable. Glucose incorporation into DSPC and PC was greater than that of AcAc and lactate. When glucose was the only exogenous substrate added to the incubation medium, it contributed 37% of total surfactant fatty acids synthesized de novo. In the presence of other substrates, the contribution of glucose to de novo fatty acid synthesis dropped to 14–20%. In the presence of unlabeled glucose,¹⁴C-labeled AcAc, lactate and βOHB contributed 52%, 40% and 19%, respectively, of the total fatty acids synthesized de novo. The rate of βOHB incorporation into surfactant lipids was only about 50% that of other substrates and was accompanied by low activity of β-hydroxybutyrate dehydrogenase measured for newborn lung. These results demonstrate that AcAc and lactate are important precursors for surfactant lipids in neonatal rat lung.     

In vitro incorporation of acetate-1-14C into the phospholipids of rabbit and human endometria

Endometria from nonpregnant and 6-day pregnant rabbits and from humans in the proliferative and secretory phases were incubated with 1-¹⁴C-acetate.¹⁴CO₂ was collected, and subsequently the amounts, specific radioactivities, and in some cases the fatty acid compositions of the isolated phospholipids were determined. Phosphatidyl choline was the phospholipid present in highest amount in endometria from both nonpregnant and pregnant rabbits, and in human endometria; this phospholipid also showed the highest degree of incorporation of¹⁴C-acetate. Pregnancy in the rabbit seemed to decrease the incorporation of¹⁴C-acetate into most of the endometrial phospholipid classes. In humans, the incorporation of acetate into phosphatidyl choline and phosphatidyl ethanolamine was lower in the secretory than the proliferative endometria. Of the fatty acids, linoleic acid in phosphatidyl choline and phosphatidyl ethanolamine of the rabbit endometria showed a significant relative increase during pregnancy and palmitoleic acid showed a decrease. This investigation was supported by a grant from the Ford Foundation.     

Effects of purified eicosapentaenoic acid on arachidonic acid metabolism in cultured murine aortic smooth muscle cells,vessel walls and platelets

The effects of highly purified eicosapentaenoic acid (97% pure) on the arachidonic acid cascade in isolated murine vascular cells and platelets were studied. The incorporation of eicosapentaenoic acid was not as active as that of arachidonic acid in platelets. The ratio of incorporation of eicosapentaenoic acid to arachidonic acid into platelet phospholipids was about 0.7. Analysis of the phospholipid fractions of platelets after labeling with¹⁴C-eicosapentaenoic acid and¹⁴C-arachidonic acid revealed that the incorporation of¹⁴C-eicosapentaenoic acid into the phosphatidylinositol fraction is significantly less than that of¹⁴C-arachidonic acid, while the incorporation of both fatty acids into other phospholipid fractions was almost the same. On the other hand, no significant difference between either fatty acid in incorporation rate, kinetics or distribution in cellular phospholipids was found in cultured aortic smooth muscle cells. Following treatment with eicosapentaenoic acid, cells produced less prostacyclin from endogenous arachidonic acid than did control cells. This was not due to the decrease in fatty acid cyclooxygenase activity, but rather, due to the decrease in arachidonic acid content in cellular phospholipids. In addition, eicosapentaenoic acid was neither converted to prostaglandin I₃ by the vascular cells nor to thromboxane A₃ by platelets. Furthermore, similar results were also obtained by in vivo experiments in which rats were fed with eicosapentaenoic acid enriched diet.