Effect of temperature on fatty acid composition in each lipid fraction of Spirometra erinaceieuropaei plerocercoids

The effects of temperature and host fatty acids on the fatty acid contents of Spirometra erinaceieuropaei plerocercoids were investigated to clarify their role in sparganosis. After 24 hr incubation at 18 C in host snake serum, omega6 series fatty acids, especially arachidonic acid in the phospholipid fraction of the plerocercoids, increased compared with those of plerocercoids incubated at 37 C. The changes in the ratio of polyunsaturated to saturated fatty acids in the phospholipid fraction of plerocercoids incubated in physiological saline for 6 hr at 10 C were almost the same as the changes at 37 C. The ratio of polyunsaturated to saturated fatty acids of the triglyceride fraction showed almost opposite change versus the phospholipid fraction. The percentage of arachidonic acid in the phospholipid fraction of plerocercoids increased during the first 3 hr of incubation and then decreased, regardless of temperature. At 37 C, the percentage of arachidonic acid in the free fatty acid fraction fell for the first 3 hr of incubation and was significantly elevated at the end of the 6-hr incubation. At 10 C, however, arachidonic acid in the free fatty acid fraction decreased for the first hour of incubation, increased at 3 hr of incubation, then decreased again. These results suggest that fatty acids of the plerocercoids are frequently exchanged between fractions. Plerocercoids can mobilize arachidonic acid to the free fatty acid fraction more quickly at lower temperature than at higher temperature. They may utilize mobilized arachidonic acid early in the infection stage to produce prostaglandins. Alternatively, they can incorporate arachidonic acid into the phospholipid fraction again when arachidonic acid is readily available in the environment.     

Factors affecting the elicitation of sesquiterpenoid phytoalexin accumulation by eicosapentaenoic and arachidonic acids in potato

Eicosapentaenoic and arachidonic acids in extracts of Phytophthora infestans mycelium were identified as the most active elicitors of sesquiterpenoid phytoalexin accumulation in potato tuber slices. These fatty acids were found free or esterified in all fractions with elicitor activity including cell wall preparations. Yeast lipase released a major portion of eicosapentaenoic and arachidonic acids from lyophilized mycelium. Concentration response curves comparing the elicitor activity of the polyunsaturated fatty acids to a cell-free sonicate of P. infestans mycelium indicated that the elicitor activity of the sonicated mycelium exceeded that which would be obtained by the amount of eicosapentaenoic and arachidonic acids (free and esterified) present in the mycelium. Upon acid hydrolysis of lyophilized mycelium, elicitor activity was obtained only from the fatty acid fraction. However, the fatty acids accounted for only 21% of the activity of the unhydrolyzed mycelium and the residue did not enhance their activity. Centrifugation of the hydrolysate, obtained from lyophilized mycelium treated with 2n NaOH, 1 molarity NaBH₄ at 100°C, yielded a supernatant fraction with little or no elicitor activity. Addition of this material to the fatty acids restored the activity to that which was present in the unhydrolyzed mycelium. The results indicate that the elicitor activity of the unsaturated fatty acids is enhanced by heat and base-stable factors in the mycelium.     

Arachidonic Acid-Induced Oxidative Injury to Cultured Spinal Cord Neurons

Spinal cord trauma can cause a marked release of free fatty acids, in particular, arachidonic acid (AA), from cell membranes. Free fatty acids, and AA by itself, may lead to secondary damage to spinal cord neurons. To study this hypothesis, cultured spinal cord neurons were exposed to increasing concentrations of AA (0.01-10 microM). AA-induced injury to spinal cord neurons was assessed by measurements of cellular oxidative stress, intracellular calcium levels, activation of nuclear factor-KB (NF-kappaB), and cell viability. AA treatment increased intracellular calcium concentrations and decreased cell viability. Oxidative stress increased significantly in neurons exposed to 1 and 10 microM AA. In addition, AA treatment activated NF-kappaB and decreased levels of the inhibitory subunit, IKB. It is interesting that manganese superoxide dismutase protein levels and levels of intracellular total glutathione increased in neurons exposed to this fatty acid for 24 h, consistent with a compensatory response to increased oxidative stress. These results strongly support the hypothesis that free fatty acids contribute to the tissue injury observed following spinal cord trauma.     

Properties of phosphatidate phosphohydrolase and diacylglycerol acyltransferase activities in the isolated rat heart. Effect of glucagon, ischaemia and diabetes.

Myocardial triacylglycerol hydrolysis is subject to product inhibition. After hydrolysis of endogenous triacylglycerols, the main proportion of the liberated fatty acids is re-esterified to triacylglycerol, indicating the importance of fatty acid re-esterification in the regulation of myocardial triacylglycerol homoeostasis. Therefore, we characterized phosphatidate phosphohydrolase (PAP) and diacylglycerol acyltransferase (DGAT) activities, enzymes catalysing the final steps in the re-esterification of fatty acids to triacylglycerols in the isolated rat heart. The PAP activity was mainly recovered in the microsomal and soluble cell fractions, with an apparent Km of 0.14 mM for both the microsomal and the soluble enzyme. PAP was stimulated by Mg2+ and oleic acid. Oleic acid, like a high concentration of KCl, stimulated the translocation of PAP activity from the soluble to the particulate (microsomal) fraction. Myocardial DGAT had an apparent Km of 3.8 microM and was predominantly recovered in the particulate (microsomal) fraction. Both enzyme activities were significantly increased after acute streptozotocin-induced diabetes, PAP from 15.6 +/- 1.1 to 28.1 +/- 3.6 m-units/g wet wt. (P less than 0.01) and DGAT from 2.23 +/- 0.11 to 3.01 +/- 0.11 m-units/g wet wt. (P less than 0.01). In contrast with diabetes, low-flow ischaemia during 30 min did not affect PAP and DGAT activity in rat hearts. Perfusion with glucagon (0.1 microM) during 30 min did not affect total PAP activity, but changed the subcellular distribution. More PAP activity was recovered in the particulate fraction. DGAT activity was lowered by glucagon treatment from 0.37 +/- 0.03 to 0.23 +/- 0.02 m-unit/mg of microsomal protein (P less than 0.05). The role of PAP and DGAT activity and PAP distribution in the myocardial glucose/fatty acid cycle is discussed.     

Extracellular release of free fatty acids by rat T lymphocytes is stimulus-dependent and is affected by dietary lipid manipulation

[(3)H]-Arachidonic acid-labelled rat T lymphocytes released radioactivity extracellularly when stimulated by the calcium ionophore A23187 or by monoclonal antibodies to some cell surface structures (CD2, CD5, CD11a, CD18, CD54, T-cell receptor) but not to others (CD49d, CD62L); release was greater with the calcium ionophore. Almost all of the radioactivity released from anti-CD2-stimulated lymphocytes was recovered in the free fatty acid fraction, whereas only about 50 per cent of that released after A23187 stimulation was recovered in this fraction. A23187 stimulation resulted in release of arachidonic acid from a variety of phospholipids (phosphatidylinositol, phosphatidylcholine and perhaps phosphatidylethanolamine), while the monoclonal antibody stimulation released arachidonic acid from phosphatidylinositol and perhaps phosphatidylcholine. Unstimulated lymphocytes released a range of fatty acids extracellularly, with palmitic acid accounting for 35-40 per cent and arachidonic acid for 5 per cent of released fatty acid. Stimulation of lymphocytes with either anti-CD2 or A23187 increased total fatty acid release 1.5- to 1.8-fold. In both cases palmitic acid remained the most predominant fatty acid released but the contribution of arachidonic acid increased. The type of lipid fed to the rats significantly influenced the amount and type of fatty acid released. Fish oil feeding significantly reduced extracellular fatty acid release by stimulated lymphocytes.     

Hydrogenation of polyunsaturated fatty acids by human colonic bacteria

Emulsions of the fatty acids linoleic (C18:2 n-6), alpha-linolenic (C18:3 n-3) and arachidonic acid (C20:4 n-6) were incubated for 4 h under anaerobic conditions with human faecal suspensions. Linoleic acid was significantly decreased (P < 0.001) and there was a significant rise (P < 0.05) in its hydrogenation product, stearic acid. Linolenic acid was also significantly decreased (P < 0.01), and significant increases in C18:3 cis-trans isomers (P < 0.01) and linoleic acid (P < 0.05) were seen. With each acid, there were non-significant increases in acids considered to be intermediates in biohydrogenation. The study provides evidence that bacteria from the human colon can hydrogenate C18 essential polyunsaturated fatty acids. However, with arachidonic acid there was no evidence of hydrogenation.     

Isolation and characterization of the three fractions (DE-I, DE-II and DE-III) of rat-liver Z-protein and the complete primary structure of DE-II

Three fractions (DE-I, DE-II and DE-III) of Z-protein (fatty acid binding protein) have been isolated from rat liver cytosol by DEAE-cellulose chromatography and characterized. They had the same molecular weight of 14000 and essentially identical amino acid composition. However, compositions of endogenous fatty acids were found to differ strikingly from one another. Long-chain fatty acids detected in DE-II were palmitic, stearic, oleic, linoleic and arachidonic acids. In contrast to DE-II, DE-III contained mainly arachidonic acid. Molar ratios of endogenous long-chain fatty acids to both DE-II and DE-III were estimated to be around 1.0. Unlike the latter two fractions, DE-I was virtually lipid-free. Analyses of the three fractions by polyacrylamide gel electrophoresis, electrofocusing and DEAE-cellulose chromatography before and after delipidation suggested that the difference between DE-I and DE-II was in part due to fatty acids bound to DE-II. In contrast, DE-III appeared to be somewhat different from these forms in its protein structure, though tryptic peptide mappings of the three fractions did not reveal clear differences among them. Analysis of the primary structure was made on the most abundant fraction, DE-II, to investigate the relationship among the three fractions and to other proteins. The protein was a single chain consisting of 127 amino acid residues and had a mostly acetylated NH2 terminus and a free sulfhydryl group. The complete sequence of Z-protein showed striking homology to cellular retinoid binding proteins and peripheral nerve myelin P2 protein, which indicated the presence of a new family of cellular lipid-binding proteins diverged from a common ancestor. A possible intragenic duplication of Z-protein was also suggested.     

Postmortem brain fatty acid profile of levodopa-treated Parkinson disease patients and parkinsonian monkeys

Fatty acids play a critical role in brain function but their specific role in the pathophysiology of Parkinson disease (PD) and levodopa-induced motor complications is still unknown. From a therapeutic standpoint, it is important to determine the relation between brain fatty acids and PD because the brain fatty acid content depends on nutritional intake, a readily manipulable environmental factor. Here, we report a postmortem analysis of fatty acid profile by gas chromatography in the brain cortex of human patients (12 PD patients and nine Controls) as well as in the brain cortex of monkeys (four controls, five drug-naive MPTP monkeys and seven levodopa-treated MPTP monkeys). Brain fatty acid profile of cerebral cortex tissue was similar between PD patients and Controls and was not correlated with age of death, delay to autopsy or brain pH. Levodopa administration in MPTP monkeys increased arachidonic acid content (+7%; P < 0 .05) but decreased docosahexaenoic acid concentration (-15%; P < 0.05) and total n-3:n-6 polyunsaturated fatty acids ratio (-27%; P < 0.01) compared to drug-naive MPTP animals. Interestingly, PD patients who experienced motor complications to levodopa had higher arachidonic acid concentrations in the cortex compared to Controls (+13.6%; P < 0.05) and to levodopa-treated PD patients devoid of motor complications (+14.4%; P < 0.05). Furthermore, PD patients who took an above-median cumulative dose of levodopa had a higher relative amount of saturated fatty acids but lower monounsaturated fatty acids in their brain cortex (P < 0.01). These results suggest that changes in brain fatty acid relative concentrations are associated with levodopa treatment in PD patients and in a non-human primate model of parkinsonism.     

Lipid and arachidonic acid accumulation in naturally regressing porcine corpora lutea

Patterns of luteal lipid and arachidonic acid accumulation were examined in relation to luteal progesterone and prostaglandin F synthesis in 30 sows and gilts between days 8 and 18 of the estrous cycle. Net $\text{in vitro}$ release of progesterone from luteal tissue declined from 722 ng/100 mg tissue at day 8 to 81 ng/100 mg tissue at day 18. Although statistical significance was not present, net prostaglandin F release increased slightly from 8.6 to 13.9 ng/100 mg tissue. Luteal free cholesterol, esterified cholesterol, and free fatty acid contents did not change between days 8 and 18 whereas triglycerides accumulated rapidly between days 14 and 18 of the estrous cycle. Phospholipids increased between days 8 and 12, plateaued at 20.2 mg/g between days 14 and 16, and decreased to 15.4 mg/g on day 18. Between days 12 and 18, arachidonic acid increased from 19.4 to 34.8% in cholesterol esters, from 10.1 to 22.5% in triglycerides, and from 12.3 to 27.2% in luteal free fatty acids. Arachidonic acid in luteal phospholipids increased from 21.3 to 25.1% between days 14 and 16 of the estrous cycle. Luteal regression was associated with conservation of arachidonic acid. Based on blood plasma lipid fatty acid compositions, the corpus luteum elongated and desaturated essential fatty acids. Within porcine corpora lutea, calculated free arachidonic acid content was adequate for maintenance of prostaglandin synthesis.     

Characterization of a Ca2+-stimulated lipid peroxidizing system in the sea urchin egg

Addition of calcium chloride to an egg homogenate of Strongylocentrotus purpuratus stimulates O2 consumption which is not inhibited by millimolar cyanide. Results strongly suggest that Ca2+-stimulated O2 consumption is at least partially the result of polyunsaturated fatty acid oxidation. First, addition of arachidonic acid (AA), or other polyunsaturated fatty acids, to the homogenate enhance Ca2+-stimulated O2 consumption; this enhancement, by AA, being coupled to its oxidation to a hydroxy fatty acid. Second, calcium stimulates a lipase activity in the homogenate that is capable of releasing free fatty acids. Third, Ca2+-stimulated O2 consumption and AA oxidation have virtually identical calcium requirements and pH optima. The sequence of events then is that upon calcium addition to the homogenate, lipase activity is increased which liberates free fatty acids. At the same time calcium also activates a polyunsaturated fatty acid oxygenase, possibly lipoxygenase, that converts the free fatty acids to hydroxy fatty acids. The possible physiological importance of this reaction is underscored by the high affinity for Ca2+ [approximately 10(-7)M], an ion known to increase above the required levels at fertilization. The pH activity profile also suggests possible physiological modulation because a pH change of 6.8 increasing to 7.2, as suggested to occur after fertilization, yields almost a twofold increase in O2 consumption. Egg homogenates from many other invertebrate species have the ability to oxidize AA in a Ca2+-dependent fashion. For the investigated species, the presence of Ca2+-stimulated O2 consumption and AA oxidation correlates with the presence of cyanide insensitive respiration in the intact egg.     

Effects of postdecapitation ischemia on the metabolism of [14C]arachidonic acid and [14C]palmitic acid in the mouse brain

The effect of postdecapitation ischemia on the labeling of the free fatty acid pool and their incorporation in lipids was examined during the first 10 min after decapitation in mouse brain that had been injected intracerebrally with either [1-14C]arachidonic acid or [1-14C]palmitic acid. One min after decapitation, animals injected with labeled arachidonic acid exhibited a greatly reduced incorporation of label in brain phospholipids, diglycerides, and triglycerides. When radioactive palmitic acid was used, brain lipids exhibited considerably less inhibition of label. However, a similar degree of inhibition was observed 10 min after decapitation with both fatty acids. At this time, free arachidonic acid had decreased 84% as compared to the 24% decrease observed in the controls, and about 77% of the free palmitic acid remained in the free fatty acid fraction as compared with 30% in the controls. This decreased labeling may reflect ATP shortage that affects the fatty acid activation-reacylation reactions or the enzymes involved. Alternatively, the enhanced endogenous free arachidonic acid may compete with the radiolabeled arachidonic acid resulting in an inhibition of lipid labeling. Inhibition of label may have been greater in radiolabeled arachidonic acid than palmitic because of the larger accumulation of the former endogenous fatty acid during early ischemia.     

Changes of chemical and nutrient composition of porcine blood during fermentation by <Emphasis Type="Italic">Aspergillus oryzae</Emphasis>

A solid-state fermentation (SSF) of a mixture of porcine blood and wheat bran with a ratio of 8:1 by Aspergillus oryzae was investigated. Water content, pH, crude protein, heme and total iron, free amino acids (FAA) and total fatty acids (TFA) of the fermented mixture were determined at 0, 40, 80 and 120 h, respectively, and protein hydrolysis were analyzed with SDS-PAGE accordingly. The results showed that, during the fermentation, water contents and pH decreased significantly (P < 0.05) from 68.33% to 59.94%, 7.18% to 4.48%, respectively. Heme iron content changed slightly (P > 0.05). With the degradation of large protein molecules, free amino acids in the mixture increased from 872.83 mg l⁻¹ to 11560.94 mg l⁻¹ (P < 0.05). Content of free isoleucine, methionine and cystine, deficient in fresh porcine blood increased (P < 0.05) after fermentation. Percentages of saturated fatty acids such as C14:0, C17:0 and C18:0 in the total fatty acids decreased significantly (P < 0.05), and those of polyunsaturated fatty acids C18:1, C18:2, C18:3, C20:1 and C20:2 increased significantly from 27.06% to 47.90% (P < 0.05). The results indicated that Aspergillus oryzae could ferment porcine blood and bran mixture and change its chemical and nutrient composition.     

Degradation of Arachidonoyl-Labeled Phosphatidylinositols by Brain Synaptosomes

Abstract: Incubation of synaptosomes together with 1-acyl-2-[¹⁴C]arachi-donoyl-sn-glycerophosphoinositols (GPI) and sodium deoxycholate yielded diacylglycerols and free arachidonic acid. Diacylglycerol formation is attributed to hydrolysis by the diacyl-GPI-specific phospholipase C (EC 3.1.4.10), and this reaction requires sodium deoxycholate for optimal activity. The free arachidonic acid formed is attributed to hydrolysis of diacyl-GPI by phospholipase A (EC 3.1.1.5). Free fatty acid release was observed during incubation, even in the absence of bile salts, but this process was preferentially stimulated by sodium taurocholate. The release of fatty acids was not specific for diacyl-GPI, as similar release was obtained during incubation with other phosphoglycerides. In the presence of deoxycholate (2 mg/ml), the release of diacylglycerols was maximal at a diacyl-GPI concentration around 1.0 mM. However, the free fatty acid release was linear with respect to the substrate at least up to 1.4 mM. The rate of diacylglycerol release from diacyl-GPI was more rapid in the initial 30 min, whereas the free fatty acid release was linear with time up to 2 h. Under this incubation condition, calcium was found to stimulate both types of hydrolytic action, although the concentration needed to achieve this stimulation was rather high. This type of labeled precursor is potentially useful for studies of the different modes of diacyl-GPI degradation by enzymes in brain subcellular membranes.     

Arachidonoyl transacylase in human platelets. Coenzyme A-independent transfer of arachidonate from phosphatidylcholine to lysoplasmenylethanolamine

Human platelets contain an enzyme that catalyzes CoA-independent release of arachidonic acid from phosphatidylcholine with concomitant incorporation into plasmenylethanolamine. Addition of lysoplasmenylethanolamine (10-80 microM) to a crude membrane preparation of prelabeled platelets (0.24 mg of protein/ml) induces transfer of [3H]arachidonate from endogenous phosphatidylcholine to lysoplasmenylethanolamine (0.8 nmol of arachidonic acid/min/mg of protein). The transacylation reaction occurs in the absence of Ca2+, has a broad pH optimum from 7 to 8, is not affected by excess unlabeled arachidonic acid, and is inhibited by N-ethylmaleimide (0.2 mM) and Triton X-100 (0.1 mg/ml). The enzyme shows a high specificity toward the acyl donor (phosphatidylcholine), transfers fatty acids in the order: arachidonic greater than eicosatrienoic greater than oleic, and preferentially acylates lysoplasmenylethanolamine but also other lysophosphatides (lysophosphatidylethanolamine greater than lysophosphatidylserine greater than lysophosphatidylinositol = 0). Platelet acyltransferase, on the other hand, acylates ethanolamine lysophosphatides with free arachidonic acid in the order: lysophosphatidyl-ethanolamine greater than lysoplasmenylethanolamine. These results suggest that a distinct acylation mechanism exists for introduction of arachidonic acid into plasmalogen phosphatides. In stimulated platelets, the transacylase may play an additional role in the controlled release of esterified arachidonic acid for synthesis of the biologically active oxygenated metabolites.     

Mechanism of modulation of the plasma membrane Ca(2+)-ATPase by arachidonic acid

The intracellular level of long chain fatty acids controls the Ca(2+) concentration in the cytoplasm. The molecular mechanisms underlying this Ca(2+) mobilization are not fully understood. We show here that the addition of low micromolar concentrations of fatty acids directly to the purified plasma membrane Ca(2+)-ATPase enhance ATP hydrolysis, while higher concentration decrease activity, exerting a dual effect on the enzyme. The effect of arachidonic acid is similar in the presence or absence of calmodulin, acidic phospholipids or ATP at the regulatory site, thereby precluding these sites as probable acid binding sites. At low arachidonic acid concentrations, neither the affinity for calcium nor the phosphoenzyme levels are significantly modified, while at higher concentrations both are decreased. The action of arachidonic acid is isoenzyme specific. The increase on ATP hydrolysis, however, is uncoupled from calcium transport, because arachidonic acid increases the permeability of erythrocyte membranes to calcium. Oleic acid has no effect on membrane permeability while linoleic acid shows an effect similar to that of arachidonic acid. Such effects might contribute to the entry of extracellular Ca(2+) following to fatty acid release.     

Effect of Bicuculline-Induced Status Epilepticus on Prostaglandins and Hydroxyeicosatetraenoic Acids in Rat Brain Subcellular Fractions

Abstract: Rat cerebrum, prelabeled in vivo by intraventric-ular injection of [1-¹⁴C]arachidonic acid, was used to assess cyclooxygenase and lipoxygenase reaction products in total homogenates, cytosol, synaptosomes, and microsomes. Effects of bicuculline-induced status epilepticus on arachi-donic acid metabolism in synaptosomes and microsomes were also measured. Lipoxygenase activity, resulting in the synthesis of hydroxyeicosatetraenoic acids (HETEs), and cyclooxygenase activity, resulting in the synthesis of prostaglandins (PGs), were measured by reverse-phase and normal-phase HPLC with flow scintillation detection. Endogenous lipoxygenase products in synaptosomes were identified by capillary gas chromatography-mass spectrometry. PGs and HETEs were detected in all subcellular fractions. The synaptosomal fraction showed the highest lipoxygenase activity, with 5-HETE, 12-HETE, and leukotriene B₄ as the major products. Following bicuculline-induced status epilepticus, endogenous free arachidonic acid and other fatty acids accumulated in synaptosomes, but not in microsomes. Incorporation of [1-^l4C]arachidonic acid into synaptosomal and microsomal phospholipids was decreased after bicuculline treatment. Bicuculline-induced status epilepticus resulted in increased synthesis of HETEs in synaptosomes. PG synthesis increased in the microsomal fraction. When [1-¹⁴C]arachidonic acid-labeled synaptosomes and microsomes were incubated for 1 h at 37°C the synthesis of eicosa-noids, particularly PGD₂, was increased significantly in bi-cuculline-treated rats, as compared with untreated rats. Depolarization (45 mM K⁺) of synaptosomes induced a loss of [1-¹⁴C]arachidonic acid from phosphatidylinositol, and increased the synthesis of PGD₂ and HETEs, an effect that was enhanced in bicuculline-treated rats. This study localizes changes in arachidonic acid metabolism and lipoxygenase activity resulting from bicuculline-induced status epilepticus in the brain subcellular fraction enriched in nerve endings.     

Patterns of fatty acid release from endogenous substrates by human platelet homogenates and membranes.

We describe a method for measuring the release of fatty acids from endogenous substrates of human platelet homogenates and membranes. The method depends on the availability of lipids whose fatty acids are odd-chained and therefore suitable as internal reference compounds that, at the time of lipid extraction, can be added to an incubation to permit subsequent quantification of the content of free fatty acids or fatty acids esterified to specific lipids. We found four types of lipolytic activities in human platelets. In homogenates at pH 4.0 a triglyceride lipase operated as shown by the synchrony of triglyceride degradation and release of glycerol and those fatty acids that are the predominant constituents of triglycerides. However, enough arachidonic acid was released at this pH level to suggest some phospholipid breakdown, since triglycerides hold relatively small amounts of this acid. With membranous preparations, in the alkaline pH range there were two peaks of fatty acid release with accompanying degradation of phospholipids. At pH 8.5, where release of the saturated acids, palmitic and stearic, predominated, their sum was 3.5 times that of arachidonic acid. At pH 9.5 the release of palmitic and stearic acids was only slightly below their peak values; however, the release of arachidonic acid nearly equaled the sum of the saturated acids. Linoleic acid was not released in representative amounts by those reactions that released arachidonic acid, despite the overwhelming propensity of both to be esterified at the 2-position of phospholipids. Pertinently, the choline phospholipids are linoleic-rich and the non-choline phospholipids linoleic-poor, while both have a generous endowment of arachidonic acid. With this in mind, we raise the possibility that the phospholipase A2 of human platelets is an endoenzyme because of its tendency to act on those phospholipids that are thought to comprise the inner layer of the cell membrane.     

Turnover of plasma free arachidonic and oleic acids in men and women.

The turnover of plasma free arachidonic and oleic acids was determined in healthy men and women. The plasma pool of arachidonic acid in the men was 75 per cent higher than in the women. The fractional turnover of arachidonate was 0.80 +/- 0.04 min(-1) in the women and 0.47 +/- 0.04 min(-1) in the men. The turnover rate of arachidonic acid was similar in both sexes; calculated per kg body weight it was significantly higher in the women. No sex differences were observed in the concentration or turnover of plasma free oleic acid when corrected for differences in body size. The composition of the free fatty acid fraction differed between the sexes, the female subjects having a lower proportion of saturated fatty acids and higher proportions of oleic and eicosenoic acids. The results indicate that the metabolism of polyunsaturated fatty acids in man is influenced by gonadal steroid hormones.     

Reduced labeling of brain phosphatidylinositol,triacylglycerols, and diacylglycerols by [1-14C]arachidonic acid after electroconvulsive shock: Potentiation of the effect by adrenergic drugs and comparison with palmitic acid labeling

The effect of electroconvulsive shock on the labeling of phospholipids and neutral lipids in mice brains was examined after intracerebral injection of [1-¹⁴C] arachidonic acid or [1-¹⁴C]palmitic acid. Electroconvulsive shock reduced greatly the removal of radiolabeled arachidonic acid from the free fatty acid pool. At the same time, the incorporation of arachidonic acid was partially inhibited in triacylglycerol, diacylglycerol, and phosphatidylinositol, whereas the incorporation of [1-¹⁴C]palmitic acid was not affected. Pretreatment with desipramine and pargyline potentiated the lipid effect of electroconvulsive shock in neutral glycerides. These electroconvulsive shock-induced changes reflect alterations in the metabolism of intracerebrally injected arachidonic acid, but not of similarly injected palmitic acid. From the available data whether decreased ATP, enzyme inhibition or other factors are involved cannot be ascertained. Moreover, the electroconvulsive shock-enhanced endogenous free arachidonic acid may possibly dilute the injected radiolabeled fatty acid, thus decreasing its availability for arachidonoyl-coenzyme A synthesis. Hence, a partial inhibition of the activation-acylation of these fatty acids, primarily arachidonic acid, also may be involved in the seizure-induced accumulation of free fatty acids in the brain.     

Differentiation of phospholipases A in mitochondria and lysosomes of rat liver

Highly purified mitochondria from rat liver contain a phospholipase A that catalyzes removal of 2-fatty acids, with a pH optimum above pH 8.0. Lysosomal preparations appeared to have two phospholipases A associated with them, one with a pH optimum at about pH 4.0, the second between pH 6.0 and 7.0. Mitochondrial phospholipase A hydrolyzed exogenous phospholipid as fast as or faster than endogenous phospholipid. The difference in specific radioactivity of (14)C-ethanolamine-labeled endogenous mitochondrial phospholipid before and after incubation indicates that a fraction of mitochondrial phosphatidyl ethanolamine is hydrolyzed more rapidly than the mitochondrial phospholipids as a whole. Acyl bond hydrolysis of exogenous and endogenous phospholipid by mitochondria was stimulated by free fatty acid, Ca(++), or in certain cases, monoacyl phospholipids or by treatments that disrupt the mitochondrial membrane. Of various fatty acids tested, lauric, myristic, oleic, and linoleic were most effective. ADP and ATP inhibited mitochondrial phospholipase, probably because they compete for Ca(++). Mg(++) also behaved as a competitive inhibitor; the effect was overcome by relatively little Ca(++).