CHANGES IN ACYL GROUP COMPOSITION OF DIACYL-GLYCEROPHOSPHORYLETHANOLAMINE, ALKENYLACYL-GLYCEROPHOSPHORYLETHANOLAMINE AND DIACYL-GLYCEROPHOSPHORYLCHOLINE IN MYELIN AND MICROSOMAL FRACTIONS OF MOUSE BRAIN DURING DEVELOPMENT

—Age-related changes in acyl group composition of diacyl-glycerophosphorylethanolamine (GPE), alkenylacyl-GPE and diacyl-glycerophosphorylcholine (GPC) were examined in myelin and microsomal fractions of mouse brain during development. In general, the phosphoglycerides in the myelin fraction showed an increase in the proportions of 18:1 and 20:1 and a decrease in the proportions of 16:0, 20:4(n-6) and 22:6(n-3) with increasing age. These changes were especially obvious with the acyl groups of alkenylacyl-GPE. The acyl group profiles of phosphoglycerides in the microsomal fraction were different from those in the myelin fraction. During development, there was an increase in 22:6 and a decrease in 20:4 in the phosphoglycerides of microsomes. These changes were especially obvious with the diacyl-GPE. Starting from 2 weeks of age, there was also an increase in the proportions of 18:1 and 20:1 in alkenylacyl-GPE in the microsomal fraction but this change was not as dramatic as that in the myelin fraction. In general, the acyl groups of diacyl-GPC in both myelin and microsomal fractions showed only little age-related changes as compared to the ethanolamine phosphoglycerides. Results suggest an induction in the synthesis of monoenoic fatty acids in brain during development. The monoenoic fatty acids synthesized during this period are rapidly and preferentially incorporated into the ethanolamine plasmalogen for further utilization in synthesis of the myelin membranes.     

Phospholipids and acyl groups in subcellular fractions from human cerebral cortex

Subcellular fractionation of human brain cortex obtained at autopsy yielded microsomal and synaptosome-rich fractions from the gray matter and microsomal and purified myelin fractions from the white matter. The phospholipids of myelin were high in plasmalogens, and the molar ratio of alkenyl acyl sn-glycero-3-phosphorylethanolamine to diacyl sn-glycero-3-phosphorylethanolamine was 4. The acyl groups of the myelin phosphoglycerides were enriched in monoenes (mainly 18:1 and 20:1) and a tetraene, 22:4(n - 6). The phospholipids in the synaptosome-rich fraction were high in diacyl sn-glycero-3-phosphorylcholine, and the molar ratio of the alkenyl acyl sn-glycero-3-phosphorylethanolamine to diacyl sn-glycero-3-phosphorylethanolamine was 0.88. The acyl groups of synaptosomal ethanolamine phosphoglycerides were rich in 22:6(n - 3) but contained a very low amount of 20:1. The lipid composition of microsomes from the gray matter was different from that of microsomes from the white matter but was nearly identical with that of the synaptosome-rich fraction. Except for a slightly lower proportion of alkenyl acyl sn-glycero-3-phosphorylethanolamine and sphingomyelin, the lipid composition of microsomes from the white matter was also similar to that of the myelin. There were also species-related differences between the brain lipid composition of human and subhuman primates and that of the rodents. Furthermore, the brain lipid composition in normal human subjects is rather constant and does not seem to be affected much by individual variations.     

SYNAPTOSOMAL PLASMA MEMBRANES. ACYL GROUP COMPOSITION OF PHOSPHOGLYCERIDES and (Na++ K+)-ATPase ACTIVITY DURING FATTY ACID DEFICIENCY

Abstract— Essential fatty acid deficiency was induced in mice after feeding a fatty acid deficient diet for 6 months. Activity of the (Na⁺+ K⁺)-ATPase in the total brain homogenates and in isolated synaptosomal plasma membranes was significantly higher ( P & lt; 0 05) in the deficient mice than the controls. Analysis of the acyl group composition of phosphoglycerides in brain as well as in the synaptosomal plasma membranes showed that mice fed the deficient diet had increased levels of 20:3(n-9) and 22:3(n-9) and decreased levels of 20:4(n-6) and 22:4(n-6). However, acyl group changes varied among individual phosphoglycerides and were most obvious in the two species of ethanolamine phosphoglycerides. A decrease in 22:6(n-3) level was also observed in some phosphoglycerides of the synaptosomal plasma membranes especially the diacyl- sn -glycerophosphorylserine. In this experiment, a new solvent system for chromatographic separation of the diacyl- sn -glycerophosphorylserine and diacyl- sn -glycerophosphorylinositol was reported. The separation technique was suitable for analysis of acyl group composition of individual phosphoglycerides by gas-liquid chromatography. The results were consislent with a positive correlation of the non-polar acyl groups of brain membranes with the active ion transport activity. The increase in enzymic activity during deficient state may be the result of a biological adaptation due to structural alteration of the brain membranes.     

Acyl and alkenyl group composition of brain subcellular fractions of goldfish (Carassius auratus L.) acclimated to different environmental temperatures

Goldfish were acclimated to 5, 15, and 30°C, and the acyl group composition of choline phosphoglycerides (CPG) and ethanolamine phosphoglycerides (EPG) from whole brain and brain subcellular particles was examined. With the exception of synaptosomal CPG, the acyl group composition of CPG from whole brain and subcellular particles, including myelin, from cold-acclimated fish showed little response to the change in environmental temperature. Those changes that did occur were consistent with the expected trend toward a higher degree of unsaturation of the CPG acyl groups in fish acclimated to 5°C. The acyl group composition of CPG from synaptosomes of the cold-acclimated fish did, however, differ markedly in having a reduced unsaturation index (U.I.) and unsaturated: saturated fatty acid ratio (UFA:SFA) which was caused mainly by the decrease in 226n-3 content. In contrast, changes in the acyl group composition of EPG on cold acclimation were greater than those observed in any CPG fraction. The generally expected trend toward greater unsaturation was observed only in mitochondrial and myelin EPG. Moreover, in all fractions the amount of 226n-3 in EPG was lower at decreased environmental temperatures. In the synaptosomal and microsomal EPG, the reduction in 226n-3 was such that a markedly reduced U.I. was obtained. It is suggested that two compensatory mechanisms maintain the necessary degree of membrane permeability and fluidity in order to prevent transition to a crystalline state at lower temperatures.     

Metabolism of the ethanolamine phosphoglycerides of mouse brain myelin and microsomes

Abstract— Three groups of six mice each were killed 1, 4 and 7 days after an intracerebral injection of [1,2-¹⁴C]ethanolamine. The specific radioactivities of the acid-labile ethanolamine phosphoglycerides (ethanolamine plasmalogens) and of the acid-stable ethanolamine phosphoglycerides (diacyl and alkyl acyl glycerophosphoryletholamines) from myelin and microsomal fractions were determined. All of these brain ethanolamine phosphoglycerides turn over rapidly with an apparent half-life of less than 3 days. The biosynthesis of alkenyl acyl glycerophosphorylethanolamines from diacyl glycerophosphorylethanolamines in mouse brain myelin or microsomes is unlikely.     

ACYL GROUP COMPOSITION OF METABOLICALLY ACTIVE LIPIDS IN BRAIN: VARIANCES AMONG SUBCELLULAR FRACTIONS AND DURING POSTNATAL DEVELOPMENT

Using a combination of preparative TLC and GLC technique, the content and acyl group composition of diacyl-glycerophosphoinositols, diacyl-glycerophosphates, diacylglycerols and triacyl-glycerols in brain tissue were determined. The level of diacyl-glycerophosphoinositols in 40 day-old mouse brain was 2.7 μmol/g tissue as compared to 40–170 nmol/g for other minor lipids. The acyl groups of diacyl-glycerophosphoinositols were enriched in 18:0 and 20:4 (n-6). This characteristic acyl group profile was found in microsomes, synaptosomes, and in myelin. The acyl groups of diacyl-glycerophosphates and diacylglycerols were comprised mainly of 16:0, 18:0, 18:1 and 20:4 (n-6). In rat brain subcellular fractions, the acyl groups of diacylglycerols and diacyl-glycerophosphates in the microsomal fraction had a higher proportion of 22:6 (n-3) than those in the myelin and synaptosomal fractions. The acyl groups of the myelin lipids were higher in 18:l and lower in 20:4 (n-6) as compared to those in the microsomal and synaptosomal fractions. The triacylglycerols in brain exhibited an unusual acyl group profile which included small proportions of 14:0, 16:1, 20:4 (n-6), 22:4 (n-6) and 22:6 (n-3). Except for an increase in 18:1 and a corresponding decrease in 16:0 which was found in diacyl-glycerophosphoinositols, no apparent acyl group change was observed in other metabolically active lipids during postnatal brain development.     

FATTY ACIDS OF LECITHIN IN SUBCELLULAR FRACTIONS DURING MATURATION OF BRAIN

Abstract— A study has been made of the fatty acyl profiles of lecithin in subcellular fractions of the brain in rat, guinea pig and rabbit. It was found that cerebral lecithins consisted of at least two groups with dissimilar fatty acyl profiles. The group obtained from myelin showed little variation with age of the rats or among two other species examined. The changes in lecithin fatty acyl composition of brain homogenates were in agreement with a progressively greater contribution of myelin lecithins to brain homogenate lecithins with increasing age.     

Positional and species analysis of membrane phospholipids extracted from goldfish adapted to different environmental temperatures.

1. The proportion of ethanolamine phosphoglycerides in microsomal fractions of goldfish intestine increases at low environmental temperatures. The fatty acyl composition also changes, the proportion of C22:6 and C20:4 fatty acids increasing in positions 1 and 2 and position 2 respectively. The proportion of C16:0 and C18:0 fatty acids falls in position 1 and there is an apparent switch of C18:1 and C20:1 fatty acids from position 2 to position 1. 2. The proportion of choline phosphoglycerides does not depend on the previous environmental temperature of the fish. Temperature-dependent changes in fatty acyl composition in positions 1 and 2 take place in a way similar to that described for ethanolamine phosphoglycerides, but in this case C22:6 substitution is confined to position 2. 3. Choline phosphoglycerides have been further separated into 7 different molecular species. The amounts of species 3 to 7 increase and the amount of species 2 decreases at low adaptation temperature. These changes only account for part of total change in fatty acyl composition. The remaining changes occur by chain substitution within species. 4. Present results show temperature adaptation to be highly complex, involving both quantitative and qualitative changes in different phospholipids. The possible physiological significance of these changes are discussed together with the effects these changes might have on cholesterol-phospholipid interactions.     

Positional Distribution of Acyl and Alk-1-enyl Groups in Grey and White Matter Ethanolamine and Choline Phosphoglycerides of a Marsupial, the Koala (Phascolarctos cinereus)

The major phosphoglycerides in grey and white matter from the brain of the koala have been separated and examined. The major polyunsaturated fatty acids present in both the diacyl- and alk-1-enyl acylglycerophosphorylethanolamines from grey matter were 22:6 omega 3, 20:4 omega 6, and 22:4 omega 6. In both grey and white matter, 22:6 omega 3 and 20:4 omega 6 were concentrated in the 2-position of diacylglycerophosphorylethanolamines and 22:4 omega 6 in the 2-position of alk-1-enylacylglycerophosphorylethanolamines; polyunsaturated fatty acid levels were higher in diacylglycerophosphorylethanolamines. Ethanolamine phosphoglyceride fractions from grey matter were enriched in polyunsaturated fatty acids compared with those from white matter. The acyl groups 18:0, 18:1, and 16:0 and their alk-1-enyl analogues were prominent in grey and white matter ethanolamine phosphoglycerides; 18:1 was dominant in white matter alk-1-enylacylglycerophosphorylethanolamines. The plasmalogen composition of ethanolamine phosphoglycerides was 55% in grey matter and 76% in white matter. Choline phosphoglycerides contained negligible plasmalogen and low polyunsaturated fatty acid levels. Diacylglycerophosphorylcholine was characterized by high levels of 16:0 and 18:1. Similar acyl group distributions were estimated in the 1-position in both grey and white matter, 16:0 being present at greater than 50%. The presence of the molecular species 18:0/22:6 omega 3 was indicated in grey matter diacylglycerophosphorylethanolamine, 18:1/18:1 in white matter alk-1-enylcylglycerophosphorylethanolamine, and 16:0/18:1 in white matter diacylglycerophosphorylcholine.     

Effect of temperature acclimatization on the fatty acid composition of goldfish intestinal lipids

1. The fatty acid composition of whole goldfish, whole-intestinal mucosa, intestinal mucosal membranes and individual phospholipids extracted from mucosal membranes were measured, fish adapted to different temperatures being used. 2. Alterations of the adaptation temperature did not noticeably affect the fatty acid composition of the whole-fish lipids, but there were marked changes in the fatty acids of lipids extracted from homogenates of goldfish intestinal mucosa. These changes were more pronounced in a membrane fraction prepared from these homogenates. Raising the adaptation temperature by 20 degrees C halved the percentage of C(20:1), C(20:4) and C(22:6) fatty acids and nearly doubled the percentage of C(18:0) and C(20:3) fatty acids recovered. 3. Choline phosphoglycerides constituted about one-half and ethanolamine phosphoglycerides about one-quarter of the total membrane phospholipids. 4. The fatty acids of choline and ethanolamine phosphoglycerides were more susceptible to temperature-dependent changes than were the phosphoglycerides of inositol or serine. 5. The increase in C(18:0) fatty acid that occurred in membranes of warm-adapted fish was greatest for ethanolamine phosphoglycerides, but increases also occurred in other phospholipid fractions and in membrane neutral lipids.     

Decrease of Brain Phospholipid Synthesis in Free-Moving n-3 Fatty Acid Deficient Rats

Abstract: The autoradiographic method with [¹⁴C]-docosahexaenoic acid ([¹⁴C]22:6 n-3) was used to determine whether a diet deficient in n-3 fatty acids, inducing a decrease in 22:6 n-3 circulating level, was associated with changes in local rates of phospholipid synthesis in the rat brain. As compared with rats fed a normal diet (peanut plus rapeseed oil), a n-3 fatty acid deficiency [peanut oil group (P group)] induced a generalized decrease (?35 to ?76%) of 22:6 n-3 incorporation rates into phospholipids in all the regions examined. This effect was confirmed by using [³H]22:6 n-3 infusion by biochemical analysis and quantifications corrected for the contribution of docosahexaenoate derived from lipid store recycling to the unesterified pool, taken as the precursor pool for phospholipid synthesis in the whole brain. In normal or n-3 fatty acid-deficient rats, the values of the brain-to-plasma 22:6 n-3 specific activity ratio (Ψ) were similar (0.03), indicating that a considerable endogenous source of 22:6 n-3 (97%), likely derived from phospholipid degradation, dilutes the specific activity of the tracer coming from plasma. Using the specific activity of 22:6 n-3 in plasma instead of brain would thus lead to a gross underestimation of the rate of phospholipid synthesis. The results also demonstrate that the pattern of ¹⁴C or ³H distribution in brain lipids was not modified by the n-3 fatty acid-deficient diet. The major lipids labeled were phospholipids, particularly phosphatidylethanolamine. Nevertheless, the unesterified 22:6 n-3 concentrations in plasma and brain were significantly reduced (eight- and threefold, respectively) in the P group. In addition, the proportion of 22:6 n-3 in the brain total lipid fraction, total phospholipids, and phosphatidylcholine, -ethanolamine, and -serine was significantly decreased in n-3 fatty acid-deficient rats. This was partially compensated for by an increase in the 22:5 n-6 level. These results are discussed in relation to the limitation of 22:6 n-3 use to quantify, by the quantitative autoradiographic method, changes in local rates of phospholipid synthesis in rat brain.     

Effects of dietary lipids on behaviour, lipid biosynthesis and lipid composition, in rat platelets

Rats of either sex were fed for 18 and 34 weeks respectively diets containing 40% (by weight) lipids with polyunsaturated fatty acids representing 1.34% or 13.2% of total calories. Platelet reactivity to thrombin, platelet fatty acid composition and incorporation of [14C]acetate into platelet lipids were investigated. Diets rich in saturated fatty acids markedly increased platelet sensitivity to thrombin. The concentration of 20:3 and 22:3 of the (n - 9) series and of 20:3 and 22:5 of the (n - 6) series were increased at the expense of 18:2 and 22:4 of the (n - 6) family in platelet lipids. 20:4 (n - 6) was unchanged. The fatty acid changes were more pronounced in male rats and after 34 weeks. [14C]Acetate incorporation into total platelet lipids and particularly into choline phosphoglycerides and ceramides was lower in animals fed saturated fats. This diet reduced the synthesis of 16:0 and of 22:4(n - 6) in platelet total fatty acids, while that of 22:3(n - 9) was markedly enhanced. This study showed that long-term feeding of high-saturated-low-polyunsaturated fat diets in rats induced marked changes in platelet lipid synthesis and composition, in both sexes. The lipid synthesis modification appears to be more pronounced in males than in females. The changes in the fatty acids 20:3(n - 9), 22:3(n - 9) and 22:4(n - 6) appeared to be closely related to platelet behaviour. The balance between the content and synthesis of these last fatty acids might be of significance for the effect of diet on thrombogenesis.     

Changes in fatty acid composition of peripheral nerve myelin in essential fatty acid deficiency

Severe essential fatty acid deficiency (EFAD) was induced by feeding weanling rats a diet free of essential fatty acids 8 months after weaning. The fatty acid compositions of phospholipids and glycosphingolipids in peripheral nerve myelin were compared in rats with and without EFAD. With the deficient diet, 20:3ω9 was found in the major myelin phospholipids. The level of 18:1 was increased and the levels of 18:2ω6, 20:4ω6, and 22:4ω6 were decreased. Both sphingomyelin and cerebroside showed higher proportion of 24:1 and lower proportions of 24:0 in EFA-deficient rats than in control rats. The fatty acid chain elongating system in myelin cerebroside was also depressed by EFAD. A two- to sevenfold increase of the ratio 20:4ω6 to 20:3ω6 was found in myelin phospholipids of regenerated nerve from rats fed control diet. However, this ratio was suppressed by EFAD diet. The biochemical index (20:3ω9/20:4ω6) for EFAD was not affected by crush injury. These results suggest that dietary EFAD in postweaning rats can induce fatty acid alterations in peripheral nerve myelin without resulting in detectable changes in function or structure and that myelin lipids may be sequestered and reused during nerve degeneration and regeneration.     

Dietary alpha-linolenic acid deficiency in adult rats for 7 months does not alter brain docosahexaenoic acid content, in contrast to liver, heart and testes.

In adult rats, 22:6(n - 3) dietary deficiency does not affect brain membranes, but has a significant effect on some other visceral organs. 60-day-old male rats fed a diet containing sufficient amounts of both linoleic and alpha-linolenic acid were divided into three groups. One group continued the same diet; the second was fed a diet containing 2% sunflower oil, the third was fed 10% sunflower oil (sunflower oil contains linoleic acid, but trace amount of alpha-linolenic acid). Animals were killed different times after receiving the new diets (1 to 31 weeks). For animals fed the diets containing only sunflower oil, deficiency in cervonic acid content (DHA, docosahexaenoic acid, 22:6(n - 3)) was not detected in whole brain, myelin or nerve endings within 31 weeks. In contrast, this acid progressively declined in liver, heart and testes up to 3 weeks and remained nearly stable thereafter. In parallel to the reduction of cervonic acid content, 22:5(n - 6) content increased in liver and heart, but not in testes. It also increased in brain, nerve endings and myelin from week 3, 6 and, 9 respectively. These results suggest that brain cervonic acid is highly preserved or is maintained at the expense of other organs.     

Influence of dietary fat on the lipid composition of rat brain synaptosomal and microsomal membranes.

The modulation of rat brain microsomal and synaptosomal membrane lipid by diet fat was examined. Brain synaptosomal and microsomal membrane composition was compared for rats fed on diets containing either soya-bean oil (SBO), SBO plus choline, SBO lecithin, sunflower oil (SFO), chow or low-erucic acid rape-seed oil (LER) for 24 days. Cholesterol and phosphatidylcholine levels in both membranes were altered by diet. Diet fat also affected the microsomal content of sphingomyelin. Change in membrane phosphatidylcholine level was related to the relative balance of omega-6, omega-3 and monounsaturated fatty acids within the diets fed. The highest phosphatidylcholine levels appeared in membranes of animals fed on SBO lecithin and the lowest in those fed on LER. Microsomal membrane cholesterol and sphingomyelin content increased by feeding on SBO lecithin. In both synaptosomal and microsomal membranes a highly significant correlation was observed between membrane phosphatidylcholine and cholesterol content. The fatty acyl composition of phospholipids from both membranes also altered with diet and age. Alteration in fatty acid composition was observed in response to dietary levels of omega-6, omega-3 and monounsaturated fatty acids, but the unsaturation index of each phospholipid remained constant for all diet treatments. These changes in lipid composition suggest that dietary fat may be a significant modulator in vivo of the physicobiochemical properties of brain synaptosomal and microsomal membranes.     

METABOLISM OF ARACHIDONOYL PHOSPHOGLYCERIDES IN MOUSE BRAIN SUBCELLULAR FRACTIONS

Abstract— Mouse brain subcellular fractions were prepared at 1, 12, and 24 h and 3 and 8 days after intracerebral injections of [1-¹⁴C]arachidonate. Initially, radioactivity was mainly distributed in the microsomal and synaptosomal fractions, but the proportion of radioactivity in the myelin increased from 5 to 16% within 8 days. Radioactivity of the microsomal lipids started to decline at 1 h after injection, and the decay was represented by two pools with half-lives of 19 h and 10 days, respectively. Radioactivity in the synaptosomal and myelin fractions did not reach a maximum until 24 h after injections. The half-life for turnover of synaptosomal lipids was 9 days.
The decline of radioactivity measured in the microsomal fraction was due mainly to diacyl-GPC and diacyl-GPI, since radioactivity of other phosphoglycerides (diacyl-GPS, diacyl-GPE and alkenyl-acyl-GPE) continued to increase for 12-24 h. In this fraction, half-lives of 10-14 h were obtained for the fast turnover pools of diacyl-GPC and diacyl-GPI, and slow turnover pools with half-lives of 7 days for diacyl-GPI and 10-14 days for other phosphoglycerides were also present. Among the synaptosomal phosphoglycerides, radioactivity of diacyl-GPI declined in a biphasic mode, thus exhibiting half-lives of 5 h and 5 days. Incorporation of labelled arachidonate into diacyl-GPE and diacyl-GPS in the synaptosomal fractions was observed for a period of 24 h. The half-lives for these phosphoglycerides ranged from 8 to 12 days. Results of the study have demonstrated the presence of small pools of arachidonoyl-GPI in synaptosomal and microsomal fractions which were metabolically more active than other arachidonoyl containing phosphoglycerides.     

Fat absorption in essential fatty acid deficiency: a model experimental approach to studies of the mechanism of fat malabsorption of unknown etiology

Male rats were made deficient in essential fatty acids by feeding them a fat-free diet supplemented with 4% tripalmitin for 8-12 wk from the time of weaning. After feeding 0.5 ml of [(14)C]triolein or [(3)H]oleic acid, 72-hr stool recoveries of radioactivity were significantly greater in deficient rats than in chow-fed controls. Essential fatty acid deficiency did not reduce the absorptive capacities for triolein or for a medium-chain fat, trioctanoin, measured after 3 and 2 hr of maximal-rate duodenal infusion. In everted jejunal slices from essential fatty acid-deficient rats, uptake of micellar [(14)C]oleic acid at 0-1 degrees C was similar to that of controls, but the rate of incorporation of fatty acid into triglyceride after rewarming to 37 degrees C was significantly reduced. The specific activities of the microsomal esterifying enzymes, acyl CoA:monoglyceride acyltransferase and fatty acid CoA ligase in jejunal mucosa were 30% lower in essential fatty acid-deficient rats. However, the total microsomal enzyme activity adjusted to constant weight did not differ significantly in deficient rats compared with controls. After intraduodenal perfusion of triolein, accumulation of lipid in the intestinal wall was increased in the deficient rats. Because over 90% of the absorbed mucosal lipid was present as triglyceride, essential fatty acid deficiency appears to affect the synthesis or release of chylomicron lipid from the intestine. Analysis of regions of intestine showed that this delay in transport was most marked in the midportion of the small intestine.     

The effect of chronic ethanol consumption on the fatty acid composition of phosphatidylinositol in rat liver microsomes as determined by gas chromatography and 1H-NMR.

Cell membranes and vesicles composed of extracted phospholipids isolated from rats chronically-fed ethanol develop a resistance to disordering by ethanol in vitro (membrane tolerance) and a decreased partitioning of ethanol into the membranes. The anionic lipid phosphatidylinositol (PtdIns) is the only microsomal phospholipid from the ethanol-fed rats that confers tolerance to vesicles of microsomal phospholipids from control rats in a paradigm where phospholipid classes are sequentially swapped. To investigate the molecular basis of this adaptation, the fatty acid content of microsomal PtdIns extracted from the livers of rats chronically fed ethanol for 5 weeks and their calorically-matched controls was analyzed by gas-liquid chromatography (GLC) and 1H-NMR spectroscopy. Chronic ethanol consumption caused an 8.4% decrease in arachidonic acid [20:4(n - 6)], a 20.0% increase in oleic acid [18: 1(n - 9)] and a 47.1% increase in the quantitatively minor fatty acid [20:3(n - 6)]. 1H-NMR was used to quantitatively assay compositional changes in the delta 5 olefinic moiety of the acyl chains in PtdIns, an approach that should be broadly applicable to other lipid systems. After chronic ethanol feeding PtdIns had decreased delta 5 unsaturates (-7.9% NMR, -8.2% GLC) and a corresponding increase in delta 5 saturates (+5.4% NMR, +5.3% GLC). In the other phospholipids, chronic ethanol feeding caused alterations in the fatty acid compositions specific for each phospholipid. PtdIns was the only microsomal phospholipid that exhibited a significant decrease in both the polyunsaturate pool and the ratio of the total olefinic content to the saturated fatty acid content. The major adaptive response in rat liver microsomal PtdIns to chronic ethanol administration involves a decrease in arachidonic acid [20:4 (n - 6)], which is partly compensated for by increases in oleic acid [18:1(n - 9)] and eicosatrienoic acid [20:3 (n - 6)], resulting in a depressed unsaturation and polyunsaturation index. The decreased unsaturation at the delta 5 position may have special functional relevance, due to the proximity of this position to the membrane surface, where ethanol is believed to reside. Whether these acyl changes are merely coincident with, or causative of, membrane tolerance requires further elucidation.     

EFFECTS OF DIFFERENT DIETARY LEVELS OF ESSENTIAL FATTY ACIDS ON THE FATTY ACID COMPOSITION OF ETHANOLAMINE PHOSPHOGLYCERIDES IN MYELIN AND SYNAPTOSOMAL PLASMA MEMBRANES

Abstract— Three dietary levels of essential fatty acids (EFA), 3 0, 0 75 and 0 07 calorie-% were fed to rats for two generations or more. Myelin was isolated at the ages of 18, 30, 45 and 120 days and synaptosomal plasma membranes at 18, 30 and 45 days. No difference was found in the lipid composition between the dietary groups in either subcellular fraction. The fatty acid patterns of ethanolamine phosphoglycerides (EPG) were analysed. In myelin the proportions of 18:1 and 20:1 increased with age, while those of 20:4 (n-6) and 22:6 (n-3) decreased, in synaptosomal plasma membranes the proportions of 20:4 (n-6) decreased with age, but 22:6 (n-3) increased and the sum of the polyunsaturated fatty acids was constant. At no age were significant differences found between the proportions of saturated and monounsaturated fatty acids, in either myelin or the synaptosomal plasma membrane fraction, when the different dietary groups were compared. In myelin from rats fed 007 calorie-% EFA the proportions of 20:4 (n-6) were slightly lower than in the two other groups, while those of 22 6 (n-3) were considerably lower. The synaptosomal plasma membranes fraction of rats fed O-07 calorie-% EFA had equal or slightly larger amounts of 20:4 (n-6) than in the two other groups, while 22:6 (n-3) was considerably smaller. In both subcellular fractions the decreased proportion of fatty acids of linoleic and linolenic acid series was compensated for by an increase in 20:3 (n-9) and 22:3 (n-9). The sum of these two fatty acids was equal in the EPG of myelin and synaptosomal plasma membranes at 18 days of age. At 30 and 45 days of age a lower value was found in the synaptosomal plasma membranes, while in the myelin fraction a slight decrease was found only at 120 days of age.     

The in vivo incorporation of linolenic acid into neuronal and glial cells and myelin

Abstract— Neurons, astrocytes, oligodendrocytes, and myelin were prepared from 21-day-old rat brain at various times after intracerebral injection of [1-¹⁴C]linolenate. Comparisons of phospholipid specific radioactivity demonstrated that the oligodendrocytes were much more active than neuronal, astroglial, or myelin fractions. This is consistent with the concept that the oligodendrocyte is responsible for synthesis of the relatively large mass of myelin sheath. Initially the phosphatidylcholine fraction was more active than the phosphatidylethanolamine fraction, but during the 36 h after injection the former decreased in radioactivity while the latter fraction showed an increase. Fatty acid elongation occurred rapidly. Within 2h after injection, 2/3 of the label had been converted to elongated products (20:4. 20:5, 22:5 and 22:6). All three cell types apparently contained the enzymes necessary to incorporate, elongate, and desaturate linolenic acid and this occurred at similar rates in each cell type. No direct precursor-product relationship was found between the lipids of oligodendrocytes and myelin. There was, however, a lag in the appearance of elongated fatty acids in the phosphoglycerides of myelin. indicating that the polyunsaturated fatty acids in myelin were synthesized elsewhere and transported into the myelin sheath.