Arachidonic and other tissue fatty acids of Culex pipiens reared with various concentrations of dietary arachidonic acid

Chloroform/methanol extracts were prepared from groups of Culex pipiens reared in synthetic dietary media provided with various concentrations of arachidonic acid. Extracts were analyzed by gas-liquid chromatography to determine the fatty acid composition of whole extracts and also of phospholipid and triacylglycerol fractions separated by thin-layer chromatography from the whole extracts. The same extracts were also tested for their ability to support flight of adult C. pipiens reared in basal synthetic diet containing various concentrations of the extracts: this provided a bioassay for the presence of arachidonic acid or related polyunsaturates in the extracted lipid, since adults can fly only if provided, as larvae, with dietary arachidonic or related fatty acids. For comparison, chromatographic and bioassay data obtained from normal stock mosquitoes, reared in crude septic medium, are also presented. All extracts were shown by gas-liquid chromatography to contain some arachidonic acid and other polyunsaturated fatty acids. The proportions of arachidonic acid in extracts from mosquitoes reared in synthetic media were greater the greater the concentration of dietary arachidonic acid provided; and in the bioassay, extracts induced more flight activity in test mosquitoes the higher the dietary arachidonic acid provided for extracted mosquitoes. Extracts from stock-reared mosquitoes were more active in the bioassay than synthetic dietreared extracts, even though gas-liquid chromatography indicated lower proportions of arachidonic acid in stock-reared extract. However, stock-reared extract contained a substantial proportion of gammalinolenic acid, which is flight active for C. pipiens, as well as more linolenic acid and a large amount of linoleic acid, both of which are semi-active for flight; thus, stock-reared extract contained a higher overall proportion of flight-inducing fatty acids. Proportions of polyunsaturates in the phospholipid fractions of extracts from synthetic diet-reared mosquitoes were much greater than in the unfractionated extracts, whereas polyunsaturates were virtually absent from the triacylglycerol fractions, indicating a sequestering of polyunsaturates into phospholipids.     

The essential dietary fatty acid requirement of the tufted apple budmoth, Platynota idaeusalis

The tufted apple budmoth, Platynota idaeusalis (Walker), was reared non-axenically for two successive generations on a casein-based semisynthetic diet. The qualitative essential fatty acid requirement for growth, development and normal pupal-adult ecdysis was studied using the non-axenic casein-based semisynthetic diets with and without various 99% pure fatty acids. Linoleic or linolenic acids caused accelerated larval development; linoleic, linolenic and arachidonic acids showed similar activity in body weight gain and survival to pupal-adult ecdysis. Linoleic or linolenic acids were active in alleviating wing deformities; arachidonic acid was partially active in alleviating wing deformities at the one dietary concentration evaluated. Activity of arachidonic acid as an essential fatty acid for P. idaeusalis is unique among insects, except for mosquitoes. The essential fatty acid deficiency syndrome of the adult, resulting from the larvae feeding on fat-deficient diets, was greatly reduced when larvae were fed on a diet adequate in essential fatty acid during either their early or late development.     

Prostaglandin synthetase inhibitors modulate the effect of essential dietary arachidonic acid in the mosquito Culex pipiens

Effects of various inhibitors of prostaglandin metabolism on essential fatty acid function in Culex pipiens were examined by rearing the mosquito in synthetic dietary media containing arachidonic acid and putative prostaglandin inhibitors in various combinations. Both non-steroidal and steroidal anti-inflammatory drugs variously inhibited overall development and the arachidonic acid-dependent viability of newly emerged adults. In many cases such inhibitory effects could be counteracted by increased concentrations of dietary arachidonic acid, indicating that in the mosquito, as in mammals, these drugs interfered with arachidonic acid function specifically. In the cases of non-steroidal anti-inflammatorials (indomethacin, phenylbutazone and acetaminophen), which are known to inhibit enzymes of the prostaglandin synthetase complex, such inhibition is construed to indicate that prostaglandinogenesis may be among the physiological functions underlying the essentiality of arachidonic acid for the mosquito.     

Amino acid requirements of the mosquito Culex pipiens: asparagine essential

When any of the ten “rat essential” amino acids was omitted singly from a fully-defined synthetic dietary medium, newly-hatched Culex pipiens larvae were unable to develop to the second instar. With proline omitted, development was greatly retarded and survival to the adult stage reduced. Without aspargine (but not aspartic acid) growth and development ceased in most individuals before larval-pupal ecdysis, and no adults were obtained. These twelve amino acids are considered nutritionally essential for this mosquito. With glycine omitted singly, development was markedly retarded, but survival to the adult stage was not affected; thus this amino acid is required for good growth, but these experiments do not demonstrate it as essential. Single omission of alanine, aspartic acid, cysteine, glutamic acid or amide, serine or tyrosine had virtually no effect on development and they are therefore considered nutritionally non-essential. With diets containing the twelve culex-essential amino acids only, very little development occurred, but augmentation with either glycine or serine allowed growth and development almost as good as with the complete amino acid mixture. Augmentation of the essential twelve with alanine, cysteine, glutamic acid/amide, or tyrosine singly failed to improve development. The requirement for dietary asparagine shown by these studies appears to be unique among insects so far studied. In particular, another mosquito, Aedes aegypti, has no such requirement.     

Polyunsaturated fatty acids of mosquitos reared with single dietary polyunsaturates

Stock adults of Culex pipiens and tarsalis reared in crude media had a third of their phospholipid fatty acids as polyunsaturates, mainly 18C but including prominent proportions of arachidonic (20:4n6) and eicosapentaenoic (20:5n3) acids. Adults reared with synthetic media devoid of polyunsaturated fatty acids and therefore unable to fly at emergence contained no more than trace amounts of any polyunsaturate. With synthetic media containing single polyunsaturates the following findings emerged. Of four polyunsaturates known to be highly effective essential fatty acids individually 20:4n6 or 20:5n3 appeared unchanged in tissue phospholipids in proportions reflecting dietary concentrations; dietary 22:4n6 or 22:6n3 (docosahexaenoic acid) appeared also as 20:4n6 or 20:5n3, respectively, retroconverted from the administered dietary fatty acids, which were detected only in traces. Two moderately effective dietary fatty acids, 18:3n6 (γ-linolenic) and 20:3n6 (homo-γ-linolenic), which support weak flight at emergence, appeared in tissue phospholipids respectively as 18:3n6 only, or as similar proportions of 18:3n6 and 20:3n6, this latter indicating shortening to the 18C analogue as well as accumulation of the dietary 20C acid. Six other polyunsaturates [18:2n6 (linoleic), 18:3n3 (linolenic) and their 20C and 22C analogues], all considered slightly effective as essential fatty acids although unable to support proper flight, appeared in tissue phospholipid in dose-related proportions as the 18C basal n6 or n3 family analogues, with only traces of the higher analogues when these were the dietary fatty acids provided, indicating sequential chain shortening within each series, n6 or n3, no interconversion of n6 and n3 members (also shown by all other data), and efficient accumulation of the resultant 18C polyunsaturates. These findings show no capability for de novo synthesis of polyunsaturated fatty acids, afford an insight into the metabolic interrelations of diet-derived polyunsaturates and indicate a primary importance for endogenous arachidonic and eicosapentaenoic acids in mosquito essential fatty acid physiology.     

Long-chain polyenoics and the essential dietary fatty acid requirement of the waxmoth, Galleria mellonella

The essential fatty acid requirement for normal pupal-adult ecdysis in Galleria mellonella was studied using non-axenic casein-based semisynthetic diets with or without various 99% pure fatty acids. The abilities of linoleic and linolenic acids to alleviate faulty adult emergence differed markedly, linolenic acid being 10-fold more potent than linoleic acid. One other ω6 polyunsaturated fatty acid, C20:2ω6, resembled its analogue, linoleic acid (18:2ω6), in efficacy at high dosage, but three others, C18:3ω6, C20: ω6 and C20:4ω6 (arachidonic acid), were without effect. Of five ω3 polyunsatures tested, C22:3ω3 and C20:3ω3 were as effective as linolenic acid (C18:3ω3), their shorter-chained analogue. Docosahexaenoic acid (C22:6ω3) was totally ineffective, but eicosapentaenoic acid (C20:5ω3), though supporting no perfect emergences, produced some active adults having wing malformations only, and was therefore considered partially active. It is suggested that a C18 polyunsaturate is physiologically required by G. mellonella and can be derived from various dietary longer-chained analogues by simple carbon chain shortening so long as there are no additional double bonds carboxylwards of an active di- or trienoic sequence. The partial activity of C20:5ω3 suggests there may additionally be a physiological requirement for this or a related long-chain polyunsaturate. The possibility of multiple essential fatty acid requirements in Lepidoptera in general is discussed.     

Tissue polyunsaturated fatty acids and a digestive phospholipase A2 in the primary screwworm,Cochliomyia hominivorax

We report on the presence of arachidonic acid in larval and adult tissues of the primary screwworm, Cochliomyia hominivorax and of the secondary screwworm, C. macellaria. Arachidonic acid is present in the phospholipids of whole animal extracts of both species. This fatty acid appears to be accumulated during the larval stages, because proportions of arachidonic acid were higher in adults than in larvae. These insects probably obtain the arachidonic acid from dietary phospholipids. We also report on a phospholipase A₂ activity in midgut preparations from third instars of the primary screwworm. Phospholipase A₂ is responsible for hydrolyzing fatty acids from the sn-2 position of dietary phospholipids to release essential fatty acids. The screwworm enzyme is similar to mammalian digestive phospholipase A₂s because it depends on calcium for high catalytic activity, it is sensitive to the site-specific inhibitor oleyloxyethylphosphorylcholine, and it interacts with heparin. We further characterized the screwworm midgut phospholipase A₂ by altering the reaction conditions, including reaction time, radioactive substrate concentration, protein concentration, pH and temperature. We speculate that the biological significance of this enzyme relates to acquiring essential fatty acids, including arachidonic acid, from dietary phospholipids.     

Metabolism of n-3 polyunsaturated fatty acids and modification of phospholipids in cultured rabbit aortic smooth muscle cells

The metabolism of the linolenic acid family (n-3) of fatty acids, e.g., linolenic, eicosapentaenoic, and docosahexaenoic acids, in cultured smooth muscle cells from rabbit aorta was compared to the metabolism of linoleic and arachidonic acids. There was a time-dependent uptake of these fatty acids into cells for 16 hr (arachidonic greater than docosahexaenoic, linoleic, eicosapentaenoic greater than linolenic), and the acids were incorporated mainly into phospholipids and triglycerides. Eicosapentaenoic and arachidonic acids were incorporated more into phosphatidylethanolamine and phosphatidylinositol plus phosphatidylserine and less into phosphatidylcholine than linolenic and linoleic acids. Docosahexaenoic acid was incorporated into phosphatidylethanolamine more than linolenic and linoleic acids and into phosphatidylinositol plus phosphatidylserine less than eicosapentaenoic and arachidonic acids. Added linolenic acid accumulated mainly in phosphatidylcholine and did not decrease the arachidonic acid content of any phospholipid subfraction. Elongation-desaturation metabolites of linoleic acid did not accumulate. Cells treated with eicosapentaenoic acid accumulated both eicosapentaenoic and docosapentaenoic acids mainly in phosphatidylethanolamine and the arachidonic acid content was decreased. Added docosahexaenoic acid accumulated mainly in phosphatidylethanolamine and decreased the content of both arachidonic and oleic acids. The following conclusions are drawn from these results. The three n-3 fatty acids are utilized differently in phospholipids. The arachidonic acid content of phospholipids is reduced by eicosapentaenoic and docosahexaenoic acids, but not by linolenic acid. Smooth muscle cells have little or no desaturase activity, but have significant elongation activity for polyunsaturated fatty acids.     

Comparison of fatty acid contents and composition in major lipid classes of larvae and adults of mosquitoes (Diptera: Culicidae) from a steppe region

Emerging aquatic insects, including mosquitoes, are known to transfer to terrestrial ecosystems specific essential biochemicals, such as polyunsaturated fatty acids (PUFA). We studied fatty acid (FA) composition and contents of dominant mosquito populations (Diptera: Culicidae), that is, Anopheles messeae, Ochlerotatus caspius, Oc. flavescens, Oc. euedes, Oc. subdiversus, Oc. cataphylla, and Aedes cinereus, inhabited a steppe wetland of a temperate climate zone to fill up the gap in their lipid knowledge. The polar lipid and triacylglycerol fractions of larvae and adults were compared. In most studied mosquito species, we first found and identified a number of short‐chain PUFA, for example, prominent 14:2n‐6 and 14:3n‐3, which were not earlier documented in living organisms. These PUFA, although occurred in low levels in adult mosquitoes, can be potentially used as markers of mosquito biomass in terrestrial food webs. We hypothesize that these acids might be synthesized (or retroconverted) by the mosquitoes. Using FA trophic markers accumulated in triacylglycerols, trophic relations of the mosquitoes were accessed. The larval diet comprised green algae, cryptophytes, and dinoflagellates and provided the mosquitoes with essential n‐3 PUFA, linolenic, and eicosapentaenoic acids. As a result, both larvae and adults of the studied mosquitoes had comparatively high content of the essential PUFA. Comparison of FA proportions in polar lipids versus storage lipids shown that during mosquito metamorphosis transfer of essential eicosapentaenoic and arachidonic acids from the reserve in storage lipids of larvae to functional polar lipids in adults occurred.     

Lipid utilization in adult Pieris brassicae with special reference to the rôle of linolenic acid

Fatty acids of adult Pieris brassicae and the incorporation of dietary linolenic acid-1-¹⁴C into adult (and egg) lipids were analysed 1 and 9 days after ecdysis. Females grown on a leaf diet retained palmitic, palmitoleic, and oleic acids but lost linoleic and linolenic acids during adult life, while males utilized their fatty acids more evenly. On an artificial diet both sexes retained palmitic acid but utilized palmitoleic and oleic acids. In both cases females laid eggs with a high palmitic and oleic acid content.Analysis of thorax flight muscles (artificial diet) revealed that 67·9% of the lipids in 1-day females and 83·6% in 9-day females was phospholipid (PL). During adult life linolenic acid increased in thorax neutral lipids (NL) from 14·6 to 20·0% in females and from 18·5 to 30·0% in males. Males incorporated more linolenic acid-1-¹⁴C especially in fat body and flight muscle PL than females. The majority of this was recovered from phosphatidyl cholines (PTC) in 1-day adults whereas in 9-day adults phosphatidyl ethanolamines (PTE) and another compound, most likely cardiolipin, contained more label (29·0% in PTC, 33·1% in PTE, 34·9% in cardiolipin, and 2·0% in sphingomyelin in the thorax of females). The females also incorporated the label into egg lipids (42·2% in PL, 57·8% in NL). There was recovered from PTC 54·5% of the label in egg PL.Most of the label in thorax NL was found to be in free fatty acids (FFA). The label disappeared from triglycerides during adult life and tended to accumulate in FFA (82·7% in 9-day females) while in diglycerides the label did not vary during adult life (17·2% in 9-day post-emergence females). PTC apparently is a fairly labile PL type which is utilized in muscle whereas PTE and cardiolipin may be more structural in function and accumulated more label from linolenic acid with increasing adult age. Linolenic acid, then, essentially is a structural fatty acid and its rôle appears to be mainly in the structures of flight muscle membranes and organelles.     

Fatty acid composition and incorporation of arachidonic acid into phospholipids of hemocytes from the tobacco hornworm Manduca sexta

The fatty acid compositions were determined for total lipids, triacylglycerols, phospholipids and four phospholipid fractions, including phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine/phosphatidylinositol (PS/PI) and cardiolipin (CA) obtained from hemocytes and cell-free serum from second day, fifth instar larvae of the tobacco hornworm Manduca sexta and the standard Manduca rearing medium. The hemocyte fatty acid profiles were considerably different from the profiles of the medium the insects were reared on and from the profiles of the cell-free serum. Hemocyte neutral lipids had lower proportions of polyunsaturated fatty acids than phospholipids. The fatty acid profiles of PC, PE, PS/PI and CA differ from each other and from the total lipid profiles, indicating selective fatty acid incorporation into hemocyte phospholipid species. Studies with radioactive arachidonic acid similarly indicated selective incorporation of polyunsaturated fatty acids into hemocyte lipids. Under our in vitro conditions, >40% of the total radioactivity was incorporated into hemocyte lipids. About 93% of the incorporated radioactivity was found in phospholipids. Within phospholipids. most of the radioactivity was associated with PC (46%), and less with PE (28%) and PS/PI (21%). Very little radioactivity was recovered in CA (0.9%).     

The fatty acid composition of placenta in intrauterine growth retardation

To examine the impact of intrauterine growth retardation (IUGR) on essential fatty acids in human placenta, fatty acid composition in total acylglycerol and in the major phosphoglycerides phosphatidylcholine (PC) and phosphatidylethanolamine (PE), of 15 placentas from small for gestational age (SGA) births was compared with that of 7 control placentas. The acylglycerol fatty acid content was similar between the two groups, but the proportion of fatty acids of the linoleic acid series, including arachidonic acid, was significantly lower in SGA placentas. When the fatty acid composition in PC was studied, the reduction in fatty acids of the linoleic acid series was even more striking, and fatty acids of the linolenic acid series was also significantly less in the SGA group. These fatty acid changes in placenta membrane phospholipids can affect the transport of important nutrients to the fetal compartment. The decreased level of arachidonic acid and docosahexanoic acid might also lead to a disturbed formation of fetal thromboxane and prostacyclin. However, cord plasma PC fatty acid patterns were nearly identical in the two groups suggesting that in IUGR, the essential fatty acids will be transported to the fetus at the expense of the placenta.     

Manipulation of fatty acid composition of membrane phospholipid and its effects on cell growth in mouse LM cells

Fatty acid composition of the phospholipids of mouse LM cells grown in suspension culture in serum-free chemically defined medium was modified by supplementing the medium with various fatty acids bound to bovine serum albumin.Following supplementation with saturated fatty acids of longer than 15 carbons (100 μM) profound inhibition of cell growth occurred; this inhibitory effect was completely abolished when unsaturated fatty acids were added at the same concentration. Supplementing with unsaturated fatty acids such as linoleic acid, linolenic acid or arachidonic acid had no effect on the cell growth.Fatty acid composition of membrane phospholipids could be manipulated by addition of different fatty acids. The normal percentage of unsaturated fatty acids in LM cell membrane phospholipids (63%) was reduced to 35–41% following incorporation of saturated fatty acids longer than 15 carbon atoms and increased to 72–82% after addition of unsaturated fatty acids.A good correlation was found between the unsaturated fatty acid content of membrane phospholipids and cell growth. When incorporated saturated fatty acids reduced the percentage of unsaturated fatty acids in membrane phospholipids to less than 50%, severe inhibition of the cell growth was found. Simultaneous addition of an unsaturated fatty acid completely abolished this effect of saturated fatty acids.     

Fatty acid and lipid analysis of the house cricket,Acheta domesticus

The fatty acid content and composition of the house cricket Acheta domesticus have been investigated in entire insects at different developmental stages and in selected organs of male and female adults. We have also determined the fatty acid composition of the various lipid classes within extracts of the organs of adult female insects. Fatty acids were analysed by capillary gas chromatography or mass spectrometry as their methyl esters (FAMEs) after direct transesterification of insect material or separated lipid classes.The major esterified fatty acids in all extracts were palmitate (C_16:0), stearate (C_18:0), oleate (C_18:1) and linoleate (C_18:2). Levels of esterified fatty acid varied considerably between organs but the fatty acid compositions showed only small variations. The levels of polyunsaturated fatty acids of the C₁₈ series were considerably higher in phospholipid fractions than in other lipid classes. Triacylglycerols formed the major lipid class in ovaries, fat-body and newly-laid eggs, whereas diacylglycerols and phospholipid predominate in the haemolymph. Triacylglycerols, phospholipids, diacylglycerols and free fatty acids were all found in significant amounts in the gut tissue.     

The influence of linoleic acid and linolenic acid on adult moth emergence of Homona coffearia from meridic diets in vitro

The fatty acids linoleic and linolenic acids have been found to be critical dietary supplements for the successful adult emergence of Homona coffearia reared in meridic diets in vitro. When the levels of these fatty acids were sub-optimal, the moths were able to emerge only partially and a few that emerged fully were deformed with naked wings. In the presence of optimal amounts of these fatty acids, the Δ⁷ sterol, ergosterol, available in the brewer's yeast provided in the diets was found to be adequate for growth and adult emergence. The availability of linoleic acid, which appeared to be the more critical requirement, was sufficient for successful adult emergence, provided that the diet was supplemented with additional amounts of ergosterol. The above two fatty acids seemed to be the only critical dietary supplements offered by whole tea leaves incorporated in a previously described oligidic diet. The provision of a dietary source of a Δ⁷ sterol was found essential as this insect was unable to utilize cholesterol.     

Prostaglandin precursor fatty acids in serum and bile as influenced by oophorectomy, contraceptive steroids and pregnancy. An experimental study in the cat

Variations in the occurrence of prostaglandin precursor fatty acids might be of importance for the pathogenesis of gallstones. Pregnancy and use of contraceptive steroids increase the risk of gallstones. The present study reports the relative fatty acid composition in serum and biliary phospholipids studied by gas-liquid chromatography in four groups of female cats, which were on a standard diet: 1) oophorectomized animals, 2) animals on contraceptive steroids, 3) pregnant animals and 4) control animals. It was consistently found that the portions of palmitic and linoleic acid were higher and stearic and arachidonic acid were lower in biliary than in serum lecithin. In biliary lysolecithin, sphingomyelin and cephaline there were only small portions of linoleic and negligible amounts of arachidonic acid. Oophorectomy, contraceptive steroids or pregnancy did not induce any gross changes in the fatty acid pattern of lecithin in serum or bile. In animals treated with contraceptive steroids a reduced portion of linoleic acid was seen in the bile lecithin, and in pregnant animals there was a reduction of omega 3 and omega 6 fatty acids in biliary lecithin.     

Essential fatty acid uptake and esterification in primary culture of rat hepatocytes

Primary cultures of adult rat hepatocytes were used to compare the uptake and esterification of essential polyunsaturated fatty acids (18:2, 20:3 and 20:4 of the n-6 series) with those of palmitic and oleic acids. The uptake of unesterified fatty acids was linearly related to the free fatty acid/albumin molar ratio for 14 h and did not depend on the unbound free fatty acid level. Whatever the initial free fatty acid/albumin molar ratio, it dropped to 0.5 +/- 0.1 mM after 14 h, thus showing that hepatocytes have a high capacity for clearing free fatty acids from the medium at high free fatty acid/albumin molar ratios. The free fatty acid uptake become saturable when the free fatty acid and albumin concentrations were raised and the free fatty acid/albumin ratio remained constant. This strongly suggests that albumin-hepatocyte interaction mediates free fatty acid uptake. This uptake was identical whatever the fatty acid tested and did not depend on the relative amounts of fatty acids when they were added simultaneously. Triacylglycerol accumulation and synthesis, monitored by labelled fatty acids, were related to the free fatty acid/albumin molar ratio and exhibited no specificity for the series of fatty acids tested. Triacylglycerols were enriched in all the fatty acids tested by up to 60%, and fatty acid incorporation into diacylglycerols and triacylglycerols reflected the free fatty acid composition of the medium. By contrast, neither the level nor the synthesis of phospholipids varied with free fatty acid/albumin, but the rate of phospholipid turnover depended on the fatty acids tested. Accumulation of these acids was smaller in phospholipids than in triacylglycerols. When linoleic and arachidonic acids were added together, phospholipids (especially phosphatidylethanolamine and phosphatidylinositol) were more enriched in arachidonic acid than triacylglycerols. This might be due to the specificity for fatty acid of the enzymes involved in phospholipid metabolism.     

Alteration of fatty acid composition of LM cells by lipid supplementation and temperature.

Alteration of the fatty acid composition of monolayer cultures of LM cells grown in chemically defined medium was achieved by supplementation with fatty acids complexed to bovine serum albumin. Phospholipids containing up to 40% linoleate were found in cells grown in medium containing 20 mu g of linoleate/ml. Incorporation of linoleate into phospholipids reached a plateau after 12-24 hr, and cells remained viable for at least 3-4 days. Although linoleic, linolenic, and arachidonic acids were incorporated into LM cells equally well, only the latter was elongated by these cells under these experimental conditions. Nonadecanoic acid was incorporated to a lesser extent than the polyunsaturated fatty acids. Phosphatidylcholine and phosphatidylethanolamine of LM cells had different fatty acid compositions; phosphatidylethanolamine contained more longer chain and unsaturated fatty acids. Cells were also grown in the absence of choline and presence of choline analogs such as N,N-dimethylethanolamine, N-methylethanolamine, 3-amino-1-propanol, and 1-2-amino-1-butanol. The analog phospholipids in these cells had fatty acid compositions which were intermediate between those of phosphatidylethanolamine and phosphatidylcholine of control cells grown in the presence of choline. Linoleate was found in both phosphatidylcholine and phosphatidylethanolamine of cells supplemented with linoleate. The sphingolipid fraction of these cells, however, did not contain significant amounts of linoleate. When linoleate was present in the phospholipids, compensatory decreases in the oleate and palmitoleate content of phospholipids were observed. Lowering of the growth temperature to 28 degrees produced an increase in unsaturate fatty acid content of the phospholipids. When linoleate was supplied to cells grown at 28 degrees, there was no further increase in the unsaturated fatty acid composition of the phospholipids. Using both fatty acid supplementation and lowered growth temperature, LM cell membranes can be produced which have phospholipids with vastly different fatty acid compositions.     

Effect of sex and gonadal hormones on rat plasma lipids during the development of an essential fatty acid deficiency

1. Male, female and castrated rats treated with oestradiol (30mug./week) or testosterone (2mg./week) were given an essential fatty acid-deficient diet containing 10% of hydrogenated coconut oil for 9 weeks. The concentrations and fatty acid composition of plasma phospholipids, cholesteryl esters and triglycerides were determined. 2. Between the second and third weeks of the deficiency, concentrations of plasma cholesteryl esters, phospholipids and triglycerides decreased, then remained relatively constant. There were no significant differences between males and females, but oestradiol caused a significant rise in plasma phospholipids and triglycerides as compared with testosterone-treated animals. 3. During the first 2 weeks of the deficiency, linoleic acid in the plasma lipids of all groups decreased to low concentrations and changed very little thereafter. 4. Female rats maintained higher percentages and concentrations of arachidonic acid and stearic acid in plasma phospholipids and arachidonic acid in cholesteryl esters than did males. Males had higher proportions of eicosatrienoic acid and oleic acid. There was no sex difference in the fatty acid composition of plasma triglycerides. 5. Oestradiol-treated rats had concentrations of cholesteryl and phospholipid arachidonate comparable with those of female rats and higher than the testosterone-treated group. Eicosatrienoic acid in the oestradiol-treated rats was high and resembled that of the male rats, apparently because of the higher concentration of plasma phospho lipids in this group. 6. Supplementation of the essential fatty acid-deficient rats with linoleate restored plasma cholesteryl and phospholipid linoleate and arachidonate nearly to normal concentrations in a single day. The increase in arachidonic acid in these fractions was accompanied by a similar quantitative decrease in eicosatrienoic acid. 7. These sex differences appear to be related to the smaller size of the female rat and to a more direct influence of oestradiol on the formation or maintenance of phospholipids rich in arachidonic acid.     

Effects of acclimation temperature on membrane phospholipids in the flesh fly Sarcophaga similis

Cold acclimation is a well‐known strategy for enhancing cold tolerance in ectotherms including insects. Nevertheless, information on the physiological mechanisms underpinning this phenomenon is still limited. Biological membrane integrity is critical for insects to perform at low temperatures, and an advantage is conferred on those insects that can adjust the composition of their membrane phospholipids. Such changes contribute to homeoviscous adaptation, a process that allows membranes to maintain a liquid–crystalline (fluid) state at low temperatures. Here we investigated phospholipids in the flesh fly Sarcophaga similis acclimated to various temperatures. Significant differences were observed in the composition of their fatty acyl chains: flies acclimated to low temperatures showed a higher proportion of palmitic and oleic acids at the expense of palmitoleic acid. Other fatty acids (stearic, linoleic, linolenic, arachidonic, eicosapentaenoic acids) were not significantly changed. The degree of unsaturation decreased in cold‐acclimated flies, but the difference was quite small. The weighted average chain length and number of double bonds were unchanged among flies acclimated to different temperatures. As temperatures decreased, the percentage of phosphatidylethanolamine increased to twice that of phosphatidylcholine. We discuss the role of these phospholipid changes in cold acclimation.