Correlation between low-temperature immunosuppression and the absence of unsaturated fatty acid synthesis in murine T cells.

1. Studies were performed to determine if the inability of murine T cells to provide primary helper function at low temperature (27 degrees C) could be correlated with their inability to synthesize unsaturated fatty acids (UFAs). 2. In the absence of exogenous oleic acid (18:1), splenocytes responded to a T-dependent (TD) Ag (trinitrophenyl-keyhole limpet hemocyanin, TNP-KLH) at 37 degrees C but not at 27 degrees C. The addition of 150 microM 18:1 almost completely restored plaque-forming cell (PFC) responses to TNP-KLH at 27 degrees C but markedly suppressed PFC responses to the TD Ag at 37 degrees C. 3. During incubation at 27 degrees C, B cells converted 3- to 5-fold more stearic acid (18:0) to 18:1 and showed a greater accumulation of monounsaturated phospholipid molecular species than did T cells. 4. Following incubation in the presence of a rescuing dose of 18:1 (150 microM), both B and T cells accumulated large amounts of dioleoyl PC. 5. It is proposed that the absence of 18:1 synthesis in T cells is responsible for the unique low temperature susceptibility of this lymphocyte population.     

Kinetics of membrane immunoglobulin capping on murine B lymphocytes. Effects of phospholipid fatty acid replacement

Detailed analyses regarding the effects of temperature and phospholipid fatty acid replacement on the capping of membrane immunoglobulin (mIg) have been performed using a recently described flow cytometric procedure (Cuchens, M. A., and Buttke, T. M. (1984) Cytometry 5, 601-609). Purified murine B cells were incubated for 12-20 h in the presence of bovine serum albumin-complexed 80 microM stearic (18:0), oleic (cis-18:1), or linoleic (cis, cis-18:2) free fatty acids. Unmodified and free fatty acid-treated cells were stained with fluorescein-conjugated rabbit anti-mouse Ig and subjected to pulse-shape (width) analyses to follow the kinetics of mIg capping. In both unmodified and free fatty acid-treated cells, capping of mIg occurred at all temperatures between 17 and 37 degrees C, but the rate of cap formation was temperature dependent. Arrhenius plots of mIg capping were linear, with activation energies ranging from 14 to 23 kcal/mol depending on the saturated/unsaturated fatty acid ratio of B cell phospholipids. Ligand-induced redistribution of mIg thus appears to be sensitive to changes in membrane acyl chain composition.     

Growth inhibition of Monodus subterraneus by free fatty acids

Monodus subterraneus is a microalga, which is known for its high eicosapentaenoic acid (EPA; 20:5omega3) content. To produce EPA commercially, high volumetric productivities of microalgae are required. These high productivities can be reached in flat panel photobioreactors with small optical paths that have to be operated at high cell densities (>10 g/L). However, at these cell densities a reduction of productivity is observed. This growth inhibition is probably caused by growth inhibitors released by the microalgae, which have been suggested to be fatty acids. Our aim was to investigate if free fatty acids produced by M. subterraneus inhibited growth of this species. Therefore a bioassay was developed and saturated, unsaturated and poly-unsaturated fatty acids occurring in Monodus were tested on their growth inhibiting properties. Growth of M. subterraneus was completely inhibited at a saturated concentration (96 microM) of palmitoleic acid (16:1omega7). But, the saturated fatty acid palmitic acid (16:0) and the mono-saturated oleic acid (18:1omega9) were much stronger inhibitors. Growth was inhibited for 50% already at concentrations of 0.4 microM 16:0 and 3 microM 18:1omega9, respectively. These fatty acids probably cause the growth inhibition in high cell density cultures of M. subterraneus.     

Fatty acid compositions of arthropod and cephalopod photoreceptors: interspecific,seasonal and developmental studies

Fatty acid compositions of the compound eyes of insects (soldier-bug, Hemiptera, and silk moth, Lepidoptera), crustaceans (crayfish and grapsid crab, Decapoda) and inner and outer segments of visual cells of a squid (Cephalopoda, Mollusca) were analyzed by gaschromatography for interspecific comparison. Fatty acid compositions showed great variation among species. In insect compound eyes, 16:0 and 18:0 were the main saturated fatty acids, and 18:1 was the dominant unsaturated fatty acid. Silk moth eyes contained, in addition, considerable amounts of 18:2 and 20:5. In crustacean compound eyes, the main saturated fatty acids were 16:0 and 18:0, and 14:0 (5.0%) was only detected in grapsid crabs; the main unsaturated fatty acids were 20:4, 20:5 and 22:6. Both whole eyes and rhabdom fraction of crayfish showed similar profiles of fatty acid compositions. Both inner and outer segments of squid retinae were characterized by high amounts of unsaturated fatty acids, especially 22:6. Compound eyes of grapsid crabs were used for the experiments on seasonal changes of fatty acid compositions. UFA/SFA ratios (weight in % of unsaturated fatty acids saturated fatty acids) were lowest (1.0) in July and highest (2.5) in March, and unsaturation indexes (average number of double bonds per molecule) were lowest (1.5) in July and highest (2.3) in March. Fatty acids 18:0 and 20:1 showed a significant correlation with the changes of seasonal temperature. Fatty acid analysis of the developing compound eyes of silk moths during the pupal stage revealed that eicosapentanoic acid (20:5) increased remarkably in parallel with the development of photoreceptive membranes, the rhabdoms. This suggests that eicosapentaenoic acid may play an important role in formation and function of rhabdoms.     

Effects of sterculic acid on stearoyl-CoA desaturase in differentiating 3T3-L1 adipocytes

The effects of sterculic acid on cell size, adiposity, and fatty acid composition of differentiating 3T3-L1 adipocytes are correlated with stearoyl-CoA desaturase (SCD) expression (mRNA and protein levels) and enzyme activity. Fluorescence-activated cell scanning (FACS) analysis showed that adipocytes differentiated with methylisobutylxanthine, dexamethasone, and insulin (MDI) plus 100 microM sterculic acid comprised a population of predominantly large cells with reduced adiposity compared to MDI-treated cells. Although both groups had similar amounts of total fat, their fatty acid profiles were strikingly different: MDI-treated cells had high levels of the unsaturated palmitoleic (Delta(9)-16:1) and oleic (Delta(9)-18:1) acids, whereas the cells cultured with MDI plus sterculic acid accumulated palmitic (16:0) and stearic (18:0) acids together with a marked reduction in Delta(9)-16:1. Although the cells treated with MDI plus sterculic acid had similar levels of scd1 and scd2 mRNAs and antibody-detectable SCD protein as the MDI-treated cells, the SCD enzyme activity was inhibited more than 90%. The accumulation of 16:0 and 18:0, together with normal levels of fatty acid synthase (FAS) and aP2 mRNAs, shows that de novo synthesis and elongation of fatty acids, as well as cell differentiation, were not affected by sterculic acid. Because of the increase in cell size in the sterculic acid-treated cells, the insulin-stimulated 2-deoxyglucose (2-DOG) uptake was determined. Compared to MDI-treated cells, the 2-DOG uptake in the cells treated with sterculic acid was not affected. These results indicate that sterculic acid directly inhibits SCD activity, possibly by a turnover-dependent reaction, without affecting the processes required for adipocyte differentiation, scd gene expression or SCD protein translation.     

Endogenous suppression of neutral-active and calcium-dependent phospholipase A2 in human polymorphonuclear leukocytes

Phospholipase A2 activity was measured in homogenized and acid-extracted human polymorphonuclear leukocytes using [1-14C]oleate-labelled autoclaved Escherichia coli as substrate. In whole homogenate and in the supernatant and particular fractions separated by centrifugation at 150,000 X g, phospholipase activity was barely detectable (1-4 pmol/h per 10(6) cell equivalents). By contrast, acid extracts of these fractions contained over 10-times as much phospholipase activity in the dialyzed supernatants (20-300 pmol/h per 10(6) cell equivalents), whereas phospholipase inhibitor(s) were found in the sediment. The acid-solubilized phospholipase A2 activity was absolutely Ca2+-dependent and optimal at pH 7.0-7.5 with 1.0 mM added Ca2+. Addition of the resuspended sediment of the acid extract dose-dependently suppressed phospholipase activity in the supernatant; less than equivalent amounts were sufficient to inhibit 95%. Suppressor activity was lipid-extractable. After thin layer chromatography of lipid extracts, the bulk of inhibitory activity was recovered from the free fatty acid region. Analysis of the fatty acids by gas liquid chromatography showed that 63% were unsaturated. All unsaturated fatty acids tested were potent inhibitors of phospholipase A2 activity (IC50 3-10 microM). Oleoyl-CoA, hydroxyeicosatetraenoic acids and leukotriene D4 were also inhibitory, while methyl oleate, saturated fatty acids and the prostaglandins E2 and F2 alpha had no effect. These in vitro data indicate that neutral-active and calcium-dependent phospholipase A2 in human polymorphonuclear leukocytes is largely suppressed by endogenous inhibitors and suggest that unsaturated fatty acids and some of their metabolites may partly account for this suppressor activity.     

Two Delta9-stearic acid desaturases are required for Aspergillus nidulans growth and development

Unsaturated fatty acids are important constituents of all cell membranes and are required for normal growth. In the filamentous fungus Aspergillus nidulans, unsaturated fatty acids and their derivatives also influence asexual (conidial) and sexual (ascospore) sporulation processes. To investigate the relationship between fatty acid metabolism and fungal development, we disrupted the A. nidulans sdeA and sdeB genes, both encoding Delta9-stearic acid desaturases responsible for the conversion of palmitic acid (16:0) and stearic acid (18:0) to palmitoleic acid (16:1) and oleic acid (18:1). The effects of sdeA deletion on development were profound, such that growth, conidial and ascospore production were all reduced at 22 and 37 degrees C. Total fatty acid content was increased over 3-fold in the DeltasdeA strain, reflected in up-regulation of the expression of the fasA gene encoding the alpha chain of the fatty acid synthase, compared to wild type. Stearic acid accumulated approximately 3-fold compared to wild type in the DeltasdeA strain, while unsaturated fatty acid production was decreased. In contrast, disruption of sdeB reduced fungal growth and conidiation at 22 degrees C, but did not affect these processes at 37 degrees C compared to wild type. Interestingly, ascospore production was increased at 37 degrees C for DeltasdeB compared to wild type. Total fatty acid content was not increased in this strain, although stearic acid accumulated 2-fold compared to wild type, and unsaturated fatty acid production was decreased. Combining the DeltasdeA and DeltasdeB alleles created a synthetic lethal strain requiring the addition of oleic acid to the medium for a modicum of growth. Taken together, our results suggest a role for sdeA in growth and development at all temperatures, while sdeB is involved in growth and development at lower temperatures.     

Uterine lipid alterations during early pseudopregnancy and following the artificial induction of decidualization by concanavalin A in QS mice

Lipid extracts of whole uterine tissue from mice were examined by gas chromatography-mass spectrometry during days 2, 3, and 4 of pseudopregnancy (day 1 = copulatory plug) and following the artificial induction of the decidual cell reaction (DCR) on day 4. The range of lipids identified during pseudopregnancy and their percentage composition on day 2 included saturated fatty acids (SFA, 38%), monounsaturated fatty acids (MUFA, 20%), polyunsaturated fatty acids (PUFA, 17%), sterols (25%), long chain alcohols (0.12%), and alkylglycerols (0.11%). Of these, the main components were the fatty acids 16:0 (21%), 18:0 (14%), cis18:1n-9 (14%), 18:2n-6 (8.5%), and cholesterol (24%). Although only subtle changes in the composition of uterine lipids occurred through days 2 and 3 of pseudopregnancy, more substantial changes were detected on day 4, at a time when the uterus normally initiates its transient “window of receptivity.” Following induction of the DCR with the lectin Concanavalin A (Con A) at this time, even greater alterations in uterine lipid composition were observed. From 20 to 1,280 min post-Con A-treatment the percentage composition of SFA in the treated left uterine horn changed from 43% to 64%, sterols from 19% to 4%, PUFA from 15% to 10%, while MUFA remained unchanged at 23%. The lipid profile of the untreated right uterine horn of these animals was similar to that of the Con A-treated left uterine horn during the early stages. However, by 1,280 min substantial differences were observed, at a time corresponding with Con A-induced uterine growth. In contrast, differences in the lipid profile of Con A- and saline-treated uteri were observed at 320 min post-treatment, a time preceding Con A-induced uterine growth. Furthermore, the tissue concentration (nmol/mg dry weight) of SFA and sterols in uterine tissue decreased significantly following Con A treatment. The results suggest that uterine lipid changes are implicated in the development of uterine receptivity, and in the remodeling of uterine tissue for successful embryonic invasion and the establishment of pregnancy. © 1996 Wiley-Liss, Inc     

Isolation and characterization of fatty acid auxotrophs from the oleaginous yeast Apiotrichum curvatum

Summary In order to improve the economic value of lipids produced by the oleaginous yeast strain Apiotrichum curvatum ATCC 20509, a search was made for mutants defective in the conversion of stearic acid to oleic acid. Mutants could be selected as unsaturated fatty acid auxotrophs, since unsaturated fatty acids are essential componenets in membrane lipids. After treatment of A. curvatum wild-type with N-methyl-N-nitro-N-nitrosoguanidine, 58 fatty-acid-requiring mutants were isolated. On the basis of (1) the growth response to saturated and unsaturated fatty acids and (2) the fatty acid composition of lipids produced by these mutants, it was concluded that only 18 of them were real unsaturated fatty acid (Ufa) mutants, while the other 40 were designated as fatty acid synthetase (Fas) mutants. It is further shown that Ufa mutants of A. curvatum are able to produce high amounts of lipids consisting of more than 90% triacylglycerols with a percentage of saturated fatty acids resembling that of cocoa butter, when grown in the presence of relatively small amounts of oleic acid in the growth medium. This may offer an economically favourable alternative in comparison with other methods that have been developed for the production of cocoa butter equivalents by microorganisms.Offprint requests to: H. Smit     

Effects of cholesterol on viability and (n - 6) fatty acid metabolism in cultured human monocyte-like cells (U937).

Effects of supplementation of growth-promoting cholesterol on metabolism of the cytotoxic (n - 6) polyunsaturated fatty acids in cultured human monocyte-like cells (U937) have been examined. U937 cells were incubated in 5% delipidated fetal bovine serum containing 0 or 38.7 microM cholesterol. The rate of uptake and the distribution of metabolites of (n - 6) fatty acids (such as 18:2(n - 6), 18:3(n - 6), and 20:3(n - 6), and 20:4(n - 6)) were examined by adding radiolabelled fatty acid at a level of 1 microgram/mL (3.3 microM for 20-carbon fatty acids and 3.6 microM for 18-carbon-fatty acids). For assessing the cytotoxicity, (n - 6) fatty acids were added to medium at a concentration of 5 micrograms/mL (16.4 microM for 20-carbon fatty acids and 17.9 microM for 18-carbon fatty acids). Cholesterol supplementation suppressed the uptake of all (n - 6) fatty acids and reduced the cytotoxic effects of 18:2(n - 6), 20:3(n - 6), and 20:4(n - 6), but not 18:3(n - 6). In addition, cholesterol supplementation increased peroxide production and metabolism of (n - 6) fatty acids in U937 cells. Thus, the differential suppressive effect of cholesterol on the cytotoxicity of different fatty acids could not be attributed to an inhibitory effect on fatty acid delta 6- and delta 5-desaturation, or to an antioxidant effect on peroxide formation.     

Changes in fatty acid compositions of mitochondria during embryonic development

1. A general trend among biomembranes of hepatocytes in the developing avian embryo is to display increasing percentages of unsaturated fatty acids, especially oleic acid (C18:1). 2. However, once increasing amounts of thyroxine appear in the plasma, mitochondria begin to exhibit increasing percentages of saturated fatty acids, primarily stearic acid (C18:0). 3. Increasing saturation of mitochondrial membrane lipids can be inhibited by exposure of embryonated eggs to 500 R of X-irradiation. 4. Injection of embryonated eggs with estrone increases the proportion of oleic acid (C18:1) in mitochondrial membranes but a balancing increase in palmitic acid (C16:0) enables their lipids to remain more saturated than unsaturated.     

Dietary fats and body lipid composition in relation to hibernation in free-ranging echidnas

Laboratory studies have shown that high levels of dietary unsaturated fatty acids prolong torpor and lower body temperatures in hibernating herbivorous rodents, which may in turn improve winter survival. The importance of nutritional ecology in relation to hibernation in insectivorous hibernators is unknown. We therefore studied fatty acid composition of dietary insects and the depot fat of echidnas Tachyglossus aculeatus (Monotremata) during the pre-hibernation season and compared depot fat fatty acid composition before and after hibernation. Echidna depot fat fatty acid composition during the pre-hibernation season was almost identical to that of the most abundant prey species, the ant Iridomyrmex sp. Oleic acid (C18:1) was by far the most common fatty acid in both Iridomyrmex sp. (60%) and echidna depot fat (62%). After about 5 months of hibernation and an 18% loss of body mass, echidna fatty acid composition had changed significantly. The percentage of the monounsaturated oleic acid (C18:1) and palmitoleic acid (C16:1) had declined, whereas that of the saturated fatty acids (C12:0, C16:0, C18:0) and the polyunsaturated linoleic acid (C18:2) had increased. Our study suggests that, unlike herbivorous rodent hibernators, echidnas rely to a large extent on monounsaturated fatty acids as fuel for hibernation, reflecting the most common fatty acid in their food. Moreover, it appears that the high concentration of monounsaturated fatty acids compensates for the moderate availability of polyunsaturates and enables them to hibernate at low body temperatures.     

Effects of fatty acid chain length and saturation on gastric inhibitory polypeptide release in obese hyperglycaemic (ob/ob) mice

Plasma gastric inhibitory polypeptide (GIP) responses to equimolar intragastrically administered emulsions of fatty acids (2.62 mmol/7.5 ml/kg) were examined in 18 h fasted obese hyperglycaemic (ob/ob) mice. Propionic acid (C3:0), a saturated short-chain fatty acid, and capric acid (C10:0), a saturated medium chain fatty acid, did not signilicantly stimulate GIP release. However, the saturated long-chain fatty acid stearic acid (C18:0), and especially the unsaturated long-chain fatty acids oleic (C18:1), linoleic (C18:2) and linolenic (C18:3) acids produced a marked GIP response. The results show that chain length and to a lesser extent the degree of saturation are important determinants of fatty acid-stimulated GIP release. The GIP-release action of long-chain, but not short-chain, fatty acids may be r e l a t e d to differences in their intracellular handling.     

Changes of Phosphatidylcholine and Fatty Acids in Germ Cells during Testicular Maturation in Three Developmental Male Morphotypes of Macrobrachium rosenbergii Revealed by Imaging Mass Spectrometry

Testis maturation, germ cell development and function of sperm, are related to lipid composition. Phosphatidylcholines (PCs) play a key role in the structure and function of testes. As well, increases of polyunsaturated fatty acids (PUFA) and highly unsaturated fatty acids (HUFA), especially arachidonic acid (ARA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) are essential for male fertility. This study is the first report to show the composition and distribution of PCs and total fatty acids (FAs) in three groups of seminiferous tubules (STs) classified by cellular associations [i.e., A (STs with mostly early germ cells), B (STs with mostly spermatids), and C (STs with spermatozoa)], in three morphotypes of Macrobrachium rosenbergii, [i.e., small male (SM), orange claw male (OC), and blue claw male (BC)]. Thin layer chromatography exhibited levels of PCs reaching maxima in STs of group B. Imaging mass spectrometry showed remarkably high signals corresponding to PC (16:0/18:1), PC (18:0/18:2), PC (18:2/20:5), and PC (16:0/22:6) in STs of groups A and B. Moreover, most signals were detected in the early developing cells and the intertubular area, but not at the area containing spermatozoa. Finally, gas chromatography-mass spectrometry indicated that the major FAs present in the testes were composed of 14:0, 16:0, 17:0, 18:0, 16:1, 18:1, 18:2, 20:1, 20:2, 20:4, 20:5, and 22:6. The testes of OC contained the greatest amounts of these FAs while the testes of BC contained the least amounts of these FAs, and there was more EPA (20:5) in the testes of SM and OC than those in the BC. The increasing amounts of FAs in the SM and OC indicate that they are important for spermatogenesis and spermiogenesis. This knowledge will be useful in formulating diets containing PUFA and HUFA for prawn broodstocks in order to improve testis development, and lead to increased male fecundity.     

Phosphatidyl choline fatty acid remodeling in the hepatic cell nuclei

This study was performed to determine whether fatty acids incorporated into liver cell nuclei phosphatidylcholine (PtdCho) could be remodeled in the isolated nuclear. For this reason, rat liver cell nuclei were incubated in vitro with [1-14C]20:4n-6-CoA. PtdCho molecular species with the highest specific activity had an unsaturated fatty acid at sn-1 and sn-2 positions (20:4-20:4>18:2-20:4>18:1-20:4). 16:0-20:4 and 18:0-20:4 PtdChos showed a minor specific activity. When labeled nuclei were reincubated in the absence of labeled substrate with the addition of cytosol, ATP and CoA, the specific activity of 20:4-20:4, 18:2-20:4 and 18:1-20:4 species decreased, while that of 16:0-20:4 and 18:0-20:4 increased. In conclusion, the asymmetric fatty acid distribution of saturated fatty acids at sn-1 position, and unsaturated fatty acids at sn-2 position of nuclear PtdCho molecular species was re-established by an acyl-CoA-dependent remodeling process.     

The lipid composition of Acer pseudoplatanus cells grown in culture

Cells of Acer pseudoplatanus were grown in batch suspension culture for 22 days. The cultures were initiated at high cell density of 2 × 10⁵ cells per ml of culture. Growth was characterised by a short lag phase, an exponential phase of rapid cell division and growth, and finally a stationary phase. Quantitative but not qualitative changes were observed in total lipid content, fatty acids and phospholipids at different stages of growth. Total lipids, phospholipids and fatty acids showed maximum concentrations in 12 day old cells. The major phospholipids isolated were phosphatidylcholine and phosphatidylethanolamine with minor amounts of phosphatidic acid and lysophosphatides. Other lipid components present were mono- and digalactosyl diglycerides, cerebrosides, sterol glucosides, free fatty acids and esterified sterol glucosides. The major constituent fatty acids were myristic acid (14:0), palmitic acid (16:0), stearic acid (18:0), oleic acid (18:1), linoleic acid (18:2) and linolenic acid (18:3). During exponential cell growth the proportion of 16:0, 18:2 and 18:3 constituted nearly 90% of the total fatty acids. Triglycerides were the major repository of myristic acid (14:0) with substantial amounts of palmitic acid (16:0), whereas phospholipids contained 16:0, 18:2 and 18:3 in high amounts.     

Fatty acid makeup of the lipids in soil and epiphytic yeasts]

The fatty acid composition of lipids was compared among yeast cultures belonging to the genera Rhodotorula, Lipomyces, and Cryptococcus. These lipids contain C10--C26 fatty acids, mainly with the even number of carbon atoms. Palmitic acid (C16 : 0) and oleic acid (C18 : 0) predominate. In the majority of the strains, the sum of unsaturated acids exceeds the sum of saturated acids. The content of unsaturated acids in the lipids of the epiphytic yeast Rhodotorula is higher than in the soil yeast Lipomyces. Besides C12--C18 acids, C22--C26 acids were identified by GLC at preset temperatures. Lignoceric acid (C24 : 0) was found for the first time in the cultures of Rhodotorula, Lipomyces, and Cryptococcus, and cerotinic acid (C16 : 0) was also detected in the Rhodotorula yeast. Fatty acids with a long chain are registered in the strains of Rhodotorula more often than in the strains of Lipomyces and Cryptococcus.     

Evidence for the regulation of fatty acid utilization in human sperm by docosahexaenoic acid

The effects of stearic (18:0), linolenic (18:3), and docosahexaenoic (22:6) acids on palmitoyl coenzyme A (CoA) formation by a long-chain fatty acid:CoASH ligase (adenosine monophosphate) (E. C. 6.2.1.3-enriched fraction from human spermatozoa were studied. Both 18:0 and 18:3 were competitive inhibitors for palmitic (16:0) acid activation with Kis of 17.7 and 5.7 microM, respectively. In contrast, 22:6 was a noncompetitive inhibitor demonstrating a Ki of 9.5 microM. These data coupled with previous studies support the conclusion that 16:0, 18:0, and 18:3 and other saturated and unsaturated fatty acids are activated by the same ligase enzyme in sperm. Although the kinetics and interactions of 22:6 are unique compared to the other fatty acids found in sperm phospholipids, we cannot discern from our data if it is activated by a separate enzyme. We propose that 22:6, or a metabolite of 22:6, may regulate free fatty acid utilization in human sperm and that this hypothesis may provide an enzymatic explanation for the changes observed in phospholipid-bound fatty acids during the epididymal maturation of sperm.     

Diet preferences of warblers for specific fatty acids in relation to nutritional requirements and digestive capabilities

During energy-demanding periods of the annual cycle such as migration or during cold days in winter, birds store fat comprised mostly of 16- or 18-carbon unsaturated fatty acids. In such situations, birds may feed selectively on foods with specific fatty acids that enable efficient fat deposition. We offered wild-caught yellow-rumped warblers Dendroica coronata paired choices between semi-synthetic diets that differed only in their fatty acid composition. Warblers strongly preferred diets containing long-chain (18:1; carbon atoms:double bonds) unsaturated, unesterified fatty acids to diets containing long-chain saturated, unesterified fatty acids (18:0) and they preferred diets containing mono-unsaturated fats (18:1) to diets containing poly-unsaturated fats (18:2). The preference for diets containing long-chain unsaturated fatty acids to diets containing long-chain saturated fatty acids was consistent in birds tested one week after capture at 21°C, one month after capture when cold-acclimated (1°C), and six weeks after capture at 21°C. Birds acclimated to a diet with 50% of the fat comprised of unesterified stearic acid (18:0) lost mass and reduced their food intake when we reduced ambient temperature from 21°C to 11°C over three days. We conclude that especially in energy-demanding situations there are limits to the yellow-rumped warblers' ability to assimilate some long-chain saturated fatty acids and that this digestive constraint can explain in part why yellow-rumped warblers prefer diets containing long-chain unsaturated fatty acids to diets containing long-chain saturated fatty acids.