Effect of eicosapentaenoic acid on triacylglycerol transport in CaCo-2 cells

The human intestinal cell line, CaCo-2, was used to study the effect of the n-3 fatty acid, eicosapentaenoic acid, on triacylglycerol secretion. In cells incubated with 250 microM eicosapentaenoic acid, the incorporation of [3H]glycerol into triacylglycerols secreted into the medium was decreased by 58% compared to cells incubated with 250 microM oleic acid. The incorporation of [3H]glycerol into cellular triacylglycerols was decreased 32% in cells incubated with eicosapentaenoic acid. In cells preincubated with [3H]glycerol to label existing triacylglycerols, the rates of secretion of preformed triacylglycerols were similar in response to the addition of either fatty acid. Initial uptake rates of the n-3 fatty acid were higher than for oleic acid. Both eicosapentaenoic acid and oleic acid were minimally oxidized to CO2. Oleic acid was predominantly incorporated into cellular triacylglycerols (62% vs. 47%), whereas more eicosapentaenoic acid was incorporated into cellular phospholipids (46% vs. 30%). Phospholipids of microsomes prepared from cells incubated with eicosapentaenoic acid were enriched in this fatty acid. The rate of synthesis of triacylglycerol and diacylglycerol acyltransferase activities were significantly less in microsomes prepared from cells incubated with eicosapentaenoic acid. Triacylglycerol mass secreted by CaCo-2 cells incubated with either fatty acid was similar. In CaCo-2 cells, eicosapentaenoic acid decreases the synthesis and secretion of newly synthesized triacylglycerol without decreasing the secretion of triacylglycerol mass. Modification of microsomal membrane phospholipid fatty acid composition is associated with a decrease in microsomal triacylglycerol synthesis and diacylglycerol acyltransferase activities.     

Eicosapentaenoic acid reduces hepatic synthesis and secretion of triacylglycerol by decreasing the activity of acyl-coenzyme A:1,2-diacylglycerol acyltransferase

The mechanism for the reduced hepatic production of triacylglycerol in the presence of eicosapentaenoic acid was explored in short-term experiments using cultured parenchymal cells and microsomes from rat liver. Oleic, palmitic, stearic, and linoleic acids were the most potent stimulators of triacyl[3H]glycerol synthesis and secretion by hepatocytes, whereas erucic, alpha-linolenic, gamma-linolenic, arachidonic, docosahexaenoic, and eicosapentaenoic acids (in decreasing order) were less stimulatory. There was a linear correlation (r = 0.85, P less than 0.01) between synthesis and secretion of triacyl[3H]glycerol for the fatty acids examined. The extreme and opposite effects of eicosapentaenoic and oleic acids on triacylglycerol metabolism were studied in more detail. With increasing number of free fatty acid molecules bound per molecule of albumin, the rate of synthesis and secretion of triacyl[3H]glycerol increased, most markedly for oleic acid. Cellular uptake of the two fatty acids was similar, but more free eicosapentaenoic acid accumulated intracellularly. Eicosapentaenoic acid caused higher incorporation of [3H]water into phospholipid and lower incorporation into triacylglycerol and cholesteryl ester as compared to oleic acid. No difference was observed between the fatty acids on incorporation into cellular free fatty acids, monoacylglycerol and diacylglycerol. The amount of some 16- and 18-carbon fatty acids in triacylglycerol was significantly higher in the presence of oleic acid compared with eicosapentaenoic acid. Rat liver microsomes in the presence of added 1,2-dioleoyl-glycerol incorporated eicosapentaenoic acid and eicosapentaenoyl-CoA into triacylglycerol to a lesser extent than oleic acid and its CoA derivative. Decreased formation of triacylglycerol was also observed when eicosapentaenoyl-CoA was given together with oleoyl-CoA, whereas palmitoyl-CoA, stearoyl-CoA, linoleoyl-CoA, linolenoyl-CoA, and arachi-donoyl-CoA had no inhibitory effect. In conclusion, inhibition of acyl-CoA:1,2-diacylglycerol O-acyltransferase (EC 2.3.1.20) by eicosapentaenoic acid may be important for reduced synthesis and secretion of triacylglycerol from the liver.     

Plasma triacylglycerol secretion in sheep. Paradoxical effects of fasting and alloxan diabetes

Plasma triacylglycerol and phospholipid concentrations were increased in fasting and diabetic sheep compared with fed animals. Secretion was measured in these animals using Triton WR1339 to block lipoprotein lipase. Triacylglycerol secretion was lowest in fed animals and, unlike non-ruminant species, increased by fasting and diabetes. These changes were in proportion to plasma free fatty acid concentration. However, no effect of Triton was found on plasma phospholipids under any of the conditions studied. It is suggested that the low rate of triacylglycerol secretion in normal animals is due to the limiting membrane found in the liver sinusoid of the sheep and that the greater rate in fasting and diabetes reflects the increased mass of intrahepatic triacylglycerol.     

Fat pad triacylglycerol fatty acid loss and oxidation as indices of total body triacylglycerol fatty acid mobilization and oxidation in starving mice

We tested our hypothesis that, kinetically, triacylglycerol fatty acids in heterogeneously labeled adipocytes behave similarly to the whole fat pad triacylglycerol fatty acid during starvation in mice. Adipose triacylglycerol fatty acids were labeled with [1-14C]palmitate (complexed to albumin) by injection of a small bolus (2-5 microliter) into either epididymal or inguinal fat pads. Both 14C-labeled triacylglycerol fatty acid spec. act. and breath 14CO2 spec. act. were monitored 30 min after tracer injection and after 24-72 h starvation. Adipose triacylglycerol fatty acid spec. act. remained approximately constant during fasting, i.e., tracer and mass disappeared at similar rates. Negligible translocation of labeled triacylglycerol fatty acid from the injection site to other parts of the same fat pad or to distant fat pads occurred. Triacylglycerol fatty acid was mobilized more slowly from epididymal than from inguinal fat pads in two of three studies. Triacylglycerol fatty acid disappearance (loss) from inguinal fat pads was more replicable than from epididymal fat pads and more closely reflected the fall in whole body total lipid during starvation. The estimated percent of breath CO2-carbon derived from adipose triacylglycerol fatty acid increased from an average of approx. 32% in the postabsorptive state to about 77% after 48 h starvation. The data help to validate the direct tracer injection technique as a means of studying adipose triacylglycerol fatty acid turnover and oxidation. This approach should be particularly useful for studying the fate of adipose triacylglycerol fatty acid when it is mobilized. e.g., during states of inanition and starvation and in response to hormones and cancer-induced cachexia.     

Effects of palm oil and transesterified palm oil on chylomicron and VLDL triacylglycerol structures and postprandial lipid response

The effects of positional distribution of triacylglycerol (TAG) fatty acids to TAG structures in chylomicrons and VLDL, and to postprandial lipemia, were studied in 10 healthy premenopausal women using a 6-h oral fat load test and a randomized, double-blind cross-over design. Molecular level information of TAG regioisomerism was obtained with a tandem mass spectrometric method. The positional distribution of fatty acids in chylomicron TAGs was similar to the respective dietary fat; 79% of the analyzed regioisomers in palm oil and 84% of the analyzed regioisomers in transesterified oil were found in chylomicron TAGs 3 h after the oral fat loads. VLDL TAGs were equal after the two fat loads in all but one regioisomer. Similarities in the fatty acid compositions of chylomicron TAGs suggest that palmitic acid was absorbed equally from both test fats. The proportion of palmitoleic acid in the chylomicrons was increased. Fat with palmitic acid predominantly in the sn-1 and sn-3 positions caused a larger incremental area of total TAGs in plasma and reduced plasma insulin values at the beginning of the postprandial response (0-90 min) compared with fat with palmitic acid randomly distributed. The relationship between TAG molecular structures in dietary fats and in lipoproteins provides new means for understanding the effects of fatty acid positional distribution on human lipid metabolism.     

Arachidonic acid as a second messenger. Interactions with a GTP-binding protein of human neutrophils.

Arachidonic acid (20:4) and other cis-unsaturated fatty acids exert direct effects on a variety of cells, effects that do not depend on the metabolism of fatty acids via cyclooxygenase or lipoxygenase pathways. In these studies arachidonic acid and other cis-unsaturated fatty acids (but not trans-unsaturated or saturated fatty acids) increased the specific binding of the nonhydrolyzable analog of GTP, [35S]GTP gamma S, to purified neutrophil membrane preparations and elicited superoxide anion generation from intact neutrophils. There was a positive correlation (r = 0.70) between the capacity of fatty acids to increase nucleotide binding and to elicit the respiratory burst. Scatchard plot analysis of binding at equilibrium demonstrated an increase in the number of available GTP binding sites in the presence of 50 microM arachidonic acid. Nonsteroidal antiinflammatory agents interfered with the arachidonic acid effect on [35S]GTP gamma S binding. ADP-ribosylation of the pertussis toxin substrate Gi alpha within the plasmalemma-reduced specific [35S]GTP gamma S binding and blocked arachidonate-dependent enhancement of binding. Moreover, pertussis toxin treatment of intact neutrophils inhibited arachidonic acid-induced superoxide anion generation. The data indicate that arachidonic acid directly activates a GTP binding protein in the neutrophil plasma membrane and may thereby act as a second messenger in signal transduction.     

Secretion and storage of newly synthesized hepatic triacylglycerol fatty acids in vivo in different nutritional states and in diabetes.

Hepatic lipid synthesis was measured in rats in vivo with 3H2O, and the appearance of label in triacylglycerol and its constituent fatty acid and glycerol moieties was determined. In rats treated with Triton WR1339, the amount of newly synthesized fatty acid secreted as very-low-density lipoprotein (VLDL) triacylglycerol was greater during the dark phase of the diurnal cycle than during the light phase (11.3 versus 4.8 mumol of 3H2O/3 h per g of liver respectively). However, the total mass of VLDL triacylglycerol secreted remained constant, as did the amount of label in the secreted triacylglycerol glycerol. Newly synthesized fatty acids comprised only a small proportion of the total VLDL triacylglycerol fatty acids (TGFA) at both times (dark phase, 7.7%; light phase, 2.4%). Starvation for 24 h resulted in a small increase in the secretion of VLDL triacylglycerol. However, the contribution from newly synthesized fatty acids was decreased. Similar effects were observed in streptozotocin-diabetic animals. During the light and dark phases of the cycle, similar quantities of newly synthesized TGFA entered the hepatic cytosol, and these amounts were much smaller than those secreted as VLDL triacylglycerol. The mass of cytosolic triacylglycerol showed a diurnal variation, with a greater concentration during the light phase than in the dark. In diabetes, the mass of triacylglycerol was increased in the cytosol, as was the incorporation of labelled acylglycerol glycerol. Diabetes also abolished the diurnal variation in the quantity of cytosolic triacylglycerol. In each group of animals the specific radioactivity of the microsomal triacylglycerol was similar to that of the respective newly secreted plasma VLDL. The specific radioactivity of the cytosolic triacylglycerol was only 15.8% (dark phase) or 16.8% (light phase) that of the microsomal triacylglycerol. This increased to 35.5% in the starved animals and 40.2% in the diabetic animals.     

Fatty acid uptake and metabolism in a human intestinal cell line (Caco-2): comparison of apical and basolateral incubation

Free fatty acids can enter the enterocyte via the apical or basolateral plasma membrane. We have used the Caco-2 intestinal cell line to examine the polarity of free fatty acid uptake and metabolism in the enterocyte. Differentiated Caco-2 cells form polarized monolayers with tight junctions, and express the small intestine-specific enzymes sucrase and alkaline phosphatase. Cells were grown on permeable polycarbonate Transwell filters, thus allowing separate access to the apical and basolateral compartments. Total uptake of [3H]palmitate bound to bovine serum albumin (palmitate-BSA 4:1) was twofold higher (P less than 0.05 or less) at the apical surface than at the basolateral surface. The relative apical and basolateral membrane surface areas of the Caco-2 cells, as measured by partition of the fluorophore trimethylammonium-diphenylhexatriene TMA-DPH), was found to be 1:3. Thus, apical fatty acid uptake was sixfold higher than basolateral uptake per unit surface area. Analysis of metabolites after incubation with submicellar concentrations of [3H]palmitate showed that the triacylglycerol to phospholipid (TG:PL) ratio was higher for fatty acid added to the apical as compared to the basolateral compartment (20% at 60 min, P less than 0.025). Little fatty acid oxidation was observed. Preincubation with albumin-bound palmitate, alone or with monoolein, increased the incorporation of both apical and basolateral free fatty acids into TG. The results suggest that the net uptake of long-chain free fatty acids across the apical plasma membrane is greater than uptake across the basolateral membrane. In addition, a small increase in the TG:PL ratio for apically, compared to basolaterally, added free fatty acids suggests that polarity of metabolism occurs to a limited extent in Caco-2 enterocytes.     

Myocardial triacylglycerol fatty acid composition in diabetes mellitus

The compositions of myocardial triacylglycerol fatty acid (TGFA) and serum free fatty acids (sFFA) were examined in control and streptozotocin-induced diabetic rats. After 12 days of diabetes, the rats were killed and the hearts excised and perfusion-washed. Tissue lipids were extracted and fractioned by sequential column, thin-layer, and gas-liquid chromatography. Results showed a marked increase in total TGFA content of the diabetic myocardium. In addition, compositions of TGFA and sFFA were altered. The compositional changes were similar, involving a shift from 16-carbon fatty acids to 18-carbon fatty acids (primarily stearate and linoleate). The change in TGFA composition was reversible with insulin treatment.     

The contribution of serum triacylglycerol to hepatic triacylglycerol turnover in the starved rat.

The present study was undertaken to evaluate quantitatively the turnover of serum triacylglycerol (triglyceride) in the starved rat and to determine whether serum triacylglycerol recycled to liver contributes a significant fraction of the total hepatic triacylglycerol turnover. Serum was labelled in vitro with [3H]trioleoylglycerol (glycerol [3H]trioleate) to provide uniform labelling of all lipoprotein species. By using the curves describing disappearance of isotope from serum and its appearance in liver, rate constants for movement of triacylglycerol out of serum (0.29 min-1) and the uptake of serum triacylglycerol by liver (0.22 min-1) were calculated. The total rate of movement (flux) of triacylglycerol in these processes, the product of rate constant and serum pool size, was calculated to be 0.39 and 0.29 mg/min per 100 g body wt. respectively. A model is postulated for whole-body triacylglycerol metabolism consistent with the present data as well as most observations in the literature. From the model it can be predicted that: (1) the entire turnover of liver triacylglycerol in the starved rat can be accounted for on the basis of contributions from serum non-esterified fatty acid and serum triacylglycerol; (2) the entire turnover of the serum triacylglycerol pool can be accounted for quantitatively on the basis of contributions from intestine and liver; (3) the release rate for triacylglycerol from liver should be 0.34 to 0.35 mg/min per 100 g body wt.; (4) triacylglycerol synthesized by liver from non-esterified fatty acid of serum and by intestine can account quantitatively for the irreversible disposal rate of triacylglycerol from serum.     

Attenuation of adipocyte triacylglycerol hydrolase activity decreases basal fatty acid efflux

Fatty acids released from adipose triacylglycerol stores by lipolysis provide vertebrates with an important source of energy. We investigated the role of microsomal triacylglycerol hydrolase (TGH) in the mobilization of adipocyte triacylglycerols through inactivation of the TGH activity by RNA interference or chemical inhibition. Attenuation of TGH activity resulted in decreased basal but not isoproterenol-stimulated efflux of fatty acids from 3T3-L1 adipocytes. Lack of TGH activity was accompanied by accumulation of cellular triacylglycerols and cholesteryl esters without any changes in the expression of enzymes catalyzing triacylglycerol synthesis (diacylglycerol acyltransferases 1 and 2) or degradation (adipose triglyceride lipase and hormone-sensitive lipase). Inhibition of TGH-mediated lipolysis also did not affect insulin-stimulated Glut4 translocation from intracellular compartments to the plasma membrane or glucose uptake into adipocytes. These data suggest that TGH plays a role in adipose tissue triacylglycerol metabolism and may be a suitable pharmacological target for lowering fatty acid efflux from adipose tissue without altering glucose import.     

Changes in triacylglycerol, diacylglycerol and free fatty acids after fertilization in developing toad embryos

The content and fatty-acid composition of triacylglycerols, diacylglycerols and free fatty acids were analyzed from the unfertilized oocyte stage to the gastrula stage in the toad Bufo arenarum Hensel. Fertilization triggered a 30% and a 40% decrease in triacylglycerol and diacylglycerol, respectively. In contrast, free fatty acid increased continuously from oocyte to gastrula stage with an accumulation of palmitate predominating. However, the observed increase in free fatty acid was too small to account for the decreases in both neutral glycerides. The decrease in triacylglycerol might be a reflection of the activation of lipolytic enzymes and the subsequent oxidation of fatty acids to meet the increased metabolic energy requirements brought on by fertilization. The diminished diacylglycerol content due to fertilization may be accounted for, at least in part, by the utilization of diacylglycerol in the synthesis of membrane phospholipids, inasmuch as their decrease occurred simultaneously with an increase in phosphatidic acid. When cell-free homogenates taken from the three stages of development (unfertilized, fertilized and gastrula) were incubated in Tris-Ringer buffer for 90 min, free fatty acid accumulated. Triacylglycerol and diacylglycerol did not change substantially during this incubation period. This fact indicates that the free fatty acid released during incubation was not derived from neutral glycerides, but probably from membrane phospholipids. The release of free fatty acid was significantly greater in samples from the fertilized oocyte stage. The results described in this paper suggest that the synthesis of membrane phospholipids, including an enhanced turnover of the acyl moiety, plays a significant role in the metabolic events activated by fertilization.     

Modulation of voltage-dependent Ca channel current by arachidonic acid and other long-chain fatty acids in rabbit intestinal smooth muscle.

The effects of arachidonic acid (AA) and other long-chain fatty acids on voltage-dependent Ca channel current (ICa) were investigated, with the whole cell patch clamp method, in longitudinal smooth muscle cells of rabbit ileum. 10-30 microM AA caused a gradual depression of ICa. The inhibitory effect of AA was not prevented by indomethacin (10 microM) (an inhibitor of cyclooxygenase) or nordihydroguaiaretic acid (10 microM) (an inhibitor of lipoxygenase). 1-(5-Isoquinolinesulfonyl)-2-methylpiperazine (H7; 25-50 microM) or staurosporine (2 microM) (inhibitors of protein kinase C) did not block the AA-induced inhibition of ICa, and application of phorbol ester (a protein kinase C activator) (phorbol-12,13-dibutyrate, 0.2 microM) did not mimic the AA action. Some other cis-unsaturated fatty acids (palmitoleic, linoleic, and oleic acids) were also found to depress ICa, while a trans-unsaturated fatty acid (linolelaidic acid) and saturated fatty acids (capric, lauric, myristic, and palmitic acids) had no inhibitory effects on ICa. Myristic acid consistently increased the amplitude of ICa at negative membrane potentials. The present results suggest the possible role of AA, and perhaps other fatty acids, in the physiological and/or pathological modulation of ICa in smooth muscle.     

Palmitic acid uptake by the rat soleus muscle in vitro.

Abstract: The rate of fatty acid uptake, oxidation, and deposition in skeletal muscles in relation to total and unbound to albumin fatty acids concentration in the medium were investigated in the incubated rat soleus muscle. An immunohistochemical technique was applied to demonstrate whether the albumin-bound fatty acid complex from the medium penetrates well within all areas of the muscle strips. It was found that the percentage of incorporation of palmitic acid into intramuscular lipids was fairly constant, independently of the fatty acid concentration in the medium, and amounted to 63-72% for triacylglycerols, 7-12% for diacylglycerols-monoacylglycerols, and 19-26% for phospholipids. Both palmitic acid incorporation into the muscle triacylglycerol stores and its oxidation to CO2 closely correlated with an increase in both total and unbound to albumin fatty acid concentrations in the incubation medium. Under conditions of increased total but constant unbound to albumin palmitic acid concentrations, the incorporation of palmitic acid into triacylglycerols and its oxidation to CO2 were also increased, but to a lower extent. This supports the hypothesis that the cellular fatty acid metabolism depends not only on the availability of fatty acids unbound to albumin, but also on the availability of fatty acids complexed to albumin.     

Modification of CaCo-2 cell membrane fatty acid composition by eicosapentaenoic acid and palmitic acid: effect on cholesterol metabolism

Membrane fatty acid composition of CaCo-2 cells was modified by incubating the cells for 8 days in medium containing 100 microM eicosapentaenoic acid or palmitic acid. The effect of membrane fatty acid changes on cholesterol metabolism was then studied. Cells incubated with eicosapentaenoic acid had significant changes in membrane fatty acid composition with an accumulation of 20:5 and 22:5 and a reduction in monoenoic fatty acids compared to cells grown in palmitic acid. Intracellular cholesteryl esters could not be detected in CaCo-2 cells grown in the presence of the n-3 polyunsaturated fatty acid. In contrast, cells incubated with the saturated fatty acid contained 2 micrograms/mg protein of cholesteryl esters. Cells grown in eicosapentaenoic acid, however, accumulated significantly more triglycerides compared to cells modified with palmitic acid. The rate of oleic acid incorporation into triglycerides was significantly increased in cells incubated with eicosapentaenoic acid. CaCo-2 cells modified by eicosapentaenoic acid had lower rates of HMG-CoA reductase and ACAT activities compared to cells modified with palmitic acid. The incorporation of the two fatty acids into cellular lipids also differed. Palmitic acid was predominantly incorporated into cellular triglycerides, whereas eicosapentaenoic acid was preferentially incorporated into phospholipids with 60% of it in the phosphatidylethanolamine fraction. The data indicate that membrane fatty acid composition is significantly altered by growing CaCo-2 cells in eicosapentaenoic acid. These modifications in membrane fatty acid saturation are accompanied by a decrease in the rates of cholesterol synthesis and cholesterol esterification.     

Selective inhibition of long-chain fatty acid uptake in short-term cultured rat hepatocytes by an antibody to the rat liver plasma membrane fatty acid-binding protein

Uptake of long-chain fatty acids by short-term cultured hepatocytes was studied. Rat hepatocytes, which were cultured for 16 h on plastic dishes (3.6 X 10(6) cells/dish), were incubated with [3H]oleate in the presence of various concentrations of bovine serum albumin as a function of the concentration of unbound [3H]oleate in the medium. At 37 degrees C initial uptake velocity (V0) was saturable (Km = 9 X 10(-8) M; Vmax = 835 pmol/min per mg protein). V0 was temperature dependent with an optimum at 37 degrees C and markedly reduced at 4 degrees C and 70 degrees C. To evaluate the biologic significance of a previously isolated rat liver plasma membrane fatty acid-binding protein as putative carrier protein in the hepatocellular uptake of fatty acids, cultured hepatocytes were treated with a monospecific rabbit antibody (IgG-fraction) to this membrane protein or the IgG-fraction of the pre-immune serum as controls. Uptake kinetics of [3H]oleate in antibody pretreated short-term cultured hepatocytes revealed a depression of Vmax by 70%, while Km was only reduced by 16% compared to controls, indicating a predominant non-competitive type of inhibition. V0 of a variety of long-chain fatty acids (oleic acid, arachidonic acid, palmitic acid, stearic acid) was reduced by 56-69%, while V0 of [35S]sulfobromophthalein, [3H]cholic acid and [14C]taurocholic acid remained unaltered. These data support the concept that in the system of cultured hepatocytes, uptake of long-chain fatty acids is mediated by the rat liver plasma membrane fatty acid-binding protein.     

The irreversible disposal rate of free fatty acids in the plasma of fed and starved rats

1. The irreversible disposal rate coefficient for free fatty acids in the plasma of fed and starved rats was determined after a single intravenous injection of [1-(14)C]palmitic acid into each rat. The dose of labelled palmitic acid was given as a complex with (131)I-labelled albumin in rat serum. The total amount of [1-(14)C]palmitic acid remaining in the plasma was determined at short times after injection from the (14)C/(131)I ratio in the injected serum and in the collected plasma. The rate coefficient was determined from the area under the curve that describes the disappearance of [1-(14)C]palmitic acid with time from the plasma. Possible sources of error in these determinations are discussed. 2. The irreversible disposal rate coefficient was significantly higher in fed rats (2.07min(-1)) than in rats which had been starved for 24h (1.53min(-1)). The possible relationship between this difference and the processes whereby free fatty acids are removed from the plasma is discussed briefly. 3. An estimate of the irreversible disposal rate for free fatty acids in plasma was made from the concentration of free fatty acids in plasma and from the volume of distribution of (131)I-labelled albumin. The irreversible disposal rate was significantly lower in the fed state than in the starved.     

Influence of psychosomatic stress in pregnant guinea-pigs on fetal lipid metabolism

After a psychosomatic stress applied to pregnant guinea-pigs, 7 or 1 day before term, plasma cortisol and non-esterified fatty acid levels increased immediately in mother and fetus. Plasma levels of cortisol and non-esterified fatty acids in newborns of mothers stressed 1 day before term were lower than in newborns of control mothers. The prenatal stress changed composition of triacylglycerol and phospholipids in newborn liver by inhibiting the postnatal increase of triacylglycerol and phospholipid stearic acid and by inhibiting the postnatal decrease in phospholipid palmitic, palmitoleic, linolenic and arachidonic acids.     

Albumin and fatty acid effects on the stimulated production of 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine (PAF) by human polymorphonuclear leukocytes.

Production of platelet-activating factor (PAF) during opsonized zymosan stimulation of human polymorphonuclear leukocytes is dependent on the concentration of extracellular albumin and on the presence of exogenous fatty acids. Fatty acid-free albumin caused a concentration-dependent increase in PAF synthesis up to 5% albumin concentrations (w/v) where the amount of PAF produced was three- to four-fold higher than in controls containing no albumin. The addition of free fatty acids, particularly arachidonic acid and palmitic acid, to 5% fatty acid-free albumin media caused a concentration-dependent decrease in PAF synthesis. A 50% inhibition of PAF synthesis was observed at an arachidonic acid concentration of 120 microM and at a palmitic acid concentration of 100 microM. The inhibition of PAF production by palmitic acid was also dependent on the concentration of extracellular albumin. In 0.5% fatty acid-free albumin media, a palmitic acid concentration of 40 microM produced a 50% inhibition in PAF synthesis. The addition of palmitic acid did not affect the release of endogenous arachidonic acid during stimulation. In contrast, the addition of stearic acid up to 120 microM in 5% fatty acid-free albumin media had no effect on PAF production. The different inhibitory effects of palmitic acid and stearic acid on PAF production may be related to differences in intracellular utilization of these two fatty acids during cell stimulation.     

Biochemistry of development in insects. Incorporation of fatty acids into different lipid classes.

1. To study the different metabolic behaviour of various stages of development of the insect Ceratitis capitata, the incorporation of labelled decanoic, lauric, myristic, palmitic, stearic, oleic, and linoleic acids into triacylglycerols by insect homogenates was investigated. The time-course of incorporation of labelled fatty acids was firstly studied by using oleic acid; it showed that after 10 min of incubation the levels of radioactivity incorporated into triacylglycerols and those remaining in the free fatty acids were practically unchanged. 2. All labelled fatty acids were efficiently incorporated by larval homogenates; however, most of the radioactivity remained as free fatty acids in the presence of pharate adult homogenates, palmitic, and stearic acids being the most scarcely incorporated by this stage of development of the insect. 3. Plots of triacylglycerol and free fatty acid radioactivites versus the stage of development defined a crossing-zone in coincidence with the larval-pupal apolysis. This metabolic difference between larval and pharate adult homogenates could not be explained through differences in the acyl-CoA synthetase activity of the insect; this enzyme activity was notably higher in pharate adult homogenates than in the larval homogenates whatever would be the nature of the fatty acid. 4. [14C]Triolein was scarcely hydrolyzed by both larval and pharate adult homogenates. 5. Double-label experiments were carried out by incorporating either [3H]oleic acid or [3H]-palmitic acid and [14C]glycerol 3-phosphate by larval and pharate adult homogenates at different incubation intervals. Diacylglycerols, triacylglycerols, and phosphoglycerides were isolated and the 14C/3H molar ratio calculated. Results suggest the existence of a different acyltransferase activity in the different stages of development of the insect.