Turnover of individual free fatty acids in man.

The use of tracer fatty acids in the study of free fatty acid (FFA) metabolism in man is reviewed in light of the present knowledge of the metabolism of individual FFA. The fractional turnovers of palmitic, stearic and oleic acids are very similar and close to the values reported for the total plasma FFA. The fractional turnover of the polyunsaturated arachidonic acid is higher and there is also a sex difference, women showing 70% higher values than men. Splanchnic fractional uptake differs considerably among the individual FFA, while muscle uptake is virtually independent of the chemical structure of the fatty acid. It is concluded that labeled oleic or palmitic acid can be used as tracers for the total FFA fraction when studying the whole body turnover in the postabsorptive state. In other situations, conclusions from result of tracer experiments should be limited to the particular fatty acid studied. For measurements of splanchnic FFA metabolism, no single fatty acid seems to be adequate as a tracer for the total FFA fraction.     

Turnover of plasma oleic acid measured by radio-gas chromatography.

Gas-liquid chromatography with radioactivity detection (Radio-GLC) was investigated as an analytical means of determining the fractional turnover rates of plasma free fatty acids. For this purpose normal dogs were infused with 1.838 muCi/min of [1-14C]oleic acid complexed with albumin and plasma samples were taken at 0 to 110 minutes. The plasma free fatty acids were isolated by a modified Dole extraction and the methyl esters, prepared by diazomethylation, were identified and quantitated by GLC and radio-GLC using radioactive methyl heptadecanoate as internal standard. The study demonstrates that physiologically feasible infusion rates and loads of radioactive acids can be found which permit accurate analyses of plasma free fatty acids by radio-GLC. During a 2-hour infusion no labeled acid other than oleic appeared in plasma indicating that the method could be used to study the turnover of a mixture of fatty acids simultaneously. These results also indicate that conventional methods of determination of radioactivity in purified extracts can be employed without concern for recycling of label among the fatty acids, at least over short periods of time. The radio-GLC technique described yields approximately 20% higher fractional turnover times for oleic acid than do standard methods.     

Effect of gender on lipid kinetics during endurance exercise of moderate intensity in untrained subjects

We evaluated lipid metabolism during 90 min of moderate-intensity (50% VO(2) peak) cycle ergometer exercise in five men and five women who were matched on adiposity (24 +/- 2 and 25 +/- 1% body fat, respectively) and aerobic fitness (VO(2) peak: 49 +/- 2 and 47 +/- 1 ml x kg fat-free mass(-1) x min(-1), respectively). Substrate oxidation and lipid kinetics were measured by using indirect calorimetry and [(13)C]palmitate and [(2)H(5)]glycerol tracer infusion. The total increase in glycerol and free fatty acid (FFA) rate of appearance (R(a)) in plasma during exercise (area under the curve above baseline) was approximately 65% greater in women than in men (glycerol R(a): 317 +/- 40 and 195 +/- 33 micromol/kg, respectively; FFA R(a): 652 +/- 46 and 453 +/- 70 micromol/kg, respectively; both P < 0.05). Total fatty acid oxidation was similar in men and women, but the relative contribution of plasma FFA to total fatty acid oxidation was higher in women (76 +/- 5%) than in men (46 +/- 5%; P < 0.05). We conclude that lipolysis of adipose tissue triglycerides during moderate-intensity exercise is greater in women than in men, who are matched on adiposity and fitness. The increase in plasma fatty acid availability leads to a greater rate of plasma FFA tissue uptake and oxidation in women than in men. However, total fat oxidation is the same in both groups because of a reciprocal decrease in the oxidation rate of fatty acids derived from nonplasma sources, presumably intramuscular and possibly plasma triglycerides, in women.     

Oxidation of nonplasma fatty acids during exercise is increased in women with abdominal obesity.

We evaluated plasma fatty acid availability and plasma and whole body fatty acid oxidation during exercise in five lean and five abdominally obese women (body mass index = 21 +/- 1 vs. 38 +/- 1 kg/m(2)), who were matched on aerobic fitness, to test the hypothesis that obesity alters the relative contribution of plasma and nonplasma fatty acids to total energy production during exercise. Subjects exercised on a recumbent cycle ergometer for 90 min at 54% of their peak oxygen consumption. Stable isotope tracer methods ([(13)C]palmitate) were used to measure fatty acid rate of appearance in plasma and the rate of plasma fatty acid oxidation, and indirect calorimetry was used to measure whole body substrate oxidation. During exercise, palmitate rate of appearance increased progressively and was similar in obese and lean groups between 60 and 90 min of exercise [3.9 +/- 0.4 vs. 4.0 +/- 0.3 micromol. kg fat free mass (FFM)(-1). min(-1)]. The rate of plasma fatty acid oxidation was also similar in obese and lean subjects (12.8 +/- 1.7 vs. 14.5 +/- 1.8 micromol. kg FFM(-1). min(-1); P = not significant). However, whole body fatty acid oxidation during exercise was 25% greater in obese than in lean subjects (21.9 +/- 1.2 vs. 17.5 +/- 1.6 micromol. kg FFM(-1). min(-1); P < 0.05). These results demonstrate that, although plasma fatty acid availability and oxidation are similar during exercise in lean and obese women, women with abdominal obesity use more fat as a fuel by oxidizing more nonplasma fatty acids.     

Studies on plasma free-fatty-acid metabolism and triglyceride synthesis of brown adipose tissue in vivo during cold-induced thermogenesis of the newborn rabbit.

Parameters of plasma free fatty acid metabolism (pool size, half time, disappearance rate, turnover time and absolute turnover rate), the influx of plasma free fatty acids into the glycerides of brown adipose tissue and the pathway of triglyceride synthesis in brown adipose tissue (glycerol-1-phosphate versus monoglyceride pathway) were examined after intravenous injection of [1-14C]palmitate in newborn rabbits. In the thermoneutral environment of 35 degrees C the turnover rate of plasma free fatty acids was 10.20 mumol/min per 100 g body weight and its flux into the glycerides of brown adipose tissue 0.367 mumol/min per 100 g body weight. Cold exposure at an ambient temperature of 20 degrees C caused a decrease to 5.84 mumol/min and 0.207 mumol/min per 100 g body weight, respectively. Both under basal conditions at an ambient temperature of 35 degrees C and under cold-induced thermogenesis at an ambient temperature of 20 degrees C triglyceride synthesis in brown adipose tissue ran through the glycerol 1-phosphate pathway.     

Isotope tracer measures of meal fatty acid metabolism: reproducibility and effects of the menstrual cycle

Oxidation and adipose tissue uptake of dietary fat can be measured by adding fatty acid tracers to meals. These studies were conducted to measure between-study variability of these types of experiments and assess whether dietary fatty acids are handled differently in the follicular vs. luteal phase of the menstrual cycle. Healthy normal-weight men (n = 12) and women (n = 12) participated in these studies, which were block randomized to control for study order, isotope ([3H]triolein vs. [14C]triolein), and menstrual cycle. Energy expenditure (indirect calorimetry), meal fatty acid oxidation, and meal fatty acid uptake into upper body and lower body subcutaneous fat (biopsies) 24 h after the experimental meal were measured. A greater portion of meal fatty acids was stored in upper body subcutaneous adipose tissue (24 +/- 2 vs. 16 +/- 2%, P < 0.005) and lower body fat (12 +/- 1 vs. 7 +/- 1%, P < 0.005) in women than in men. Meal fatty acid oxidation (3H2O generation) was greater in men than in women (52 +/- 3 vs. 45 +/- 2%, P = 0.04). Leg adipose tissue uptake of meal fatty acids was 15 +/- 2% in the follicular phase of the menstrual cycle and 10 +/- 1% in the luteal phase (P = NS). Variance in meal fatty acid uptake was somewhat (P = NS) greater in women than in men, although menstrual cycle factors did not contribute significantly. We conclude that leg uptake of dietary fat is slightly more variable in women than in men, but that there are no major effects of menstrual cycle on meal fatty acid disposal.     

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.     

Role of triglycerides in endothelial cell arachidonic acid metabolism

Arachidonic acid was incorporated into triglycerides by cultured bovine endothelial cells in a time- and concentration-dependent manner. At 75 microM or higher, more arachidonic acid was incorporated into triglycerides than into phospholipids. The triglyceride content of the cells increased as much as 5.5-fold, cytoplasmic inclusions appeared, and arachidonic acid comprised 22% of the triglyceride fatty acids. Triglyceride turnover occurred during subsequent maintenance culture; there was a 60% decrease in the radioactive arachidonic acid contained in triglycerides and a 40% decrease in triglyceride content in 6 hr. Most of the radioactivity was released into the medium as free fatty acid. The turnover of arachidonic acid, but not oleic acid in cellular triglycerides, decreased when supplemental fatty acid was added to the maintenance medium. Incorporation and turnover of radioactive arachidonic acid in triglycerides also was observed in human skin fibroblasts, 3T3-L1 cells, and MDCK cells. Other fatty acids were incorporated into triglycerides by the endothelial cells; the amounts after a 16-hr incubation with 50 microM fatty acid were 20:3 greater than 20:4 greater than 18:1 greater than 18:2 greater than 22:6 greater than 16:0 greater than 20:5. These findings indicate that triglyceride formation and turnover can play a role in the fatty acid metabolism of endothelial cells and that arachidonic acid can be stored in endothelial cell triglycerides.     

Excess body fat in men decreases plasma fatty acid availability and oxidation during endurance exercise

The effect of relative body fat mass on exercise-induced stimulation of lipolysis and fatty acid oxidation was evaluated in 15 untrained men (5 lean, 5 overweight, and 5 obese with body mass indexes of 21 +/- 1, 27 +/- 1, and 34 +/- 1 kg/m2, respectively, and %body fat ranging from 12 to 32%). Palmitate and glycerol kinetics and substrate oxidation were assessed during 90 min of cycling at 50% peak aerobic capacity (VO2 peak) by use of stable isotope-labeled tracer infusion and indirect calorimetry. An inverse relationship was found between %body fat and exercise-induced increase in glycerol appearance rate relative to fat mass (r2 = 0.74; P < 0.01). The increase in total fatty acid uptake during exercise [(micromol/kg fat-free mass) x 90 min] was approximately 50% smaller in obese (181 +/- 70; P < 0.05) and approximately 35% smaller in overweight (230 +/- 71; P < 0.05) than in lean (354 +/- 34) men. The percentage of total fatty acid oxidation derived from systemic plasma fatty acids decreased with increasing body fat, from 49 +/- 3% in lean to 39 +/- 4% in obese men (P < 0.05); conversely, the percentage of nonsystemic fatty acids, presumably derived from intramuscular and possibly plasma triglycerides, increased with increasing body fat (P < 0.05). We conclude that the lipolytic response to exercise decreases with increasing adiposity. The blunted increase in lipolytic rate in overweight and obese men compared with lean men limits the availability of plasma fatty acids as a fuel during exercise. However, the rate of total fat oxidation was similar in all groups because of a compensatory increase in the oxidation of nonsystemic fatty acids.     

Studies on the synthesis of liver phospholipids and the turnover of plasma phospholipids in non pregnant female rats using radioactive palmitate.

Using the tracer method and a compartmental model we found that 0.9 mumoles plasma free fatty acids per min are esterified to liver phospholipids. The turnover rate of plasma phospholipid fatty acids was determined to be 0.5 mumoles phospholipid fatty acids per min. The turnover time of the plasma phospholipid fatty acids was calculated to be 0.9 hours. The results indicate that only 69 per cent of plasma free fatty acids esterified to liver phospholipids are secreted by the liver into the plasma.     

Insulin and leptin do not affect fatty acid uptake and metabolism in human placental choriocarcinoma (BeWo) cells

Placental transport of long chain polyunsaturated fatty acids is important for fetal growth and development. In order to examine the effects of leptin and insulin on fatty acid uptake by the placenta, placental choriocarcinoma (BeWo) cells were used. BeWo cells were incubated for 5h at 37 degrees C in the absence or presence of different concentrations of insulin (0.6, 60, and 100 ng) or leptin (10 ng) with 200 microM of various radiolabeled fatty acids (docosahexaenoic acid, arachidonic acid, eicosapentaenoic acid, and oleic acid, mixed with 1:1 bovine serum albumin (fat free). After incubation, the uptake and distribution of these fatty acids into different cellular lipid fractions were determined. The uptakes of oleic, eicosapentaenoic, arachidonic, and docosahexaenoic acids were 15.36+/-4.1, 19.95+/-3.6, 28.56+/-8.1, and 62.25+/-9.5 nmol/mg of protein, respectively, in BeWo cells. Incubation of these cells with insulin (0.6 or 60 ng/ml) or leptin (10 ng/ml) did not significantly alter uptake of any of these fatty acids (P>0.5). Insulin or leptin also did not affect beta oxidation of fatty acids in these cells. In contrast, leptin (10 ng/ml) and insulin (0.60 ng/ml)) stimulated the uptake of oleic acid (7.4+/-2.3 nmol/mg protein) in human adipose cells, SGBS cells by 1.28- and 2.48-fold (P<0.05), respectively. The distribution of fatty acids in different cellular lipid fractions was also not affected by these hormones. Our data indicate that unlike adipose tissue, fatty acid uptake and metabolism in placental trophoblasts is not regulated by insulin or leptin.     

Measurement of arachidonic acid liberation in thrombin-stimulated human platelets. Use of agents that inhibit both the cyclooxygenase and lipoxygenase enzymes

The formation of radiolabelled oxygenated products of arachidonic acid in thrombin-stimulated, [3H]arachidonic acid-prelabelled human platelets is inhibited in a concentration-dependent manner by BW 755C (3-amino-1-[m-(trifluoromethyl)phenyl]-2-pyrazoline) or propyl gallate, both of which are combined inhibitors of lipoxygenase and cyclooxygenase. These compounds do not inhibit the thrombin-induced decrease in the radioactivity of platelet phospholipids but, instead, allow the accumulation of free radiolabelled arachidonic acid. Thrombin causes an increase in the levels of free, endogenous palmitic, stearic, oleic, linoleic and arachidonic acids of up to 10 nmol/10(9) platelets. In the presence of BW 755C or propyl gallate, further increases in the level of free arachidonic acid, of 20-50 nmol/10(9) platelets, occur. The enzyme inhibitors do not affect the accumulation of the other free fatty acids. The increase in arachidonic acid is optimal at 1 U/ml thrombin and 60% complete by 1 min at 37 degrees C. In the platelets from eight donors, the average increases in free fatty acids (in nmol/10(9) platelets) induced by 5 U/ml thrombin in 5 min at 37 degrees C in the presence of 100 microM BW 755C were 1 for linoleic acid, 3.6 for oleic acid, 4.5 for palmitic acid, 7.6 for stearic acid and 32.0 for arachidonic acid.     

Basal muscle intracellular amino acid kinetics in women and men

Sexual dimorphism in skeletal muscle mass is apparent, with men having more muscle mass and larger individual muscle cells. However, no sex-based differences have been detected in blood forearm phenylalanine turnover, although whole body leucine oxidation has been reported to be greater in men than in women. We hypothesized that sex differences in intracellular amino acid turnover may account for these discrepancies, with men having a higher intracellular turnover than women. We studied young, healthy women (women, n = 8) and men (men, n = 10) following an overnight fast. Phenylalanine, leucine, and alanine muscle intracellular kinetics were assessed using stable isotope methodologies, femoral arteriovenous blood sampling, and muscle biopsies. Muscle intracellular amino acid kinetics were reported relative to both leg volume and lean leg mass because of sex differences in leg volume and in muscle and fat distribution. When expressed per leg volume (nmol.min(-1).100 ml leg volume(-1)), phenylalanine net balance (women: -16 +/- 4, men: -31 +/- 5), release from proteolysis in the blood (women: 46 +/- 9, men: 75 +/- 10) and intracellular availability (women: 149 +/- 23, men: 241 +/- 35), and alanine production, utilization, and intracellular availability were higher in men (P < 0.05). However, when the kinetic parameters were normalized per unit of lean leg mass, all differences disappeared. Muscle fractional synthetic rate was also not different between women and men. We conclude that there are no sex-based differences in basal muscle intracellular amino acid turnover when the data are normalized by lean mass. It remains to be determined if there are sex differences in intracellular amino acid metabolism following anabolic or catabolic stimuli.     

The effect of a free radical scavenger and platelet-activating factor antagonist on FFA accumulation in post-ischemic canine brain

The effects of the platelet-activating factor antagonist BN 50739 and a free radical scavenger dimethyl sulfoxide on the accumulation of free fatty acids in post-ischemic canine brain are reported. Following 14 min of complete normothermic ischemia and 60 min of reperfusion, the total brain FFAs were approximately 150% higher than in the control group (p<0.05). Perfusion with the platelet-activating factor antagonist BN50739 in its diluent dimethyl sulfoxide during 60 min of post-ischemic reoxygenation resulted in a 61.8% (p<0.01) reduction in the total brain free fatty acid accumulation. Palmitic, stearic, oleic, linoleic, and arachidonic acids decreased by 53.8%, 63.5%, 69.0%, 47.4%, and 57.2%, respectively. Although dimethyl sulfoxide alone caused stearic and arachidonic acids to return to the normal concentration range, BN 50739 had a significant influence on recovery of palmitic, oleic, and linoleic acids and was previously shown to provide significant therapeutic protection against damage to brain mitochondria following an ischemic episode. Because free fatty acid accumulation is one of the early phenomena in cerebral ischemia, this study provides evidence to support the hypothesis that both platelet-activating factor and free radicals are involved in initiating cerebral ischemic injury.     

Multiple Interactions of Unsaturated Fatty Acids with Opiate and Ouabain Binding Sites and β-Adrenergic Sensitive Adenylate Cyclase System

Abstract

The unsaturated fatty acids oleic, linoleic and arachidonic inhibited binding of ligands to the ouabain, opiate, and β-adrenergic plasma membrane receptors. Low concentrations of fatty acids slightly increased the binding of ouabain to its binding sites. The effect of these fatty acids on β-adrenergic sensitive adenylate cyclase was more complex. 0.2–0.3 mM fatty acids increased adenylate cyclase activity, while higher concentrations of arachidonic and linoleic acids, but not oleic acid     

A long-lasting facilitation of hippocampal neurotransmission via a phospholipase A2 signaling pathway.

Phospholipase A2, which is linked to a protein kinase C pathway, hydrolyzes phosphatidylcholine into cis-unsaturated free fatty acids and lysophosphatidylcholine (lysoPC). The present study investigated the effect of the free fatty acids, such as arachidonic, oleic, linoleic, and linolenic acid, and lysoPC on neurotransmission by monitoring population spikes (PSs) from the granular cell layer of rat hippocampal slices. All the free fatty acids and lysoPC examined here gradually increased PS amplitude to a different extent, the effect being evident 60 min after treatment. No significant synergistic enhancement in the PS amplitude was not induced by arachidonic acid following oleic acid, linoleic acid or lysoPC. The results of the present study, thus, demonstrate that phospholipase A2-linked free fatty acids and lysoPC are employed in the sustained facilitation of hippocampal neurotransmission, suggesting a significant role of a phospholipase A2 signaling pathway in the neuroplasticity.     

Fatty acid transduction of nitric oxide signaling: multiple nitrated unsaturated fatty acid derivatives exist in human blood and urine and serve as endogenous peroxisome proliferator-activated receptor ligands

Mass spectrometric analysis of human plasma and urine revealed abundant nitrated derivatives of all principal unsaturated fatty acids. Nitrated palmitoleic, oleic, linoleic, linolenic, arachidonic and eicosapentaenoic acids were detected in concert with their nitrohydroxy derivatives. Two nitroalkene derivatives of the most prevalent fatty acid, oleic acid, were synthesized (9- and 10-nitro-9-cis-octadecenoic acid; OA-NO2), structurally characterized and determined to be identical to OA-NO2 found in plasma, red cells, and urine of healthy humans. These regioisomers of OA-NO2 were quantified in clinical samples using 13C isotope dilution. Plasma free and esterified OA-NO2 concentrations were 619 +/- 52 and 302 +/- 369 nm, respectively, and packed red blood cell free and esterified OA-NO2 was 59 +/- 11 and 155 +/- 65 nm. The OA-NO2 concentration of blood is approximately 50% greater than that of nitrated linoleic acid, with the combined free and esterified blood levels of these two fatty acid derivatives exceeding 1 microm. OA-NO2 is a potent ligand for peroxisome proliferator activated receptors at physiological concentrations. CV-1 cells co-transfected with the luciferase gene under peroxisome proliferator-activated receptor (PPAR) response element regulation, in concert with PPARgamma, PPARalpha, or PPARdelta expression plasmids, showed dose-dependent activation of all PPARs by OA-NO2. PPARgamma showed the greatest response, with significant activation at 100 nm, while PPARalpha and PPARdelta were activated at approximately 300 nm OA-NO2. OA-NO2 also induced PPAR gamma-dependent adipogenesis and deoxyglucose uptake in 3T3-L1 preadipocytes at a potency exceeding nitrolinoleic acid and rivaling synthetic thiazo-lidinediones. These data reveal that nitrated fatty acids comprise a class of nitric oxide-derived, receptor-dependent, cell signaling mediators that act within physiological concentration ranges.     

Comparison of thermoregulatory responses between men and women immersed in cold water.

Eleven women (age = 24.4 +/- 6.3 yr, mass = 65.0 +/- 7.8 kg, height = 167 +/- 8 cm, body fatness = 22.4 +/- 5.9%, mean +/- SD) were immersed to neck level in 18 degrees C water for up to 90 min for comparison of their thermal responses with those of men (n = 14) in a previous similarly conducted protocol. Metabolic rate increased about three times resting levels in men and women, whereas the rate of rectal temperature cooling (DeltaT(re)/Deltat) in women (0.47 degrees C/h) was about one-half that in men. With use of all data, DeltaT(re)/Deltat correlates with the ratio of body surface area to size and the metabolic rate of shivering correlates inversely to the square root of body fatness. No significant gender differences in total metabolic heat production normalized for body mass or surface area were found among subjects who completed 90 min of immersion (9 women and 7 men). Nor was there a gender difference in the overall percent contribution ( approximately 60%) of fat oxidation to total heat production. Blood concentrations of free fatty acids, glycerol, beta-hydroxybutyrate, and lactate increased significantly during the 90-min immersion, whereas muscle glycogen sampled from the right quadriceps femoris vastus lateralis decreased (free fatty acids, glycerol, and beta-hydroxybutyrate were higher in women). When the subjects were subgrouped according to similar body fatness and 60 min of immersion (6 women and 5 men), no significant gender differences emerged in DeltaT(re)/Deltat, energy metabolism, and percent fat oxidation. These findings suggest that no gender adjustments are necessary for prediction models of cold response if body fatness and the ratio of body surface area to size are taken into account and that a potential gender advantage with regard to carbohydrate sparing during cold water immersion is not supported.     

Distribution of phospholipid molecular species containing arachidonic acid and cholesterol in V79-UF cells

V79-UF cells were isolated from Chinese hamster V79 cells as a cell line that requires exogenous unsaturated fatty acids for growth. V79-UF cells incorporated arachidonic acid into phospholipids. The molecular species of diacyl phosphatidylcholine and phosphatidylethanolamine containing arachidonic acid comprised 61.4 and 70.5% of the total phospholipid molecular species in total membranes and 58.1 and 64.7% in plasma membrane, respectively. Polyunsaturated molecular species were distributed in a higher amount in the intracellular membranes than in the plasma membrane. No significant difference was seen in the diffusion coefficient between the plasma membranes from cells supplemented with oleic and arachidonic acids in spite of a distinct difference in the degree of unsaturation between the molecular species of these plasma membranes. The amount of cholesterol in the plasma membrane was higher in the cells grown in the presence of arachidonic acid than in those grown in the presence of oleic acid.