Plasma Arachidonic Acid Concentrations Research Articles

Investigating the plasma-liver-brain axis of omega-3 fatty acid metabolism in mouse knock-in for the human apolipoprotein E epsilon 4 allele

The metabolism of docosahexaenoic acid (DHA), an omega-3 fatty acid, is different in carriers of APOE4, the main genetic risk factor for late-onset Alzheimer's disease. The brain relies on the plasma DHA pool for its need, but the plasma-liver-brain axis in relation to cognition remains obscure. We hypothesized that this relationship is compromised in APOE4 mice considering the differences in fatty acid metabolism between APOE3 and APOE4 mice. Male and female APOE3 and APOE4 mice were fed either a diet enriched with DHA (0.7 g DHA/100 g diet) or a control diet for 8 months. There was a significant genotype × diet interaction for DHA concentration in the liver and adipose tissue. In the cortex, a genotype effect was found where APOE4 mice had a higher concentration of DHA than APOE3 mice fed the control diet. There was a significant genotype × diet interaction for the liver and hippocampal arachidonic acid (AA). APOE4 mice had 20–30% lower plasma DHA and AA concentrations than APOE3 mice, independent of diet. Plasma and liver DHA levels were significantly correlated in APOE3 and APOE4 mice. In APOE4 mice, there was a significant correlation between plasma, adipose tissues, cortex DHA and the Barnes maze and/or with a better recognition index. Moreover, higher AA levels in the liver and the hippocampus of APOE4 mice were correlated with lower cognitive performance. Our results suggest that there is a plasma-liver-brain axis of DHA that is modified in APOE4 mice. Moreover, our data support that APOE4 mice rely more on plasma DHA than APOE3 mice, especially in cognitive performance. Any disturbance in plasma DHA metabolism might have a greater impact on cognition in APOE4 carriers.

α-lipoic acid ameliorates inflammation state and oxidative stress by reducing the content of bioactive lipid derivatives in the left ventricle of rats fed a high-fat diet

Lipid mediators derived from arachidonic acid (AA) are implicated with the occurrence of inflammation and oxidative stress. The current knowledge of AA metabolism focuses on searching for the therapeutic strategy to subvert affected AA metabolism. The aim of our study was to evaluate the potential protective effect of chronic α-lipoic acid (α-LA) supplementation on myocardial inflammation state and oxidative stress in obesity-related cardiovascular dysfunction. The experiment was carried out on male Wistar rats receiving a standard or a high-fat diets with intragastric α-LA administration for 8 weeks. Plasma and myocardial AA concentrations were determined using the gas-liquid chromatography (GLC). The Western blot technique was used to examine the expression of proteins from the inflammatory pathway. The content of selected cytokines, inflammatory mediators, and oxidative stress indicators was detected by the ELISA, colorimetric, and multiplex assay kits. Our results revealed that α-LA caused a notable reduction in AA content, mainly in the phospholipid fraction with a simultaneous diminishment in the synthesis of pro-inflammatory mediators, i.e., prostaglandin E2, leukotrienes B4 and C4 by decreasing the expression of COX-2 and 5-LOX. α-LA also augmented the level of antioxidative SOD2 and GSH and decreased the level of lipid peroxidation products, which improved oxidative system impairment in the left ventricle tissue. The data clearly showed that α-lipoic acid has a significant role in inflammation and oxidative stress development ameliorating the risk of cardiac obesity induced by high-fat feeding.

Electronic and Tobacco Cigarettes Alter Polyunsaturated Fatty Acids and Oxidative Biomarkers.

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Postpartum meloxicam administration alters plasma haptoglobin, polyunsaturated fatty acid, and oxylipid concentrations in postpartum ewes

BackgroundPostpartum inflammation is a natural and necessary response; however, a dysfunctional inflammatory response can be detrimental to animal productivity. The objective of this study was to determine the effects of a non-steroidal anti-inflammatory drug (meloxicam) on ewe postpartum inflammatory response, ewe plasma polyunsaturated fatty acid and oxylipid concentrations, and lamb growth.ResultsAfter lambing, 36 Hampshire and Hampshire × Suffolk ewes were sequentially assigned within type of birth to control (n = 17) or meloxicam orally administered on d 1 and 4 of lactation (MEL; 90 mg, n = 19). Milk and blood samples were collected on d 1 (prior to treatment) and d 4. Milk glucose-6-phosphate was not affected by MEL. Plasma haptoglobin (Hp) concentrations were less for MEL ewes; control ewes with greater d 1 Hp concentrations had elevated Hp on d 4, but this was not the case for MEL-treated ewes. Treatment with MEL increased plasma arachidonic acid concentration by more than 4-fold in ewes rearing singles but decreased concentrations of 9,10-dihydroxyoctadecenoic acid, prostaglandin F2α, 8-iso-prostaglandin E2, and 8,9-dihydroxyeicosatetraenoic acid. Nine oxylipids in plasma had interactions of treatment with d 1 Hp concentration, all of which revealed positive associations between d 1 Hp and d 4 oxylipid concentrations for CON, but neutral or negative relationships for MEL. MEL decreased 13-hydroxyoctadecadienoic acid:13-oxooctadecadienoic acid ratio and tended to increase 9-hydroxyoctadecadienoic acid:9-oxooctadecadienoic acid ratio (both dependent on d 1 values), indicating progressive metabolism of linoleic acid-derived oxylipids occurred by enzymatic oxidation after MEL treatment. Meloxicam reduced oxylipids generated across oxygenation pathways, potentially due to an improved redox state.ConclusionsPostpartum MEL treatment of ewes decreased plasma concentrations of Hp and several oxylipids, with the greatest impact in ewes with biomarkers reflecting a greater inflammatory state before treatment. Anti-inflammatory strategies may help resolve excessive postpartum inflammation in some dams.

Lipoprotein(a) concentration is associated with plasma arachidonic acid in subjects with familial hypercholesterolaemia.

Elevated lipoprotein(a) (Lp(a)) is associated with CVD and is mainly genetically determined. Studies suggest a role of dietary fatty acids (FA) in the regulation of Lp(a); however, no studies have investigated the association between plasma Lp(a) concentration and n-6 FA. We aimed to investigate whether plasma Lp(a) concentration was associated with dietary n-6 FA intake and plasma levels of arachidonic acid (AA) in subjects with familial hypercholesterolaemia (FH). We included FH subjects with (n 68) and without (n 77) elevated Lp(a) defined as ≥75 nmol/l and healthy subjects (n 14). Total FA profile was analysed by GC-flame ionisation detector analysis, and the daily intake of macronutrients (including the sum of n-6 FA: 18 : 2n-6, 20 : 2n-6, 20 : 3n-6 and 20 : 4n-6) were computed from completed FFQ. FH subjects with elevated Lp(a) had higher plasma levels of AA compared with FH subjects without elevated Lp(a) (P = 0·03). Furthermore, both FH subjects with and without elevated Lp(a) had higher plasma levels of AA compared with controls (P < 0·001). The multivariable analyses showed associations between dietary n-6 FA intake and plasma levels of AA (P = 0·02) and between plasma levels of Lp(a) and AA (P = 0·006). Our data suggest a novel link between plasma Lp(a) concentration, dietary n-6 FA and plasma AA concentration, which may explain the small diet-induced increase in Lp(a) levels associated with lifestyle changes. Although the increase may not be clinically relevant, this association may be mechanistically interesting in understanding more of the role and regulation of Lp(a).

Marked elevations in pro-inflammatory polyunsaturated fatty acid metabolites in females with irritable bowel syndrome

Irritable bowel syndrome (IBS) is the most common functional gastrointestinal disorder referred to gastroenterologists. Although the pathophysiology remains unclear, accumulating evidence points to the presence of low-level immune activation both in the gut and systemically. Circulating polyunsaturated fatty acids (PUFA) have recently attracted attention as being altered in a variety of disease states. Arachidonic acid (AA), in particular, has been implicated in the development of a pro-inflammatory profile in a number of immune-related disorders. AA is the precursor of a number of important immunomodulatory eicosanoids, including prostaglandin E(2) (PGE(2)) and leukotriene B(4) (LTB(4)). We investigated the hypothesis that elevated plasma AA concentrations in plasma contribute to the proposed pro-inflammatory profile in IBS. Plasma AA and related PUFA were quantified by gas chromatography analysis in IBS patients and controls. Both PGE(2) and LTB(4) were measured in serum using commercially available ELISA assays. AA concentrations were elevated in our patient cohort compared with healthy controls. Moreover, we demonstrated that this disturbance in plasma AA concentrations leads to downstream elevations in eicosanoids. Together, our data identifies a novel proinflammatory mechanism in irritable bowel syndrome and also suggests that elevated arachidonic acid levels in plasma may serve as putative biological markers in this condition.

Distribution, interconversion, and dose response of n−3 fatty acids in humans

n-3 Fatty acids have important visual, mental, and cardiovascular health benefits throughout the life cycle. Biodistribution, interconversion, and dose response data are reviewed herein to provide a basis for more rational n-3 dose selections. Docosahexaenoic acid (DHA) is the principal n-3 fatty acid in tissues and is particularly abundant in neural and retinal tissue. Limited storage of the n-3 fatty acids in adipose tissue suggests that a continued dietary supply is needed. A large proportion of dietary alpha-linolenic acid (ALA) is oxidized, and because of limited interconversion of n-3 fatty acids in humans, ALA supplementation does not result in appreciable accumulation of long-chain n-3 fatty acids in plasma. Eicosapentaenoic acid (EPA) but not DHA concentrations in plasma increase in response to dietary EPA. Dietary DHA results in a dose-dependent, saturable increase in plasma DHA concentrations and modest increases in EPA concentrations. Plasma DHA concentrations equilibrate in approximately 1 mo and then remain at steady state throughout supplementation. DHA doses of approximately 2 g/d result in a near maximal plasma response. Both dietary DHA and EPA reduce plasma arachidonic acid concentrations. Tissue contents of DHA and EPA also increase in response to supplementation with these fatty acids. Human milk contents of DHA are dependent on diet, and infant DHA concentrations are determined by their dietary intake of this fatty acid. We conclude that the most predictable way to increase a specific long-chain n-3 fatty acid in plasma, tissues, or human milk is to supplement with the fatty acid of interest.

Inhibition of leukotriene synthesis, pharmacokinetics, and tolerability of a novel dietary fatty acid formulation in healthy adult subjects

Background: Numerous studies have explored dietary-management strategies for decreasing leukotriene synthesis by inflammatory cells through supplementation with polyunsaturated fatty acids such as gamma-linolenic acid (GLA) and eicosapentaenoic acid (EPA). Objectives: This study sought to determine the optimal daily intake, ratios, and formulation of dietary GLA and EPA required to safely reduce leukotriene biosynthesis in healthy individuals, and to evaluate the pharmacokinetics and safety profile of such a formulation. Methods: Two preliminary trials were conducted to determine the minimum effective levels of GLA and EPA intake needed to reduce leukotriene biosynthesis and prevent increases in plasma arachidonic acid (AA) concentrations. These preliminary trials were followed by a single-center, randomized, double-blind, placebo-controlled, parallel-group, escalating-intake inpatient trial of a dietary GLA/EPA emulsion (PLT 3514) in healthy adult subjects. Subjects consumed either 10, 20, or 100 g of the PLT 3514 emulsion (respectively containing 0.75 g GLA + 0.5 g EPA, 1.5 g GLA + 1 g EPA, and 7.5 g GLA + 5 g EPA), or a placebo emulsion containing olive oil daily for 14 days. Plasma fatty acids were measured by gas chromatography. Stimulated whole blood leukotrienes were measured by high-performance liquid chromatography with ultraviolet detection. Results: Thirty subjects were included in the preliminary trials; 47 subjects were enrolled in the escalating-intake trial, of whom 42 completed the study. In the preliminary trials, intake of GLA 1.5 g/d in gelatin capsules decreased the capacity to synthesize leukotrienes but increased plasma levels of AA (both, P < 0.05). Inclusion of 0.25 or 1 g of dietary EPA prevented the increase in plasma AA concentrations. Dietary GLA and EPA showed significantly enhanced bioavailability when consumed in 20 g PLT 3514 emulsion compared with consumption in gelatin capsules ( P < 0.05), resulting in a reduction in the amount of intake required to block leukotriene biosynthesis. Pharmacokinetic analyses indicated that fasting plasma GLA and EPA levels plateaued within 7 days' daily consumption at all levels of intake, whereas the time to maximum plasma concentration (T max) was shorter for GLA than for EPA. The T max was similar on days 1 and 14 for both GLA and EPA. There were no clinically significant between-group differences in changes in vital signs, mean clinical laboratory values, or abbreviated hematology laboratory tests, or significant differences in the occurrence of treatment-emergent adverse events between the group consuming up to 20 g/d of the GLA/EPA emulsion and the group consuming placebo. Conclusion: Consumption of specific proportions and intake levels of dietary GLA and EPA in a novel emulsion formulation inhibited leukotriene biosynthesis and appeared to be well tolerated in this population of healthy adult subjects.

Comparison of Triglycerides and Phospholipids as Supplemental Sources of Dietary Long-Chain Polyunsaturated Fatty Acids in Piglets

Addition of arachidonic acid (AA) and docosahexaenoic acid (DHA) to infant formula promotes visual and neural development. This study was designed to determine whether the source of dietary long-chain polyunsaturated fatty acids (LCPUFA) affected overall animal health and safety. Piglets consumed ad libitum from 1 to 16 d of age a skim milk-based formula with different fat sources added to provide 50% of the metabolizable energy. Treatment groups were as follows: control (CNTL; no added LCPUFA), egg phospholipid (PL), algal/fungal triglyceride (TG) oils, TG plus PL (soy lecithin source) added to match phospholipid treatment (TG + PL) and essential fatty acid deficient (EFAD). Formulas with LCPUFA provided 0.6 and 0.3 g/100 g total fatty acids as AA and DHA, respectively. CNTL piglets had 40% longer ileal villi than PL piglets (P < 0.03), but the TG group was not different from the CNTL group. Gross liver histology did not differ among any of the formula-fed groups (P > 0.1). Apparent dry matter digestibility was 10% greater in CNTL, TG and TG + PL groups compared with PL piglets (P < 0.002). No differences in alanine aminotransferase were detected among treatments, but aspartate aminotransferase was elevated (P < 0.03) in PL piglets compared with TG + PL piglets. Total plasma AA concentration was greater in the TG group compared with CNTL piglets (P < 0.05). Total plasma DHA concentrations were greater in TG piglets compared with PL (P < 0.06) or CNTL (P < 0.02) piglets. These data demonstrate that the algal/fungal TG sources of DHA and AA may be a more appropriate supplement for infant formulas than the egg PL source based on piglet plasma fatty acid profiles and apparent dry matter digestibilities.

Lipid status and long-chain polyunsaturated fatty acid concentrations in adults and adolescents with phenylketonuria on phenylalanine-restricted diet.

Blood lipid studies are reported in 25 adults and 2 adolescents with PKU who had been on phenylalanine-restricted diets for a mean period of 22.6 years (range 7-39 years). Measurements included plasma concentrations of phenylalanine, cholesterol, lipoproteins, triglycerides and fatty acid profiles, including the analysis of seven fatty acids in plasma and red blood cells. Lipid screening identified 7 subjects with significantly elevated cholesterol/HDL ratios ranging from 5.6 to 10.3. Triglyceridaemia was documented in 5 of these 7, with concentrations ranging between 0.24 and 4.5 mmol/L (219-402 mg/dl) with a mean of 3.5 mmol/L (310 mg/dl). The fatty acid analyses demonstrated slight but statistically significant reductions in the concentrations of long-chain polyunsaturated fatty acids (LCPUFA), including plasma docosahexaenoic (DHA) and arachidonic acid (AA), and red blood cell DHA concentrations. The pattern resembles that reported previously in children, but alterations in the mean levels are less severe. In six of the adult patients plasma DHA or AA concentrations were less than 50% of controls. Since DHA and AA have important physiological roles, including brain and retinal function, it is recommended that blood lipid concentrations be monitored in all patients with PKU, including adults, and that DHA and AA supplementation be provided, particularly in those patients in whom the blood concentrations of these substances are reduced significantly.

Low Arachidonic Acid Rather than α-Tocopherol Is Responsible for the Delayed Postnatal Development in Offspring of Rats Fed Fish Oil Instead of Olive Oil during Pregnancy and Lactation

This study was designed to compare in rats the effects of dietary fish oil and olive oil during pregnancy and lactation on offspring development, fatty acid profile and vitamin E concentration. From d 0 of pregnancy, female Sprague-Dawley rats were divided into two groups that were fed purified diets that differed only in their nonvitamin lipid components. One diet contained 10 g fish oil/100 g diet (FOD), whereas the other contained 10 g olive oil/100 g diet (OOD). At d 20 of gestation, maternal adipose tissue fatty acid profile did not differ between rats fed the two diets, whereas both maternal and fetal plasma and liver arachidonic acid (AA) contents were proportionally lower and eicosapentaenoic (EPA) and docosahexaenoic (DHA) acid contents were higher in the FOD group than in the OOD group. alpha-Tocopherol concentration was lower in maternal and fetal plasma, liver and brain in the FOD group than in the OOD group. The postnatal increase in body weight and length was less and body and psychomotor maturation indices were delayed in pups from FOD-fed dams compared with those from OOD-fed dams. This difference was maintained when pups were cross-fostered at birth, with the delay in postnatal development present in the pups suckling dams fed FOD during lactation. At age 21 d, pups suckling dams fed FOD had lower AA and higher EPA and DHA concentrations in brain phospholipids. Although alpha-tocopherol in plasma and liver was lower in pups suckling dams fed FOD rather than OOD, brain alpha-tocopherol concentrations did not differ. Milk yield and milk alpha-tocopherol and AA concentrations were lower and EPA and DHA were higher in the milk of dams fed FOD compared with those fed OOD. Postnatal development indices and the proportion of plasma, liver and brain AA concentrations, although not plasma, liver and brain alpha-tocopherol concentrations, recovered to the values found in dams fed OOD when the FOD was supplemented with gamma-linolenic acid. However, postnatal development indices were not recovered when the FOD was supplemented with sufficient exogenous vitamin E to increase plasma and liver alpha-tocopherol concentrations above those in dams fed OOD. Thus, although feeding FOD during pregnancy and lactation decreases both alpha-tocopherol and AA concentrations, the latter deficiency rather than the former seems to be responsible for delayed postnatal development of rat pups.

Supplementation of postmenopausal women with fish oil rich in eicosapentaenoic acid and docosahexaenoic acid is not associated with greater in vivo lipid peroxidation compared with oils rich in oleate and linoleate as assessed by plasma malondialdehyde and F2-isoprostanes

Although the replacement of dietary saturated fat with unsaturated fat has been advocated to reduce the risk of cardiovascular disease, diets high in polyunsaturated fatty acids (PUFAs) could increase lipid peroxidation, potentially contributing to the pathology of atherosclerosis. The objective of this study was to examine indexes of in vivo lipid peroxidation, including free F(2)-isoprostanes, malondialdehyde (MDA), and thiobarbituric acid reacting substances (TBARS), in the plasma of postmenopausal women taking dietary oil supplements rich in oleate, linoleate, and both eicosapentaenoic acid and docosahexaenoic acid. Fifteen postmenopausal women took 15 g sunflower oil/d, providing 12.3 g oleate/d; safflower oil, providing 10.5 g linoleate/d; and fish oil, providing 2.0 g EPA/d and 1.4 g DHA/d in a 3-treatment crossover trial. Plasma free F(2)-isoprostane concentrations were lower after fish-oil supplementation than after sunflower-oil supplementation (P: = 0.003). When plasma free F(2)-isoprostane concentrations were normalized to plasma arachidonic acid concentrations, significant differences among the supplements were eliminated. Plasma MDA concentrations were lower after fish-oil supplementation than after sunflower-oil supplementation (P: = 0.04), whereas plasma TBARS were higher after fish-oil supplementation than after sunflower oil (P: = 0.003) and safflower oil (P: = 0.001) supplementation. When plasma MDA concentrations were normalized to plasma PUFA concentrations, significant differences were eliminated, but TBARS remained higher after fish-oil supplementation than after sunflower oil (P: = 0.01) and safflower-oil (P: = 0.0003) supplementation. With fish-oil supplementation, there was no evidence of increased lipid peroxidation when assessed by plasma F(2)-isoprostanes and MDA, although plasma TBARS was higher than with sunflower-oil and safflower-oil supplementation.

Plasma arachidonic acid and serum thromboxane B 2 concentrations in phenylketonuric children negatively correlate with dietary compliance

The study addresses the relationship of plasma arachidonic acid and thromboxane production with the dietary compliance in treated phenylketonuric patients, whose vegan-like dietary pattern makes them a useful model to evaluate the effects of the near-total avoidance of animal fats. Thirteen treated phenylketonuric children were compared with twelve healthy controls for arachidonic acid intake, plasma fatty acids and platelet thromboxane B 2 production, assessed as accumulation of this eicosanoid in serum. The calculated intake of arachidonic acid was lower in phenylketonurics than in controls and this was associated with lower levels in plasma lipids. Plasma arachidonic acid concentrations and serum thromboxane B 2 levels correlated with the last 12 months phenylalanine levels, taken as negative indicator of dietary compliance. A direct relationship between plasma arachidonic acid concentration and thromboxane B 2 production was observed only in phenylketonuric patients ( r = 0.74, P = 0.01). While well-compliant PKU subjects have low arachidonic acid and thromboxane concentrations in plasma, the low compliance with animal food avoidance, evoking higher phenylalanine levels, results in elevation of both plasma arachidonic acid and serum thromboxane B 2. This gives support to the hypothesis that the consumption of animal fats may affect the production of arachidonic acid-derived platelet eicosanoids.

Effects of chronic fetal hyperinsulinemia on plasma arachidonic acid and prostaglandin concentrations

In adult diabetic subjects and infants of diabetic mothers, hyperglycemia has been associated with increased intravascular thromboxane and decreased prostacyclin production. Because of the association between states of altered insulin concentration and prostaglandin metabolism, we hypothesized that chronic experimentally induced fetal hyperinsulinemia results in perturbations in fetal arachidonic acid and prostaglandin metabolism. Arachidonic acid, thromboxane B 2 (the stable breakdown product of thromboxane A 2), and 6-keto-prostaglandin F 1α (the stable breakdown product of prostacyclin) were determined in the arterial blood of chronically catheterized fetal sheep after 9 to 12 days of continuous insulin (15 U · day -1, n = 7) or placebo ( n = 5) infusion. Fetal insulin infusion resulted in fetal hypoglycemia and a reduction in fetal arterial plasma arachidonic acid concentration (p < 0.01). In addition, the concentration of thromboxane B 2 relative to 6-keto-prostaglandin F 1α was significantly reduced in the insulin-treated group compared with the placebo-treated group (p < 0.03). We conclude that fetal hyperinsulinemia in sheep produces perturbations in prostaglandin metabolism with reductions in the plasma arachidonic acid concentration and in the plasma concentration of thromboxane A 2 relative to prostacyclin. The hyperinsulinemic-hypoglycemic state in the fetus influences the relative proportion of the vasoconstricting to the vasodilating prostaglandins, thereby potentially modulating fetal vasomotor tone.

Lipid malnutrition of patients with liver cirrhosis: effect of low intake of dietary lipid on plasma fatty acid composition.

The plasma fatty acid composition of cirrhotic patients and their dietary intake of fatty acids were determined. Significantly lower plasma arachidonic, docosahexaenoic, dihomo-gamma-linolenic and eicosapentaenoic acid levels were observed in cirrhotic patients than in healthy controls. A remarkably low dietary intake of polyunsaturated fatty acids supplied from fish, vegetable oil and pulses was shown in cirrhotic patients. Positive correlations were observed between plasma arachidonic acid concentrations and clearance rate of indocyanine green (KICG) (r = 0.826, p less than 0.05) and between dihomo-gamma-linolenic acid levels and cholinesterase activities (r = 0.841, p less than 0.05). From these results, we conclude that a supply of polyunsaturated fatty acids is necessary for the nutritional treatment of patients with liver cirrhosis.

Failure of acute hypoxia to alter pulmonary prostaglandin metabolism in dogs

We studied the effects of acute hypoxia (Fi02=0.09–0.11, 20 min,.) on transpulmonary plasma prostaglandin (PG) concentrations in ten anaesthetized, paralyzed, artificially ventilated dogs. Concentrations of 6-keto-PGF1α, TxB2, PGE2, PGF2α, and 13, 13-dihydro-15-keto-PGF2α were measured from the pulmonary artery and abdominal aorta using radioimmunoassay. In an additional six dogs, the effects of arachidonic acid (AA) infusions (100 mg/kg/min) during normoxia and acute hypoxia were determined. Compared to normoxic conditions, acute hypoxia increased pulmonary artery pressure (p<0.0), decreased both the arterial oxygen tension (Pa02) and the alveolar-to-arterial oxygen tension gradient (A-aD02) (p <0.05), but did not affect transpulmonary plasma PG concentrations. AA infusions significantly (p <0.05) increased 6-keto-PGF1α independent of Fi02. Acute hypoxia failed to elicit a pulmonary pressor response in the AA-treated animals although Pa02 and A-aD02 decreased (p<0.5). These data in healthy dogs suggest that (1) acute hypoxia does not alter net pulmonary PG metabolism, (2) prostacyclin synthesis is stimulated by increased plasma AA concentrations and (3) this effect may block normal pressor responses to hypoxic stimuli.