Cellular interactions between n-6 and n-3 fatty acids: a mass analysis of fatty acid elongation/desaturation, distribution among complex lipids, and conversion to eicosanoids.

The biologic effect of eicosanoids depends in large measure upon the relative masses in tissues of eicosanoids derived from the n-6 fatty acids, dihomogammalinolenic acid and arachidonic acid, and the n-3 fatty acid, eicosapentaenoic acid. Generation of this tissue balance is related to the relative cellular masses of these precursor fatty acids, the competition between them for entry into and release from cellular phospholipids, and their competition for the enzymes that catalyze their conversion to eicosanoids. In order to better understand these processes, we studied the cellular interactions of n-6 and n-3 fatty acids using an essential fatty acid-deficient, PGE-producing, mouse fibrosarcoma cell line, EFD-1. Unlike studies using cells with endogenous pools of n-6 and n-3 fatty acids, the use of EFD-1 cells enabled us to examine the metabolic fate of each family of fatty acids both in the presence and in the absence of the second family of fatty acids. Thus, the specific effects of one fatty acid family on the other could be directly assessed. In addition, we were able to replete the cells with dihomogammalinolenic acid (DHLA), arachidonic acid (AA), and eicosapentaenoic acid (EPA) of known specific activities; thus the masses of cellular DHLA, AA, and EPA, and their metabolites, PGE1, PGE2, and PGE3, respectively, could be accurately quantitated. The major findings of this study were: 1) n-6 fatty acids markedly stimulated the elongation of EPA to 22:5 whereas n-3 fatty acids inhibited the delta 5 desaturation of DHLA to AA and the elongation of AA to 22:4; 2) n-6 fatty acids caused a specific redistribution of cellular EPA from phospholipid to triacylglycerol; 3) n-3 fatty acids reduced the mass of DHLA and AA only in phosphatidylinositol whereas n-6 fatty acids reduced the mass of EPA to a similar extent in all cellular phospholipids; and 4) n-3 fatty acids caused an identical (33%) reduction in the bradykinin-induced release of PGE1 and PGE2, whereas n-6 fatty acids stimulated PGE3 release 2.3-fold. Together, these highly quantitative metabolic data increase our understanding of the regulation of both the cellular levels of DHLA, AA, and EPA, and their availability for eicosanoid synthesis. In addition, these findings provide a context for the effective use of these fatty acids in dietary therapies directed at modulation of eicosanoid production.     

Characterization and identification of cytochrome P450 metabolites of arachidonic acid released by human peritoneal macrophages obtained from the pouch of Douglas

Cytochrome P450 metabolism of arachidonic acid (AA) was investigated in human peritoneal macrophages which play a central role in chronic pelvic diseases in women (for example in endometriosis). The formation of eicosanoids other than prostaglandins (PGs) by these cells is still unknown. In non-activated macrophages obtained from women in the reproductive age, the main [(3)H]-AA metabolites coeluted with epoxyeicosatrienoic acids, dihydroxyeicosatrienoic acids (DHETs) and hydroxyeicosatetraenoic acids (HETEs) in reverse-phase HPLC. After zymosan activation a shift to PGs pathway was observed. Treatment with low doses of 2,3,7,8-tetrachlorodibenzo- p -dioxin increased the formation of a metabolite coeluting with 5,6-DHET. By gas chromatography/mass spectrometry 5,6-DHET (after beta-naphthoflavone induction), and 14,15-DHET as well as 11,12-DHET (after AA stimulation) were identified as major epoxygenase metabolites, respectively. The enantioselective formation of 12(S)-HETE was demonstrated by chiral-phase HPLC. Our findings demonstrate that non-activated peritoneal macrophages produce substantial amounts of bioactive cytochrome P450 metabolites of AA.     

Significance of myocardial eicosanoid production

Summary The precise role of eicosanoids in the development of myocardial injury during ischemia and reperfusion is still a matter of debate. Enhanced local production of these bioactive compounds appears to be a common response to tissue injury. Most likely, the cardiac tissue has the capacity to generate prostaglandins, thromboxanes as well as leukotrienes. Prostacyclin (PGI,) is the major eicosanoid produced by the jeopardized myocardium. In addition, at sites of tissue injury activation of platelets and infiltrating leukocytes results in the formation of considerable amounts of thromboxanes and leukotrienes. The production of eicosanoids requires prior release of arachidonic acid (AA) from phospholipids. Both ischemia and reperfusion are associated with a rise in the tissue level of AA. The absence of a proportional relationship between the tissue level of AA and the amounts of PGI, produced suggests that the sites of AA accumulation and PGI₂ formation are different. It is conceivable that AA accumulation is mainly confined to myocytes, whereas the capacity to synthesize PGI, mainly resides in vascular cells. Both beneficial and detrimental effects of eicosanoids on cardiac tissue have been described. Prostaglandins act as vasodilators. Besides, some of the prostaglandins, especially PGI,, are thought to possess cyto-protective properties. Thromboxanes and leukotrienes may impede blood supply by increasing smooth muscle tone. Besides, leukotrienes augment vascular permeability. Experimental studies, designed to evaluate the effect of pharmacological agents, like PGI₂-analogues and lipoxygenase and cyclo-oxygenase inhibitors, indicat that eicosanoids influence the outcome of myocardial injury. However, the delineation of the physiological significance of the locally produced eicosanoids is complicated by such factors as the wide variety of AA derivatives produced and the dose-dependency of their effects.     

The influence of chronic eicosanoid biosynthesis inhibition on life history of the greater waxmoth, Galleria mellonella and its ectoparasitoid, Bracon hebetor

Eicosanoids are oxygenated metabolites of three C20 polyunsaturated fatty acids, mainly arachidonic acid (AA; 20:4n-6), but also 20:3n-6 and 20:5n-3. Aside from their importance in biomedicine, eicosanoids act in invertebrate biology. Prostaglandins (PGs) influence salt and water transport physiology in insect rectal epithelia and in Malpighian tubules. PGs also influence a few insect behaviors, including releasing oviposition behavior and behavioral fever. Eicosanoids act in ovarian development and in insect immunity. Because eicosanoids act in several areas of insect biology, we posed the hypothesis that chronic inhibition of eicosanoid biosynthesis, in the absence of microbial challenge, can influence insect life table parameters, including developmental time, survival, adult longevity and parasitoid fecundity. Here we report that inhibiting eicosanoid biosynthesis throughout the larval life exerted minor influences on some life table parameters of the greater wax moth, Galleria mellonella and its ectoparasitoid, Bracon hebetor, however, the inhibitors strongly reduced the production and hatchability of the parasitoids’ eggs. The significance of the work relates to the potentials of understanding and targeting eicosanoid systems as a platform for developing new technologies of insect pest management. As seen here, the impact of targeting eicosanoid systems is seen in crucial moments of insect life histories, such as reproduction or immune challenge rather than in overall larval development.     

Determination of endogenous tissue inflammation profiles by LC/MS/MS: COX- and LOX-derived bioactive lipids

Cyclooxygenase and lipoxygenase arachidonate products, including prostaglandins (PGs), leukotrienes (LTs), and hydroxyeicosatetraenoic acids (HETEs), are known to modulate inflammation within tissues and can serve as important etiologic factors in carcinogenesis. Eicosanoid content in tissues is typically determined either as a single molecular species through antibody-based assays or by high-performance liquid chromatography after addition of an exogenous substrate such as arachidonic acid. Unfortunately, the methods currently in use are either time-consuming or complicated. Here we report a method for simultaneously identifying eicosanoids appearing as endogenous bioactive lipids in in vivo settings using LC/MS/MS. The analyses indicate marked differences in endogenous eicosanoid content between malignant tissue types suggesting a need for selective therapeutic approaches. As a demonstration of the utility of the method, we present data to show that the technique can be used to distinguish eicosapentaenoic acid-derived formation of PGE(3) from PGE(2) in murine prostate tissue. The method has also been applied to an examination of endogenous eicosanoid metabolism in 7,12-dimethylbenz[a]anthracene (DMBA)-induced oral cancer in hamsters demonstrating the inflammatory nature of this type of cancer with elevated levels of both PGE(2) and LTB(4). In addition, the concentration of the eicosanoid 13-hydroxyoctadecadienoic acid was 67.6% lower in DMBA treated specimens than in control specimens. Thus, our method provides a powerful tool for measuring modulation of eicosanoid metabolites in various preclinical and clinical tissues and may be useful in studies of the endogenous changes in eicosanoid metabolism at various stages of cancer development.     

Dietary lipids modulate eicosanoid release and apoptosis of cells of a murine lung alveolar carcinoma

Dietary arachidonic acid (AA) and eicosanoids influence neoplastic cell (NC) growth, differentiation and apoptosis. Plasma membrane fatty acid and cyclooxygenase (COX) and lipoxygenase (LOX) products were investigated in lung alveolar carcinoma cells from mice fed on different diets. Two groups were fed on a basic diet plus 6% of: corn oil (rich in 18:2n-6; CO) and on olein oil (rich in 18:1n-9; O), respectively. Control group (C) received commercial diet. NC fatty acids were analyzed by GLC, and apoptosis by flow cytometry and microscopy. In NC from CO group AA levels and LOX metabolites were increased, whereas COX metabolites decreased. NC from CO compared to O group diet showed a higher count of apoptosis and increased LOX:COX ratio. High levels of AA and decreased COX eicosanoids has been involved in anti-tumoral mechanisms by increasing tumor cell apoptosis. Present data emphasizes the implications of the dietary fatty acids on the neoplastic process in this tumoral model.     

Determination of endogenous tissue inflammation profiles by LC/MS/MS: COX- and LOX-derived bioactive lipids

Cyclooxygenase and lipoxygenase arachidonate products, including prostaglandins (PGs), leukotrienes (LTs), and hydroxyeicosatetraenoic acids (HETEs), are known to modulate inflammation within tissues and can serve as important etiologic factors in carcinogenesis. Eicosanoid content in tissues is typically determined either as a single molecular species through antibody-based assays or by high-performance liquid chromatography after addition of an exogenous substrate such as arachidonic acid. Unfortunately, the methods currently in use are either time-consuming or complicated. Here we report a method for simultaneously identifying eicosanoids appearing as endogenous bioactive lipids in in vivo settings using LC/MS/MS. The analyses indicate marked differences in endogenous eicosanoid content between malignant tissue types suggesting a need for selective therapeutic approaches. As a demonstration of the utility of the method, we present data to show that the technique can be used to distinguish eicosapentaenoic acid-derived formation of PGE₃ from PGE₂ in murine prostate tissue. The method has also been applied to an examination of endogenous eicosanoid metabolism in 7,12-dimethylbenz[a]anthracene (DMBA)-induced oral cancer in hamsters demonstrating the inflammatory nature of this type of cancer with elevated levels of both PGE₂ and LTB₄. In addition, the concentration of the eicosanoid 13-hydroxyoctadecadienoic acid was 67.6% lower in DMBA treated specimens than in control specimens. Thus, our method provides a powerful tool for measuring modulation of eicosanoid metabolites in various preclinical and clinical tissues and may be useful in studies of the endogenous changes in eicosanoid metabolism at various stages of cancer development.     

Eicosanoid Profiling in an Orthotopic Model of Lung Cancer Progression by Mass Spectrometry Demonstrates Selective Production of Leukotrienes by Inflammatory Cells of the Microenvironment

Eicosanoids are bioactive lipid mediators derived from arachidonic acid¹ (AA), which is released by cytosolic phospholipase A₂ (cPLA₂). AA is metabolized through three major pathways, cyclooxygenase (COX), lipoxygenase (LO) and cytochrome P450, to produce a family of eicosanoids, which individually have been shown to have pro- or anti-tumorigenic activities in cancer. However, cancer progression likely depends on complex changes in multiple eicosanoids produced by cancer cells and by tumor microenvironment and a systematic examination of the spectrum of eicosanoids in cancer has not been performed. We used liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) to quantitate eicosanoids produced during lung tumor progression in an orthotopic immunocompetent mouse model of lung cancer, in which Lewis lung carcinoma (LLC) cells are injected into lungs of syngeneic mice. The presence of tumor increased products of both the cyclooxygenase and the lipoxygenase pathways in a time-dependent fashion. Comparing tumors grown in cPLA₂ knockout vs wild-type mice, we demonstrated that prostaglandins (PGE₂, PGD₂ and PGF_2a) were produced by both cancer cells and the tumor microenvironment (TME), but leukotriene (LTB₄, LTC₄, LTD₄, LTE₄) production required cPLA₂ expression in the TME. Using flow cytometry, we recovered tumor-associated neutrophils and 2 types of tumor-associated macrophages from tumor-bearing lungs and we defined their distinct eicosanoid profiles by LC/MS/MS. The combination of flow cytometry and LC/MS/MS unravels the complexity of eicosanoid production in lung cancer and provides a rationale to develop therapeutic strategies that target select cell populations to inhibit specific classes of eicosanoids.     

TLR-4 and sustained calcium agonists synergistically produce eicosanoids independent of protein synthesis in RAW264.7 cells

Arachidonic acid is released by phospholipase A(2) and converted into hundreds of distinct bioactive mediators by a variety of cyclooxygenases (COX), lipoxygenases (LO), and cytochrome P450s. Because of the size and diversity of the eicosanoid class of signaling molecules produced, a thorough and systematic investigation of these biological processes requires the simultaneous quantitation of a large number of eicosanoids in a single analysis. We have developed a robust liquid chromatography/tandem mass spectrometry method that can identify and quantitate over 60 different eicosanoids in a single analysis, and we applied it to agonist-stimulated RAW264.7 murine macrophages. Fifteen different eicosanoids produced through COX and 5-LO were detected either intracellularly or in the media following stimulation with 16 different agonists of Toll-like receptors (TLR), G protein-coupled receptors, and purinergic receptors. No significant differences in the COX metabolite profiles were detected using the different agonists; however, we determined that only agonists creating a sustained Ca(2+) influx were capable of activating the 5-LO pathway in these cells. Synergy between Ca(2+) and TLR pathways was detected and discovered to be independent of NF-kappaB-induced protein synthesis. This demonstrates that TLR induction of protein synthesis and priming for enhanced phospholipase A(2)-mediated eicosanoid production work through two distinct pathways.     

Chronic nutritional deprivation of n-3 α-linolenic acid does not affect n-6 arachidonic acid recycling within brain phospholipids of awake rats

Using an in vivo fatty acid model and operational equations, we reported that esterified and unesterified concentrations of docosahexaenoic acid (DHA, 22 : 6 n-3) were markedly reduced in brains of third-generation (F3) rats nutritionally deprived of alpha-linolenic acid (18 : 3 n-3), and that DHA turnover within phospholipids was reduced as well. The concentration of docosapentaenoic acid (DPA, 22 : 5 n-6), an arachidonic acid (AA, 20 : 4 n-6) elongation/desaturation product, was barely detectable in control rats but was elevated in the deprived rats. In the present study, we used the same in vivo model, involving the intravenous infusion of radiolabeled AA to demonstrate that concentrations of unesterified and esterified AA, and turnover of AA within phospholipids, were not altered in brains of awake F3-generation n-3-deficient rats, compared with control concentrations. Brain DPA-CoA could be measured in the deprived but not control rats, and AA-CoA was elevated in the deprived animals. These results indicated that AA and DHA are recycled within brain phospholipids independently of each other, suggesting that recycling is regulated independently by AA- and DHA-selective enzymes, respectively. Competition among n-3 and n-6 fatty acids within brain probably does not occur at the level of recycling, but at levels of elongation and desaturation (hence greater production of DPA during n-3 deprivation), or conversion to bioactive eicosanoids and other metabolites.     

Effect of olive oil minor components on oxidative stress and arachidonic acid mobilization and metabolism by macrophages RAW 264.7

Minor components of virgin olive oil may explain the healthy effects of the Mediterranean diet on the cardiovascular system and cancer development. The uncontrolled production of reactive oxygen species (ROS) and arachidonic acid (AA) metabolites contributes to the pathogenesis of cardiovascular disease and cancer, and inflammatory cells infiltrated in the atheroma plaque or tumor are a major source of ROS and eicosanoids. We aimed to determine the effects of squalene, beta-sitosterol, and tyrosol, which are representative of the hydrocarbons, sterols, and polyphenols of olive oil, respectively, on superoxide anion (O2(-)), hydrogen peroxide (H2O2), and nitric oxide (*NO) levels. We also studied AA release and eicosanoid production by phorbol esters (PMA)-stimulated macrophages RAW 264.7. beta-Sitosterol and tyrosol decreased the O2(-) and H2O2 production induced by PMA, and tyrosol scavenged the O2(-) released by a ROS generating system. These effects were correlated with the impairment of [3H]AA release, cyclooxygenase-2 (COX-2) expression, and prostaglandin E(2)/leukotriene B(4) synthesis in RAW 264.7 cultures stimulated by PMA. beta-Sitosterol exerted its effects after 3-6 h of preincubation. Tyrosol inhibited the [3H]AA release induced by exogenous ROS. beta-Sitosterol and tyrosol also reduced the *NO release induced by PMA, which was correlated with the impairment of inducible nitric oxide synthase (iNOS) levels. This may be correlated with the modulation of NF-kappaB activation. Further studies are required to gain more insight into the potential healthy effects of minor components of extra virgin olive oil.     

Biochemistry and physiology of n-3 fatty acids.

Considering the n-3 fatty acids to be partial agonists relative to n-6 fatty acids helps consolidate into a unified interpretation the many diverse reports and controversies on the actions of these two types of essential fatty acids. Some research reports illustrate the similarities between these two types and some emphasize the differences, leaving readers to evaluate the status of n-3 fatty acids from a viewpoint that is conceptually similar to regarding a glass of water as half empty or half full. Both n-3 and n-6 types of fatty acids must be obtained through the diet because they are not synthesized de novo by vertebrates. Both types can support important physiological and developmental processes, can form eicosanoids (prostaglandins, leukotrienes, lipoxins, etc.), can be esterified to and hydrolyzed from tissue glycerolipids, and can be metabolically elongated and desaturated to a variety of highly unsaturated fatty acids. However, some nonesterified n-6 acids are vigorously converted to potent n-6 eicosanoids that exert intense agonist actions at eicosanoid receptors, whereas the n-3 acids less vigorously form n-3 eicosanoids that often produce less intense (partial) actions. Because both types owe their presence in vertebrate tissues to dietary intake, important physiological consequences follow the inadvertent selection of different average daily dietary supplies of these two types of polyunsaturated fatty acids.     

Pulmonary surfactant phosphatidylglycerol inhibits Mycoplasma pneumoniae-stimulated eicosanoid production from human and mouse macrophages

Mycoplasma pneumoniae is a human pathogen causing respiratory infections that are also associated with serious exacerbations of chronic lung diseases. Membranes and lipoproteins from M. pneumoniae induced a 4-fold increase in arachidonic acid (AA) release from RAW264.7 and a 2-fold increase in AA release from primary human alveolar macrophages. The bacterial lipoprotein mimic and TLR2/1 agonist Pam3Cys and the TLR2/6 agonist MALP-2 produced effects similar to those elicited by M. pneumoniae in macrophages by inducing the phosphorylation of p38(MAPK) and p44/42(ERK1/2) MAP kinases and cyclooxygenase-2 (COX-2) expression. M. pneumoniae induced the generation of prostaglandins PGD(2) and PGE(2) from RAW264.7 cells and thromboxane B(2) (TXB(2)) from human alveolar macrophages. Anti-TLR2 antibody completely abolished M. pneumoniae-induced AA release and TNFα secretion from RAW264.7 cells and human alveolar macrophages. Disruption of the phosphorylation of p44/42(ERK1/2) or inactivation of cytosolic phospholipase A(2)α (cPLA(2)α) completely inhibited M. pneumoniae-induced AA release from macrophages. The minor pulmonary surfactant phospholipid, palmitoyl-oleoyl-phosphatidylglycerol (POPG), antagonized the proinflammatory actions of M. pneumoniae, Pam3Cys, and MALP-2 by reducing the production of AA metabolites from macrophages. The effect of POPG was specific, insofar as saturated PG, and saturated and unsaturated phosphatidylcholines did not have significant effect on M. pneumoniae-induced AA release. Collectively, these data demonstrate that M. pneumoniae stimulates the production of eicosanoids from macrophages through TLR2, and POPG suppresses this pathogen-induced response.     

Eicosanoids, β-cell function, and diabetes

Arachidonic acid (AA) is metabolized by cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) enzymes into eicosanoids, which are involved in diverse diseases, including type 1 and type 2 diabetes. During the last 30 years, evidence has been accumulated that suggests important functions for eicosanoids in the control of pancreatic β-cell function and destruction. AA metabolites of the COX pathway, especially prostaglandin E(2) (PGE(2)), appear to be significant factors to β-cell dysfunction and destruction, participating in the pathogenesis of diabetes and its complications. Several elegant studies have contributed to the sorting out of the importance of 12-LOX eicosanoids in cytokine-mediated inflammation in pancreatic β cells. The role of CYP eicosanoids in diabetes is yet to be explored. A recent publication has demonstrated that stabilizing the levels of epoxyeicosatrienoic acids (EETs), CYP eicosanoids, by inhibiting or deleting soluble epoxide hydrolase (sEH) improves β-cell function and reduces β-cell apoptosis in diabetes. In this review we summarize recent findings implicating these eicosanoid pathways in diabetes and its complications. We also discuss the development of animal models with targeted gene deletion and specific enzymatic inhibitors in each pathway to identify potential targets for the treatment of diabetes and its complications.     

High-throughput lipidomic analysis of fatty acid derived eicosanoids and N-acylethanolamines

Fatty acid-derived eicosanoids and N-acylethanolamines (NAE) are important bioactive lipid mediators involved in numerous biological processes including cell signaling and disease progression. To facilitate research on these lipid mediators, we have developed a targeted high-throughput mass spectrometric based methodology to monitor and quantitate both eicosanoids and NAEs, and can be analyzed separately or together in series. Each methodology utilizes scheduled multiple reaction monitoring (sMRM) pairs in conjunction with a 25 min reverse-phase HPLC separation. The eicosanoid methodology monitors 141 unique metabolites and quantitative amounts can be determined for over 100 of these metabolites against standards. The analysis covers eicosanoids generated from cycloxygenase, lipoxygenase, cytochrome P450 enzymes, and those generated from non-enzymatic pathways. The NAE analysis monitors 36 metabolites and quantitative amounts can be determined for 33 of these metabolites against standards. The NAE method contains metabolites derived from saturated fatty acids, unsaturated fatty acids, and eicosanoids. The lower limit of detection for eicosanoids ranges from 0.1pg to 1pg, while NAEs ranges from 0.1pg to 1000pg. The rationale and design of the methodology is discussed.     

Metabolic products of arachidonic acid in rats

The pattern of eicosanoid metabolites appearing in urine and feces following oral administration of radioactive arachidonic acid was investigated using rats deficient in essential fatty acids. About 70–80% of the radioactivity in the urine during the first day after feeding was adsorbed to XAD-2 resin and he represented eicosanoid metabolites, whereas the rest of the radioactivity was mainly ³H₂O. The eicosanoid metabolites were fractioned into different polarity classes using reverse phase Sep-Pak C₁₈ cartridges. Gas chromatographic analysis of the urinary metabolites following their derivatization into methyl ester-methoxime- -butyl-dimethylsilyl ethers revealed that nearly one-half of the metabolites had ECL values less than 22 and represented metabolites more oxidized than commonly described. Only 30% of the metabolites had ECL values between 26 to 32, corresponding to the values for the metabolites that originate from exogenously infused prostaglandins. A large portion of the eicosanoid metabolites was also excreted with the feces. The isotropic patterns from the reverse phase chromatography indicated that many of the fecal metabolites may be similar to those in urine although some metabolites in feces were not present in urine. Based on the specific radioactivity of the administered arachidonic acid, it appeared that at least 6 to 8 mg of eicosanoid metabolites were excreted through urine and feces within 24 hrs following an oral bolus of 60 mg arachidonic acid. The rapid increase and subsequent decrease in eicosanoid metabolite excretion after oral administration of arachidonate indicates that the dietary intake of polyunsaturated fatty acids may have a more rapid effect upon the endogenous production of eicosanoids than is generally recognized.     

Metabolic products of arachidonic acid in rats

The pattern of eicosanoid metabolites appearing in urine and feces following oral administration of radioactive arachidonic acid was investigated using rats deficient in essential fatty acids. About 70-80% of the radioactivity in the urine during the first day after feeding was adsorbed to XAD-2 resin and represented eicosanoid metabolites, whereas the rest of the radioactivity was mainly 3H2O. The eicosanoid metabolites were fractionated into different polarity classes using reverse phase Sep-Pak C18 cartridges. Gas chromatographic analysis of the urinary metabolites following their derivatization into methyl ester-methoxime-tert-butyl-dimethylsilyl ethers revealed that nearly one-half of the metabolites had ECL values less than 22 and represented metabolites more oxidized than commonly described. Only 30% of the metabolites had ECL values between 26 to 32, corresponding to the values for the metabolites that originate from exogenously infused prostaglandins. A large portion of the eicosanoid metabolites was also excreted with the feces. The isotopic patterns from the reverse phase chromatography indicated that many of the fecal metabolites may be similar to those in urine although some metabolites in feces were not present in urine. Based on the specific radioactivity of the administered arachidonic acid, it appeared that at least 6 to 8 mg of eicosanoid metabolites were excreted through urine and feces within 24 hrs following an oral bolus of 60 mg arachidonic acid. The rapid increase and subsequent decrease in eicosanoid metabolite excretion after oral administration of arachidonate indicates that the dietary intake of polyunsaturated fatty acids may have a more rapid effect upon the endogenous production of eicosanoids than is generally recognized.