Metabolism Of Endogenous Arachidonic Acid Research Articles

Activity of platelet hemostasis in newborn calves

Healthy newborn Simmental and Black Pied calves with a normal number of platelets in bloodstream don’t have reliable dynamics of the aggregation function of blood platelets with adenosine diphosphate, collagen, thrombin, ristocetin, epinephrine, as well as combinations of ADP + epinephrine, ADP + collagen, and collagen + epinephrine inducers. The level of discocytes in blood on days 1–2 was 78.5, not reliably changing until the end of the neonatal stage. In this case, the number of disco-echinocytes, spherocytes, spheroechinocytes, and bipolar forms of platelets in the bloodstream remained stably low. Maintenance during colostrum feeding of a low intensity of metabolism of endogenous arachidonic acid in platelets and of a low content of ATP, ADP, actin, and myosin in them can be considered important mechanisms providing stability of platelet aggregation activity in calves in the neonatal stage.

Novel Mechanism of the Vascular Protector Prostacyclin: Regulating MicroRNA Expression

Prostacyclin (PGI(2)) is a key vascular protector, metabolized from endogenous arachidonic acid (AA). Its actions are mediated through the PGI(2) receptor (IP) and nuclear receptor, peroxisome proliferator-activated receptor γ (PPARγ). Here, we found that PGI(2) is involved in regulating cellular microRNA (miRNA) expression through its receptors in a mouse adipose tissue-derived primary culture cell line expressing a novel hybrid enzyme gene (COX-1-10aa-PGIS), cyclooxygenase-1 (COX-1) and PGI(2) synthase (PGIS) linked with a 10-amino acid linker. The triple catalytic functions of the hybrid enzyme in these cells successfully redirected the endogenous AA metabolism toward a stable and dominant production of PGI(2). The miRNA microarray analysis of the cell line with upregulated PGI(2) revealed a significant upregulation (711, 148b, and 744) and downregulation of miRNAs of interest, which were reversed by antagonists of the IP and PPARγ receptors. Furthermore, we also found that the insulin-mediated lipid deposition was inhibited in the PGI(2)-upregulated adipocytes. The study also initiated a discussion that suggested that the endogenous PGI(2) inhibition of lipid deposition in adipocytes could involve miRNA-mediated inhibition of expression of the targeted genes. This indicated that PGI(2)-miRNA regulation could exist in broad pathophysiological processes involving PGI(2) (i.e., apoptosis, vascular inflammation, cancer, embryo implantation, and obesity).

Thrombin-stimulated DNA Synthesis in Human Cultured Airway Smooth Muscle Occurs Independently of Products of Cyclo-oxygenase or 5-Lipoxygenase

Arachidonic acid (AA) liberation and metabolism via cyclo-oxygenase or lipoxygenases may be an important regulatory pathway for mitogenic signalling in human cultured airway smooth muscle (ASM) cells. In cytokine-treated cells, thrombin markedly enhances production of the anti-mitogenic arachidonic acid metabolite, PGE2. In this study, in the absence of cytokines, we examined the role of endogenous AA metabolism in thrombin-stimulated ASM DNA synthesis. Selective inhibitors of cyclo-oxygenase of 5-lipoxygenase metabolism had no significant effect on 0.3 U/ml thrombin-stimulated DNA synthesis. However, the non-selective, redox-active lipoxygenase inhibitors NDGA and BWA4C inhibited thrombin-stimulated DNA synthesis. Under basal conditions, and following stimulation by thrombin, the levels of the AA metabolites PGE2, TxA2, and LTC4, remained below assay detection limits. Exogenous addition of AA, LTD4, or 5-, 12-, and 15-HETE and HpETE metabolites had no consistent or substantial stimulatory effect on either basal or thrombin-stimulated DNA synthesis. These data suggest that the non-selective lipoxygenase inhibitors influence DNA synthesis via effects unrelated to lipoxygenase inhibition. The lack of detection of AA metabolites, the lack of influence of selective antagonists/inhibitors of the AA pathway, and the failure of selected AA metabolites to either enhance or directly stimulate DNA synthesis suggest that in the absence of cytokines, cyclo-oxygenase and lipoxygenase metabolism has little role in signalling of human ASM DNA synthesis by thrombin.

Arachidonic Acid Metabolism in the Marine FishStenotomus chrysops(Scup) and the Effects of Cytochrome P450 1A Inducers

Cytochrome P450-mediated arachidonic acid (AA) metabolism was investigated in the marine fish scup,Stenotomus chrysops.Liver microsomes incubated with AA and NADPH produced epoxyeicosatrienoic acids (EETs) and their hydration products (dihydroxyeicosatrienoic acids, DHETs), midchain conjugated dienols (midchain HETEs), and C16- through C20-alcohols of AA (ω-terminal HETEs), all identified by HPLC and GC/MS. Gravid females had 4-fold lower AA metabolism rates than males but identical metabolite profiles. The 5,6-EET (inferred from stable metabolites) was most abundant (47% of total EETs) followed by 14,15-, 11,12-, and 8,9-EET (27, 13, and 13%, respectively). The 12-HETE represented 25% of total HETEs followed in abundance by 16-, 15-, 11-, 19-, 20-, 8-, and 9-HETE. Antibodies against scup CYP1A and a scup CYP2B-like protein inhibited liver microsomal AA metabolism by 30 and 46%, respectively. GC/MS analysis revealed EETs and DHETs as endogenous constituents in scup liver; the predominant EETs were 8,9- and 14,15-EET, followed by a lesser amount of 11,12-EET. Chiral analysis showed a preference for the S,R-enantiomers of endogenous 8,9-, 11,12-, and 14,15-EET (optical purities 80, 64, and 64%, respectively). Treatment of scup with the CYP1A inducer benzo(a)pyrene (BP) increased liver microsomal formation of EETs and HETEs by 2.7-fold in spring and 1.7-fold in summer. BP treatment did not affect microsomal EET regioselectivity, but shifted hydroxylation in favor of 19-HETE and induced 17-HETE formation. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) treatment in summer did not induce liver microsomal AA metabolism rates, yet BP and TCDD both increased endogenous EET content of liver (5- and 3-fold, respectively), with a shift to 14,15-EET. BP treatment increased the selectivity for the S,R-enantiomers of endogenous 8,9-, 11,12-, and 14,15-EET (optical purities 91, 84, and 83%, respectively). Kidney, gill, and heart microsomes all metabolized AA, at rates 10- to 30-fold less than liver microsomes. Similar amounts of endogenous 8,9- and 14,15-EET and less 11,12-EET were detected in heart and kidney, and there was a strong enantioselectivity for 8(R),9(S)-EET in heart (optical purity 78%) but not in kidney. BP treatment did not alter the total EET content in these organs but did shift the regiochemical profile in heart to favor 14,15-EET. Thus, scup liver and extrahepatic organs metabolize AA via multiple cytochrome P450 (CYP) forms to eicosanoidsin vitroandin vivo.BP or TCDD induced endogenous AA metabolism in liver, altering EET regioselectivity and, with BP, stereoselectivity. While AhR agonists alter metabolism of AA in early diverging vertebrates expressing both CYP1A and AhR, the magnitude of effects may depend upon the type of inducer.

Anandamide and delta 9-THC dilation of cerebral arterioles is blocked by indomethacin.

Anandamide (AN, arachidonyl ethanolamide) has been isolated from the brain and shown to be an endogenous ligand for the delta 9-tetrahydrocannabinol (delta 9-THC) receptor. The purpose of these studies was to determine whether AN or delta 9-THC can affect the cerebral circulation. With the use of the closed cranial window AN and delta 9-THC (10(-13)-10(-3) M) were topically applied to rabbit cerebral arterioles and effects on diameter were measured with a microscope. AN and delta 9-THC similarly induced a dose-dependent dilation starting at concentrations as low as 10(-12) M. Maximum dilation for AN was 25% and that for delta 9-THC 22%. Topical coapplication of indomethacin, a cyclooxygenase inhibitor, completely blocked dilation, whereas the free radical scavengers superoxide dismutase and catalase or the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) had no effect on AN-induced dilation. The cerebrospinal fluid level of prostaglandin E2 increased only in response to 10(-7) M and greater AN and was not affected by delta 9-THC. [3H]AN superfused through the cranial window was 20% converted to arachidonic acid. These results show that AN and delta 9-THC can modulate cerebral arterioles, likely by stimulating release and metabolism of endogenous arachidonic acid. Whether dilation is due to vasodilator eicosanoids, or other vasoactive agents whose synthesis or release is cyclooxygenase dependent, is uncertain.

Prostaglandin endoperoxide synthase-1 and -2 couple to different transmembrane stimuli to generate prostaglandin D2 in mouse bone marrow-derived mast cells.

The view that the two isoforms of prostaglandin-endoperoxide synthase (cyclooxygenase), PGHS-1 and PGHS-2, mediate physiologic and inflammatory processes, respectively, implies separate pathways of arachidonic acid metabolism with different benefits to the host. Functional segregation of these steps in endogenous arachidonic acid metabolism in a single cell in response to different stimuli is now demonstrated. When mouse bone marrow-derived mast cells developed in interleukin-3 (IL-3)-containing medium were cultured with c-kit ligand in combination with IL-10 and IL-1 beta, transient expression of PGHS-2 mRNA and protein occurred in a dose- and time-dependent fashion, accompanied by substantial release of prostaglandin D2 (PGD2) into the culture medium from 2 to 10 h. In contrast, induction of PGHS-2 did not mediate an increase in PGD2 generation in response to stimulation with IgE and antigen. After a longer period of culture, from 24 to 48 h, the expression of PGHS-1 increased, as did the increase in IgE/antigen-dependent generation of PGD2. Dexamethasone, which inhibited the induction of PGHS-2 but not PGHS-1, and a PGHS-2-selective inhibitor suppressed cytokine-induced PGD2 generation but not IgE-dependent PGD2 generation. Thus, at a time when both PGHS-1 and PGHS-2 are present in bone marrow-derived mast cells, they function independently by coupling to different stimulus-initiated pathways to PGD2 generation from endogenously derived arachidonic acid.

Increases in 5-lipoxygenase activating protein expression account for enhanced capacity for 5-lipoxygenase metabolism that accompanies differentiation of peripheral blood monocytes into alveolar macrophages.

The capacity for 5-lipoxygenase (5-LO) metabolism of endogenous arachidonic acid (AA) is greater in alveolar macrophages (AM) than in their circulating precursors, peripheral blood monocytes (PBM); however, the ability of PBM to metabolize exogenous AA to 5-LO products is comparable to that of AM. In the present study, we examined the enzymatic mechanisms by which 5-LO metabolism of AA is altered during differentiation of PBM in the lung. Resting human AM exhibited greater steady-state levels of 5-LO (7-fold) and LTA4 hydrolase (2-fold) proteins than autologous PBM; moreover, they differed from PBM in that they contained a significant amount of 5-LO associated with the particulate fraction. Importantly, AM contained 40-fold more 5-lipoxygenase activating protein (FLAP) than did PBM, which correlated well with the relative abilities of intact AM and PBM to metabolize endogenous AA to leukotrienes. The FLAP inhibitor MK-886 was unable to block leukotriene synthesis from exogenous AA in the two cell types, despite its ability to completely inhibit 5-LO metabolism of endogenous AA. These observations indicate that, although FLAP is essential for the synthesis of leukotrienes from endogenous AA, perhaps by presenting AA to 5-LO, it is not required for 5-LO metabolism of exogenous AA. The differing roles of FLAP in 5-LO metabolism of endogenous versus exogenous AA are consistent with the conclusion that it is the markedly greater expression of FLAP, rather than of 5-LO, that is primarily responsible for the increased leukotriene synthesis from endogenous AA that accompanies PBM differentiation into AM.

Changes in amniotic arachidonic acid metabolism associated with increased cyclo-oxygenase gene expression.

To study the differences in the metabolism of arachidonic acid, to prostaglandins and other eicosanoids, between amnion cells before and after labour. To study the changes in the expression of the type 1 cyclo-oxygenase gene associated with the changes in arachidonic acid metabolism. Amnion cells collected before labour, at elective caesarean section, and following spontaneous labour and delivery were established in mono-layer culture. Intracellular arachidonic acid pools were radio-labelled and the metabolic fate of endogenous archidonic acid was then studied using high performance liquid chromatography. RNA was extracted from the cell cultures and expression of the cyclooxygenase gene was studied using northern hybridisation to a sheep cyclo-oxygenase cDNA. Metabolism of endogenous arachidonic acid in amnion cells established in culture prior to labour is principally via lipoxygenase and epoxygenase enzyme pathways to di- and mono-HETEs and EET with little cyclo-oxygenase metabolism to prostaglandins. Following labour there is a large increase in arachidonic acid metabolism with a change in the cyclo-oxygenase: lipoxygenase enzyme pathway ratio in favour synthesis of prostaglandin E2. Whilst synthesis of lipoxygenase metabolites doubles, the increase in prostaglandin E2 synthesis is ten fold. Expression of the cyclo-oxygenase gene is significantly greater in cell cultures established following spontaneous labour and delivery than in those established following elective caesarean section prior to labour. In association with labour there is an increase in arachidonic acid metabolism in amnion cells and a change in the ratio of metabolism via cyclo-oxygenase and lipoxygenase enzyme pathways to increase synthesis of prostaglandin E2. This change is associated with increased expression of the cyclooxygenase gene.

Glutathione peroxidase activity and metabolism of arachidonic acid in peripheral blood mononuclear cells from elderly subjects.

1. Since ageing has been associated with a decrease in both immune responses and antioxidant defences, this study was undertaken to compare the glutathione peroxidase activity in peripheral blood mononuclear cells of healthy elderly and young donors. The mean value of glutathione peroxidase activity was significantly lower in the aged group (-36%) than that observed in the young control group (n = 10). 2. This defect was accompanied by a marked increase (+106%) in the oxygenated metabolism of endogenous arachidonic acid by lipoxygenases as judged by the radiolabel associated with hydroxyeicosatetraenoic acids in [3H]arachidonic acid-prelabelled peripheral blood mononuclear cells, whereas the cyclo-oxygenase activity, estimated by the radiolabel associated with thromboxane B2, was not significantly altered. 3. Upon stimulation by the mitogenic lectin concanavalin A, the radioactivity associated with total eicosanoids (free arachidonic acid plus hydroxyeicosatetraenoic acids plus thromboxane B2) was significantly increased over basal levels in the peripheral blood mononuclear cells of both the elderly and the control groups. However, the mitogen-induced increase was lower in the elderly group (+48%) than in the control group (+131%). Upon concanavalin A stimulation, the radioactivity of hydroxyeicosatetraenoic acids was increased by only 96% in peripheral blood mononuclear cells from the elderly group compared with 350% in control cells. Similarly, the radioactivity associated with thromboxane B2 was increased by only 82% in peripheral blood mononuclear cells from the elderly group compared with 218% in control cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Eicosanoid production by mouse peritoneal macrophages during Toxoplasma gondii penetration: role of parasite and host cell phospholipases

The metabolism of endogenous arachidonic acid by mouse resident peritoneal macrophages infected in vitro with Toxoplasma gondii was studied. Prelabeling of macrophages with [5,6,8,9,11,12,14,15-3H]arachidonic acid and challenge with tachyzoites for 15 min resulted in a high mobilization of free labeled arachidonic acid (178%) in the culture medium. The parasites also triggered the synthesis of 6-keto-prostaglandin F1 alpha (47%), prostaglandin E2 (44%), leukotrienes C4 and D4 (33%) and 5-, 12-hydroxyeicosatetraenoic acids (155%). The study indicated that during the intracellular development phase of the parasites, 6-keto-prostaglandin F1 alpha (38%), prostaglandin E2 (31%) leukotrienes C4 and D4 (15%), hydroxyeicosatetraenoic acids (43%), and free arachidonic acid (110%) were secreted into the culture medium. Pretreatment of tachyzoites with phospholipase A2 inhibitors (4-p-bromophenacyl bromide and quinacrine) and no calcium in the culture medium resulted in inhibition of tachyzoite penetration into the macrophages and a decrease of the arachidonic acid metabolism. The triggering of the arachidonic acid cascade by T. gondii was dependent on the active penetration of the parasites into the macrophages, whereas preincubation of the macrophages with phospholipase A2 inhibitors did not affect penetration or free arachidonic acid release, thereby supporting a role for parasite phospholipase in the penetration process and in arachidonic acid mobilization from macrophage membrane phospholipids. Moreover, treatment of macrophages with phospholipase A2 inhibitors decreased the activities of the cyclooxygenase and lipoxygenase pathways, also suggesting an activation of host cell phospholipase A2 by the parasite.

Vasoactive intestinal peptide and helodermin inhibit the release of cyclo-oxygenase products induced by leukotriene D 4 and bradykinin from guinea-pig perfused lung

Vasoactive intestinal peptide (VIP, 10 nM) inhibited the release of cyclo-oxygenase products, detected by both bioassay and radioimmunoassay, induced by leukotriene (LT) D 4 (3–30 pmol) and bradykinin (BK, 3–30 nmol) from guinea-pig isolated perfused lung. Helodermin (10 nM), a peptide that is structurally related to VIP, and salbutamol (10 nM), a β 2-adrenoceptor agonist, evoked a similar inhibitory effect on LTD 4-induced release of cyclo-oxygenase products. The generation of TxB 2 and 6-keto-PGF 1α following stimulation with exogenously administered arachidonic acid (30–300 nmol) was not significantly attenuated in the presence of either VIP, helodermin or salbutamol. These results show that VIP, helodermin and salbutamol are potent inhibitors of the release of cyclo-oxygenase products induced by agonists known to activate endogenous arachidonic acid metabolism in guinea-pig lung. Since the metabolism of exogenously administered arachidonic acid was not inhibited these results suggest that the inhibitory effect may be exerted on events preceding the mobilisation of arachidonic acid and may involve cyclic AMP.

Interleukin-1α-stimulated fibroblast eicosanid synthesis is not mediated by interleukin-6

Adherent human dermal fibroblasts secreted interleukin-6, prostaglandin E 2, prostaglandin I 2 and 15-hydroxyeicosatetraenoic acid (assayed by radioimmunoassay) during a 3 h incubation period. Although human dermal fibroblasts did not secrete interleukin-1α or interleukin-1β, human recombinant interleukin-1α stimulated arachidonic acid metabolism and interleukin-6 synthesis. This effect was, at least partly, dependent on de novo protein synthesis. In contrast, human recombinant interleukin-6 had no effect on the synthesis and release of the eicosanoids measured. Human recombinant interleukin-1α also stimulated the metabolism of [ 14C]arachidonic acid, but only if fibroblast were pre-incubated with the cytokine for three hours. Our data indicate that (a) fibroblasts secrete interleukin-6 but not inter-1, (b) interleukin-1α, but not interleukin-6, stimulates fibroblast arachidonic acid metabolism and (c) the mechanisms involved in the metabolism of endogenous arachidonic acid are more sensitive to human recombinant interleukin-1α than those involved in metabolism of the exogenous substrate.

The mechanisms of preterm labour; the interaction between amnion cells and leukocytes in the metabolism of arachidonic acid

Chorioamnionitis is frequently associated with preterm labour. We have used a cell culture model system to examine the effects of leukocytes upon the metabolism of endogenous arachidonic acid from within amnion cells. We have demonstrated that activated leukocytes release substances which increase the overall release and metabolism of endogenous arachidonic acid within amnion cells causing an increase in prostaglandin E 2 production as well as a smaller increase in non-cyclooxygenase metabolism. When amnion cells and leukocytes are cultured together, in addition to prostaglandin E 2 production by amnion cells, arachidonic acid released by the amnion cells appears to be metabolised by leucocytes to prostaglandin F 2 α , prostacyclin and thromboxane A 2. Prostaglandins E 2 and F 2 α are the principal cyclo-oxygenase products of this interaction. We postulate that chorioamnionitis stimulates preterm labour not only by causing an increase in prostaglandin E2 synthesis by amnion cells but by metabolism of amnion derived arachidonic acid to the powerfully oxytocic prostaglandin F 2 α by leukocytes.

Age-related changes in arachidonic acid peroxidation and glutathione-peroxidase activity in human platelets

Lipid peroxidation, vitamin E level and glutathione-peroxidase activity were determined in platelets from elderly (>68 years) and young (21–43 years) people. To further assess the platelet lipid peroxidation, the metabolism of endogenous arachidonic acid in unstimulated platelets as well as that of the exogenous one were measured in the two groups. The oxygenated metabolites of arachidonic acid were enhanced in the elder population under both conditions tested. In addition, the platelet malondialdehyde content, a marker of the overall lipid peroxidation, was also found significantly increased in platelets from aged subjects. On the other hand, the platelet vitamin E level and the glutathione-peroxidase activity were significantly depressed in the elder group compared to the young one. These results suggest that the increased platelet activation observed with age could be linked to the accumulation of lipoxygenase-dependent peroxides associated with the decreased antioxidative defence of the cells, especially glutathione-peroxidase activity.

Arachidonic acid cycloxygenase and lipoxygenase pathways are differently activated by platelet activating factor and the calcium-ionophore A23187 in a primary culture of astroglial cells

The aim of our study has been to investigate the metabolism of endogenous arachidonic acid or that of radiolabeled arachidonate in astroglial cells, stimulated with platelet activating factor (PAF) and with the calcium-ionphore A23187. Primary cultures of astroglial cells were obtained from brain cortex of one-day-old rats and were characterized by immunofluorescent staining vs glial fibrillary acidic protein. In labeled cells, diacylglycerol was formed after stimulation with platelet activating factor, whereas mainly the release of labeled arachidonic acid from phospholipids was observed after stimulation with calcium-ionophore. Both PAF and the calcium-ionophore A23187 actively stimulated the formation of the cycloxygenase products PGD 2, TXB 2 and 6-keto-PGF 1α measured by radio- or enzyme-immunoassay. Differences were observed, instead, in the formation of the lipoxygenase metabolites, the hydroxyeicosatetraenoic acids, which were measured by high pressure liquid chromatography (HPLC) with on line radiodetection for the labeled products, and Leukotriene C 4, measured by radioimmunoassay. The formation of hydroxyacids by stimulated cells was confirmed by gas chromatography-mass spectrometry (GC-MS). In labeled cells, both agonists induced the formation of 12- and 15-hydroxyeicosatetraenoic acids, whereas stimulation of unlabeled cells with calcium ionophore resulted in formation of 12-hydroxyeicosatetraeonic acid and Leukotriene C 4. Our results suggest that in astroglial cells, PAF, a compound which is produced in several tissues including brain, mobilizes a selected arachidonic acid pool, possibly associated with diacylglycerol production, from phospholipids, thus activating the conversion of the released fatty acid via the cyclo and the 12-lipoxygenase pathways.

Arachidonic acid metabolism in cultured astrocytes: Presence of 12-lipoxygenase activity in the intact cells

In our previous study, it was revealed that the exogenous arachidonic acid is mainly metabolized by the lipoxygenase pathway in the cell-free homogenate of cultured astrocytes. This is apparently in contrast with other studies reporting production and release of the cyclooxygenase products (prostaglandins and thromboxanes) by cultured astrocytes. To help specify the reason for this discrepancy, the metabolism of endogenous arachidonic acid in the intact monolayer of cultured astrocytes was examined. When the astrocytes were stimulated with calcium ionophore A23187, a peak coeluted with authentic 12-hydroxyeicosatetraenoic acid (12-HETE) on reverse-phase high-performance liquid chromatography (RP-HPLC) was observed. Formation of this peak was not affected by indomethacin, a speciic inhibitor for cyclooxygenase, but completely inhibited by BW755C, an inhibitor for both cyclooxygenase and lipooxygenases. Furthermore, the ultraviolet spectrum of the substance giving this peak agreed well with that of authentic 12-HETE. The amount of 12-HETE formed and released by the astrocytes was estimated to be 293.1 ng/mg protein/1 h. Taken together, these results suggest that the endogenous arachidonic acid is mainly metabolized by 12-lipoxygenase in the intact monolayer of astrocytes.

Glomerular stereospecific synthesis and hemodynamic actions of 8,9-epoxyeicosatrienoic acid in rat kidney

Renal glomerular and cortical metabolism of endogenous arachidonic acid by cytochrome P-450 epoxygenase yields 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acids (EET). Using gas chromatography-mass spectrometry, we measured the synthesis of 8,9-EET from an endogenous pool of arachidonic acid in normal rat kidney. The (8S,9R) isomer was favored over the (8R,9S) isomer in a ratio (%) of 59 to 41 in isolated glomeruli and 68 to 32 in cortex tissue. (8S,9R)- but not (8R,9S)-EET elicited dose-dependent vasoconstriction on intrarenal administration in the euvolemic Munich-Wistar rat. Micropuncture measurements of glomerular dynamics revealed that (8S,9R)-EET increased afferent arteriolar resistance (RA) leading to reductions in single-nephron plasma flow rate (QA), net transcapillary hydraulic pressure difference (delta P), and consequently single-nephron glomerular filtration rate (SNGFR). There was no significant change in the value of the glomerular capillary ultrafiltration coefficient (Kf). In the presence of a cyclooxygenase inhibitor, indomethacin, the effects of 8,9-EET were reversed. RA fell leading to increases in QA and delta P, with resultant augmentation of SNGFR. Under these conditions, a modest reduction if Kf was noted. Thus (8S,9R)-EET is a stereoselective renal vasoconstrictor, preferentially generated over its optical isomer, (8R,9S)-EET, suggesting that it is biologically relevant and implying specific structural requirements for EET receptor activation. The principal mechanism of action of 8,9-EET is preglomerular vasoconstriction. The vasoconstrictor effect of 8,9-EET is CO dependent.

???Ex vivo??? release of eicosanoid from human brain tissue

The specific mechanism underlying the genesis of vasogenic brain edema is still debated: the role of arachidonic acid is considered extremely important, as it is a possible activator of self-maintaining reactions enhancing the release of vasoactive and cytotoxic compounds. The relationship between arachidonic acid metabolism and brain edema has been studied primarily in brain tissue samples or in the extracellular fluid, whereas the residual capacity of perilesional tissue to synthesize and release eicosanoids has not been investigated. In the present study, perilesional samples of brain tissue were available from 4 patients operated on for brain metastasis, from 8 patients who had malignant neuroepithelial tumors, from 4 with meningiomas, and from 5 with subarachnoid hemorrhage. A brain edema index was calculated from the preoperative computed tomographic scan. The "ex vivo" method allowed determination of the residual capacity of endogenous arachidonic acid metabolism. The edema index is significantly higher in patients with brain metastasis (6.5 +/- 0.8) and neuroepithelial tumors (3.6 +/- 0.2) than in those with meningiomas (1.5 +/- 0.06), subarachnoid hemorrhage (1.7 +/- 0.18), and in controls. In patients with metastatic and neuroepithelial tumors there is a significant correlation between peritumoral brain edema and the capacity to synthesize leukotriene C4 (P less than 0.05); the capacity to synthesize leukotriene C4 is also significantly elevated after subarachnoid hemorrhage (13.91 +/- 2.6 ng/ml of incubation medium) when compared with control cases (5.56 +/- 0.91). The capacity to synthesize prostacyclin is significantly higher in patients with brain metastasis than in those with neuroepithelial tumors and meningiomas (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Endogenous Arachidonic Acid Metabolism by Calcium Ionophore A23187-stimulated Lamb Lungs: Effect of Hypoxia

We have determined eicosanoid production from endogenous arachidonic acid by neonatal lamb lungs stimulated with calcium ionophore A23187 during normoxia and hypoxia. Lungs of lambs 19 to 25 d of age were isolated and perfused with cell-free Krebs' bicarbonate buffer at a flow rate of 15 to 20 ml/kg/min. After 30 min of equilibration in a recirculating system, A23187 was added to the perfusate in a 5-microM concentration and perfusion continued for 15 min more. Eicosanoids were measured in perfusate and lung homogenate supernatant. Cyclooxygenase metabolites prostaglandin (PG) E2, thromboxane A2, and PGI2, were measured by radioimmunoassay, and 5-lipoxygenase metabolites leukotrienes (LT) B4, C4, D4, and E4 by high performance liquid chromatography. During normoxia, all three cyclooxygenase metabolites were present in perfusate, but only PGI2 and thromboxane A2 were present in lung homogenate supernatant. Prostacyclin constituted 50% of all the cyclooxygenase products measured. LTC4 and LTD4 were detected in both perfusate and lung homogenate supernatant with little production of LTE4 and LTB4. During hypoxia, the profile of cyclooxygenase products was unchanged and prostacyclin production was not increased. However, the profile of leukotriene metabolites was altered. LTC4 synthesis was markedly reduced. The synthesis of LTE4 and LTB4 was increased 10-fold, with most of the leukotrienes being retained in lung tissue. We conclude that hypoxia significantly alters leukotriene metabolism of endogenous arachidonic acid by calcium ionophore-stimulated lungs. The increased production by stimulated lungs during hypoxia of LTE4, a substance that may increase lung capillary permeability, and that of LTB4, a powerful chemoattractant, may be important contributing factors to lung injury.

Morphological Aspects Sodium lauryl sulfate stimulates the metabolism of endogenous arachidonic acid in epidermal cell suspensions

Morphological Aspects Sodium lauryl sulfate stimulates the metabolism of endogenous arachidonic acid in epidermal cell suspensions