Prostaglandin Synthesis In Cells Research Articles

Prostaglandin dehydrogenase (PGDH) in granulosa cells of primate periovulatory follicles is regulated by the ovulatory gonadotropin surge via multiple G proteins

The ovulatory gonadotropin surge increases granulosa cell prostaglandin synthesis as well as prostaglandin dehydrogenase (PGDH), the key enzyme responsible for prostaglandin metabolism. To investigate gonadotropin regulation of PGDH in the primate follicle, monkey granulosa cells were obtained across the 40-h periovulatory interval. PGDH activity was low before the ovulatory hCG stimulus, peaked 12–24 h after hCG, and was low again 36 h after hCG administration. Granulosa cells maintained in vitro with hCG showed a similar temporal pattern of PGDH. The LH/CG receptor can utilize multiple signaling pathways to regulate intracellular events. Gonadotropin-stimulated cAMP appears to act primarily via the Epacs to increase PGDH mRNA, protein, and activity. In contrast, PLC activation of PKC likely decreases PGDH mRNA, protein, and activity late in the periovulatory interval. Increased, then decreased PGDH activity may delay accumulation of prostaglandins in the follicle until late in the periovulatory interval, contributing to timely ovulation in primates.

Linking NO Production and Prostaglandin Synthesis in Inflammation

Principal inflammatory responses in mammals include the induction of nitric oxide and prostaglandin synthesis in cells of the immune system. Kim et al. report that the enzymes that produce these molecules, nitric oxide synthase and cyclooxygenase-2, respectively, interact in macrophage cells. Nitric oxide synthase delivers NO to cyclooxygenase-2. This modification of cycooxygenase-2 by nitric oxide, known as S -nitrosylation, activates the enzyme. This synergism between the two systems may help in the design of potential novel anti-inflammatory drugs. S. F. Kim, D. A. Huri, S. H. Snyder, Inducible nitric oxide synthase binds, S-nitrosylates, and activates cyclooxygenase-2. Science 310 , 1966-1970 (2005). [Abstract] [Full Text]

Phospholipase A2 Inhibitors as Potential Anti-Inflammatory Agents

Phospholipase A(2) (PLA(2))-catalyzed hydrolysis of membrane phospholipids results in the stoichiometric production of a free fatty acid, most importantly arachidonic acid, and a lysophospholipid. Both of these phospholipid metabolites serve as precursors for inflammatory mediators such as eicosanoids or platelet-activating factor (PAF). Since it was initially discovered that non-steroidal anti-inflammatory drugs inhibit prostaglandin synthesis, a vast amount of drug development has been performed to selectively inhibit the production of the inflammatory metabolites of arachidonic acid while preserving their protective role. This research has culminated in the development of selective cyclooxygenase-2 (COX-2) inhibitors that act on the inducible, inflammatory COX enzyme, but do not affect the constitutive prostaglandin synthesis in cells that is mediated via COX-1. The development of PLA(2) inhibitors as potential anti-inflammatory agents has also been extensively pursued since the release of arachidonic acid from membrane phospholipids by PLA(3) is one of the rate-limiting factors for eicosanoid production. In addition to the production of eicosanoids, PLA(2)-catalyzed membrane phospholipid hydrolysis is also the initiating step in the generation of PAF, a potent inflammatory agent. Thus, inhibition of PLA(2) activity should, in theory, be a more effective anti-inflammatory approach. However, developing an inhibitor that would be selective for the production of inflammatory metabolites and not inhibit the beneficial properties of PLA(2) has so far proved to be elusive. This review will focus on agents used currently to inhibit PLA(2) activity and will explore their possible therapeutic use.

Analysis of the Secretory Phospholipase A2 That Mediates Prostaglandin Production in Mast Cells

Prostaglandin D2 (PGD2) synthesis in activated mast cells occurs in two phases, an early phase that is dependent on prostaglandin synthase 1 and a delayed phase that is dependent on activation-induced prostaglandin synthase 2 gene expression. Early phase PGD2 synthesis in activated mast cells also requires the activity of a secretory phospholipase A2 (PLA2). It has been thought that the secretory PLA2 expressed in mast cells is group IIa PLA2, encoded by the Pla2 g2a gene. However, activated bone marrow-derived mast cells prepared from Pla2 g2a+/+ mice and mast cells prepared from mice with a mutation in the Pla2 g2a gene both demonstrate early phase PGD2 synthesis. Moreover, mast cells from both murine strains secrete PLA2 activity following activation. Northern and reverse transcriptase/polymerase chain reaction analyses demonstrate that mast cells from Pla2 g2a+/+ and Pla2 g2a-/- mice do not express group IIa PLA2 message. Instead, Northern and reverse transcriptase/polymerase chain reaction analyses demonstrate that both Pla2 g2a+/+ and Pla2 g2a-/- mast cells express mRNA for group V PLA2, encoded by the Pla2gV gene. An antisense oligonucleotide directed against group V PLA2 is also able to inhibit both the early phase of PGD2 production and the secretion of PLA2 activity by activated mast cells. Our data suggest that (i) group IIa PLA2 does not play a significant role in murine mast cell prostaglandin synthesis, (ii) group V PLA2 mediates early mast cell PGD2 production and transcellular PGE2 production in murine mast cells, and (iii) much of the data, based on studies with chemical inhibitors and antibodies, suggesting that group IIa PLA2 is responsible for arachidonic acid mobilization needs to be reevaluated.

Ultralow concentrations of ibuprofen activate cell prostaglandin synthesis.

The interest in the prostaglandin (PG) synthesis by animal cells today grows steadily because of the difficulties in obtaining them by any other way. Murine peritoneal macrophages can under certain conditions synthesize large amounts of PGs. The effect of well-known nonsteroidal anti-inflammatory drug ibuprofen on PG synthesis by the cells using a high-performance liquid chromatography (HPLC) method with fluorescence detection of 4-bromomethyl-7-methoxy-coumarin (BrMMC) derivatives was studied. In our case, the main metabolites were PGE2 and PGF2a. The PG synthesis activation effect was shown by ibuprofen concentrations in the 10(-10)-10(-14) M range with the maximum effect of 10(-12)M. In this case, the ibuprofen effect was comparable in value with the effect of well-known cell PG synthesis activator--calcium ionophore A23187. Although the exact mechanism of such an effect is not clear at the moment, at low concentration, ibuprofen itself is able to activate PG synthesis in murine peritoneal macrophages.

Regulation of Prostaglandin Endoperoxide H Synthase-2 Expression by 2,3,7,8-Tetrachlorodibenzo-p-dioxin

We have examined the molecular mechanisms for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-stimulated prostaglandin synthesis in Mardin Darvey canine kidney cells (MDCK). TCDD stimulates prostaglandin synthesis in these cells, at least in part, by elevating prostaglandin endoperoxide H2synthase-2 (PGHS-2) levels. TCDD-stimulated transcription of the PGHS-2 gene was maximal (6-fold) within 2 h and resulted in a 100-fold increase in PGHS-2 mRNA and a 25-fold increase in PGHS-2 protein levels by 4 h. Transient transfection experiments using luciferase-reporter plasmids demonstrated that control element(s) responsible for TCDD activation of the murine PGHS-2 promoter in MDCK cells are located in the first 965 nucleotides upstream from the PGHS-2 transcriptional initiation site. A canonical xenobiotic response element, similar to those that control transcription of other well-known TCDD-sensitive genes, is present at position −157, but does not appear to be sufficient for halogenated aromatic hydrocarbon (HAH) activation of the PGHS-2 promoter. TCDD failed to stimulate transcription from the PGHS-2 promoter when reporter plasmids were transfected into Hepa 1c1c7 cells, a line which contains the functional aryl hydrocarbon receptor. It seems likely that inappropriate expression of PGHS-2 may contribute to the toxic effects of TCDD and other HAHs. In particular, PGHS-2 expression may affect those toxic reactions that involve inappropriate cellular growth, such as dermal hyperplasia and tumor formation. It is also likely that elevated synthesis of prostaglandins, which are potent regulators of immune function, could play a role in the immunotoxicity associated with HAH exposure.

Human peritoneal mesothelial cell prostaglandin synthesis: Induction of cyclooxygenase mRNA by peritoneal macrophage-derived cytokines

Increasing evidence suggests that the mesothelial cell contributes to the control of inflammation in both the normal and inflamed peritoneal cavity. The present study examines the regulation of prostaglandin production by human peritoneal mesothelial cells (HPMC) following stimulation with peritoneal macrophage-conditioned medium and the cytokines interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha). IL-1 beta and TNF-alpha stimulated significant release of prostaglandin above background levels in a time and dose dependent manner. Stimulation of HPMC with IL-1 beta (500 pg/ml) or TNF-alpha (100 pg/ml) for 24 hours resulted in the release of 24.5 +/- 4.3 (N = 11) (z = 3.40, P < 0.001 vs. control) and 19.4 +/- 4.5 (N = 10; z = 3.29, P < 0.001 vs. control) pg 6-keto-PGF1 a/micrograms cellular protein, respectively. Pretreatment of HPMC with dexamethasone (10(-6) to 10(-9) M) inhibited both constitutive and cytokine stimulated prostaglandin synthesis in a dose dependent manner. Both PMø-CM and PMø-S.epiCM stimulated 6-keto-PGF1 alpha and PGE2 synthesis by HPMC in a time and dose dependent manner (PMø-S.epiCM >> PMø-CM). Co-incubation of HPMC with PMø-S.epiCM in the presence of anti-IL-1 beta and/or anti-TNF-alpha antibody, interleukin-1 receptor antagonist or soluble TNF receptor (TNF p75) significantly reduced the capacity of these supernatants to stimulate prostaglandin synthesis. Exposure of HPMC to cytokines or PMø-S.epiCM resulted in the time dependent increase in the levels of both Cox-1 and Cox-2 mRNA as assessed by RT/PCR analysis with the greatest increase being seen for Cox-2. These data demonstrate specific stimulation of eicosanoid metabolism in HPMC by peritoneal macrophage derived cytokines, indicating the possible importance of these mediators in the activation of intraperitoneal prostaglandin synthesis. HPMC prostaglandins might act as important pro/anti-inflammatory mediators contributing to a cytokine network in the peritoneal cavity during CAPD peritonitis.

Mechanisms by which Candida albicans induces endothelial cell prostaglandin synthesis

One strategy for improving resistance to opportunistic pathogens is to determine host cellular responses during the invasion process and upregulate those responses that are relevant to host defense mechanisms. Within this context, we have shown previously that invasion of endothelial cells by Candida albicans in vitro causes increased production of prostaglandins. As a prerequisite for modulating endothelial cell prostaglandin production, we now characterize the mechanisms through which this process occurs. Endothelial cell invasion by C. albicans appeared to stimulate the conversion of arachidonic acid into prostaglandins by upregulating the synthesis of endothelial cell cyclooxygenase and increasing the activity of the endothelial cell phospholipase. The enhanced activities of these two enzymes were independent of calphostin C-sensitive protein kinase C and resulted in the increased production and extracellular secretion of prostaglandin I2 (PGI2), PGF2 alpha, and PGE2. The secretion of these prostaglandins had no effect on the amount of endothelial cell injury induced by C. albicans. The role of the increased prostaglandin secretion by endothelial cells is likely related to modulation of the leukocyte response at the candida-leukocyte-endothelial cell interface.

Glucocorticoid stimulation of amnion cell prostaglandin synthesis: suppression by protein kinase C inhibitors and independence of phorbol ester-sensitive protein kinase C

Glucocorticoids stimulate the prostaglandin E 2 production of confluent amnion cell cultures, but have no stimulatory effect on the PGE 2 output of freshly isolated human amnion cells. Since protein phosphorylation may modify the responsiveness of target cells to steroids, and activators of protein kinase C (PKC), as well as corticosteroids, promote amnion cell PGE 2 output by stimulating the synthesis of prostaglandin endoperoxide H synthase (PGHS), we investigated the possibility that PKC is involved in the glucocorticoid-induction of PGE 2 synthesis in cultured amnion cells. The dexamethasone-induced PGE 2 output of arachidonate-stimulated cells was blocked by the protein kinase inhibitors staurosporine, K-252a, H7, HA1004, and sphinganine, in a manner consistent with their effect on PKC. However, dexamethasone increased the PGE 2 production of cultures treated with maximally effective concentrations of the PKC-activator compound TPA. Moreover, dexamethasone stimulated PGE 2 synthesis in cultures which were desensitized to TPA-stimulation by prolonged phorbol ester treatment. Concentration-dependence studies showed that staurosporine completely (> 95%) blocked glucocorticoid-provoked PGE 2 synthesis at concentrations which did not inhibit TPA-stimulated prostaglandin output, and that K-252a inhibited the effect of TPA by more than 95% at concentrations which decreased the effect of dexamethasone only moderately ≈ 40%). Dibutyryl cyclic AMP had no influence on the basal- or dexamethasone-stimulated PGE 2 production, and on the staurosporine inhibition of the steroid effect. These results show that glucocorticoids and phorbol esters control amnion PGE 2 production by separate regulatory mechanisms. It is suggested that the response of human amnion cells to glucocorticoids is modulated by protein kinase(s) other than phorbol ester-sensitive PKC and cyclic AMP-dependent protein kinase.

Endothelin-1 induces stimulation of prostaglandin synthesis in cells obtained from canine airways by bronchoalveolar lavage

Endothelin-1 (ET-1), a potent mediator released by airway epithelial cells, often exerts its effects in the lung through stimulation of arachidonic acid (AA) metabolism. To investigate its range of influence, we studied the action of ET-1 on the synthesis and release of thromboxane (TX)B 2, prostaglandin (PG)D 2, and histamine from canine airways cell obtained by bronchoalveolar lavage (BAL). ET-1 (10 −10, 10 −9 and 10 −8M) stimulated production of TXB 2 and PGD 2 by BAL cell preparations in a dose-related manner in the absence of measurable histamine release. Release of TXB 2 was 10-fold higher than that of PGD 2. The effect of ET-1 on AA metabolism in alveolar macrophages was evaluated in preparations of purified (>99%) cells labelled for 20–22 hrs with 3H-AA prior to stimulation. ET-1 (10 −8, 10 −7, 10 −6M) induced significant, dose-related release of 3H-AA and its metabolites from alveolar macrophages, to levels 350% above control. These studies indicate that low levels of ET-1 can stimulate AA metabolism in resident luminal airway cells, including alveolar macrophages, and suggest that the function of these luminal cells may be modulated by the epithelium, in vivo, through the release of this peptide into the airways.

Role of protein kinase C in the regulation of prostaglandin synthesis in human endothelium.

The present study specifically addresses the role of protein kinase C (PKC) activation in human endothelial cell Ca2+ mobilization, a response that is functionally coupled to the production of the potent arachidonate (AA) metabolite, prostacyclin (PGI2). Phorbol 12-myristate 13-acetate (PMA), alpha-thrombin, and sodium fluoride (NaF), a direct G-protein activator, produced a rapid and time-dependent translocation of PKC from the cytosol to the membrane. Activation of PKC by brief pretreatment of human umbilical vein endothelial cell (HUVEC) monolayers with PMA resulted in the inhibition of NaF-induced inositol phosphate increases and attenuation of both alpha-thrombin- and NaF-activated increases in intracellular Ca2+ (Ca2+i). Ca2+ mobilization induced by ionophore A23187 was not affected by PKC preactivation, suggesting PKC-dependent negative feedback inhibition of phosphatidylinositol (PI)-specific phospholipase C (PLC). Agonist-stimulated AA release and PGI2 synthesis in PMA-pretreated cultured human endothelial cells, however, was potentiated, and the enhanced PGI2 synthesis produced by A23187, NaF, and alpha-thrombin was dependent upon the dose of PMA. Treatment of HUVEC monolayers with an intracellular Ca2+ chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N'N'-tetraacetic acid-acetoxymethylester (BAPTA-AM), dramatically reduced alpha-thrombin-, NaF-, and A23187-induced PGI2 synthesis, demonstrating the importance of Ca2+i availability in PGI2 synthesis. BAPTA pretreatment did not inhibit PMA-induced PKC activation, and BAPTA-mediated inhibition of agonist-stimulated PGI2 synthesis was partially attenuated by prior PMA pretreatment. Staurosporine, a potent PKC inhibitor, at concentrations that inhibited PKC-induced phosphorylation of histone-1, augmented both alpha-thrombin- and NaF-induced production of inositol phosphates but markedly inhibited alpha-thrombin-, NaF-, and A23187-induced PGI2 synthesis. The downregulation of PKC activity by prolonged PMA treatment (18 h) produced similar inhibition of PGI2 synthesis by these agonists (approximately 50% inhibition). These studies indicate that the integrated phospholipase A2 and PLC activities are under complex regulation by factors that include both PKC activation and [Ca2+i]. PKC exerts dual effects on prostaglandin synthesis via negative regulation of Gp-coupled PI-specific PLC and positive feedback regulation of AA release and PGI2 synthesis. PKC is thus a critical determinant in the regulation of human endothelial cell prostaglandin synthesis by both receptor-mediated and G-protein-dependent cellular activation.

IL-1α increases arachidonyl-COA: Lysophospholipid acyltransferase activity and stimulates [ 3H] arachidonate incorporation into phospholipids in rat mesangial cells

The proinflammatory cytokine interleukin-1α is a potent stimulus of prostaglandin synthesis. We have previously shown that IL-1 amplifies mesangial cell prostaglandin synthesis by inducing synthesis of a non-pancreatic phospholipase A 2. Phospholipase A 2 activation results in the formation of lysophospholipids and free fatty acids. We now investigate the effects of IL-1α on reacylation of lysophospholipids. Incubations with IL-1α for 24 hours significantly stimulated mesangial cell [ 3H] arachidonic acid incorporation but not [ 3H] oleic acid incorporation into phosphatidylinositol and phosphatidylethanolamine. Lysophospholipid acyltransferase activity was measured in vitro. Cytokine treatment increased enzyme activity when lysophosphatidylcholine, lysophosphatidylethanolamine and lysophosphatidylinositol were used as exogenous substrates. We conclude that IL-1 promotes cellular phospholipid remodeling by stimulating the deacylation and reacylation of phospholipids.

Regulation of endothelial cell prostaglandin synthesis by glutathione.

Prostaglandin synthesis in in vitro systems is dependent on glutathione and peroxide concentrations. We tested the effects of glutathione depletion and H2O2 exposure on prostaglandin synthesis in cultured porcine aortic endothelial cells. Depletion of glutathione using buthionine sulfoximine (BSO), diethylmaleate, and 2,4-chlorodinitrobenzene increased prostaglandin synthetic capacity. Production of prostacyclin, but not prostaglandin E2, from exogenous arachidonic acid was significantly greater than in controls. Glutathione depletion also resulted in enhanced production of prostacyclin from exogenous prostaglandin H2. These responses were not due to direct effects of glutathione-depleting agents on prostaglandin synthetic enzymes. Exposure to H2O2 also altered prostaglandin synthetic capacity in endothelial cells. While 5 microM H2O2 stimulated prostaglandin production from exogenous arachidonate, 25 and 50 microM were found to be inhibitory. Prostaglandin synthetic capacity was greater in BSO-treated cells which were exposed to 5 and 10 microM H2O2 than in cells exposed to H2O2 alone. However, prostaglandin synthetic capacity was greatly reduced in BSO-treated cells exposed to 50 microM H2O2. Thus, normal levels of cellular glutathione exert an inhibitory influence on prostaglandin synthesis. However, glutathione depletion increases the sensitivity of prostaglandin synthesis to inhibition by 50 microM H2O2.

Suppression of bacterial cell wall-induced polyarthritis by recombinant gamma interferon

Group A streptococcal cell wall fragments (SCW) induce erosive polyarthritis, characterized by synovial cell hyperplasia and intense mononuclear cell infiltration, in susceptible rats. Because of the known antiproliferative and immunomodulatory effects of interferon (IFN), we evaluated the effect of systemically administered alpha, beta and gamma IFN on the evolution of these destructive lesions. Treatment with gamma IFN not only reduced the acute response, but had an even greater suppressive effect on the chronic mononuclear cell-mediated destructive phase of the disease (articular index 10.2 +/- 1.2 for SCW only versus 3.8 +/- 0.7 for SCW + gamma IFN; p less than 0.01). Treatment with gamma IFN was more effective in the suppression of the arthritis than alpha, beta IFN. Histopathologic evaluation of the joints demonstrated that gamma IFN-treated animals had significantly fewer inflammatory cells, and less synovial hyperplasia and erosions than the SCW controls. gamma IFN suppression of mononuclear cell prostaglandin synthesis and synovial fibroblast proliferation was consistent with its anti-arthritic effects. These data indicate that the pathophysiology of SCW-induced erosive polyarthritis is subject to regulatory control by gamma IFN and that the mechanisms of suppression may be relevant in the treatment of rheumatoid arthritis.

Inhibition of prostaglandin synthesis after metabolism of menadione by cultured porcine endothelial cells.

We have examined the effects of menadione on porcine aortic endothelial cell prostaglandin synthesis. Addition of 1-20 microM menadione caused a dose- and time-dependent inhibition of stimulated prostaglandin synthesis with an IC50 of 5 microM at 15 min. Concentrations greater than 100 microM menadione were necessary to increase 51Cr release from prelabeled cells. Recovery of enzyme inactivated by menadione required a 6-h incubation in 1% serum. In a microsomal preparation, menadione was shown to have no direct effect on conversion of arachidonic acid to prostaglandins. In intact cells menadione caused only a 40% inhibition of the conversion of PGH2 to prostacyclin. Enzymes involved in the incorporation and the release of arachidonic acid were not affected by menadione (20 microM, 15 min). Menadione undergoes oxidation/reduction reactions in intact cells leading to partial reduction of oxygen-forming, reactive oxygen species. In our cells menadione was found to increase KCN-resistant oxygen consumption. Further, an increased accumulation of H2O2 was observed with a time course consistent with menadione-induced inhibition of prostaglandin synthesis. We conclude that menadione at sublethal doses caused inhibition of prostaglandin synthesis. The mechanism involves inactivation of PGH2 synthase by a reactive species resulting from metabolism of menadione by endothelial cells.

Recovery of porcine aortic endothelial cell prostaglandin synthesis following inhibition by sublethal concentrations of hydrogen peroxide

Confluent monolayers of porcine aortic endothelial cells exposed for 10 min to 100 μM H 2O 2 lose their capacity to produce prostaglandins in response to addition of saturating exogenous arachidonic acid. Significant recovery of prostaglandin I 2 and E 2 synthesis occurred within 3 h and full enzymatic capacity returned by 6 h. Reducing the injury by exposure to half the amount of H 2O 2 allowed prostaglandin I 2 production to recover to a greater extent in 3 h, while cells exposed for 60 min to either 0.5 or 1.0 mM H 2O 2 demonstrated no recovery. Pre-treatment with either actinomycin D or cycloheximide also prevented recovery following exposure to 100 μM peroxide. Injured cells did not recover when incubated with balanced salts after removal of peroxide, while incubation with medium 199 allowed for the complete return of synthetic capacity. Addition of 1% fetal calf serum in medium 199 did not facilitate recovery. Production of prostaglandins from endogenous arachidonic acid, released by either bradykinin or the ionophore A23187, was also inhibited by H 2O 2 exposure, however, full recovery of this stimulated synthesis occurred within 3 h. Cycloheximide pre-treatment completely inhibited recovery of bradykinin-induced prostaglandin I 2 synthesis. These data demonstrate that sublethal concentrations of H 2O 2 irreversibly inactivate fatty acid cyclooxygenase and that synthesis of new enzyme is required for recovery. This return of activity occurs more rapidly for production of prostaglandins from endogenous arachidonic acid compared with production following addition of exogenous substrate.

Dynamic response of PG synthesis to peptide hormones and osmolality in renal tubular cells.

A superfusion technique was adapted to collagenase-dispersed renal medullary and cortical tubular cells to study prostaglandin (PG) synthesis in response to arginine vasopressin (AVP), angiotensin II (ANG II), bradykinin (BK), Ca2+ ionophore A23187, and to changes in osmolality. Medullary and cortical cells promptly responded to the stimuli by an increase in PGE2 and PGF2 alpha production, whereas 6-keto-PGF1 alpha was not detected. AVP and BK were active on medullary cells, and ANG II was active mainly on cortical cells. A23187 stimulated PG synthesis in both cells but predominantly in the medulla. PG synthesis was dependent on the presence of extracellular Ca2+. The Ca2+ entry blocking agents verapamil and lanthanum did not inhibit the PG response to AVP, BK, and ANG II. Thus peptide hormone-stimulated PG synthesis in renal tubular cells did not depend on Ca2+ influx through channels blocked by these agents. Hyperosmolar NaCl or mannitol stimulated PG synthesis in cortical and, more markedly, in medullary cells. Hyperosmolar urea inhibited PGE2 synthesis stimulated by peptide hormones, NaCl, and A23187 in both cell preparations. In conclusion, the superfusion of isolated tubular cells is a useful method to study the dynamic aspects of renal PG release in response to various sequentially applied stimuli.

The Influence of Dietary Essential Fatty Acids on Rat Immunocompetent Cell Prostaglandin Synthesis and Mitogen-Induced Blastogenesis

Sprague-Dawley rats were fed diets including 10% corn oil (CO), 10% hydrogenated coconut oil (HCO) or 10% linseed oil (LO), and immune cell populations isolated from peripheral blood and spleen were examined for alterations in prostaglandin E (PGE) synthesizing capacity and mitogen-induced blastogenesis. Culture conditions were optimized by incubating the cells in serum obtained from animals fed the same diet. The fatty acid profiles of these sera reflected the composition of the dietary fat ingested. Both the LO and HCO diet treatments resulted in significantly lower PG-synthesizing capacity by both unstimulated and phytohemagglutinin (PHA)-stimulated peripheral blood mononuclear cells or splenocytes when compared to the CO group. Mitogen-induced [3H]thymidine uptake by splenocytes from rats fed the HCO diet was twofold higher than responses observed in cells from animals fed the LO or CO diets. The results suggest that mitogenesis is not influenced by the diet-induced change in immune cell PGE2 synthesizing capacity. Enhanced [3H]thymidine incorporation was associated with a greater degree of saturation of dietary fat.

Effects of bovine parathyroid hormone and 1,25-dihydroxyvitamin D3 on the production of prostaglandins by cells derived from human bone

Local production of prostaglandins by osteoblasts may be important in controlling the bone resorbing activity of some hormones which have receptors on osteoblasts. We have demonstrated that osteoblast-like cells derived from human bone can incorporate [14C]arachidonic acid into phospholipids and synthesise immunoreactive PGE. Parathyroid hormone increases both the release of incorporated arachidonic acid and the synthesis of PGE. This is the first demonstration of modulation of bone cell prostaglandin synthesis by a bone resorbing hormone.

Interferon-mediated inhibition of prostaglandin synthesis in human mononuclear leukocytes

In this study, the question of whether human leukocyte-derived and fibroblast-derived interferon had an effect on prostaglandin metabolism in human peripheral blood mononuclear cells has been considered. Both leukocyte- and fibroblast-derived interferon were potent inhibitors of mononuclear cell prostaglandin synthesis at low physiological concentrations. Inhibition required a minimum incubation of 1 hr. Interferon had no effect on release of arachidonic acid; synthesis of hydroxy fatty acids was slightly increased.