The Presynaptic Effects of Arachidonic Acid and Prostaglandin E2 at the Frog Neuromuscular Junction

Arachidonic acid and prostaglandin E₂ decreased the frequency of miniature endplate potentials with producing any changes in the their amplitude-time parameters. Arachidonic acid and prostaglandin E₂ decreased the quantum composition of endplate currents and the amplitude of the third phase of the nerve ending response, which reflects currents though potential-dependent K⁺ channels. A perineural method was used to demonstrate that arachidonic acid and prostaglandin E₂ suppressed the nerve ending Ca²⁺ current. The cyclooxygenase blocker indomethacin increased neurotransmitter secretion and decreased the third phase of the nerve ending response. The effects of arachidonic acid and prostaglandin E₂ on evoked neurotransmitter release were not seen in the presence of indomethacin, while the third phase of the response continued to show a reduction. It is suggested that prostaglandin E₂ mediates the effects of arachidonic acid on spontaneous and evoked neurotransmitter secretion, Ca²⁺ currents, and Ca²⁺-dependent K⁺ currents. In addition, arachidonic acid and prostaglandin E₂ had their own effects on potential-dependent K⁺ currents in nerve endings. __________ Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 91, No. 3, pp. 268–276, March, 2005.     

Nitric oxide production by Leishmania-infected macrophages and modulation by prostaglandin E2

Nitric oxide (NO), produced by the nitric oxide synthase (iNOS) enzyme, is the most-important molecule responsible for the killing of Leishmania parasites by macrophages. In previous work we have demonstrated that, after activation with recombinant human interferon-γ and/or bacterial lipopolysaccharide, human macrophages infected with Leishmania infantum are able to produce nitric oxide and to express nitric oxide synthase. The arachidonate derivative prostaglandin E₂ has been shown to modulate various macrophage activities, and in particular nitric oxide production, sometimes with opposite effects, related to experimental conditions. In this work we have evaluated nitric oxide release and parasite killing by peripheral blood-derived L. infantum-infected human macrophages in vitro stimulated with lipopolysaccharide and simultaneously treated with prostaglandin E₂. Experiments were also performed in the presence of the nitric oxide synthase inhibitor l-N ^G monomethylarginine (l-NMMA) and of the cyclooxygenase inhibitor indomethacin. Nitric oxide release in supernatants of macrophage cultures was measured by the Griess reaction for nitrites. Parasite killing was microscopically evaluated by fluorescent dyes. Results demonstrated that macrophages stimulated with lipopolysaccharide and treated with prostaglandin E₂ exhibited increased nitric oxide producation and parasite killing, which were significantly reduced by either l-NMMA or indomethacin. In indomethacin-treated macrophages, nitric oxide production and leishmanicidal ability were partially restored by the addition of exogenous prostaglandin E₂. Taken together, these results indicate that prostaglandin E₂ may be involved in nitric oxide production, and possibly in the host-protective immune response against Leishmania. Moreover, the demonstration of a stimulatory role of prostaglandin E₂ on nitric oxide production induced by intracellular pathogens in humans is interesting in the light of a possible pharmacological regulation of nitric oxide by modulation of prostaglandin E₂ synthesis. Received: 27 March 2001 / Accepted: 24 August 2001     

Development of antitumor activity in LPS-stimulated mouse granuloma macrophages

Macrophage-mediated antitumor activity is believed to be regulated by E-type prostaglandins released by target cells or even by macrophages themselves. In these studies we showed that a subcutaneous injection of polyacrylamide beads (Biogel P100), induced in mice, a population of immature macrophages which became fully cytostatic to syngeneic P815 mastocytoma when pulsed in vitro with lipopolysaccharide (LPS). Blockade of prostaglandin synthesis by indomethacin prevented LPS effect and led to a substantial resumption of target growth. Addition of PGE₂ did not reverse the indomethacin effect but inhibited macrophage-mediated cytostatic activity. These findings suggest that acquisition of cytostatic properties by macrophages is, at a certain stage of their maturation, under the control of both PGE₂ and another endogenously produced eicosanoid.     

Natural killer (NK) and antibody-dependent cellular cytotoxicity (ADCC) activities can be differentiated by their different sensitivities to interferon and prostaglandin E1

Though purported to be identical cells (or in identical populations of cells), the natural killer (NK) cell mediating spontaneous natural cytotoxicity and the killer (K) cell mediating antibody-dependent cellular cytotoxicity (ADCC) may not be totally identical, at least in susceptibility to regulation by the immunomodulators prostaglandin E₁ (PGE₁) and interferon (IFN). We demonstrate here that NK cells are always enhanced by IFN, while K cells are inhibited from binding targets, resulting in fewer effectors at optimal concentrations of antibody. Only at 10- to 100-fold suboptimal concentrations of antibody is ADCC activity enhanced. As measured by magnitude of inhibition and dose-response titration, ADCC activity is less sensitive to the effects of PGE₁ than is NK activity in the⁵¹Cr release assay and single-cell assay. After overnight incubation with or without PGE₁, whatever sensitivity ADCC activity had to PGE₁ is lost. However, NK cells incubated in the presence of PGE₁ overnight are still sensitive to inhibition. Indomethacin boosts NK activity without having any effect on ADCC activity. Finally, NK activity is substantially reduced by overnight incubation of cells at room temperature, which has no effect on K cells.     

Mitogenic actions of orthoclone OKT3 on human peripheral blood lymphocytes: Effects of monocytes and serum components

The Orthoclone monoclonal antihuman T lymphocyte antibody, OKT3, induced maximal DNA, RNA and protein synthesis in peripheral mononuclear blood cells (PMBC) at concentrations as low as 10 ng ml⁻¹. This pronounced mitogenic activity was highly dependent on the presence of monocytes: removal of these cells from PMBC suspensions by complement (C)-dependent lysis with the antimonocyte antibody OKM1, completely abrogated the proliferative responsiveness of the remaining lymphocytes. The addition of adherent cells to OKM1-treated PMBC demonstrated the strict monocyte requirement for the mitogenic activity of OKT3. Mitogenic responses to OKT3 were most marked when PMBC were cultured in media containing heat-inactivated fetal calf serum (FCS) but they were considerably weaker in cultures supplemented with heat-inactivated human serum (HS). Moreover, aggregated human IgG and its Fc fragments (but not monomeric IgG and its Fab fragments) inhibited the mitogenicity of OKT3: their inhibition could be explained by stimulation of monocytes, resulting in increased prostaglandin E release, since (a) prostaglandin E₂ itself strongly suppressed OKT3 activity and (b) indomethacin blocked the inhibitory effects of aggregated HuIgG.The present data demonstrate that OKT3 shows a particular pattern of mitogenicity: the strict monocyte requirement, the inhibitory effects of HS, aggregated human IgG and prostaglandin E₂ were not observed for the phytomitogen PHA.     

Re-establishment of gap junctional intercellular communication (GJIC) between human endometrial carcinomas by prostaglandin E2

Reduced intercellular communication via gap junctions is correlated with carcinogenesis. Gap junctional intercellular communication (GJIC), between normal human endometrial epithelial cells is enhanced when endometrial stromal cells were present in culture. This enhancement of GJIC between normal epithelial cells also occurs when they are cultured in medium conditioned by stromal cells. This observation indicated that a soluble compound (or compounds) produced and secreted by stromal cells mediates GJIC in epithelial cells. Previous studies have shown that endometrial stromal cells release prostaglandin E₂ (PGE₂) and prostaglandin F_2α (PGF_2α) under physiological conditions. When we evaluated the response of normal endometrial epithelial cells to various concentrations of PGE_2, we found enhanced GJIC with 1 nM PGE₂. This is a smaller increase in GJIC than that induced by medium conditioned by stromal cells. When the extracellular concentration of PGE₂ was measured after incubation with stromal cells, it was found to be similar to the concentrations showing maximal GJIC between the normal epithelial cells. When indomethacin was used to inhibit prostaglandin synthesis by stromal cells, GJIC was reduced but not eliminated between normal endometrial epithelial cells. These observations suggest that although PGE₂ secreted by stromal cells is an important mediator of GJIC between the epithelial cells, it is not the sole mediator. Transformed endometrial epithelial cells did not demonstrate GJIC even in the presence of stromal cells. However, we were able to re-establish GJIC in transformed epithelial cells when we added PGE₂ to the cells. Our findings show that PGE₂ may serve as an intercellular mediator between stromal and epithelial cells that regulates GJIC in normal and malignant epithelial cells. This suggests that maintenance of GJIC by preserving or replacing PGE₂ secretion by endometrial stromal cells may have the potential to suppress carcinogenesis in endometrial epithelial cells.     

Relationship of the suppression of macrophage mediated tumor cytotoxicity in conjunction with secretion of prostaglandin from the macrophages of breast cancer patients

Peripheral blood monocyte derived macrophages obtained from breast cancer patients are noncytotoxic towards human tumor cells. However, when indomethacin, a prostaglandin synthetase inhibitor, was added to the macrophage tumor cell incubation mixture, the breast cancer patient's macrophages became capable of killing the tumor cells. Furthermore, the macrophage preparations obtained from breast cancer patients demonstrated a 64% increase in the secretion of PGE₂, when compared with macrophages obtained from normal donors. It is already known that prostaglandin can inhibit both natural lymphocyte cytotoxicity and antibody dependent cell-mediated cytotoxicity against human tumor cells in vitro. These results indicate that increased synthesis of prostaglandin can also inhibit macrophage mediated cytotoxicity. Therefore, it is possible that manipulation of this mechanism might enhance the effectiveness of the macrophage response and should be a consideration in assessing macrophage-tumor cell interaction in vitro and in vivo.     

Prostaglandin E2 release from dermis regulates sodium permeability of frog skin epithelium

In the present study we have compared the effects of increased intracellular Ca²⁺ in whole frog skin and isolated epithelium (Rana temporaria). Cellular Ca²⁺ was increased by the use of the endoplasmic reticulum Ca²⁺ ATPase inhibitor, thapsigargin. Serosal addition of thapsigargin to the whole frog skin increased the Na⁺ transport by increasing the apical Na⁺ permeability. This could be blocked by the addition of indomethacin or by removal of Ca²⁺ from the serosal solution. The increase in Na⁺ transport was accompanied by an increased prostaglandin E₂ release. This indicated that the response in Na⁺ transport was due to a Ca²⁺ dependent activation of the prostaglandin E₂ synthesis. Addition of thapsigargin to isolated epithelia inhibited the Na⁺ transport and had no effect on the prostaglandin E₂ release, though the prostaglandin E₂ release from the isolated epithelia could be increased by the addition of arachidonic acid. Addition of prostaglandin E₂ increased the cAMP contents of the isolated epithelia significantly, whereas thapsigargin had no significant effect on the cAMP level. Our results demonstrate that serosal addition of thapsigargin causes a release of prostaglandin E₂ from the dermis below the transporting epithelium. The prostaglandin E₂ diffuses to the epithelium where it activates the Na⁺ transport by increasing cellular cAMP. The epithelium itself does not contribute significantly to the prostaglandin E₂ synthesis. Furthermore an increase in intracellular Ca²⁺ in the epithelial cells without a concomitant increase in prostaglandin E₂ release leads to an inhibition of the active Na⁺-transport.     

Prostaglandin-induced changes on mitogen-activated bone marrow cells

The mitogenic activation of bone marrow cells by dextran sulfate was inhibited by prostaglandin E₂ and enhanced by addition of a prostaglandin synthetase inhibitor such as indomethacin. In contrast, dextran sulfate-induced mitogenesis of spleen cells appeared enhanced by prostaglandin E₂ and inhibited by indomethacin. This dextran sulfate activation of bone marrow cells was partially dependent on phagocytic accessory cells, and the effect of indomethacin on dextran sulfate activation appeared only when macrophages were present in the cultures.When purified bone marrow lymphocytes were used, the dextran sulfate-induced mitogenesis was macrophage-independent, and the presence of indomethacin did not induce any enhancement in the response.Since dextran sulfate acts as a general leukocyte activator, the possibility of a differential modulation of these cells by prostaglandins and prostaglandin synthetase inhibitors is suggested.     

Pharmacological and biochemical activities of Tenoxicam (Ro 12-0068), a new non-steroidal anti-inflammatory drug

Tenoxicam, a new non-steroidal anti-inflammatory drug has been compared with piroxicam and indomethacin in a range of pharmacological and biochemical inflammation test systems. In a chronic (17-day) adjuvant arthritis in the rat, tenoxicamand piroxicam were equally effective in reducing several indices of inflammation and were less ulcerogenic and better tolerated than indomethacin. The oxicams reduced the oedematous and cellular components of a carrageenan pleurisy at 4 hours while at 24 hours they increased exudate volume and selectively inhibited the accumulation of mononuclear cells. These agents also reduced the inflammatory component of a delayed hypersensitivity response to methylated bovine resum albumin in the mouse. The oxicams were about 100-fold less active than indomethacin as inhibitors of prostaglandin synthetase but all three compounds reduced about equally the release of prostaglandin E₂ from phagocytosing rat PMN and interleukin 1-stimulated human rheumatoid synovial cells. The compounds had no effect on the release of superoxide anion, lysosomal enzymes or collagenase from cultured cells, neither did they inhibit isolated collagenase. Only indomethacin stabilized albumin against heat denaturation.     

Synergism in the repression of COX-2- and TNFα-induction in platelet activating factor-stressed human neural cells

Platelet activating factor (PAF; β-acetyl-γ-O-hexadecyl-l-α-phosphatidylcholine) triggers a rapid pro-inflammatory gene expression program in primary cultures of human neural (HN) cells. Two genes and gene products consistently induced after PAF treatment are the cytosoluble prostaglandin synthase cycloooxygenase-2 (COX-2) and the pro-apoptotic tumor necrosis factor alpha (TNFα). Both of these mediators are associated with the activation of inflammatory signaling, neural cell dysfunction, apoptosis and brain cell death, and both have been found to be up-regulated after brain injury in vivo. In this study we investigated the effects of the non-halogenated synthetic glucocorticoid budesonide epimer R (BUDeR), the novel PAF antagonist LAU-0901, and the electron spin trap and free radical scavenger phenyl butyl nitrone (PBN), upon early COX-2 and TNFα gene activation and prostaglandin E₂ (PGE₂) release in PAF-stressed primary HN cells. The data indicate that these three biochemically unrelated classes of inflammatory repressors act synergistically in modulating PAF-induced up-regulation of COX-2, TNFα, and PGE₂ by quenching oxidative stress or inflammatory signaling, resulting in increased HN cell survival. These, or analogous classes of compounds, may be useful in the design of more effective combinatorial pharmacotherapeutic strategies in the treatment of complex neuro-inflammatory disorders.     

Extensive polynucleate giant cell formation after X-irradiation or addition of colchicine in SV40 transformed Syrian hamster cells

Summary X-irradiation of Syrian hamster cells transformed by simian virus 40 which exhibited evidence of the presence of the viral genome was consistently followed by extensive polynucleate giant cell formation.With the possible exception of cells derived from an adenovirus 12-induced tumor this phenomenon has not been observed in other Syrian hamster cell systems, i.e. lines of oncogenic cells originally exposed to SV₄₀ virus but in which no evidence of the viral genome could be subsequently demonstrated; cells transformed by polyoma virus; a line of oncogenic cells not associated with virus; continuous lines and primary cultures of normal cells.Extensive post-irradiation polynucleate giant cell formation did not occur in SV₄₀-transformed lines of human cells; in primary cultures of human cells of various tissue origin; in lines of cells derived from human malignant tumors. A line of African green monkeys cells (Cercopithecus aethiops) after irradiation also failed to react in this manner.Treatment with colchicine of SV₄₀-transformed hamster and human cells induced extensive polynucleate giant cell formation only in hamster cell systems. Therefore the effect of colchicine appears to parallel that of irradiation.Various possible mechanisms to account for the phenomenon of post-irradiation and colchicine-induced polynucleate giant cell formation in hamster cells bearing the SV₄₀ genome are suggested and discussed.Dedicated to the Honor of the 60th birthday of ProfessorSven Gard. Supported in part by Grant No. AI-01992-08 from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, U.S.P.H.S. Bethesda, Maryland.Post Doctoral Research Fellow, Rockefeller Foundation.U.S.P.H.S. Research Development Career Award No.5-K3-AI-14,617,02.U.S.P.H.S. Special Fellow, No. 2-F3-CA-13,444-03, National Cancer Institute, National Institutes of Health.     

Time-course of phospholipase A2, eicosanoid release and cellular accumulation in rat immunological air pouch inflammation

Phospholipase A₂ activity in the rat air pouch cavity was determined after induction of a reverse passive Arthus reaction. Time-course of phospholipase A₂ activity appeared to correlate with increased prostaglandin E₂ levels in inflammatory exudate and with the influx of mononuclear inflammatory cells.Local administration of anti-inflammatory drugs such as dexamethasone, indomethacin, or a PLA₂ inhibitor such as p-bromophenacyl bromide significantly inhibited exudate volume, cellular influx, granuloma formation, exudate PGE₂ levels and PLA₂ activity, to varying degrees. Dexamethasone treatment significantly reduced all parameters determined, whereas p-bromophenacyl bromide had a significant inhibitory effect on PLA₂ activity and PGE₂ release, and indomethacin only restored PGE₂ levels.These results show that PLA₂ is neither the only nor the most important factor involved in the development of subchronic inflammation.     

Dissociation between renal prostaglandin E2 and renin release. Effects of glucagon,dopamine and cyclic AMP in dogs

VIKSE, A., BUGGE, J., DAHL, E. & KIIL, F. 1985. Dissociation between renal prostaglandin E₂ and renin release. Effects of glucagon, dopamine and cyclic AMP in dogs. Acta Physiol Scand 125 , 619–626. Received 14 March 1985, accepted 10 May 1985. ISSN 0001–6772. University of Oslo, Institute for Experimental Medical Research, Ullevaal Hospital, Norway. To examine the relationship between prostaglandin E₂ (PGE₂) and renin release, glucagon, dopamine and dibutyryl cyclic AMP (DB-cAMP) were infused into dog kidneys during autoregulatory dilation of preglomerular vessels. Autoregulatory vasodilation, which enhances PGE₂ and renin release, was induced by renal arterial constriction or ureteral occlusion. Glucagon infusion increased both PGE₂ and renin release during autoregulatory vasodilation, and renin release was almost abolished after inhibiting PGE₂ release by indomethacin. In contrast, dopamine and DB-cAMP infused during autoregulatory vasodilation increased renin release without significantly changing PGE₂ release. Stimulation of renin release was not dependent on vasodilatory effects, which for all drugs were greatly diminished during autoregulatory vasodilation. Hence, glucagon stimulates both PGE₂ and renin release. Most of the increase in renin release during glucagon infusion is prostaglandin-dependent since indomethacin greatly reduced the stimulatory effect. In contrast, dopamine and DB-cAMP stimulate renin release without increasing PGE₂ release as previously found for β-adrenergic stimulation.     

Are prostaglandins cytoprotective in the human large intestine?—the effect of indomethacin on rectal mucosal function and prostaglandin E2 releasein vivo

To test the hypothesis that prostaglandins are cytoprotective in the human large intestine, we investigated the effect of withdrawal of treatment with indomethacin suppositories on bowel habit and on rectal mucosal electrolyte transport and prostaglandin production in 8 patients taking such treatment for rheumatological disorders. Discontinuation of indomethacin doubled rectal mucosal prostaglandin E₂ release (p<0.05) measured byin vivo rectal dialysis. Although there was no significant overall change in stool frequency, stool consistency, rectal bleeding or sodium absorption (also assessed by rectal dialysis), sigmoidoscopic appearance (p=0.05), rectal mucosal potential difference (p<0.05) and potassium transport (p=0.01) each reverted towards normal on indomethacin withdrawal. These results accord with the theory that, as in the upper gastrointestinal tract, prostaglandins may play a role in the maintenance of rectal mucosal structure and function.     

Modulation of antitumour activity of macrophages by regulation of eicosanoids and cytokine production

Production and release of arachidonic acid (AA) compounds (eicosanoids: prostaglandins-cycloxygenase and leukotrienes-lipoxygenase) and monokines (TNF-α, IL-1 and others) play an essential role in the expression of antitumour activity of macrophages (MO). We investigated the possibility of inducing the antitumour activity of peritoneal murine and human MO by regulating their production of eicosanoids and monokines. The antitumour activity of MO was inversely correlated to production of PGE₂ and directly correlated to production of leukotrienes (LTC₄ and LTD₄). Thus, indomethacin rendered murine MO cytostatic against tumour cells and enhanced the antitumour activity of human peritoneal macrophages from renal patients on CAPD (continuous ambulatory peritoneal dialysis), and leukotriene inhibitors (NDGA-nordihydroguaiaretic acid and AA861) prevented antitumour cystostatic activity of MO. Human peritoneal MO collected during periods of inflammation (infectious peritonitis) were more active against tumour cells, especially when cultured in the presence of LPS, and their activity was correlated to increase with the release of TNF and of IL-1β. Human peritoneal MO from inflammation-free patients reacted against a human tumour cell line if cultured with LPS and TPA (phorbol-myristate acetate) and were therapeutically effective against the same palpable s.c. tumours implanted in nude mice.     

Reciprocal correlation between the expression of cyclooxygenase-2 and E-cadherin in human bladder transitional cell carcinomas

Carcinoma cells become more motile and invasive via downmodulation of E-cadherin. Cyclooxygenase-2 (COX-2) expression is associated with tumor invasion and metastasis. The aim of this study is to investigate the relationship between the expression of COX-2 and E-cadherin in a bladder cancer cell line and human bladder transitional cell carcinoma (TCCs). Phorbol 12-myristate 13-acetate (PMA) treatment for 5637 bladder cancer cells increased COX-2 expression, slightly induced Slug expression, and decreased E-cadherin expression. Ectopic expression of COX-2 or prostaglandin E₂ (PGE₂) treatment for 5637 cells reduced E-cadherin expression. This finding was confirmed by the result that knockdown of COX-2 expression or indomethacin administration increased the expression of E-cadherin. When compared with cells’ motility in serum-free medium, the treatment of PMA and PGE₂ increased cell motility, and indomethacin treatment slightly decreased cell motility. In the tissues of bladder TCCs, COX-2 expression was inversely correlated with membranous E-cadherin expression and positively correlated with nuclear β-catenin expression. The expression of COX-2 and nuclear β-catenin expression was significantly higher in TCCs of high grade and invasive growth than in TCCs of low grade and noninvasive growth. In contrast, membranous E-cadherin expression was more decreased in tumors of high grade and invasive growth. In addition, nuclear β-catenin expression was significantly related to tumor recurrence. We suggest that COX-2 pathway reduces membranous E-cadherin expression in bladder TCCs and their expression pattern may provide important information in predicting the clinical behavior of bladder TCCs.     

Xenogeneic responses in vitro in the Syrian hamster, Mesocricetus auratus. I. Evidence for a normal T cell repertoire.

We have investigated the ability of Syrian hamster lymphocytes to generate cytotoxic responses against classical MHC molecules on xenogeneic cells. Our data show that hamster lymph node cells can be stimulated in an in vitro primary mixed lymphocyte culture by irradiated rat or mouse lymphoid cells to produce a substantial cytotoxic response assayed on 51Cr-labelled xenogeneic blasts. Using congenic recombinant rat and mouse targets, the specificity of the cytotoxic activity could be localized to genetic regions known to determine classical class I histocompatibility antigens in these two species. In addition, specific cytotoxicity could be demonstrated on transfectant target cells expressing only the relevant rat class I molecules, and specific cytotoxicity could be inhibited by a monoclonal antibody specific for a rat classical class I molecule. Elimination of B cells did not affect the ability of the responder population to generate xenogeneic cytotoxicity. In further experiments it was shown that hamster xenogeneic killers could distinguish between two subtly modified forms of a rat classical class I molecule essentially as efficiently as can allogeneic rat killers. Finally, lymph node cells from female hamsters primed in vivo with male hamster cells were able to generate weak but significant male-specific cytotoxicity after boosting in vitro. In sum, our experiments show that the general outline of the cytotoxic T cell repertoire of the Syrian hamster is conventional. These results suggest that monomorphic class I molecules expressed by the Syrian hamster probably function normally to direct the differentiation of its cytotoxic T cell repertoire.     

Correlation of leukocyte interleukin-1 production with the stimulation of prostaglandin and tissue factor synthesis by human umbilical vein endothelial cells

Human leukocyte suspensions (neutrophils 80–85%, monocyte 15–20%) were incubated alone or with cultured human umbilical vein endothelial cells. Leukocytes were either directly added to the endothelial cell cultures or separated from them by a 0.4 micron insert filter. Supernatants or cell lysates were obtained at 0.5, 1, 2, and 4 hours of incubation. Supernatants were assayed for the prostacyclin (PGI₂) metabolite 6-keto prostaglandin F₁ and prostaglandin E₂ (PGE₂) by radioimmunoassay and for interleukin-1 (IL-1) by the thymocyte co-mitogen assay. Cell lysates were analyzed for cell-associated procoagulant activity (PCA). Co-incubation of endothelial cells with leukocytes stimulated the synthesis of PGI₂, PGE₂, and PCA. These biochemical changes correlated partially with the release of IL-1 beta. The results suggest that IL-1 released in monocyte/neutrophil co-cultures can produce prothrombotic (increased PCA expression) and inflammatory changes (increased synthesis of vasodilatory and permeability enhancing PGI₂ and PGE₂) in endothelial cells. Neutrophils may represent a source of the released IL-1 and/or may act to stimulate monocyte release of this cytokine and thus play an important role in vascular pathology by a mechanism unrelated to their more direct cytotoxic activity.