The effect of prostaglandin E1 on experimental colitis in the rat

Prostaglandin E₁ (PGE₁) is known to have a strong vasodilator effect and to block coagulation and inflammation in high concentrations. The aim of this study has been to investigate whether PGE₁ has an inhibitory effect on inflammation in experimental colitis. Experimental colitis was produced by rectal instillation of 10% acetic acid in 60 rats. These were divided into prostaglandin (PG) (n = 30) and control groups (n = 30). Twelve hours later, an intraperitoneal injection of 2 μg PGE₁ in 1 ml saline was given to the PG group and 1 ml saline to the control group. This was repeated daily and the animals were sacrified in groups of 10 on the 3rd, 7th and 10th day. Histopathological examination and hydroxyproline determination for assessment of collagen synthesis were performed. PGE₁ significantly decreased inflammation on third day with the hydroxyproline level significantly higher in the PG group compared with the control group (p < 0.05). This difference was however not significant at the 7th and 10th day. The present study supports a beneficial role for prostaglandin E₁ in reducing the severity of colonic inflammation following chemically induced colitis but only in the early stages of development.

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Résumé. La prostaglandine E₁ (PGE₁) est connue pour avoir une action vasodilatatrice importante et pour bloquer la coagulation et l'inflammation à haute concentration. Le but de cette étude est de déterminer si PGE₁ a un effet inhibiteur sur l'inflammation dans la colite expérimentale. Une colite expérimentale a été produite par l'instillation rectale d'une solution à 10% d'acide acétique chez 60 rats. Ces derniers ont été divisés en deux groupes de 30 sujets: l'un recevant de la prostaglandine (PG) et l'autre servant de témoin. Douze heures après l'induction de la colite, une injection intrapéritonéale de 2 μg de PGE₁ solution dans 1 ml de sérum a été administrée au groupe PG et 1 ml de sérum au goupe témoin. Cette injection a été répétée de manière quotidienne et les animaux ont été sacrifiés aux 3e, 7e et 10e jours. Des études histo-pathologiques et une détermination du taux d'hydroxyproline pour évaluer la synthèse du collagène ont été réalisées dans tous les cas. PGE₁ diminue de manière significative l'inflammation au 3e jour et le taux d'hydroxypoline est nettement plus élevé que dans le groupe témoin (P < 0,05). Cette différence n'est toutefois pas significative au 7e ni au 10e jours. Cette étude souligne le r?le bénéfique de la prostaglandine E₁ réduisant la sévérité d'une inflammation colique secondaire à une colite chimique expérimentale; cet apport n'est toutefois visible que dans les premiers jours de l'inflamma-tion.

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Accepted: 16 December 1996     

Mucosal and plasma prostaglandin E2 in ulcerative colitis.

BACKGROUND/AIMS: Despite extensive studies, the role of prostaglandins in the course of inflammatory bowel diseases and their possible usefulness as predictive indicators of inflammation, remain largely speculative. The aim of this study was to determine whether mucosal and plasma concentrations of prostaglandin E2 (PGE2) are affected by the clinical course and degree of colonic injury in patients with ulcerative colitis. METHODOLOGY: PGE2 concentration was measured with an enzyme immunoassay (EIA) in biopsies of rectal mucosa and in the plasma of 38 patients with ulcerative colitis and 12 controls. Patients were divided into groups according to mild or severe clinical course of the disease, and with respect to scored endoscopical picture. RESULTS: Ulcerative colitis resulted in an increase of mucosal and plasma concentrations of PGE2, that was significantly elevated in patients with a severe clinical course of the disease. These concentrations increased depending on degree of mucosal injury. A significant, positive correlation with endoscopical score regarding plasma and mucosal PGE2 concentration, as well as between them, was found. CONCLUSIONS: Plasma and mucosal PGE2 rise simultaneously with degree of colonic injury. Because of a good correlation with mucosal injury and PGE2 content, measurement of plasma PGE2 could be considered as a possible surrogate marker of bowel inflammation.     

Effect of inhibition of prostaglandin E2 production on pancreatic infection in experimental acute pancreatitis

Objective. Acute pancreatitis is one the important causes of systemic inflammatory response syndrome (SIRS). SIRS results in gut barrier dysfunction that allows bacterial translocation and pancreatic infection to occur. Indomethacin has been used to reduce inflammatory process and bacterial translocation in experimental models. The purpose of this study was to determine the effect of inhibition of prostaglandin E2 (PGE2) production on pancreatic infection. Materials and methods. An experimental model of severe acute pancreatitis (AP) was utilized. The animals were divided into three groups: sham (surgical procedure without AP induction); pancreatitis (AP induction); and indomethacin (AP induction plus administration of 3 mg/kg of indomethacin). Serum levels of interleukin (IL)-6 and IL-10, PGE2, and tumor necrosis factor (TNF)-α were measured 2 h after the induction of AP. We analyzed the occurrence of pancreatic infection with bacterial cultures performed 24 h after the induction of AP. The occurrence of pancreatic infection (considered positive when the CFU/g was >105), pancreatic histologic analysis, and mortality rate were studied. Results. In spite of the reduction of IL-6, IL-10, and PGE2 levels in the indomethacin group, TNF-α level, bacterial translocation, and pancreatic infection were not influenced by administration of indomethacin. The inhibition of PGE2 production did not reduce pancreatic infection, histologic score, or mortality rate. Conclusion. The inhibition of PGE2 production was not able to reduce the occurrence of pancreatic infection and does not have any beneficial effect in this experimental model. Further investigations will be necessary to discover a specific inhibitor that would make it possible to develop an anti-inflammatory therapy.     

Effect of dopamine on prostaglandin E2 content in gastric mucosa

The effects of dopamine (DA) on the prostaglandin (PG) E2 content of rat gastric mucosa was investigated. There was a 17.5% increase in gastric mucosal blood flow (BF) after administration of DA (5 micrograms/kg/min iv). After pretreatment with fusaric acid (FA), an antagonist of dopamine beta hydroxylase, DA increased BF by 27.8%. The PGE2 content in DA and DA + FA groups increased at rates of 45.8% and 42.4%, respectively. The PGE2 content in gastric mucosa after incubation following Basso's method, increased in the DA, DA + FA and noradrenaline (NA) groups to 3.32 +/- 0.40 micrograms/g, 3.30 +/- 0.39 micrograms/g and 3.37 +/- 0.42 micrograms/g respectively. It is concluded that there are no differences in PGE2 content among the DA, DA + FA and NA groups. The mechanism by which PGE2 content increases after administration of DA is the direct action of DA and/or increasing BF. It is suspected that DA directly affects PGE2 synthesis, however the possibility that DA is metabolized to NA, which secondarily results in increased PGE2 synthesis, cannot be excluded.     

Effect of PO2 on prostaglandin E2 production in renal cell cultures

There is evidence both from in vivo and in vitro studies which suggests that hypoxia stimulates the synthesis of prostanoids in some tissues. In the present study, the in vitro production of prostaglandin E2 (PGE2) was studied in three different renal cell lines incubated at various PO2 values between 143 and 3 mm Hg for 24 h. In rat kidney mesangial cell cultures, PGE2 production increased up to 99 ng PGE2/mg protein at 7 mm Hg O2, compared to 52 ng/mg at 143 mm Hg O2, but was lowered at 26 ng/mg at 3 mm Hg O2. PGE2 production by the pig kidney tubule cell lines LLC-PK1 and PK-15 was insensitive to PO2 changes. Because PGE2 production is known to be Ca2+-dependent and was indeed stimulated by the Ca-ionophore A 23187, effects of hypoxia on 45Ca2+-fluxes were also studied. In none of the 3 cell lines, net 45Ca-influx was altered after incubation at low PO2. However, net 45Ca-efflux increased during hypoxic incubation of mesangial cells possibly as a result of intracellular Ca-mobilization. These results indicate that hypoxia stimulates PGE2 synthesis in mesangial but not in tubule cell cultures. However, at very low PO2 values, or anoxia, the formation of cyclic endoperoxides from arachidonic acid may be lowered. Since mesangiocytes are smooth muscle-like cells, the hypoxia-induced synthesis of relaxing prostanoids could play a role in the regulation of smooth muscle tone.     

Inhibition of complement-factor-5a-induced inflammatory reactions by prostaglandin E2 in experimental meningitis

The possible role of complement factor 5a (C5a) and prostaglandin E2 (PGE2) in cerebrospinal fluid (CSF) pleocytosis and protein accumulation was assessed in a rabbit model of meningitis. Intracisternally administered C5a caused a rapid, early influx of leukocytes into CSF that peaked at 1 h after injection; by 6 h, cell counts were slightly higher than those in controls. Administration of PGE2 or saline did not induce detectable CSF leukocytosis. Coadministration of PGE2 with C5a decreased CSF leukocytosis in a dose-related fashion. Protein concentration increased 30 min after administration of C5a, peaked after 1 h, and remained elevated for 6 h. PGE2 caused a dose-related increase in protein content after 2 h, whereas coadministration caused an inversely dose-related inhibition of the C5a-induced protein influx into CSF. These data suggest that PGE2 in the subarachnoid space exerts an inhibitory action on the C5a-mediated response that is probably not related to its direct effects on protein extravasation.     

Effect of ibuprofen on gross pathology, bacterial count, and levels of prostaglandin E2 in experimental staphylococcal osteomyelitis

Infections with Staphylococcus aureus were induced in rat tibiae without sclerosing agents. Animals received ibuprofen or 0.9% NaCl. Both ibuprofen-treated and control animals developed a progressively more-destructive disease over 12 days. Gross tibial pathology was significantly reduced in animals receiving ibuprofen for both six and 12 days postinfection. Radiographic evidence of osteomyelitis was attenuated at 12 days. Geometric mean counts of S. aureus were, however, not significantly changed by ibuprofen treatment. Mean levels of prostaglandin E2 (PGE2) were highest in untreated controls. Ibuprofen treatment of infected animals was associated with a much-reduced mean value of PGE2. Ibuprofen-treated infected tibiae disclosed less PGE2 than did either ibuprofen- or NaCl-treated uninfected tibiae.     

Effect of prostaglandin E2 on masculine sexual behaviour in the rat

Intracerebral infusion of prostaglandin E2 (PGE2) facilitated copulatory behaviour of long-term castrated rats. Castrated rats were given daily systemic injections of testosterone propionate (50 microgram) or oil vehicle, and then 30 min before behavioural testing they received an intrahypothalamic infusion of either PGE2 or saline. Rats receiving PGE2 in addition to systemic testosterone showed more copulatory behaviour than those receiving PGE2 or testosterone alone.     

The effect of sulphasalazine withdrawal on rectal mucosal function and prostaglandin E2 release in inactive ulcerative colitis

We have used in vivo rectal dialysis to assess mucosal prostaglandin E2 (PGE2) release and water and electrolyte transport before and 2 weeks after withdrawal of oral sulphasalazine in eight patients with inactive ulcerative colitis. Although rectal mucosal PGE2 release was unaffected by withdrawal of sulphasalazine, significant reductions in mucosal potential difference (P less than 0.01) and net absorption of water (P less than 0.05), sodium (P less than 0.05), and chloride occurred (P less than 0.05). Clinical assessment showed no change in disease activity. Sulphasalazine withdrawal thus has a detrimental effect on large-intestinal salt and water transport, which does not appear to be mediated through changes in net mucosal prostaglandin production.     

Distribution of prostaglandin E2 and prostaglandin F2 alpha receptors in human myometrium

Human myometrium was studied for specific binding of PGE2 and PGF2 alpha. PGF2 alpha-binding was almost undetectable, but specific binding sites for PGE2 with high affinity (KD = 2.7 +/- 0.4 x 10(-9) M were demonstrated. The binding capacity for PGE2 exhibited a topically different distribution pattern with the highest values in the central parts and low to undetectable levels in the cervical region. Binding characteristics were analyzed by receptor kinetics, revealing a homogeneous receptor population. Binding capacity in uteri obtained from post-menopausal women was of the order of 900-940 fmol/mg protein. Oestrogen pre-treatment and pregnancy were associated with a 3-fold reduction of the PGE2-binding capacity.     

Roles of prostaglandin E2 in cardiovascular diseases

Prostaglandin E2 (PGE(2)) is produced in inflammatory responses and regulates a variety of immunological reactions through 4 different receptor subtypes; EP1, 2, 3 and 4. However, the precise role of each receptor in cardiovascular disease has not yet been elucidated. Enhanced expression of some EPs has been observed in clinical and experimental cardiovascular diseases. EP agonists have been developed to clarify the role of each receptor. Recently, we developed a novel selective agonist to examine the effects of EP4 on cardiac transplantation, myocardial ischemia, and myocarditis. Of note, a selective EP4 agonist attenuated inflammatory cytokines and chemokines via attenuation of macrophage activation in inflammatory heart diseases. In this review article, we discuss the effects of PGE(2) receptor agonists on the development of cardiovascular diseases.     

Effect of prostaglandin E2 on gastric mucosal bleeding caused by aspirin

The effect of prostaglandin E₂ on gastric mucosal bleeding caused by aspirin was studied. Blood in serial gastric washings was measured chemically for 30 min. Normal blood loss was equivalent to 0.05 ml/day. Aspirin, 600 mg four times daily, increased gastric bleeding on day 1; bleeding was further increased on day 2. On day 2, ingestion of 0.5 mg of prostaglandin E₂ 15 min before 600 mg of aspirin reduced the gastric microbleeding caused by aspirin. Prostaglandin E₂, 0.5 mg four times daily, did not change the normal blood loss. No consistent changes in gastric emptying or in secretion of chloride were detected.This work was supported in part by a grant from The Upjohn Company, Kalamazoo, Michigan.     

Effect of sucralfate on experimental colitis in the rat

The therapeutic effect of sucralfate on ulcerated gastric and duodenal mucosa is well known. There is, however, almost no information about its activity in colitis. Experimental colitis was produced in rats by rectal instillation of 1 ml of 10 percent acetic acid, and 1.5 ml of a 20 percent suspension of sucralfate was then administered every 12 hours for various lengths of time. Study animals and appropriate controls were killed after 3, 7, 10, or 14 days. The distal colons were studied macroscopically and histologically. Colonic prostaglandin E₂ levels were measured in animals killed after 3, 7, 10, or 14 days. The macroscopic score was significantly improved 10 and 14 days after induction of colitis, although the histologic appearence was unchanged. Acetic acid administration increased and sucralfate treatment reduced prosta-glandin E₂ levels in colitic animals on days 3 and 7, but not later. The present study supports a role for sucralfate in the treatment of colitis, but further studies on the mechanism of its effect and on its clinical activity are indicated. Supported by ABIC Pharmaceutical Company, Netanya, Israel.     

Microparticles stimulate the synthesis of prostaglandin E2 via induction of cyclooxygenase 2 and microsomal prostaglandin E synthase 1

Objective

Microparticles are small vesicles that are released from activated or dying cells and that occur abundantly in the synovial fluid of patients with rheumatoid arthritis (RA). The goal of these studies was to elucidate the mechanisms by which microparticles activate synovial fibroblasts to express a proinflammatory phenotype.

Methods

Microparticles from monocytes and T cells were isolated by differential centrifugation. Synovial fibroblasts were cocultured with increasing numbers of microparticles. Gene expression was analyzed by real‐time polymerase chain reaction and confirmed by Western blotting and enzyme immunoassay. Arachidonic acid labeled with tritium was used to study the transport of biologically active lipids by microparticles. The roles of NF‐κB and activator protein 1 (AP‐1) signaling were analyzed with electrophoretic mobility shift assay and transfection with small interfering RNA and IκB expression vectors.

Results

Microparticles strongly induced the synthesis of cyclooxygenase 2 (COX‐2), microsomal prostaglandin E synthase 1 (mPGES‐1), and prostaglandin E₂ (PGE₂). In contrast, no up‐regulation of COX‐1, mPGES‐2, cytosolic PGES, or phospholipase A₂ was observed. The induction of PGE₂ was blocked by selective inhibition of COX‐2. Microparticles activated NF‐κB, AP‐1, p38, and JNK signaling in synovial fibroblasts. Inhibition of NF‐κB, AP‐1, and JNK signaling reduced the stimulatory effects. Arachidonic acid was transported from leukocytes to fibroblasts by microparticles. Arachidonic acid derived from microparticles was converted to PGE₂ by synovial fibroblasts.

Conclusion

These results demonstrate that microparticles up‐regulate the production of PGE₂ in synovial fibroblasts by inducing COX‐2 and mPGES‐1. These data provide evidence for a novel mechanism by which microparticles may contribute to inflammation and pain in RA.

     

Oral antisecretory activity of prostaglandin E2 in man

We studied the oral gastric antisecretory activity of prostaglandin E₂ in three groups of six normal volunteers. Each volunteer was studied twice, once after receiving prostaglandin E₂ (0.5, 1.0, or 2.0 mg) and the other time after receiving placebo administered in a double-blind, randomized fashion. Gastric acid secretion was stimulated with a liquid protein meal from 1/2 to 1 1/2hr after drug administration. Acid secretion was quantitated using the technique of intragastric titration. Acid secretion after 0.5 mg of prostaglandin E₂ was no different than after placebo administration, but 1.0 mg and 2.0 mg of prostaglandin E₂ inhibited 58% (6.68±7.64 meq vs 14.67±6.75 meq, P<0.02) and 76% (2.38±2.38 meq vs 11.50±3.51, P<0.01) respectively, of gastric acid production compared to placebo therapy. After oral administration, prostaglandin E₂ in man is antisecretory with an ED₅₀ of 1.1 mg.