Antagonistic actions of prostaglandins E2 and F2 alpha on the isolated lungs of the frog, Rana esculenta L

Isolated lungs of the frog, Rana esculenta L., when incubated in amphibian Ringer solution for 30 min, produced a prostaglandin E2-like substance (27.1 +/- 3.8 ng/g w.w.), as determined by bioassay on the isolated rat stomach strip. The release of PGE2-like substance from skin, heart and bowel is also reported. The activity of synthetic prostaglandins E2 (PGE2) and F2 alpha (PGF2 alpha) on the muscular contractility of frog isolated lungs was investigated: PGE2 and PGF2 alpha relaxed and contracted respectively in a dose-dependent manner this preparation, a result similar to that obtained in mammals.     

Mechanisms of prostaglandin E2-induced interleukin-6 release in astrocytes: possible involvement of EP4-like receptors, p38 mitogen-activated protein kinase and protein kinase C.

The expression of cyclooxygenase-2 (COX-2) and the synthesis of prostaglandin E2 (PGE2) as well as of cytokines such as interleukin-6 (IL-6) have all been suggested to propagate neuropathology in different brain disorders such as HIV-dementia, prion diseases, stroke and Alzheimer's disease. In this report, we show that PGE2-stimulated IL-6 release in U373 MG human astroglioma cells and primary rat astrocytes. PGE2-induced intracellular cAMP formation was mediated via prostaglandin E receptor 2 (EP2), but inhibition of cAMP formation and protein kinase A or blockade of EP1/EP2 receptors did not affect PGE2-induced IL-6 synthesis. This indicates that the cAMP pathway is not part of PGE2-induced signal transduction cascade leading to IL-6 release. The EP3/EP1-receptor agonist sulprostone failed to induce IL-6 release, suggesting an involvement of EP4-like receptors. PGE2-activated p38 mitogen-activated kinase (p38 MAPK) and protein kinase C (PKC). PGE2-induced IL-6 synthesis was inhibited by specific inhibitors of p38 MAPK (SB202190) and PKC (GF203190X). Although, up to now, EP receptors have only rarely been linked to p38 MAPK or PKC activation, these results suggest that PGE2 induces IL-6 via an EP4-like receptor by the activation of PKC and p38 MAPK via an EP4-like receptor independently of cAMP.     

Prostaglandin E2 attenuation of sheep lung responses to endotoxin

Prostaglandin (PG) E2 can inhibit inflammatory responses of neutrophils and lymphocytes, including eicosanoid release. Diffuse lung injury after endotoxemia in sheep is accompanied by sequestration of neutrophils and lymphocytes in the lungs, and eicosanoids mediate some of the pathophysiology of the response. To determine whether exogenous PGE2 could prevent the endotoxin response, we measured pulmonary hemodynamics, gas exchange, and lung lymph responses to infusion of Escherichia coli endotoxin (0.5 micrograms/kg iv over 30 min) in unanesthetized sheep in the presence and absence of PGE2 (0.5 micrograms.kg-1.min-1) infused intravenously for 4 h beginning 0.5 h before endotoxin infusion. We also measured lung lymph concentrations of thromboxane B2 (TxB2) and prostacyclin metabolite, 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), by radioimmunoassay and leukotriene B4 (LTB4) by gas chromatography-mass spectrometry. PGE2 decreased endotoxin-induced pulmonary hypertension and hypoxemia and markedly attenuated the lymph flow and lymph protein clearance responses. PGE2 also attenuated endotoxin-induced increases in lung lymph TxB2 and 6-keto-PGF1 alpha and decreased lymph LTB4 flow after endotoxin without decreasing lymph LTB4 concentrations. We conclude that PGE2 infusion attenuates lung dysfunction caused by endotoxemia, possibly by preventing endogenous release of other eicosanoids.     

Effects of selective and non-selective COX inhibitors on antigen-induced release of prostanoid mediators and bronchoconstriction in the isolated perfused and ventilated guinea pig lung

The contribution of cycloxygenase (COX)-1 and COX-2 in antigen-induced release of mediators and ensuing bronchoconstriction was investigated in the isolated perfused guinea pig lung (IPL). Antigen challenge with ovalbumin (OVA) of lungs from actively sensitised animals induced release of thromboxane (TX)A(2), prostaglandin (PG)D(2), PGF(2)(alpha), PGI(2) and PGE(2), measured in the lung effluent as immunoreactive TXB(2), PGD(2)-MOX, PGF(2)(alpha), 6-keto PGF(1)(alpha) and PGE(2), respectively. This release was abolished by the non-selective COX inhibitor flurbiprofen (10 microM). In contrast, neither the selective COX-1 inhibitor FR122047 nor the selective COX-2 inhibitor celecoxib (10 microM each) significantly inhibited the OVA-induced bronchoconstriction or release of COX products, except for PGD(2). Another non-selective COX inhibitor, diclofenac (10 microM) also significantly inhibited antigen-induced bronchoconstriction. The data suggest that both COX isoenzymes, COX-1 and COX-2 contribute to the immediate antigen-induced generation of prostanoids in IPL and that the COX-1 and COX-2 activities are not associated with different profiles of prostanoid end products.     

Prostacyclin production by rat aorta "in vitro" is increased by the combined action of dipyridamole plus pentoxifylline

The present study evaluates the effect of dipyridamole and pentoxifylline, individually and in combination, on PGI2-like production and arachidonic acid metabolism of rat aorta "in vitro". Pentoxifylline 100 microM and dipyridamole 92 and 184 microM increased PGI2-like activity, as measured by the platelet aggregation inhibitory capacity of the aortic ring incubates, by 71%, 46% and 60% respectively; a greater increase in PGI2-like activity was observed with the combination of the drugs than when they were used separately. This effect was observed even at the lowest doses assayed. In fact, dipyridamole 9.2 microM plus pentoxifylline 1 microM increased the PGI2-like activity by 30% while the individual increase was 4.5% and 10.6% respectively. To obtain more information on the effect of the dipyridamole-pentoxifylline combination on arachidonic acid metabolism, arteries were incubated with (1-14C) arachidonic acid, and the 6-keto-PGF1 alpha and PGE2 quantified. Dipyridamole 92 microM plus pentoxifylline 1 and 10 microM increased 6-keto-PGF1 alpha and PGE2 production by about 30% and 48% respectively while the combination with pentoxifylline 100 microM increased the 6-keto-PGF1 alpha 76.5% and the PGE2 50%. The possible biological effect and therapeutic implications of increased PGI2 production by the arteries due to the dipyridamole-pentoxifylline combination remains to be ascertained.     

Effects of lysine clonixinate on cyclooxygenase I and II in rat lung and stomach preparations

Lysine clonixinate (LC) is a drug of antiinflammatory antipyretic and analgesic activity that produces minor digestive side-effects. This fact induced us to think that LC is possibly a weak COX-1 inhibitor. In order to investigate our hypothesis we inhibited cyclooxygenase activity with LC or indomethacin (INDO) in rat lung and stomach obtained from rats treated with lipopolysacharide (LPS) and control rats. Rat lung preparations incubated with 14C-arachidonic acid synthesise mainly PGE2. LC at 2.5 and 4.1 x 10(-5) M does not modify the basal production of PGE2 (probably COX-1) but at 6.8 x 10(-5) M significantly inhibited PGE2 production (approximately 48.5% inhibition, P<0.001). On the other hand, INDO at 10(-6) inhibited the basal production of PGE2 by around 73%. In LPS-treated rats, the production of PGE2 was significantly higher than in the lungs of control rats, probably due to the induction of COX-2. The addition of LC at 2.7 and 4.1 x 10(-5) M recovered the control values of PGE2 inhibiting, probably only from COX-2 activity. LC at higher concentrations (6.8 x 10(-5) M) and INDO 10(-6) M inhibited PGE2 formed by COX-2 and also partly by COX-1 activity.     

PGE2 secretion from organ cultured gastric mucosa: correlation with cyclooxygenase activity and endogenous substrate release.

In gastrointestinal research the in vitro release of prostaglandins from incubated or cultured biopsies is a widely used method to estimate prostaglandin synthesis. We therefore investigated the rate limiting mechanisms of PGE2 release in organ cultured gastric mucosa of the rabbit, determining PGE2 secretion from organ cultured mucosal biopsies by radioimmunoassay and prostaglandin synthesizing capacity by in vitro incubation of mucosal homogenate or microsomes with [14C]-arachidonic acid. Freshly taken biopsies secreted PGE2 at an initial high rate, that decreased during the following 4 hrs of culture. This PGE2 release was dose dependently reduced by inhibitors of the prostaglandin cyclooxygenase. 5mM acetylsalicylic acid (ASA) maximally suppressed PGE2 secretion to 7% of controls, and the inhibition by ASA was quantitatively similar at every given culture period. PGE2 release was markedly increased by carbenoxolone but was only slightly activated by extracellular calcium and the Ca(++)-ionophore A23187. However, Ca++/A23187 were unable to maintain PGE2 secretion at the initial rate. PGE2 secretion was undisturbed in calcium-free medium but was reduced to 50-60% of controls by excess EDTA. The intracellular calcium chelator 1,2-bis-(2-aminophenoxy)-ethane-N,N,N',N',-tetraacetic acid-acetoxymethyl ester (BAPTA-AM) similarly inhibited PGE2 release to 72% of controls. In contrast, PGE2 release was unaffected by the intracellular calcium antagonist 3,4,5-trimethylene-bis(4-formylpyridinium bromide) dioxime (TMB-8), the calmodulin antagonists N-(6-aminohexyl)-1-5-chloro-1-naphthalenesulfonamide (W-7) and calmidazolium (compound R24571) or various direct inhibitors of endogenous arachidonic acid release like tetracaine, bromophenacyl bromide, neomycin or low dose quinacrine, indicating that the reduction of PGE2 release by EDTA or BAPTA may be mediated by mechanisms different from substrate release. In contrast, an inhibition of PGE2 secretion by quinacrine at high concentrations (greater than or equal to 0.8 mM) was attributed to a direct inhibition of the prostaglandin cyclooxygenase, similar to ASA. Finally, the reduction of the prostaglandin synthesizing capacity by ASA was strongly correlated with the inhibition of PGE2 secretion, also at low concentrations and minor degrees of inhibition. From these data we conclude, that the activity of the prostaglandin cyclooxygenase is rate limiting for PGE2 secretion from organ cultured mucosal biopsies rather than arachidonic acid release by a phospholipase A2. This should be considered for interpretation of studies based on prostaglandin release from cultured mucosa.     

Release of tumor necrosis factor-alpha from macrophages. Enhancement and suppression are dose-dependently regulated by prostaglandin E2 and cyclic nucleotides

PGE2 has previously been shown to suppress various leukocyte functions. In this study, we examined whether PGE2 would affect release of TNF-alpha from rat resident peritoneal macrophages. Two different, dose-dependent effects were observed: low PGE2 concentrations (0.1 to 10 ng/ml) stimulated, whereas higher concentrations (greater than 10 ng/ml) suppressed TNF-alpha release. PGE2-stimulated TNF-alpha production was dependent on de novo protein synthesis and was associated with an intracellular rise of cGMP. The importance of cGMP as an intracellular messenger for PGE2 was confirmed by the following evidence: (1) low PGE2 concentrations preferentially increased cGMP and not cAMP and (2) cGMP, either exogenously added or endogenously generated by sodium nitroprusside, were efficient stimulators of TNF-alpha production. In contrast, agents increasing intracellular cAMP concentrations such as PGE1, higher PGE2 doses, isoproterenol, and theophylline, all suppressed TNF-alpha synthesis. Only resident, but not casein-elicited or Corynebacterium parvum-activated macrophages, were stimulated by low PGE2 concentrations to increase TNF-alpha production. In tumor cytotoxicity assays, PGE2-activated macrophages were active only against TNF-alpha-sensitive target cells. These findings demonstrate that TNF-alpha synthesis in macrophages is up-regulated by cGMP and down-regulated by cAMP, which indicates that cyclic nucleotides act as intracellular messengers for extracellular signals of macrophage activation.     

Streptococcus pneumoniae induced p38 MAPK- and NF-kappaB-dependent COX-2 expression in human lung epithelium

Streptococcus pneumoniae is a major cause of community-acquired pneumonia and death from infectious diseases in industrialized countries. Lung airway and alveolar epithelial cells comprise an important barrier against airborne pathogens. Cyclooxygenase (COX)-derived prostaglandins, such as PGE(2), are considered to be important regulators of lung function. Herein, we tested the hypothesis that pneumococci induced COX-2-dependent PGE(2) production in pulmonary epithelial cells. Pneumococci-infected human pulmonary epithelial BEAS-2B cells released PGE(2). Expression of COX-2 but not COX-1 was dose and time dependently increased in S. pneumoniae-infected BEAS-2B cells as well as in lungs of mice with pneumococcal pneumonia. S. pneumoniae induced degradation of IkappaBalpha and DNA binding of NF-kappaB. A specific peptide inhibitor of the IkappaBalpha kinase complex blocked pneumococci-induced PGE(2) release and COX-2 expression. In addition, we noted activation of p38 MAPK and JNK in pneumococci-infected BEAS-2B cells. PGE(2) release and COX-2 expression were reduced by p38 MAPK inhibitor SB-202190 but not by JNK inhibitor SP-600125. We analyzed interaction of kinase pathways and NF-kappaB activation: dominant-negative mutants of p38 MAPK isoforms alpha, beta(2), gamma, and delta blocked S. pneumoniae-induced NF-kappaB activation. In addition, recruitment of NF-kappaB subunit p65/RelA and RNA polymerase II to the cox2 promoter depended on p38 MAPK but not on JNK activity. In summary, p38 MAPK- and NF-kappaB-controlled COX-2 expression and subsequent PGE(2) release by lung epithelial cells may contribute significantly to the host response in pneumococcal pneumonia.     

On the multiplicity of platelet prostaglandin receptors. I. Evaluation of competitive antagonism by aggregometry

Methods for the evaluation of competitive interactions at receptors associated with platelet activation and inhibition using aggregometry of human PRP have been developed. The evidence supports the suggestion that PGE1 and PGI2 share a common receptor for inhibition of platelet reactivity, but only a portion (if any) of the aggregation stimulation associated with PGE2 is the result of PGE2 binding (without efficacy) to this receptor. PGE2 (at .3-20 microM) is an effective antagonist of PGE1, PGI2, and PGD2 producing a shift of about one order of magnitude in the IC50-values obtained from complete aggregation inhibition dose response curves. The antagonism of PGD2 inhibition is particularly notable, 80 nM PGE2 levels are detectable. This and other actions of PGE2 indicate another platelet receptor for PGE2. PGE1 acts at both the PGE2 and PGI2 receptor. Other substances showing PGI2-like actions only at high doses (1-30 microM), display additive responses with PGI2 indicative of decreased affinity for the I2/E1 receptor and the absence of PGE2-like aggregation stimulation activity. PGI2 methyl ester has intrinsic inhibitory action not associated with in situ ester hydrolysis. The methyl ester is dissaggregatory showing particular specificity for inhibition of release and second wave aggregation.     

Arachidonic acid metabolism in isolated rat aorta. Dependence of prostacyclin biosynthesis on extracellular potassium concentration

Slices of rat aorta were incubated in Krebs-Ringer bicarbonate buffer for measurements of immunoreactive 6-ketoprostaglandin F1 alpha, thromboxane (TX) B2, prostaglandin (PG)E2, and PGF2 alpha, and in Tris buffer (pH 9.3) for determination of prostacyclin (PGI2)-like activity. No significant generation of TXB2, PGE2, or PGF2 alpha by rat aortic tissue could be detected. The time-dependent release of 6-keto-PGF1 alpha Krebs-Ringer bicarbonate buffer closely correlated with PGI2 generation in alkaline Tris buffer. During a 30-min incubation period, 6-keto-PGF1 alpha, release was 79.8 +/- 3.3 pmol/mg at a buffer potassium concentration of 3.9 mmol/liter and significantly increased by 23% to 98.3 +/- 8.5 pmol/mg (P less than 0.025) in the absence of potassium in the incubation medium. A smaller decrease in buffer potassium concentration to 2.1 mmol/liter and an increase to 8.8 mmol/liter did not significantly alter aortic 6-keto-PGF1 alpha release. Changes in the incubation buffer sodium concentration from 144 mmol/liter to either 138 or 150 mmol/liter at a constant potassium concentration of 3.9 mmol/liter did not alter the recovery of 6-keto-PGF1 alpha. Our results support the concept that PGI2 is the predominant product of arachidonic acid metabolism in rat aorta. They further show that PGI2 can be recovered quantitatively as 6-keto-PGF1 alpha under the present in vitro conditions. In addition, this in vitro study points to the potassium ion as a modulator of vascular PGI2 synthesis with a stimulation at low potassium concentrations.     

O2 metabolites and neutrophil elastase synergistically cause edematous injury in isolated rat lungs

Addition of glucose oxidase (GO) increased H2O2 concentrations and decreased antielastolytic activities of beta-D-glucose containing perfusates of isolated rat lungs. Pretreatment with GO also caused acute edematous injury (increased lung weight gains, increased recovery of Ficoll in lung lavages, and increased pulmonary arterial pressures) in isolated lungs perfused with purified human neutrophil elastase (NE). Acute edematous injury in isolated lungs pretreated with GO and then NE exceeded levels found in lungs following addition of GO or NE alone or NE before GO. Simultaneous addition of catalase (an H2O2 scavenger) or methoxy-succinyl-L-alanyl-L-alanyl-prolyl-L-valine-chloromethyl ketone (an NE inhibitor, but not aminotriazole-inactivated catalase, N-tosyl-L-phenyl-alanine chloromethyl ketone (a chymotrypsin inhibitor) or N-alpha-p-tosyl-L-lysine chloromethyl ketone (a trypsin inhibitor), prevented acute edematous injury in isolated lungs perfused with both GO and NE. This observation indicated that injury was dependent on both H2O2 and NE, especially since the relative inactivating specificities of the inhibitors for H2O2 or NE, respectively, were confirmed under similar conditions in vitro. The synergistic nature of the interaction between H2O2 and NE-mediated injury was further clarified when GO- and NE-induced lung injury was prevented by addition of an oxidant-resistant NE inhibitor (Eglin-C), but not an oxidant-sensitive NE inhibitor (human alpha 1-protease inhibitor, alpha 1PI). Moreover, treatment with H2O2 also decreased the ability of alpha 1PI but not Eglin-C to decrease NE activity in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)     

Interleukin 1 is present in normal human epidermis

We investigated the presence of interleukin 1 (IL 1)-like molecules in normal unstimulated human epidermal tissue. Epidermis from 21 healthy individuals that was prepared by two different methods showed prostaglandin E2 (PGE2) and collagenase stimulating activity for human dermal fibroblasts. All epidermal extracts tested were positive for thymocyte comitogenic activity (lymphocyte activating factor; LAF). Removal of the horny layer decreased epidermal IL 1-like activity. In contrast to epidermal tissue, freshly isolated peripheral blood mononuclear cells (PBMC) contained no detectable PGE2 stimulatory activity. They could, however, produce PGE2 stimulatory activity after culture and stimulation with phytohemagglutinin (PHA) and concanavalin A (Con A). Little membranous IL 1-like activity could be detected in epidermal extracts when using a method that has previously rendered membranous IL 1 from murine proteose peptone-elicited peritoneal macrophages. Gel filtration chromatography yielded double peaks at m.w. approximately 30,000 and approximately 17,000 for all three activities. High pressure liquid chromatography (HPLC) analysis identified two species with a m.w. of approximately 17,000, and one approximately 30,000 species nondissociable in detergent, all having superposable PGE2 and collagenase stimulatory as well as LAF activity. These results establish the existence of IL 1-like molecules, together with a possible precursor, in normal human epidermis. The release of these preformed epidermal IL 1 stores might be important in vivo.     

Release of prostaglandins from healthy and sensitized guinea-pig lung and trachea by histamine.

The effects of histamine and its antagonists on the release of prostaglandin E and F2alpha (PGE and PGF2alpha) and the 15-keto-13,14-dihydro PGF2alpha/E (metabolites) were examined in minced and whole perfused guinea pig lung. Lung fragments released considerable amounts of prostaglandins into the incubation media with time alone: parenchyma more PGF2alpha than PGE, trachea more PGE than PGF2alpha. The levels of PGF2alpha found in the filtrates of both tissues on per gram basis were about the same, whereas the concentrations of PGE were several fold higher in the media of incubated trachea. In contrast to lung, trachea released only trace amounts of metabolites. These differences in synthesis and turnover are probably of importance for maintenance of the adequate ventilation-perfusion ratios. The process of sensitization caused a significant increase in the outflows of PGF2alpha and metabolites from the lung fragments. The PGE to PGF2alpha ratio was decreased in both parenchymal and tracheal tissues. Increased spontaneous release of prostaglandins was also found in whole perfused sensitized lung. This was consistent with the hypothesis that sensitization with antigen alters the biochemical properties of the organism. Incubation of lung fragments with histamine had only a small additional effect on the liberation of prostaglandins, since the baseline release was high due to the trauma of mincing. However, histamine perfusion of whole lung caused severalfold increase in the outflows of prostaglandins. Pretreatment with pyrilamine (histamine receptor 1 antagonist) decreased the subsequent release of PGF2alpha by histamine. On the other hand, pretreatment with metiamide (histamine receptor 2 antagonist) diminished the subsequent release of PGE. It is suggested that stimulation of histamine receptor 1 is predominantly (but not solely) related to the synthesis of PGF2alpha, and stimulation of the receptor 2 is related to the synthesis of PGE.     

Prostaglandin release by slow reacting substance from guinea pig and human lung tissue.

Slow reacting substance (SRS) injected into the pulmonary artery released prostaglandins E (PGE) and F2alpha (PGF2alpha) and the 15-keto-13, 14-dihydro PG metabolites from non-sensitized and ovalbumin sensitized, isolated, perfused guinea pig lungs. PGs were also released from lungs incubated with SRS. Sensitized lungs released more PGs in both types of preparations. Indomethacin inhibited the effect of SRS. Passively sensitized human lung fragments, in parallel to guinea pig lung, released PGE, PGF2alpha and the metabolites when incubated with SRS or antigen. In in vivo experiments, SRS and arachidonic acid given intravenously increased the airway insufflation pressure in anesthetized quinea pigs. These effects, but not the action of injected PGF2alpha and histamine, were abolished by indomethacin. The results indicate that one of the modes of SRS action is by release of PGs, and are consistent with the hypothesis that PGs are predominantly "secondary" mediators (in the temporal sense) of the antigen-antibody reaction.     

Rat lung glutathione release: response to oxidative stress and selenium deficiency

We performed experiments to characterize the glutathione-dependent metabolism occurring during tert-butyl hydroperoxide infusion in isolated perfused rat lungs and to examine the effect of selenium deficiency on this metabolism. Selenium deficiency resulted in decreased lung glutathione peroxidase activity but normal glutathione reductase activity and glutathione content. Infusion of the hydroperoxide into control lungs caused a proportional increase in tissue glutathione disulfide (GSSG) concentration and release of GSSG into the perfusate up to an infusion rate of 250 nmol of tert-butyl hydroperoxide X min-1 X 100 g body wt-1. Infusion rates greater than this resulted in continued rise of tissue GSSG concentrations but GSSG release into the perfusate plateaued. Infusion of tert-butyl hydroperoxide into selenium-deficient rat lungs resulted in much lower concentrations of tissue GSSG and GSSG release into the perfusate; however, release in the selenium-deficient rat lung was also found to be saturable at infusion rates of 450 nmol of tert-butyl hydroperoxide X min-1 X 100 g of body wt-1. Selenium deficiency in the rat decreases the rate of reduction of infused tert-butyl hydroperoxide by glutathione and may predispose the lung to free radical damage.     

Prostaglandin E2 Induces Ca2+ Release from Ryanodine/Caffeine-Sensitive Stores in Bovine Adrenal Medullary Cells via EP1-Like Receptors

Prostaglandin E2 (PGE2) causes Ca2+ release from intracellular Ca2+ stores and stimulates phosphoinositide metabolism in bovine adrenal medullary cells. These results have been interpreted as PGE2 induces Ca2+ release from inositol trisphosphate (IP3)-sensitive stores. However, we have recently shown that pituitary adenylate cyclase-activating polypeptide (PACAP), bradykinin, and angiotensin II release Ca2+ from caffeine/ryanodine-sensitive stores, although they cause a concomitant increase of intracellular IP3. In light of these results, the mechanism of PGE2-induced Ca2+ release was investigated in the present study. PGE2 dose-dependently caused a transient but consistent Ca2+ release from internal Ca2+ stores. The PGE2-induced Ca2+ release was unaffected by cinnarizine, a blocker of IP3-induced Ca2+ release. By contrast, it was potently inhibited by prior application of caffeine and ryanodine. Although IP3 production in response to PGE2 was abolished by the phospholipase C inhibitor U-73122, Ca2+ release in response to PGE2 was unaffected by U-73122. The PGE2-induced Ca2+ release was unaffected by Rp-adenosine 3',5'-cyclic monophosphothioate, an inhibitor of protein kinase A, and forskolin, a cyclic AMP (cAMP)-elevating agent, did not cause Ca2+ release. The EP1 agonist 17-phenyl-trinorPGE2 and the EP1/EP3 agonist sulprostone mimicked the Ca(2+)-releasing effects of PGE2, whereas the EP2 agonist butaprost or the EP2/EP3 agonist misoprostol caused little or no Ca2+ release. The EP1 antagonist SC-51322 significantly suppressed the Ca2+ release response induced by PGE2, whereas the EP4 antagonist AH-23828B had little effect. These results suggest that PGE2, acting on EP1-like receptors, induces Ca2+ release from ryanodine/caffeine-sensitive stores through a mechanism independent of IP3 and cAMP and that PGE2 may share the same mechanism with PACAP and the other peptide ligands in causing Ca2+ release in bovine adrenal medullary cells.     

Assessment of plasma leukotriene and prostaglandin levels during adjuvant arthritis and kaolin-induced paw oedema in rats

Plasma levels of some arachidonic acid metabolites were investigated in acute and chronic models of inflammation in rats. As a model of chronic inflammation, adjuvant arthritis in rats induced by the injection of Freund's complete adjuvant, and as an acute model for inflammation, kaolin-induced paw oedama were used. Plasma leukotriene(LT) C4-like and prostaglandin(PG) E2-like activities were quantitated by bioassay in guinea-pig ileum and rat stomach fundus respectively. In the course of adjuvant arthritis, plasma levels of LTC4- and PGEi2-like activities were increased. Plasma LTC4-like activity reached a maximum within 3 weeks, while PGE2-like activity reached a maximum 10 days after adjuvant injection. In the early phase of adjuvant arthritis, levels of both LTC4- and PGE2-like activities were found to be low but both activities were increased in the late phase of inflammation.     

Inotropic effect of PGE1 and PGE2 on isolated rat atria. Influence of adrenergic mechanisms

The effects of a wide range of PGE1 and PGE2 concentrations on the isometric developed tension of isolated rat atria beating spontaneously or paced at a fixed rate, were explored. PGE1 only produced a negative inotropic effect (NIE), whereas PGE2 elicited a biphasic inotropic action; negative at low concentrations and positive (PIE) at higher ones. Phenoxybenzamine and phentolamine failed to modify either the NIE or the PIE, but subthreshold exogenous norepinephrine abolished the NIE, suggesting a presynaptic inhibitory effect of PGEs on the adrenergic neurotransmitter release. Auricles pretreated with subthreshold norepinephrine react with a PIE to PGE1, but not to PGE2. On the contrary in the presence of subthreshold methoxamine the PIE of PGE2 was increased whereas the action of PGE1 was not modified.