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Query: UMLS:C0432222 (SEM)
 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The bridging of IgE receptors on rat basophilic leukemia cells (RBL-2H3) results in a number of biochemical events that accompany histamine secretion. Prominent among these is the release of arachidonic acid from cellular phospholipids, which could be due to the activation of phospholipase enzymes. In the present experiments we studied the intracellular activation of phospholipase A2 (PLA2) during histamine release. RBL-2H3 cells were stimulated through the IgE receptor, and the homogenates were prepared and tested for phospholipase A2 activity on 1-stearoyl-2-[14C]arachidonyl-sn-3-phosphatidylcholine. The amount of activity in the homogenates was dependent on the concentration of secretagogue used to activate the cells. Under optimal conditions there was a 1.86 +/- 0.12-fold (mean +/- SEM, N = 44) increase in the activity found in homogenates of stimulated cells. Activity was present in homogenates prepared 30 sec after cell activation, was optimal between 5 and 10 min, and decreased later. In time course experiments the PLA2 activation preceded histamine release. The activation of the enzyme in the cell occurred in the presence of 10 microM EGTA in the extracellular medium, which completely inhibited release of arachidonic acid and histamine. However, the activity of the enzyme required Ca2+. The PLA2 activity in the homogenates and the extent of cell stimulation for histamine release were maximal at the same concentration of antigen, and both were blocked by the addition of a monovalent hapten. The enzyme in the homogenates was capable of cleaving arachidonic acid from different phospholipids. The production of lysophospholipids could play a critical role in histamine release from cells. These results demonstrate the activation of PLA2 enzyme in cellular homogenates during the secretory process.
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PMID:Phospholipase A2 stimulation during cell secretion in rat basophilic leukemia cells. 241 21

The development of irreversible myocardial ischemic injury is associated with progressive degradation of membrane phospholipids, accumulation of arachidonate and other free fatty acids, and electrolyte derangements, including calcium accumulation. To study the relationship between arachidonate release and calcium loading during adenosine triphosphate (ATP) depletion in cardiac myocytes, the effects of two purported phospholipase inhibitors, mepacrine and U26,384, were evaluated. Cultured neonatal rat ventricular myocytes were pretreated for 90 minutes with 5 to 10 microM U26,384 (a steroidal diamine) or 10 to 50 microM mepacrine (an alkyl acridine) and then treated for 3 hours with 30 microM of the metabolic inhibitor, iodoacetic acid (IAA), with or without an additional dose of drug. IAA treatment resulted in a marked reduction in ATP level and a several-fold increase in free fatty acid radioactivity released from myocytes prelabeled with tritiated arachidonic acid (3H-AA). U26,384 produced substantial inhibition of the increased 3H-AA release, and was effective when given as a single pretreatment dose before IAA exposure or as continuous treatment before and during IAA exposure (for example, with 5 microM U26,384, the percentage of 3H-AA release versus IAA alone was 8% +/- 2% [SEM] [N = 15] for pretreatment only and 13% +/- 4% [N = 10] for continuous treatment). Mepacrine also resulted in significant reduction in 3H-AA release, but was more effective when given as continuous treatment (for example, with 50 microM mepacrine, the percentage of 3H-AA release versus IAA alone was 43% +/- 9% [N = 6] for pretreatment only and 22% +/- 7% [N = 9] for continuous treatment). More detailed analysis showed that U26,384 and mepacrine blocked the IAA-induced redistribution of 3H-AA into free fatty acids from other lipid species. Electron probe x-ray microanalysis of freeze-dried cryosections revealed marked electrolyte derangements in myocytes exposed to IAA, including a 24-fold increase in cellular Ca, a four fold increase in cellular Na, and a seven fold decrease in cellular K, and associated changes in cytoplasm and mitochondria. U26,384 treatment markedly reduced these electrolyte abnormalities, and maintained normal Ca levels in some protocols. Mepacrine treatment was less effective, but did produce normal Ca levels in 50% of myocytes. Prevention of IAA-induced cellular hypercontraction and blebbing also was observed. These data support the hypothesis that reduction of free fatty acid accumulation by inhibition of accelerated phospholipid degradation is associated with protection of myocytes from calcium loading and morphologic damage during inhibition of ene
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PMID:Association between inhibition of arachidonic acid release and prevention of calcium loading during ATP depletion in cultured rat cardiac myocytes. 250 56

Oxytocin at a physiological concentration stimulated the immediate release of free arachidonic acid from dispersed human decidual cells in a perfusion system. This indicates that oxytocin activates phospholipase(s) thus enhancing prostaglandin synthesis. The effect of oxytocin on the release of [3H]-arachidonic acid from decidual cells of women in labor was significantly greater (1036 +/- 207, mean dpm +/- SEM, n = 23) than from those of women not-in-labor (505 +/- 121 dpm, n = 12) or with endometrial cells of non-pregnant women (711 +/- 210 dpm, n = 18), and correlates well with reported oxytocin receptor concentrations in these tissues. These new findings are consistent with a role for endogenous oxytocin in stimulating prostaglandin synthesis at the onset of parturition.
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PMID:Oxytocin stimulates the release of arachidonic acid and prostaglandin F2 alpha from human decidual cells. 284 Jun 90

Mepindolol is a newly developed beta-adrenergic blocking agent, which differs from other available beta-blockers in its ability to counteract the chronotropic effect of catecholamines without depressing myocardial contractility. This study was designed to assess whether mepindolol administration is effective in reducing infarct size. Accordingly, 53 rats were randomly assigned to 3 groups: group 1 (n = 16) underwent coronary artery occlusion without receiving any treatment, and was used as control; group 2 (n = 19) was treated with mepindolol (1 mg/kg s.c.) 5 min and every 8 hours after occlusion, for 48 hours; group 3 (n = 18) underwent a sham-operation. No difference in mortality was found among groups. The animals were sacrificed 48 hours after occlusion and the left ventricle homogenized and centrifuged. Infarct size was calculated from the residual creatine phosphokinase activity, and found to average 52.4 +/- 7.8% (mean +/- SEM) of the left ventricle in control rats and 35.6 +/- 5.4% in treated rats (p less than 0.05), indicating a 32.1% reduction of infarct size. The phospholipid content of the supernatants was also measured: it averaged 0.08 microgram P/mg of protein in sham-operated rats and 0.61 + 0.04 micrograms P/mg of protein in control animals, showing that coronary ligation induced a degradation of myocardial phospholipids. Mepindolol-treated rats, however, showed a phospholipid concentration of 0.70 +/- 0.04 microgram P/mg of protein (p less than 0.05), suggesting that the drug was able to prevent ischemia-induced phospholipase activation.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Mepindolol reduction of the degradation of phospholipids and the necrosis induced by myocardial ischemia]. 286 Nov 35

The ascitic form of a chemically-induced pancreatic ductal adenocarcinoma in the Syrian golden hamster was very bloody and indistinguishable from blood macroscopically. Unlike blood, the bloody fluid remained unclotted at room temperature. To explore the possibility of presence of anticoagulants, we mixed 40% cell-free fluid with 60% normal human plasma and tested the clottability of the mixture with standard techniques. Plasma containing the fluid showed markedly prolonged activated partial thromboplastin time (APTT), thrombin time (TT) and recalcification time (RCT), and normal prothrombin time (PT) and reptilase time (RT). Comparing the prolongation of APTT of samples containing the fluid to those containing a commercial heparin, the fluid contained an anticoagulant activity equivalent to 0.436 +/- 0.03 unit heparin per ml (mean +/- SEM, n = 14). In addition to prolonging the APTT, TT and RCT, the fluid also inhibited the clotting and amidolytic activities of thrombin. "Heparsorb" had nearly completely neutralized the anticoagulant activity in fluid samples, while protamine sulfate was only partially effective. Incubation of fluid with pronase or phospholipase did not affect its anticoagulant activity; incubation with heparinase had only a minimal effect. Electrophoresis of an alkali digested fluid on cellulose acetate revealed the presence of heparan sulfate. The native ascitic fluid also contained other hemostatic components including platelets, fibrinogen and antithrombin III, but their concentrations were much lower than in blood. Apparently, heparan sulfate in the neoplastic effusion is largely responsible for the bloody ascites tumor remaining unclotted.
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PMID:Anticoagulant activity in cell-free peritoneal fluid of an experimental pancreatic ascites tumor. 300 55

Hepatocyte isolated by collagenase perfusion of livers of male Fischer-344 rats, and treated with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) (50 microM for 30 min at 37 degrees C) to inhibit glutathione reductase, were significantly more vulnerable to cytotoxicity of the bipyridyl herbicide diquat than similarly treated cells of Sprague-Dawley rats. Without compromise of cell defenses by BCNU, diquat was not cytotoxic to hepatocytes from either strain. Microsomal enzyme induction with phenobarbital (80 mg/kg ip for 3 days before hepatocyte isolation) did not potentiate killing of Fischer hepatocytes by diquat. Specific activities of NADPH-cytochrome P-450 reductase in isolated Fischer and Sprague-Dawley rat liver microsomes utilizing 1 mM diquat as acceptor were 0.085 +/- 0.017 and 0.076 +/- 0.028 mumol/mg.min (mean +/- SEM, N = 5), respectively, indicating the capacity for very active redox cycling of diquat by this route in both strains. The serine protease inhibitor, phenylmethylsulfonyl fluoride (100 microM), had no effect on diquat cytotoxicity, but both leupeptin (100 micrograms/ml) and antipain (50 or 100 microM) were able to delay, through not completely prevent, diquat-induced cell death. The phospholipase inhibitors, chlorpromazine (50 or 100 microM) and dibucaine (50 or 100 microM), similarly delayed but did not prevent cell death. Diquat increased the rate of hepatocyte phospholipid hydrolysis, measured as release into the suspending medium of [14C]arachidonic acid previously incorporated into hepatocyte lipids, but although chlorpromazine decreased phospholipid hydrolysis to the control rate, only partial protection against diquat cytotoxicity was seen. These data suggest that activation of phospholipase A2 and proteases by elevation of cytosolic free Ca2+ cannot account entirely for the loss of cell viability observed in the presence of cytotoxic concentrations of diquat.
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PMID:Lethal injury by diquat redox cycling in an isolated hepatocyte model. 342 16

During pregnancy the activity of coagulation factor VII in plasma increases up to 248% (SEM 16) (n = 18) at 40 weeks even when all precautions to avoid cold activation are taken. This increase is at all times during pregnancy, delivery and puerperium entirely due to the presence in vivo of what is most likely a phospholipid-factor VII complex. This complex is sensitive to phospholipase C, so that treatment with the enzyme reduces the activity of pregnant plasma down to that of non-pregnant controls. When present in the complex factor VII has a higher specific activity and an altered conformation with a more accessible active site as demonstrated by increased susceptibility to inactivation by diisopropylfluorophosphate. Factors II and X are increased to 136% (SEM 4) and 171% (SEM 6) (n = 18) without being sensitive to phospholipase C. The increase during pregnancy and the decrease after delivery of the phospholipase-sensitive factor VII activity have been followed.
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PMID:Clotting factor VII during pregnancy, delivery and puerperium. 394 1

Factor Xa binds to platelets provided that factor Va is present on the platelet surface, an interaction that results in a striking acceleration of the conversion of prothrombin to thrombin. Thrombin then initiates fibrin formation, induces platelet aggregation, and stimulates the intraplatelet synthesis of thromboxane A2 (TXA2). Addition of thrombin (2.4-14.4 nM) to platelet-rich plasma increased the basal level of TXA2, measured as thromboxane B2, from less than 0.5 pmol per 10(8) platelets to (mean +/- SEM) 100 +/- 22 and 250 +/- 10 pmol per 10(8) platelets, respectively. Treatment of platelet-rich plasma with increasing concentrations of factor Xa (1-12 nM) prior to the addition of thrombin progressively inhibited the production of TXA2. Thrombin (9.6 nM), which produced 93% of the maximal formation of TXA2, was inhibited 70% by factor Xa (10 nM). To identify which of these steps in thromboxane synthesis was inhibited by factor Xa, platelets labeled with [14C]arachidonic acid were exposed to thrombin and products of prostaglandin synthesis were separated by thin-layer chromatography. In contrast to the inhibition of TXA2 synthesis, prostaglandin E2 and prostaglandin F2 alpha synthesis were not inhibited suggesting that neither phospholipase(s) nor cycloxygenase was involved. The inhibition of TXA2 formation by factor Xa could be reversed by increasing the molar ratio of thrombin to factor Xa to 5.5. Incubation of platelets with an IgG fraction of a human monoclonal antifactor V antibody, previously shown to inhibit factor Xa binding, was found to block factor Xa inhibition of TXA2 synthesis. The inhibition of TXA2 synthesis requires the presence of the active site serine of factor Xa and is not specific for TXA2 formation induced by thrombin because it is also demonstrable when the agonist is ADP. Further, factor Xa does not require additional plasma components for its action because its inhibitory effects are detected in gel-filtered platelets. The effect of factor Xa was evident at physiological (1.3 mM) calcium concentrations. These results indicate that factor Xa binding to platelets through factor Va not only stimulates thrombin formation but also has a countervailing effect by inhibiting TXA2 formation.
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PMID:Inhibition of thromboxane A2 synthesis in human platelets by coagulation factor Xa. 657 68

Binding to PTH to its cell surface receptor activates both adenylyl cyclase and phospholipase-C, leading to elevation of cytosolic cAMP and free Ca2+. We have shown previously that extracellular nucleotides interact with P2U and P2Y subtypes of purinoceptor on osteoblastic cells, both linked to Ca2+ mobilization. In the present study, we investigated possible interactions between nucleotide and PTH signaling pathways in osteoblastic cells. The cytosolic free Ca2+ concentration ([Ca2+]i) of UMR-106 osteoblastic cells was monitored by fluorescence spectrophotometry. PTH (0.01-1 microM; bovine 1-84 or human 1-34) induced a small transient elevation of [Ca2+]i, lasting less than 1 min. A number of nucleotides, including ATP, UTP, and UDP, induced transient elevation of [Ca2+]i and potentiated the subsequent Ca2+ response to PTH. Of the nucleotides tested, UDP was the most effective at potentiating the PTH-induced Ca2+ transient. Treatment of cells with UDP (100 microM for 2.5 min), but not inorganic phosphate or uridine, reversibly potentiated the Ca2+ response to PTH (0.1 microM) by 11 +/- 2-fold (mean +/- SEM; n = 39). In contrast, UDP did not affect the cAMP response to PTH, indicating a selective action on Ca2+ signaling. Potentiation of the Ca2+ signal was still observed in the absence of extracellular Ca2+, establishing that nucleotides enhance PTH-induced release of Ca2+ from intracellular stores. Studies using selective purinoceptor agonists suggest that potentiation of PTH signaling is mediated by the P2U receptor subtype. In vivo, nucleotides released during trauma or inflammation may modulate PTH-induced Ca2+ signaling in osteoblasts.
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PMID:Extracellular nucleotides potentiate the cytosolic Ca2+, but not cyclic adenosine 3', 5'-monophosphate response to parathyroid hormone in rat osteoblastic cells. 789 78

We investigated the effects of bestatin, a prototype leukotriene A4 (LTA4) hydrolase inhibitor, on leukotriene (LT) formation and pulmonary artery perfusion pressure (Ppa) in isolated, perfused rat lungs. In lung parenchymal strips stimulated with a 10 microM concentration of the Ca2+ ionophore A23187, bestatin inhibited LTB4 formation with an IC50 = 10.4 +/- 30 microM (mean +/- SD, N = 4). It did not alter cysteinyl LT formation, confirming that it inhibited LTA4 hydrolase selectively, without inhibiting phospholipase, 5-lipoxygenase, or LTC4 synthase. In isolated, perfused lungs stimulated with 10 microM A23187, 300 microM bestatin inhibited LTB4 release by 72.2 +/- 10.6% (mean +/- SEM, N = 6, P < 0.01) but had no significant effect on LTE4 formation (P > 0.5). In these perfused lungs, bestatin did not alter the change in Ppa following stimulation with A23187. This effect is consistent with the insubstantial re-direction of LTA4 toward formation of vasospastic cysteinyl LTs. Separate experiments used lungs from rats treated with lipopolysaccharide endotoxin in vivo, prior to isolation, perfusion, and stimulation with 5 microM formyl-methionyl-leucyl-phenylalanine, in vitro. In these inflamed lungs, 750 microM bestatin inhibited LTB4 formation (P < 0.05) and increased LTE4 formation (P < 0.05), compatible with selective inhibited LTB4 hydrolase. The re-direction of LTA4 metabolism toward formation of cysteinyl LTs by inflamed, perfused lungs did not cause an increase in P(pa).
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PMID:Modulation of pulmonary leukotriene formation and perfusion pressure by bestatin, an inhibitor of leukotriene A4 hydrolase. 804 14


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