Oxidative response of neutrophils to platelet-activating factor is altered during acute ruminal acidosis induced by oligofructose in heifers

Reactive oxygen species (ROS) production is one of the main mechanisms used to kill microbes during innate immune response. D-lactic acid, which is augmented during acute ruminal acidosis, reduces platelet activating factor (PAF)-induced ROS production and L-selectin shedding in bovine neutrophils in vitro. This study was conducted to investigate whether acute ruminal acidosis induced by acute oligofructose overload in heifers interferes with ROS production and L-selectin shedding in blood neutrophils. Blood neutrophils and plasma were obtained by jugular venipuncture, while ruminal samples were collected using rumenocentesis. Lactic acid from plasma and ruminal samples was measured by HPLC. PAF-induced ROS production and L-selectin shedding were measured in vitro in bovine neutrophils by a luminol chemiluminescence assay and flow cytometry, respectively. A significant increase in ruminal and plasma lactic acid was recorded in these animals. Specifically, a decrease in PAF-induced ROS production was observed 8 h after oligofructose overload, and this was sustained until 48 h post oligofructose overload. A reduction in PAF-induced L-selectin shedding was observed at 16 h and 32 h post oligofructose overload. Overall, the results indicated that neutrophil PAF responses were altered in heifers with ruminal acidosis, suggesting a potential dysfunction of the innate immune response.

Effect of platelet-activating factor on cell proliferation & NF-kappaB activation in airway smooth muscle cells in rats.

BACKGROUND & OBJECTIVE: Despite the established pro-inflammatory actions of platelet activating factor (PAF) observed on chronic obstructive pulmonary disease (COPD), its action on airway remodeling has been still unclear. It has been reported that nuclear factor-kappa B (NF-kappaB) activity is necessary for ASMC proliferation. Further, PAF has been identified as the proximal inducer of NF-kappaB. The present study was thus aimed to investigate the effect of PAF on airway smooth muscle cells (ASMC) proliferation and to evaluate the potential role of NF-kappaB in this regulation. METHODS: Healthy male Sprague-Dowley rats of 6-8 wk age were used for obtaining ASMCs. 3-(4,5- dimethylthiazole-2-yl)-2,5-diphenyltetrazolium-bromide (MTT) assay was to investigate the effects of PAF on ASMC proliferation and to confirm its optimum concentration for action. Additionally, cell proliferation was also examined using cell cycle assay by flow cytometry and immunocytochemical staining for proliferating cell nuclear antigen (PCNA). And NF-kappaB DNA-binding activity was assayed by electrophoretic mobility shift assay (EMSA). RESULTS: PAF stimulated ASMC proliferation with its peak at 100 nM. At this optimum concentration, PAF significantly increased the cell proliferation index (PI) and the PCNA-positive rate in the ASMCs, as well as NF-kappaB DNA- binding activity. Whereas, 20 mM N-acetylcysteine (NAC) pre-treatment effectively blocked all of these events. INTERPRETATION & CONCLUSION: The present findings demonstrated that PAF could promote ASMC proliferation, suggesting its potential involvement in airway remodeling. Our study also suggested the promising action of 20 mM NAC on the alleviation of airway remodeling due to direct inhibition of ASMC proliferation. The involved mechanism would be relevant to the change of NF-kappaB activation in ASMCs.

Molecular mechanisms involved in human platelet aggregation by synergistic interaction of platelet-activating factor and 5-hydroxytryptamine

Our recent studies have shown that co-activation of Gq and Gi proteins by 5-hydroxytryptamine (5-HT) and adrenaline show synergism in human platelet aggregation. This study was conducted to examine the mechanism(s) of synergistic interaction of 5-HT and platelet activating factor (PAF) in human platelets. We show that PAF, but not 5-HT, increased platelet aggregation in a concentration-dependent manner. However, low concentrations of 5-HT (2 microM) potentiated platelet aggregation induced by subthreshold concentration of PAF (40 nM) indicating a synergistic interaction between the two agonists and this synergism was blocked by receptor antagonists to either 5-HT or PAF. 5-HT also potentiated the effect of PAF on thromboxane A2 (TXA2) formation and phosphorylation of extracellularly regulated mitogen-activated protein kinases (ERK1/2). The synergism of 5-HT and PAF in platelet aggregation was inhibited by calcium (Ca2+) channel blockers, verapamil and diltiazem, phospholipase C (PLC) inhibitor, U73122, cyclooxygenase (COX) inhibitor, indomethacin, and MEK inhibitor, PD98059. These data suggest that synergistic effect of 5-HT and PAF on human platelet aggregation involves activation of PLC/Ca2+, COX and MAP kinase pathways.

Molecular mechanisms involved in human platelet aggregation by synergistic interaction of platelet-activating factor and 5-hydroxytryptamine

Our recent studies have shown that co-activation of Gq and Gi proteins by 5-hydroxytryptamine (5-HT) and adrenaline show synergism in human platelet aggregation. This study was conducted to examine the mechanism(s) of synergistic interaction of 5-HT and platelet activating factor (PAF) in human platelets. We show that PAF, but not 5-HT, increased platelet aggregation in a concentration-dependent manner. However, low concentrations of 5-HT (2 microM) potentiated platelet aggregation induced by subthreshold concentration of PAF (40 nM) indicating a synergistic interaction between the two agonists and this synergism was blocked by receptor antagonists to either 5-HT or PAF. 5-HT also potentiated the effect of PAF on thromboxane A2 (TXA2) formation and phosphorylation of extracellularly regulated mitogen-activated protein kinases (ERK1/2). The synergism of 5-HT and PAF in platelet aggregation was inhibited by calcium (Ca2+) channel blockers, verapamil and diltiazem, phospholipase C (PLC) inhibitor, U73122, cyclooxygenase (COX) inhibitor, indomethacin, and MEK inhibitor, PD98059. These data suggest that synergistic effect of 5-HT and PAF on human platelet aggregation involves activation of PLC/Ca2+, COX and MAP kinase pathways.

Prevencion del dano intestinal mediante la utilizacion de un antagonista del factor de activacion plaquetaria en el trasplante intestinal / Prevention of intestinal damage through the utilization of an antagonist of the platelet activating factor in intestine transplantation

Se realiza un estudio comparativo en ratas singenicas de la cepa Wistar con objeto de valorar los efectos de preservacion del injerto al utilizar el antagonista del factor de activacion plaquetaria, WEB-2086. en la valoracion ultraestructural se ha podido comprobar los efectos de esta sustancia al nivel de las celulas epiteliales de intestino trasplantado

Synaptic messenger substances in memory processes

Nitric oxide (NO), carbon monoxide (CO), the platelet-activating factor (PAF) and arachidonic acid are released by stimulated neurons, enhance glutamate release at nerve terminals and have been proposed as synaptic messengers involved in plastic phenomena, such as the long-term potentiation of glutamatergic synapses. Long-term potentiation has been suggested to be a basic mechanism of memory processes. The microinjection of inhibitors of the synthesis of NO and CO or of antagonists of the receptors to PAF into brain structures known to be involved in memory (hippocampus, amygdala, entorhinal cortex), during its early phases, causes amnesia. This indicates that NO, CO and PAF modulate the early phases of memory, perhaps by modulating long-term potentiation. In addition, microinjections of a NO releaser or of a soluble form of PAF into the hippocampus produce memory enhancement.

Induction of acrosome reaction in fresh and frozen-thawed bovine spermatozoa by platelet activating factor.

In vitro capacitation has been induced in fresh and frozen spermatozoa of Karan Swiss (KS) and Karan Fries (KF) crossbred cattle by using a phospholipid-platelet activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine). The capacitation was monitored by examining acrosome reaction (AR) and motility at various levels of platelet activating factor (PAF) and at the end of each incubation time. On an average, with the increase in incubation time, there was a gradual decrease in motility and increase in acrosome reaction in both fresh as well as frozen spermatozoa. As PAF level increased, the motility of fresh sperms decreased and their acrosome reaction increased dramatically. However, in frozen-thawed semen, the motility remained almost the same and increase in AR of frozen spermatozoa was not pronounced. PAF level of about 100 microM was observed to be most optimum as at this level AR improved significantly without much loss of motility.

Paf antagonists do not modify IgE antibody production in mice

The effect of selective PAF antagonists on the in vivo production of IgE antibodies was investigated. The anti-ovalbumin IgE antibody content was estimated by passive cutaneous anaphylactic reaction (PCA) in the plasma of Balb/c mice 10 days after immunization with ovalbumin and alum. The PAF antagonists, BN 52021 (5 mg/kg, ip), BN 50730(20 mg/kg, ip) BN 50730 (20 mg/kg, po), WEB 2086 (2 mg/kg, ip) and WEB 2170 (5 mg/kg, ip) were administered 1 h before immunization and twice a day for 8 days thereafter. The effect of the antagonists on the PAF-induced vasopermeability was also assayed. In the immunized mice the level of antiovalbumin IgE antibody, estimated by PCA titer, was 1/640. The treatment with the PAF antagonists did not change this level. At the concentrations employed, the antagonists BN 50730, WEB 2086 and WEB 2170 significantly reduced the PAF-induced vascular permeability. These results suggest that PAF does not seem to have a relevant effect on the production of IgE antibodies in vivo in the system used in the present study

PAF-acether and the acute inflammatory reaction

PAF-aceter é um fosfolipídio que exerce um papel importante na reaçäo inflamatória aguda. No modelo experimental do edema da para de rato e pleurisia, a reaçäo induzida pelo PAF era acompanhada de hemoconcentraçäo, embora esses processos pareçam ser mediados por mecanismos distintos. Antagonistas específicos do PAF, como BN 52021 e WEB 2086, inibem 60% do edema induzido pelo PAF. Leucotrienos e mecanismos histaminérgicos envolvendo receptores H2 parecem participar no processo. A participaçäo do sistema adrenérgico e de metabólitos da ciclooxigenase é controversa. Infiltraçäo de leucócitos, observada após a injeçäo de PAF, e plaquetas näo säo necessárias para a formaçäo de edema. Auto-dessensibilizaçäo induzida pelo PAF pôde ser observada, sendo seletiva e dependente a interaçäo do PAF com receptores específicos em um processo de regulaçäo depressiva ("dow-regulation"). Nenhuma participaçäo deo PAF foi observada na reaçäo inflamatória induzida pela carregenina, contrariamente áquela provocada pelo zimosan, que é principalmente dependente do PAF-aceter

Pleural eosinophil infiltration induced by PAF-acether is not a desensitizable phenomenon

This study investigated the effect of successive daily intrathoracic (it) injections of PAF-acether upon its demonstrated ability to generate eosinochemotaxin(s). Repeated administration of PAF-acether led to a selective state of desensitization, characterized by a gradual reduction of its ability to induce exudation. Concomitantly, however, there was a progressive pleural accumulation of eosinophilis leading to a 7-fold increase in the eosinophil counts after the 4th restimulation. The generation of eosinochemotaxin(s) elicited by PAF-acether was not modified by desensitization, as detected by transferring the cell-free pleural fluid from donor to recipient animals. We conclude that, in contrast to exudation, eosinophil tissue infiltration induced by PAF-acether is not a desensitizable phenomenon

Effect of metronidazole on platelet aggregation

The removal of T. cruzi bloodstream trypomastigotes (BTRYS) from the circulation is mediated mostly by the mononuclear phagocytic system (MPS). In the present study we investigated the nonspecific and the immune clearance of BTRYS in groups of 4 mice whose MPS activity was either enhanced by BCG treatment or depressed by silica treatment. Treatment with BCG resulted in a significant increase in the nonspecific clearance of both carbon particles (100% after 6 min) and BTRYS (60% after 5 min) 28 days after BCG treatment but there was bi change in the immune clearance of the parasites. Pretrteatment of the animals with silica induced a significant reduction of the colloidal carbon clearance (80% less than control 15 min later) but did not alter the nonspecific or the immune clearance of BTRYS. We conclude that the removal of the opsonized parasites from the circulation is due to a mechanism different from that of the nonspecific clearance

Effect of PAF-acether on the reactivity of the isolated rat myometrium

In non-pregnant rat isolated uterine strips PAF-acether (1-1000 nM) produced contractile effects on 74% of the preparations tested which were concentration-dependent in 44% of the cases (EC50 = 28 nM). All the preparations tested exhibited contractile responses to either acetylcholine or potassium. PAF-acether was less potent on myometrial strips from pregnant animals (EC50 = 0.3 micronM) and was only effective on 24% of the preparations tested. A second contractile concentration-response curve was reproducible in only 14% of the preparations from non-pregnant rats (EC50 = 13 nM), whereas all strips from pregnant animals were completely refractory to a second challenge with PAF-acether. These results indicate that PAF-acether induces contraction of the isolated rat myometrium within the Ssame range of concentration at which it is active in other tissues

Late eosinophil mobilization induced by PAF-acether in the pleural cavity of rats

In view of the rapid degradation of PAF in biological fluids, this study was designed to determine if late eosinophil infiltration induced in rats by PAF was deriived from its direct chemotatic action. A significant and selective 5-fold increase in the pleural eosinophil counts was detected 24 h after intrapleural PAF injection. The transfer of 6-h PAF washings to the pleural cavity of recipient rats also induced a 3-fold selective accumulation of eosinophils. The protein synthesis inhibitor cycloheximide abolished the pleural eosinophil migration and the generation of transferable chemotactic activity when administered to donor but not to recipient rats. These findings suggest that a secondary protein mediator accounts for the late eosinophil mobilization induced by PAF

Tracheal responsiveness to histamine, PAF-acether and acetylcholine in normal and actively ovalbumin-sensitized guinea pigs

The contractile effects of histamine (His), PAF-acether (PAF) and acetylcholine (Ach) were analyzed in tracheal rings from normal and ovalbumin-sensitized (OAS) guinea pigs. Although maximal responses to all agonists were enhanced in preparations from OAS guinea pigs, only the EC50 of Ach was significantly decreased. Previous treatment with 1 micronM indomethacin (IND) or 10 micronM quinacrine (QUIN) markedly displaced the dose-response curves for Ach on OAS preparations to he left, whereas the EC50 of His was only increased by QUIN. PAF-responses, however, were completely abolished by IND in preparations from both senstized and unsensitized animals. These results indicate that ovalbumin sensitization significantly affects the tracheal response to Ach, His and PAF, an effect that appears to be mediated by arachidonic acd metabolites

Adrenalectomy exacerbates paw edema without interfering with desensitization induced by PAF-acether in rats

Subcutaneous injection of PAF-acether into rat's paw to a local inflammatory response (edema) followed by desensitization after repeated injections of the substance. The desensitizing effect was not modified by previous adrenalectomy, whereas the inflammatory response observed after the first injection of PAF-acether was exacerbated. This finding suggests that adrenal hormones may act as modulators of PAF-induced inflammatory reactions. Because LY 171883, an LTD4 blocker, inhibited the edema which follows the first injection of PAF-acether, we suggest that leukotrienes may play an important role in the phenomenon