Blood Platelet-activating Factor Levels Research Articles

Elevated Platelet Activating Factor Level in Ischemia-Related Arrhythmia and Its Electrophysiological Effect on Myocardium

ObjectiveThe mechanism through which platelet activating factor (PAF) induces cardiac electrical activity and arrhythmia is not well understood and previous studies have suggested a potential involvement of ion channels in its action. The present study was aimed to clarify the role of PAF in fatal arrhythmias following acute myocardia infarction (AMI) and the underlying mechanism. Methods(1) Blood PAF levels were measured among 72 AMI patients at the time of diagnosis with AMI and 48 h later, and their electrocardiogram (ECG) was recorded continuously. (2) Ischemia simulation and surface electrocardiogram were conducted in 20 pigs and their PAF levels were measured. (3) PAF perfusion and standard microelectrode recording were performed on guinea pig papillary muscles. ResultsIn both humans and pigs, elevated PAF levels were detected in AMI and simulated ischemia, respectively, and even higher PAF levels were found when fatal arrhythmias occurred. In guinea pig myocardium, PAF induced a shortening of action potential duration at 90% level of repolarization (APD90)under non-ischemic conditions and a more pronounced shortening under early simulated ischemic conditions. ConclusionAMI and ischemia are associated with increased PAF levels in humans and pigs, which are further raised when fatal arrhythmia follows. The effects of PAF on the myocardium may be mediated by multiple ion channels.

Platelet activating factor levels and metabolism in tangier disease: a case study

BackgroundTangier disease (TD) is a phenotypic expression of rare familial syndrome with mutations in the ABCA1 transporter. The risk of coronary artery disease in patients with TD is variable. On the other hand the pivotal role of Platelet-Activating Factor (PAF) mediator in atheromatosis was found. Plasma lipoproteins are transporters of the PAF acetylhydrolase (PAF-AH) in cells and known as lipoprotein-phospholipase A2 (Lp-PLA2) in plasma and regulators of PAF levels in blood. In addition, PAF can be biosynthesized from the remodeling and the de novo pathways in which Lyso-platelet activating factor-acetyltransferase (Lyso-PAF-AT) and platelet activating factor-cholinephosphotransferase (PAF-CPT) are the regulatory enzymes. The aim of this study is to investigate in a TD patient with a unique mutation (C2033A), the concentration of PAF in blood, the Equivalent Concentration for 50% aggregation (EC50) values of platelet rich plasma (PRP) toward PAF, adenosine diphosphate (ADP) and thrombin, and the activities of PAF metabolic enzymes Lp-PLA2, PAF-AH, Lyso-PAF-AT and PAF-CPT.MethodsThe EC50 value of PRP was measured by an aggregometer. The determination of the specific activity of PAF-CPT and Lyso-PAF-AT was made after in vitro enzymatic assay, chromatographic separation and measurement of the produced PAF in a biological assay with washed rabbit platelets. The determination of PAF-AH and Lp-PLA2 was made after an in vitro enzymatic assay from the decay of radioactive PAF.ResultsThe TD patient had lower bound-PAF values in blood, decreased specific activity of PAF-CPT and Lyso-PAF-AT, increased specific activity of PAF-AH in platelets and leukocytes and Lp-PLA2 activity in plasma compared to healthy women. The EC50 of PAF and Thrombin were higher compared to healthy women.ConclusionThe increased Lp-PLA2 activity, as well as, the decreased activities of PAF-CPT and Lyso-PAF-AT, explain the decreased bound-PAF level in TD patient and the EC50 of PAF. However, total PAF is in a normal range and this probably can explain one of the reasons this TD patient has no CAD.

Platelet-Activating Factor Involvement in Thioacetamide-Induced Experimental Liver Fibrosis and Cirrhosis

Platelet-activating factor (PAF) is a potent lipid inflammatory mediator acting on cells through its specific receptor. Plasma PAF-acetylhydrolase (PAF-AH) is the main enzyme that inactivates PAF in blood, participating in its homeostasis. The objective of this study was to investigate the involvement of PAF in the liver fibrotic process using an experimental animal model. Liver fibrosis was induced in adult male Wistar rats by administration of thioacetamide (TAA) in drinking water (300 mg/l) for three months. The animals were sacrificed at time 0 (control group) and after 1, 2, and 3 months. PAF levels in liver and blood and PAF-AH activity in plasma were determined. Liver histopathological examination was also performed. TAA administration resulted in progressively increased liver fibrosis, leading finally to the formation of cirrhotic nodules in the liver. Throughout the experiment PAF levels in liver tissue remained stable. "Total" ("free" plus "bound") PAF levels in blood decreased, reaching statistically significant differences in the first and third months compared with the control group (P < 0.05). "Free" PAF levels in blood were higher at one month (P < 0.05) and decreased gradually thereafter. In all treated groups, "bound" PAF levels in blood decreased whereas plasma PAF-AH activity increased (P < 0.05) compared with the control group. Our data indicated alterations of PAF levels in blood and PAF-AH activity during fibrosis induction, implicating participation of PAF in the liver fibrotic process.

In vivo antiatherogenic properties of olive oil and its constituent lipid classes in hyperlipidemic rabbits

Background and aim The consumption of olive oil has been associated with lower incidence of cardiovascular disease in the Mediterranean countries. This may be due in part to the action of platelet-activating factor (PAF) antagonists which we have previously demonstrated to be present in olive oil. In order to assess the in vivo effects of olive oil lipids and PAF in the development of atherosclerosis, the effects of diet supplementation with olive oil (OO), olive oil polar lipid extract (OOPLE) and olive oil neutral lipid extract (OONLE) were studied in rabbits fed a cholesterol-enriched diet. Methods and results Rabbits were fed for 45 days with atherogenic diet (Group A) supplemented with OO (Group B), OOPLE (Group C) or OONLE (Group D). Lipoprotein profiles, plasma in vitro oxidation, blood PAF levels, PAF-induced platelet aggregation and PAF-acetylhydrolase (PAF-AH) activity, were measured on day 0 and 45. Atherosclerotic lesions formed in the aortic wall and wall elasticity were assessed on day 45. Changes in lipid profile were in accordance with previous studies. Blood PAF levels were higher in group A and decreased in group D on day 45. In rabbits fed an atherogenic diet (Group A) blood PAF and PAF-AH increased, atherosclerotic lesions formed and the elasticity of vessel walls declined. In animals fed olive oil (Group B) or OOPLE (Group C) blood PAF-AH increased, platelet aggregation was attenuated, less oxidation occurred in plasma, lesion thickness was reduced and vessel walls retained elasticity. Most of these beneficial changes were not seen in animals fed OONLE (Group D) although blood PAF and plasma oxidation were lower. Conclusions The antiatherogenic effects of OO result from OOPLE. The beneficial effect of these factors is linked to PAF metabolism and proaggregant activity.

Platelet-activating factor (PAF) involvement in acetaminophen-induced liver toxicity and regeneration

Acetaminophen-induced toxicity has been attributed to cytochrome P-450-generated metabolites, which covalently modify target proteins. However, the mechanism of liver injury pathogenesis needs to be further elucidated. Platelet-activating factor (PAF) is one of the mediators involved in inflammatory tissue alterations associated with acute liver failure. In this study, alterations in blood PAF levels and the serum activity of PAF-acetylhydrolase (PAF-AH) were investigated over the time course of liver injury and regeneration induced by acetaminophen treatment in rats. The administration of a toxic dose of acetaminophen (3.5 g/kg) in rats caused acute hepatic injury, as evident by alterations of biochemical (serum enzymes: ALT, AST and ALP) and liver histopathological (degree of inflammation and apoptosis) indices between 20 and 40 h post-treatment. The hepatic damage was followed by liver regeneration, made evident by three independent indices ([3H]thymidine incorporation into hepatic DNA, liver thymidine kinase activity and hepatocyte mitotic index), presenting a peak at 72 h. The PAF levels were elevated at 24 and 28 h, presenting a remarkable peak at 32 h post-treatment. PAF-AH activity presented different kinetics to that of PAF. The enzyme activity was relatively low at all time points examined before the rise in PAF activity, peaking later, at 72, 84 and 96 h. Our data demonstrate that PAF is involved in the pathogenesis of acute liver failure and in augmented compensatory liver tissue repair post-acetaminophen treatment. However, the putative role of PAF during liver toxicity and regeneration remains to be established.

Platelet-activating factor does not mediate circulatory failure induced by 35-GHz microwave heating.

Sustained whole-body exposure of anesthetized rats to 35-GHz radiofrequency radiation produces localized hyperthermia and hypotension, leading to circulatory failure and death. The physiological mechanism underlying the induction of circulatory failure by 35-GHz microwave (MW) heating is currently unknown. The purpose of this study was to determine whether platelet-activating factor (PAF) contributes to the hypotensive state induced by MW heating. Ketamine-anesthetized rats were instrumented for the measurement of arterial blood pressure, ECG and temperature at five sites. Administration of the PAF-receptor antagonist WEB 2086 (0.5 or 5 mg/kg) following the induction of circulatory failure (defined as a decrease in mean arterial blood pressure to 75 mmHg) failed to reverse the hypotension induced by MW heating and consequently did not alter the subsequent survival time. Furthermore, pretreatment with WEB 2086 at either dose did not alter subsequent mean arterial blood pressure, temperature responses to MW heating or survival time. Finally, MW heating did not alter either blood PAF levels or serum or lung PAF acetylhydrolase levels. Taken together, these results demonstrate that PAF does not mediate the hypotension induced by 35-GHz MW heating.

Deregulated platelet-activating factor levels and acetylhydrolase activity in patients with idiopathic IgA nephropathy.

Platelet-activating factor (PAF) is a phospholipid mediator with potent inflammatory activities. PAF stimulates IgA synthesis by B cells while IgA aggregates enhance PAF production by neutrophils and mesangial cells. These results led us to investigate blood PAF levels and plasma acetylhydrolase (AHA, the PAF catabolic enzyme) activity in patients with idiopathic IgA nephropathy (IgAN). PAF and AHA levels were investigated using the platelet aggregation assay and degradation of (3)H-labelled PAF, respectively. The genotype of AHA with regard to the G994-->T mutation in exon 9 was assessed by an allele-specific polymerase chain reaction. Blood PAF levels were significantly (P:=0.003, Mann-Whitney U:-test) elevated in IgAN patients (50.6+/-6.8 pg/ml, n=33) compared with healthy controls (18+/-5 pg/ml, n=18). In contrast, plasma AHA levels were significantly (P:=0.0001, Mann-Whitney U:-test) reduced in patients with IgAN (61+/-2 nmol/ml/min, n=51) compared with healthy controls (78+/-4 nmol/ml/min, n=53). G994-->T transversion in exon 9 of AHA was not found in any of the IgAN patients. Elevated circulating levels of PAF in IgAN patients might result from an insufficient AHA probably related to environmental factors rather than genetic ones. The mechanism and the precise role of the PAF/AHA deregulation in IgAN patients remain to be clarified.

No evidence for a putative involvement of platelet-activating factor in systemic lupus erythematosus without active nephritis.

BACKGROUND: Platelet-activating factor (PAF) seems to be implicated in systemic lupus erythematosus (SLE) patients with associated renal diseases. AIMS: In this study, we ensured the role of PAF in SLE patients without renal complications. METHODS: Blood PAF and acetylhydrolase activity, plasma soluble phospholipase A(2), and the presence of antibodies against PAF were investigated in 17 SLE patients without active nephritis and in 17 healthy controls. RESULTS: Blood PAF levels were not different (p=0.45) between SLE patients (6.7+/-2.8 pg/ml) and healthy subjects (9.6+/-3.1 pg/ml). Plasma acetylhydrolase activity (the PAF-degrading enzyme) was significantly (p=0.03) elevated in SLE patients (57.8+/-6.4 nmol/min/ml) as compared with controls (37.9+/-2.6 nmol/min/ml). Plasma soluble phospholipase A(2) (the key enzyme for PAF formation) was not different (p=0.6) between SLE patients (59.1+/-5.1 U/ml) and controls (54.7+/-2.4 U/ml). Antibodies against PAF were detected only in 3/17 SLE patients. Flow cytometry analysis did not highlight PAF receptors on circulating leukocytes of SLE patients. CONCLUSION: This clinical study highlights no evidence for a putative important role of PAF in SLE patients without active nephritis.

Effect of Human Natural Xenoantibody Depletion and Complement Inactivation on Early Pig Kidney Function

Preformed xenoreactive natural antibodies (XNA) and complement mediate hyperacute xenograft rejection (HXR) in pig-to-human discordant xenotransplantation. In a pig kidney-human blood xenoperfusion model, we investigated whether XNA depletion and/or human complement inactivation preserved early pig kidney function. Pig kidneys were perfused for 180 min with pig blood (AUTO group, n = 8), human blood (HETER group, n = 6), complement-inactivated human blood (COMi group, n = 5), XNA-depleted human blood (ABd group, n = 5) or complement-inactivated and XNA-depleted human blood (ABd&COMi group, n = 5). HETER kidneys were rejected after 15–30 min and showed vascular microthrombi and interstitial hemorrhages. XNA depletion and/or complement inactivation prevented HXR. The glomerular filtration rate in ABd, COMi and ABd&COMi groups was significantly lower than in the AUTO group. Also, beyond 60 min, the COMi group showed a significantly lower glomerular filtration rate than that observed in ABd and ABd&COMi groups. Kidneys from ABd, COMi and ABd&COMi groups displayed endothelial cell edema, as well as higher soluble P-selectin levels and a higher renal myeloperoxidase content than the AUTO group kidneys. COMi and ABd&COMi groups had a significantly lower renal myeloperoxidase level than the HETER group. Also, in contrast to HETER and ABd groups, these complement-inactivated groups failed to show a positive correlation between P-selectin and renal myeloperoxidase. We also investigated platelet-activating factor (PAF) as possible mediator for these functional and pathologic changes. We found that blood PAF levels were similar in HETER, ABd, COMi and ABd&COMi groups and significantly higher than in the AUTO group. Also, when PAF was added to porcine endothelial cell monolayers, morphological changes due to cytoskeleton contraction were observed, and these changes were prevented by preincubation with a PAF receptor antagonist. In conclusion, although depletion of XNA and/or complement inactivation prevent HXR, the pig kidney function is not preserved at the level of the autologous combination. The PAF overproduction observed in the xenogenic combination, which is independent of the presence of XNA and complement, may be, at least in part, responsible for early endothelial cell morphological changes still present when HXR is prevented.

Eicosanoid and cytokine levels in plasma of patients during mesenteric infarction

Multible organ failure (MOF) induced by mesenteric infarction is associated with a high mortality rate. This study reports eicosanoid and cytokine levels in the blood of three atherosclerotic patients who ultimately died from MOF induced by mesenteric infarction. High plasma levels of 6- keto-prostaglandin (PG) F1α (the stable metabolite of PGI2), interleukin (IL)-6 and IL-8 are observed whereas plasma tumour necrosis factor alpha (TNFα), TxB2 (the stable metabolite of TxA2), PGE2, leukotrienes (LT)B4 and LTC4, and whole blood platelet-activating factor levels are not different from values obtained in similarly severe atherosclerotic patients. This short report questioned the clinical involvement of TNFα during such a pathology where a persistent translocation of endotoxin has been observed through the gut endothelial barrier. Activation of phospholipase A2 is suggested by the increase in the stable metabolite of PGI2 and might be by itself or through lipidic metabolites, a major systemic stimulus of IL-6 and IL-8 production.

Altered platelet-activating factor levels and acetylhydrolase activities are associated with increasing severity of bronchopulmonary dysplasia.

Lipid inflammatory mediators are thought to play an important role in the pathogenesis of neonatal lung injury and bronchopulmonary dysplasia (BPD). Because preliminary studies from the intensive care nursery of the University of Tennessee Medical Center, Knoxville, revealed linear increased in blood platelet-activating factor (PAF) levels in very low birthweight infants developing chronic lung disease and lower cord blood PAF acetylhydrolase activities in premature infants, it was theorized that altered platelet-activating factor levels and PAF acetylhydrolase activities are associated with increasing severity of BPD. Platelet-activating factor levels (blood and tracheal lavage) and PAF acetylhydrolase activities (blood and tracheal lavage) were measured over days 1 to 2, 3 to 5 and 6 to 7 in 16 ventilated infants and weekly in 9 infants with bronchopulmonary dysplasia. Platelet-activating factor values were normalized per nanogram of lavage blood urea nitrogen. Severity of bronchopulmonary dysplasia was estimated using the scoring system developed by Toce. Mean blood and lavage PAF levels and PAF acetylhydrolase activities were compared in infants developing bronchopulmonary dysplasia with those without the disease over the first seven days of life. Infants developing chronic lung disease were significantly smaller and of younger gestational age. In infants with bronchopulmonary dysplasia, higher PAF levels in blood were seen on days 3 to 5, along with increased lavage acetylhydrolase activities on days 1 to 2. Increased levels of PAF in lavage on days 3 to 5 were associated with increasing severity of bronchopulmonary dysplasia. Altered blood and lavage platelet-activating factor levels and PAF acetylhydrolase activities appear to be associated with the pathogenesis and severity of bronchopulmonary dysplasia.

Altered Platelet-Activating Factor Levels and Acetylhydrolase Activities Are Associated With Increasing Severity of Bronchopulmonary Dysplasia

<h2>ABSTRACT:</h2> Lipid inflammatory mediators are thought to play an important role in the pathogenesis of neonatal lung injury and bronchopulmonary dysplasia (BPD). Because preliminary studies from the intensive care nursery of the University of Tennessee Medical Center, Knoxville, revealed linear increases in blood platelet-activating factor (PAF) levels in very low birth-weight infants developing chronic lung disease and lower cord blood PAF acetylhydrolase activities in premature infants, it was theorized that altered platelet-activating factor levels and PAF acetylhydrolase activities are associated with increasing severity of BPD. Platelet-activating factor levels (blood and tracheal lavage) and PAF acetylhydrolase activities (blood and tracheal lavage) were measured over days 1 to 2, 3 to 5 and 6 to 7 in 16 ventilated infants and weekly in 9 infants with bronchopulmonary dysplasia. Platelet-activating factor values were normalized per nanogram of lavage blood urea nitrogen. Severity of bronchopulmonary dysplasia was estimated using the scoring system developed by Toce. Mean blood and lavage PAF levels and PAF acetylhydrolase activities were compared in infants developing bronchopulmonary dysplasia with those without the disease over the first seven days of life. Infants developing chronic lung disease were significantly smaller and of younger gestational age. In infants with bronchopulmonary dysplasia, higher PAF levels in blood were seen on days 3 to 5, along with increased lavage acetylhydrolase activities on days 1 to 2. Increased levels of PAF in lavage on days 3 to 5 were associated with increasing severity of bronchopulmonary dysplasia. Altered blood and lavage platelet-activating factor levels and PAF acetylhydrolase activities appear to be associated with the pathogenesis and severity of bronchopulmonary dysplasia.

Platelet aggregability to platelet activating factor at rest and after exercise in patients with coronary artery disease.

The platelet response to the aggregatory effect of platelet-activating factor (PAF) in relation to blood PAF levels, serum PAF-acetylhydrolase (PAF-AH) activity and to their lipidaemic profile, was studied in 44 patients with coronary artery disease undergoing exercise tests. The PAF EC50 values in 21 patients with positive exercise test results were found to be significantly decreased at rest compared with 21 normal subjects (12.6 +/- 3.9 nM and 24.9 +/- 11.7 nM respectively) (P<0.0001). Moreover, the maximal percentage of aggregation to 50 nM PAF was found to be significantly increased (20.0 +/- 4.3% vs 13.5 +/- 3.6%, respectively) (P<0.0001). By contrast, the PAF EC50 values and the maximal percentage of aggregation in 23 patients with negative exercise test results were not statistically significantly different from the control group (25.2 +/- 11.4 nM and 14.1 +/- 4.7%, respectively). At the end of exercise, the PAF EC50 values and the maximal percentage of aggregation did not change in any group, and there were no significant differences in the whole-blood PAF levels either at rest or at the end of exercise. In patients with positive exercise test results, the PAF-AH activity at rest was significantly higher compared with the control group (37.2 +/- 8.0 nmol.ml(-1).min(-1) vs 32.4 nmol.ml(-1).min(-1), (P<0.03), whereas the enzyme activity did not differ in patients with negative exercise test results compared to controls (33.6 +/- 6.1 nmol.ml(-1).min(-1)). There was no change in PAF-AH activity during exercise in any group. The enzyme activity was positively correlated to the serum total and low density lipoprotein (LDL) cholesterol levels in the control group and in patients with negative exercise test results, whereas no correlation was found between PAF-AH activity and total or LDL cholesterol levels in patients with positive exercise test results.

The Production of Platelet-Activating Factor (PAF) during Hemodialysis with Cuprophane Membrane. Does the Calcium Concentration in the Dialysate Play Any Role on It?

There is evidence that PAF may be produced during hemodialysis (HD) mainly when using cuprophane membrane (CU). It is also known that PAF production is dependent on the amount of extracellular calcium (ECa2+). In the present study, we investigated the production of PAF during HD with CU as well as the role of the Ca2+ in the dialysate with respect to PAF production. Five hemodialyzed patients were studied in two consecutive HD sessions (the first performed using dialysate without Ca2+ and the second with a Ca2+ concentration of 3.25 mEq/L) and at different times during the sessions the circulating PAF levels as well as the leukocyte and platelet counts were measured. The results demonstrated that a) PAF was indeed produced during HD with CU, b) the highest PAF levels in blood were observed between 5 and 15 minutes from the beginning of HD, at which time the lowest circulating leukocyte and platelet count were measured and c) PAF levels in blood were inversely proportional to the Ca2+ concentration in the dialysate (with the exceptional case of the 15 minutes), although we expected the opposite results.

A simple and precise method for the routine determination of platelet‐activating factor in blood and urine

A simple and precise method is described for the measurement of platelet-activating factor (PAF) in blood and urine. The method involves the isolation of PAF from blood samples by two successive steps. In the first step, blood proteins are precipitated with ethanol and the "free" PAF, i.e., the PAF which is extractable with ethanol, is recovered. In the second step, "bound" PAF, i.e., PAF not extractable with ethanol, is extracted from the protein precipitate with chloroform/methanol/water. The extraction of PAF from urine samples requires only the ethanol extraction step. "Free" and "bound" PAF are then each fractionated by silicic acid column chromatography, and the methanol/water eluent containing PAF is then further fractionated by high-performance liquid chromatography using an isocratic solvent system of acetonitrile/methanol/water. PAF is then quantitated by measuring its ability to induce platelet aggregation in an aggregometer. Application of the method to blood and urine samples from twenty-three healthy volunteers revealed PAF levels in blood of 140-480 pg/mL (630-254.4 pg "free" PAF/mL and 64-225.6 pg "bound" PAF/mL), and of 1.2-4.0 pg PAF/mL in urine. The method overcomes various technical problems and was shown to be very precise. It should prove useful for monitoring PAF levels in various disease conditions.

Increased levels of blood platelet‐activating factor in bronchial asthmatic patients with active symptoms

Levels of platelet-activating factor (PAF) in blood from 12 bronchial asthmatic patients (six atopic and six nonatopic) were measured by radioimmunoassay after lipid extraction and separation by high-performance liquid chromatography. None of the patients were given disodium cromoglycate and prednisolone, and they were instructed to take only regular medications during the tests. Blood was drawn from the patients in a fasting state, and PAF levels were compared between the times when they were free of asthmatic symptoms and when they had mild spontaneous attacks. Ten (six atopic and four nonatopic) out of 12 patients, when they had the asthmatic attacks, showed higher levels of PAF than when they were free of the symptoms. Blood PAF levels of the patients with the active symptoms were significantly higher than those of normal healthy control subjects, suggesting that PAF may play a role in bronchial asthma.

Urinary excretion of platelet activating factor in patients with immune-mediated glomerulonephritis

We have investigated whether human immune-mediated glomerulonephritis is associated with changes in platelet activating factor (PAF) biosynthesis. Urinary PAF, taken as a marker of its renal synthesis, was significantly higher in patients with membranous nephropathy (N = 9) than in healthy controls (N = 8). This was not due to a lower degradation of PAF since urinary acetylhydrolase activity was comparable in patients and controls. A significant positive correlation between urinary excretion of PAF and proteinuria was observed. PAF generation was comparable in polymorphonuclear cells isolated from patients with membranous nephropathy and controls. PAF levels in blood from patients with membranous nephropathy were significantly lower than in controls, suggesting that the excessive generation of PAF is confined to the kidney. The results document that signs of renal disease activity in human membranous nephropathy are associated with an excessive renal synthesis of PAF.

Metabolism of platelet-activating factor in neutrophils isolated from Pichinde virus-infected guinea pigs.

Metabolism of platelet-activating factor (PAF) was studied in cultured polymorphonuclear neutrophils (PMNs) obtained from Pichinde virus-infected strain 13 guinea pigs. Neutrophils obtained from control and infected guinea pigs on postinoculation days 10 and 14 were incubated with [3H]lyso-PAF, [3H]PAF, or [3H]acetate. After incubation for 1 h at 37 degrees C, formation of [3H]acyl-PAF from either [3H]lyso-PAF or [3H]PAF increased significantly in PMNs from infected guinea pigs compared to control PMNs. Furthermore, total radioactivity from [3H]lyso-PAF or [3H]PAF was higher in PMNs from infected animals than in those from controls. However, compared to PAF production by control PMNs, production of PAF by infected PMNs was unchanged. These results suggest that PMNs may not be the major source of increased blood PAF levels during Pichinde viral disease.

Effect of SRI 63-675 on hemodynamics and blood PAF levels during porcine endotoxemia

We evaluated the effect of SRI 63-675, a specific platelet-activating factor (PAF) receptor antagonist, on hemodynamics and PAF biosynthesis during 4 h of porcine endotoxemia. Hexadecyl PAF was extracted from blood, purified by normal-phase and reverse-phase high-performance liquid chromatography (RP-HPLC), and quantitated by stable isotope dilution and thermospray mass spectrometry. Infusion of either saline or SRI 63-675 alone caused no change in hexadecyl PAF concentrations. In contrast, endotoxin increased blood hexadecyl PAF concentrations from 1.5 +/- 0.1 ng/ml at 0 h (baseline) to a peak value of 8.3 +/- 1.9 ng/ml at 0.5 h of endotoxemia (P less than 0.05). Blood PAF levels gradually declined toward the baseline value after 0.5 h of endotoxemia. Because endotoxin did not modify plasma acetylhydrolase activity ex vivo, the increased hexadecyl PAF levels were probably secondary to increased PAF biosynthesis and not decreased biodegradation. Bioassay of RP-HPLC fractions that were derived from endotoxemic blood and that eluted at a retention time consistent with [3H]alkyl PAF caused aggregation of washed rabbit platelets that was inhibited by SRI 63-675. The PAF receptor antagonist blocked the 0.5 h endotoxin-induced increase in blood hexadecyl PAF concentration concomitant with blockade of thrombocytopenia. The endotoxin-induced pulmonary hypertension, decreased cardiac index, and increases in pulmonary vascular resistance and alveolar-arterial O2 gradient were attenuated by SRI 63-675. The data suggest that PAF-stimulated PAF biosynthesis may substantially contribute to blood hexadecyl PAF levels and cardiopulmonary dysfunction during the initial phase of endotoxemia.