Acetyl glyceryl ether phosphorylcholine-stimulated human platelets cause pulmonary hypertension and edema in isolated rabbit lungs. Role of thromboxane A2

Spirulina platensis Suppressed iNOS and Proinflammatory Cytokines in Lipopolysaccharide-Induced BV2 Microglia

The disease burden of neurodegenerative diseases is on the rise due to the aging population, and neuroinflammation is one of the underlying causes. Spirulina platensis is a well-known superfood with numerous reported bioactivities. However, the effect of S. platensis Universiti Malaya Algae Culture Collection 159 (UMACC 159) (a strain isolated from Israel) on proinflammatory mediators and cytokines remains unknown. In this study, we aimed to determine the anti-neuroinflammatory activity of S. platensis extracts and identify the potential bioactive compounds. S. platensis extracts (hexane, ethyl acetate, ethanol, and aqueous) were screened for phytochemical content and antioxidant activity. Ethanol extract was studied for its effect on proinflammatory mediators and cytokines in lipopolysaccharide (LPS)-induced BV2 microglia. The potential bioactive compounds were identified using liquid chromatography-mass spectrometric (LC-MS) analysis. Ethanol extract had the highest flavonoid content and antioxidant and nitric oxide (NO) inhibitory activity. Ethanol extract completely inhibited the production of NO via the downregulation of inducible NO synthase (iNOS) and significantly reduced the production of tumor necrosis factor (TNF)-α and interleukin (IL)-6. Emmotin A, palmitic amide, and 1-monopalmitin, which might play an important role in cell signaling, have been identified. In conclusion, S. platensis ethanol extract inhibited neuroinflammation through the downregulation of NO, TNF-α and IL-6. This preliminary study provided insight into compound(s) isolation, which could contribute to the development of precision nutrition for disease management.

Platelets in lung biology

Platelets and the lungs have an intimate relationship. Platelets are anucleate mammalian blood cells that continuously circulate through pulmonary vessels and that have major effector activities in hemostasis and inflammation. The lungs are reservoirs for megakaryocytes, the requisite precursor cell in thrombopoiesis, which is the intricate process by which platelets are generated. Platelets contribute to basal barrier integrity of the alveolar capillaries, which selectively restricts the transfer of water, proteins, and red blood cells out of the vessels. Platelets also contribute to pulmonary vascular repair. Although platelets bolster hemostatic and inflammatory defense of the healthy lung, experimental evidence and clinical evidence indicate that these blood cells are effectors of injury in a variety of pulmonary disorders and syndromes. Newly discovered biological capacities of platelets are being explored in the context of lung defense, disease, and remodeling.

Significant involvement of CCL2 (MCP-1) in inflammatory disorders of the lung

Mounting evidence suggests that CCL2 (MCP-1) and its hematopoietic cell receptor CC chemokine receptor 2 (CCR2) are involved in inflammatory disorders of the lung. In animal models of allergic asthma, idiopathic pulmonary fibrosis (IPF), and bronchiolitis obliterans syndrome (BOS), CCL2 expression and protein production are increased and the disease process is attenuated by CCL2 immunoneutralization. Mechanisms by which CCL2 may be acting include recruitment of regulatory and effector leukocytes; stimulation of histamine or leukotriene release from mast cells or basophils; induction of fibroblast production of transforming growth factor-beta (TGF-beta) and procollagen; and enhancement of Th2 polarization. Recently, polymorphism for CCL2 has been described with increased cytokine-induced release of CCL2 by monocytes and increased risk of allergic asthma. These studies identify potentially important roles for CCL2 in these lung inflammatory disorders. While CCL2 inhibition in patients with acute respiratory distress syndrome (ARDS) may be hazardous by interfering with defense against bacteremia, future studies are needed to determine if CCL2/CCR2 antagonism will offer breakthrough therapy for patients with allergic asthma, IPF, or BOS, and to confirm the hypothesis that CCL2 polymorphism places patients at greater risk for these disorders.

A study of mechanisms underlying amitriptyline-induced acute lung function impairment

In this study possible mechanisms underlying the vaso- and bronchoconstriction caused by the tricyclic antidepressant drug amitriptyline in isolated rat lungs were investigated. Some features here are similar to those apparent in adult respiratory distress syndrome and acute lung injury. Amitriptyline exposure (50 and 100 microM) caused a dose-related, pronounced, and rapid vaso- (50 microM, 30 min, p < 0.001 and 100 microM, 30 min, p < 0.001) and bronchoconstriction (50 microM, 30 min, p = 0.01 and 100 microM, 30 min, p < 0.001). The maximal noted decrease in perfusion flow was 28 +/- 2.9% at 25 min and 80 +/- 4.5% at 30 min for 50 and 100 microM amitriptyline, respectively. The maximal noted decrease in airway conductance was 29 +/- 4.7% at 25 min and 68 +/- 5.0% at 30 min. To investigate mechanisms thought to be involved in amitriptyline-induced lung function impairment, lungs were treated with several different substances including antiinflammatory agents, antioxidants, inhibitors of enzymes involved in the arachidonic acid cascade, physiological antagonists, and neurogenic antagonists. A significant reduction of amitriptyline-induced vasoconstriction was observed when lungs were treated with the protein kinase inhibitor staurosporine (3 microM, 30 min, p < 0.001), the NO-donor S-nitrosoglutathione (100 microM, 30 min, p < 0.001) and the combined endothelin A/endothelin B receptor antagonist PD 145065. This latter inhibitor caused a significant attenuation of late vasoconstriction (1 microM, 60 min, p = 0.03). The amitriptyline-induced bronchoconstriction was attenuated by the beta(2)-agonist salbutamol (1 microM, 30 min, p = 0.03) and the platelet-activating factor antagonist WEB2086 (10 microM, 30 min, p = 0.03). Staurosporine had an initial protective effect on bronchoconstriction (3 microM, 5 min, p = 0.003), while PD145065 significantly decreased bronchoconstriction 60 min after start of amitriptyline exposure (1 microM, 30 min, p = 0.003). This indicates that endothelin as well as platelet activating factor and protein kinase activation are important in mediating amitriptyline-induced lung function impairment in our experimental model and perhaps also in acute lung injury.

Nitric oxide (NO) modulation of PAF-induced cardiopulmonary action: interaction between NO synthase and cyclo-oxygenase-2 pathways

1. To further investigate into the mechanisms of PAF-induced cardiopulmonary actions, we examined the effects of the nitric oxide synthase (NOS) inhibitor L-N(omega)-nitro-L-arginine (L-NNA), of the specific cyclooxygenase-2 (COX-2) inhibitor NS 398, and of the combined presence of both COX and NOS inhibitors on the PAF responses in the heart lung preparation of guinea-pig (HLP). 2. In HLPs perfused with homologous blood, dose-response curves for the haemodynamic and bronchial effects of PAF (1 - 32 ng) were carried out in the absence or presence of L-NNA (200 microM). L-NNA caused an increase in the resting pulmonary arterial pressure (PAP) without affecting the other basal values, and strongly potentiated the bronchoconstriction and pulmonary hypertension elicited by PAF. An enhancement of the PAF-induced actions on right atrial pressure (RAP) and cardiac output (CO) was also observed. All the effects of L-NNA were antagonized by L-arginine (2 mM). 3. The presence of L-NNA in the perfusing blood of HLPs failed to affect the pulmonary hypertensive and bronchoconstrictor responses induced by the thromboxane A(2) mimetic U46619 (0.05 - 1.6 microg), 5-hydroxytryptamine (0.1 - 1.6 microg), and histamine (0.1 - 1.6 microg), thus suggesting that these PAF secondary mediators are not responsible for the hyper-responsiveness to PAF induced by L-NNA. 4. Blocking COX-2 pathway with NS 398 (15 - 30 microM) did not alter the cardiopulmonary resting variables. However, a reduction of the PAF-mediated pulmonary hypertension, but not of bronchoconstriction, was observed. When L-NNA was added to the perfusing medium of HLPs pre-treated with NS 398 or with indomethacin (15 microM), the basal PAP values were enhanced. However, in the combined presence of COX and NOS inhibitors, only a slight increase in the hypertensive responses to the highest doses of PAF was observed, whereas the PAF mediated actions at bronchial and cardiac level were unaffected. 5. This study indicates that (i) the cardiopulmonary actions induced by PAF are specifically modulated by endogenous NO through the NOS pathway, and (ii) COX-2 isoform is involved in the pulmonary hypertensive, but not bronchoconstrictor, effects of PAF. Furthermore, an interaction between PAF stimulated COX, particularly COX-2, and NOS pathways appears to take a functional role at both bronchial and cardiovascular level.

Role of platelet-activating factor in cardiovascular pathophysiology

Platelet-activating factor (PAF) is a phospholipid mediator that belongs to a family of biologically active, structurally related alkyl phosphoglycerides. PAF acts via a specific receptor that is coupled with a G protein, which activates a phosphatidylinositol-specific phospholipase C. In this review we focus on the aspects that are more relevant for the cell biology of the cardiovascular system. The in vitro studies provided evidence for a role of PAF both as intercellular and intracellular messenger involved in cell-to-cell communication. In the cardiovascular system, PAF may have a role in embryogenesis because it stimulates endothelial cell migration and angiogenesis and may affect cardiac function because it exhibits mechanical and electrophysiological actions on cardiomyocytes. Moreover, PAF may contribute to modulation of blood pressure mainly by affecting the renal vascular circulation. In pathological conditions, PAF has been involved in the hypotension and cardiac dysfunctions occurring in various cardiovascular stress situations such as cardiac anaphylaxis and hemorrhagic, traumatic, and septic shock syndromes. In addition, experimental studies indicate that PAF has a critical role in the development of myocardial ischemia-reperfusion injury. Indeed, PAF cooperates in the recruitment of leukocytes in inflamed tissue by promoting adhesion to the endothelium and extravascular transmigration of leukocytes. The finding that human heart can produce PAF, expresses PAF receptor, and is sensitive to the negative inotropic action of PAF suggests that this mediator may have a role also in human cardiovascular pathophysiology.

Protective role of pulmonary nitric oxide in the acute phase of endotoxemia in rats

We present for the first time direct continuous assay of NO concentration (porphyrinic sensor) in the lung parenchyma of Sprague-Dawley rats in vivo during endotoxemia. Intravenous infusion of lipopolysaccharide (LPS, 2 mg x kg(-1) x min(-1) for 10 minutes) stimulated an acute burst of NO from constitutive NO synthase (NOS) that peaked 10 to 15 minutes after the start of LPS infusion, mirroring a coincident peak drop in arterial pressure. NO concentration declined over the next hour to twice above pre-LPS infusion NO levels, where it remained until the rats died, 5 to 6 hours after LPS infusion. The chronic drop in arterial pressure observed from 70 minutes to 6 hours after the start of LPS infusion was not convincingly mirrored by a chronic increase in NO concentration, even though indirect NO assay (Griess method, assaying NO decay products NO2-/NO3-) showed that NO production was increasing as a result of continuous NO release by inducible NOS. A NOS inhibitor, N(omega)-nitro-L-arginine (L-NNA, 10 mg/kg i.v.) injected 45 minutes before LPS infusion, resulted in sudden death accompanied by macroscopically/microscopically diagnosed symptoms similar to acute respiratory distress syndrome <25 minutes after the start of LPS infusion. Pharmacological analysis of this L-NNA+LPS model by replacing L-NNA with 1-amino-2-hydroxy-guanidine (selective inhibitor of inducible NOS) or by pretreatment with S-nitroso-N-acetyl-penicillamine (NO donor), camonagrel (thromboxane synthase inhibitor), or WEB2170 (platelet-activating factor receptor antagonist) indicated that in the early acute phase of endotoxemia, LPS stimulated the production of cytoprotective NO, cytotoxic thromboxane A2, and platelet-activating factor.

Platelet activating factor and thromboxane B2 production after cardiopulmonary bypass

Platelet-activating factor (PAF) is believed to have a central role in the pathogenesis of ischemia-reperfusion injury. The purpose of this study was to investigate the relationships among production of PAF, thromboxane B2 (T alpha B2), and cardiopulmonary sequelae in patients undergoing coronary artery bypass graft surgery (CABGS). Venous blood from nine patients (eight men, one woman) undergoing scheduled CABGS, was sampled from central venous catheters before anesthetic induction, pre-cardiopulmonary bypass (CPB), 10 and 30 minutes post-CPB, 10 and 30 minutes post-aortic declamping, and 120 minutes and 24 hours after the conclusion of CPB. Plasma levels of PAF and T alpha B2 were determined by radioimmunoassay kits (Amersham Canada Ltd.). PAF and T alpha B2 were significantly different between high-risk patients (group I; Canadian Cardiovascular Society class 3-4; n = 4) and low-risk patients (group II; Canadian Cardiovascular Society class 2; n = 5): group I PAF = 960 pg/mL, group II PAF = 159 pg/mL (P = 0.0029); group I T alpha B2 = 320 pg/mL, group II T alpha B2 = 229 pg/mL (P = 0.0262). Group I PAF was significantly greater than group II PAF: before CPB = 825 pg/mL (group I), 138 pg/mL (group II); during initiation of CPB = 1600-2015 pg/mL (group I), 158-200 pg/mL (group II) (P = 0.0143). Correlations between duration of CPB and peak PAF (r = 0.7049, P = 0.0339), peak PAF level, and time to extubation (r = 0.8863, P = 0.0079) were significant. PAF levels were different in patients requiring postoperative epinephrine (2124 +/- 700 pg/mL) or dopamine (667 +/- 266 pg/mL) (P = 0.0042). The production of PAF is determined by preoperative patient characteristics and duration of CPB. Increased levels of PAF in patients with unstable angina, left main coronary artery disease, or recent myocardial infarction are associated with the need for increased inotropy and prolonged ventilatory support following CABGS. The degree of PAF production during CPB may be a factor in postoperative instability in high-risk patients.

Role of superoxide and nitric oxide in platelet-activating factor-induced acute lung injury, hypotension, and mortality in rats

OBJECTIVE

To investigate the role of superoxide and nitric oxide in platelet-activating factor-induced acute lung injury, hypotension, and mortality.

DESIGN

Prospective, randomized, controlled, experimental study.

SETTING

University research laboratory.

SUBJECTS

Anesthetized male Wistar rats (180 to 220 g) were studied.

INTERVENTIONS

In the first set of experiments, animals were divided into three groups. Group 1 received platelet-activating factor (2 microg/kg i.v.). Group 2 received recombinant human superoxide dismutase (50,000 U/kg i.v.) 30 mins before platelet-activating factor injection. Group 3 received vehicle agents. In the second set of experiments, animals were divided into six groups that received N(G)-nitro-L-arginine (L-NNA), a selective inhibitor of nitric oxide synthesis, or L-arginine, the physiologic precursor of nitric oxide synthesis: a) vehicles (i.v.); b) vehicle plus L-arginine (100 mg/kg i.v.); c) vehicle plus L-NNA (10 mg/kg i.v.); d) vehicle plus platelet-activating factor (2 microg/kg i.v.); e) L-arginine plus platelet-activating factor; and f) L-NNA plus platelet-activating factor. The first intravenous administration was given 5 mins before the second intravenous injection for each group.

MEASUREMENTS AND MAIN RESULTS

In the first set of experiments, vascular labeling with Monastral blue B demonstrated diffuse microvascular injury in the alveolar capillary beds 2 hrs after platelet-activating factor challenge. Thiobarbituric acid-reactive substances in the lung significantly increased at 2 hrs after platelet-activating factor injection. Platelet-activating factor treatment also resulted in an increased concentration of total protein, albumin, and Evans blue dye in bronchoalveolar lavage fluid at 2 hrs after administration, suggesting platelet-activating factor induction of increased alveolar permeability. The platelet-activating factor-induced alveolar microvascular injury, lipid peroxidation, and increased alveolar permeability were inhibited by pretreatment with recombinant human superoxide dismutase. Although L-NNA alone did not affect alveolar permeability in the second set of experiments, L-NNA treatment before platelet-activating factor challenge significantly aggravated platelet-activating factor-induced increased alveolar permeability 2 hrs after platelet-activating factor challenge. Platelet-activating factor also produced a rapid decrease in blood pressure that was not ameliorated by treatment with L-NNA. However, L-NNA pretreatment was associated with a significant increase in platelet-activating factor-caused mortality within 6 hrs. All rats survived with L-arginine treatment before platelet-activating factor challenge. L-NNA treatment decreased nitrate/nitrite concentration, an index of total nitric oxide production, in plasma.

CONCLUSIONS

These results indicate that superoxide, the derived active oxygen species, and lipid peroxidation are implicated in the pathogenesis of platelet-activating factor-induced acute lung injury. Nitric oxide does not play a major role in platelet-activating factor-induced hypotension. Nitric oxide appears to play a protective role in the acute lung injury and mortality induced by platelet-activating factor.

Involvement of nitric oxide and eicosanoids in platelet-activating factor-induced haemodynamic and haematological effects in dogs

1. Platelet-activating factor (PAF) is a phospholipid mediator with potent cardiovascular and haematological actions. But its mechanisms of action in vivo have not been fully elucidated, probably due to difficulties arising from previous findings that the effects of PAF are largely mediated by the release of a variety of other autacoids. In the present study, the roles of nitric oxide and eicosanoids in the effects of PAF (0.01-0.25 microgram kg-1 i.v.) on systemic and pulmonary vasculatures and circulating blood cell count were pharmacologically evaluated in anaesthetized dogs. 2. Higher doses of PAF (> 0.1 microgram kg-1) produced a biphasic systemic hypotension. The first hypotension seen 30 s after the injection was accompanied by a decrease in systemic vascular resistance, thrombocytopenia and leukopenia, while the second hypotension seen 1-2 min after PAF was accompanied by a marked rise in pulmonary vascular resistance and decreases in aortic blood flow and cardiac contractility. Lower doses of PAF (0.01 - 0.05 microgram kg-1) caused only the first responses in a dose dependent manner. 3. Pretreatment with indomethacin inhibited the second responses to PAF without affecting the first responses. The thromboxane A2/prostaglandin H2 (TP)-receptor antagonist vapiprost blocked the PAF-induced rise in pulmonary vascular resistance. AA-861, a 5-lipoxygenase inhibitor, attenuated the PAF-induced cardiac depression. The nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester inhibited the PAF-induced early decrease in systemic vascular resistance. 4. All observed changes in haemodynamics and blood cell count after PAF were almost abolished by TCV-309, a PAF-receptor antagonist. 5. Reproducible hypotension and thrombocytopenia produced by a lower dose of PAF (0.05 microgram kg-1) were respectively attenuated and potentiated by pretreatment with NG-nitro-L-arginine, another nitric oxide synthase inhibitor. Administration of L-arginine reversed the effects of the nitric oxide synthase inhibitor. 6. These results indicate that PAF-receptor-mediated production of not only eicosanoids but also nitric oxide may contribute to the cardiovascular and haematological responses to PAF in the dog.

Biochemical and cellular effects of heparin-protamine injection in rabbits are partially inhibited by a PAF-acether receptor antagonist

The origin of the thrombocytopenia and leucopenia induced by protamine-heparin complexes is unknown. We studied the biochemical and cellular effects of protamine (6 mg x kg-1, i.v.) injected after heparin (5 mg x kg-1, i.v.) in New Zealand rabbits. After protamine injection (0.5 min) increases in blood platelet-activating factor (PAF-acether, PAF) (27.6 +/- 27.6 to 148.2 +/- 48.9 pg x ml-1, P < 0.05), thrombocytopenia (403 +/- 64 to 166 +/- 13 cells x 10(-3) x mm-3, P < 0.05) and leucopenia (7650 +/- 930 to 4300 +/- 668 cells x mm-3, P < 0.05) were noted. Plasma thromboxane B2 increased at 1 min (125.6 +/- 24.4 to 879.7 +/- 141.0 pg x ml-1, P < 0.01). Protamine alone induced no change. Indomethacin (3 mg x kg-1, i.v.) did not counteract the effects of heparin-protamine. Pretreatment with the PAF receptor antagonist BN 52021 [9H1, 7a-(epoxymethano)-1 H,6aH-cyclopenta[c]furo[2,3-b]furo-[3',2',3,4]cyclopenta[1,2-d]fur an-5,9, 12(4H)trione,3-tert-butylhexahydro-4,7b,11 hydroxy-8 methyl] alone (3 mg x kg-1, i.v.) delayed thrombocytopenia and reduced plasma thromboxane B2 concentration but did not modify leucopenia. Thus thrombocytopenia and thromboxane B2 release triggered by heparin-protamine may be potentiated by the release of PAF.

Platelet-activating factor (PAF)-induced platelet aggregation. Modulation by plasma adenosine and methylxanthines

This study examined the role of plasma adenosine in the modulation of platelet-activating factor (PAF) activity on platelet aggregation and serotonin (5-HT) release in human platelet-rich plasma (PRP). In addition, the effects of methylxanthines (e.g. theophylline and caffeine) were studied on PAF-induced platelet aggregation in PRP isolated from blood samples from healthy subjects. Also, PAF-induced platelet aggregation was examined in PRP samples of patients receiving theophylline treatment. These studies demonstrate that plasma adenosine levels (0.1 to 0.3 microM) play a key role in negative modulation of PAF activity on platelet aggregation and 5-HT release. After depletion of plasma adenosine, the platelet-aggregating activity of PAF was increased greatly (> 10-fold). PAF at concentrations of 0.1 to 12 microM caused no 5-HT release in PRP containing normal amounts of adenosine (blood collected in the presence of 2'-deoxycoformycin and dilazep), whereas PAF at 0.1 microM caused 5-HT release (45%) in adenosine-depleted PRP, demonstrating that plasma adenosine is much more inhibitory of 5-HT release than platelet aggregation. The adenosine antagonists theophylline (50 microM), caffeine (50 microM) and a xanthine derivative, 3,7-dimethyl-l-propargylxanthine (DMPX, 10 microM) (a more specific adenosine A2 receptor antagonist), potentiated PAF activity on platelet aggregation in PRP samples containing adenosine. Also, patients receiving theophylline treatments showed significantly greater platelet aggregation induced by PAF in their PRP samples. PAF induced a rapid increase (80% in 15 sec) in intracellular Ca2+ mobilization, which was strongly inhibited by adenosine (IC50, 0.3 microM). Our studies suggest that agents that can increase plasma adenosine levels (e.g. inhibitors of adenosine uptake and adenosine metabolism) or methylxanthines may be useful in altering (inhibiting or enhancing, respectively) PAF actions on platelets and other tissues.

Bimodal effect of platelet-activating factor (PAF) on airways responsiveness in the rabbit

The role of platelet-activating factor (PAF) to increase airways responsiveness is unclear. Since PAF has unusual dose-response characteristics in vitro, this study investigated the effects of different doses or concentrations of PAF given by intravenous and aerosol administration in anesthetized rabbits. Aerosol PAF caused a dose-dependent decrease in SGL. Intravenous administration of PAF was associated with thrombocytopenia and neutropenia, whereas aerosol administration of PAF did not alter the numbers of circulatory cells. With either administration, no inflammatory cells were recovered by lavage nor was there evidence of a gross inflammatory process within the lung. Furthermore, there was no evidence of a late asthmatic response. Intravenous PAF caused a bimodal change in airways responsiveness with a significant increase in the effective concentration causing 50% of the maximal change in SGL (EC50SGL) at low doses (0.06-06 micrograms/kg h-1) and a significant decrease in EC50SGL (an increase in responsiveness) at higher doses (1.2-2.4 micrograms/kg/h-1). Aerosol PAF decreased EC50SGL significantly at the higher doses (100-250 micrograms). These changes in EC50SGL, after both administrations, were still apparent at 3 1/2 and 4 h. In conclusion PAF has a dose-dependent, biphasic, and persistent effect on airways responsiveness, which may be independent of circulating inflammatory cells.

Effect of PAF on rat lung vascular permeability: role of platelets and polymorphonuclear leucocytes

1. The objectives of the present experiments were to assess the contribution of polymorphonuclear leucocytes (PMNLs), platelets and their products such as thromboxane A2 (TxA2), histamine and 5-hydroxytryptamine to platelet activating factor (PAF)-mediated protein extravasation in rat lungs. 2. Intravenous injection of PAF (1.0 and 5.0 micrograms kg-1) increased dose-dependently (up to 7.5 fold) the vascular permeability of the trachea, upper and lower bronchi to Evans blue dye (EB), a marker of albumin extravasation. The permeability of the pulmonary parenchyma was not affected significantly by PAF. 3. Thrombocytopenia induced by administration of the IgG fraction of goat anti-rat platelet serum (APS; 15 mg 100 g-1, i.p., 16-18 h) reduced by 55, 58 and 40% the effects of the lower dose of PAF (1.0 microgram kg-1) and by 31, 23 and 15% the effects of the higher dose of PAF (5.0 micrograms kg-1) on the permeability of the trachea, upper and lower bronchi respectively to albumin. 4. PMNL depletion induced by administration of rabbit anti-rat polymorphonuclear serum (ANS; 2 mg kg-1, i.v., 24 h) did not reduce significantly the effects of the lower dose of PAF (1.0 microgram kg-1) on the airways, however the effects of the higher dose of PAF (5.0 micrograms kg-1) on the permeability of the trachea, upper and lower bronchi to albumin were reduced by 43, 25 and 23% respectively. 5. The injection of both the anti-platelet and the anti-PMNL sera reduced by 61, 62 and 96% the effects of the lower dose of PAF (1.0 microg kg-1) and by 44, 39 and 47% the effects of the higher dose of PAF (5.0 microg kg-1) on the permeability of the trachea, upper and lower bronchi respectively.6. The combined injection of the TxA2-mimetic (U-44069; 5.0 microg kg-1) and PAF (1.0 and 5.0 microg kg-1)in thrombocytopenic rats overcame the vascular permeability decrease induced by APS treatment.7. Pretreatment of the animals with a combination of antagonists to histamine (mepyramine;3.0 mg kg-1) and 5-hydroxytryptamine (methysergide; 2.5 mg kg-1) did not cause a significant inhibition of the effect of PAF (1.0 and 5.0 microg kg-1) on EB extravasation in the airways.8. These data show that the effect of intravenous PAF on rat vascular permeability is partly modulated by polymorphonuclear leucocyte and platelet activation. Our results suggest that following its release,TxA2 could increase postcapillary hydrostatic pressure by inducing a venoconstriction and potentiate the extravasation elicited by PAF. These results do not suggest a major role for histamine and/or 5-hydroxytryptamine on PAF-induced albumin extravasation.

Variations of blood PAF-acether levels during coronary artery surgery

Extracorporeal circulation (ECC) is associated with thrombocytopenia and transient leukopenia. After ECC and coronary artery bypass graft (CABG) surgery, some patients can develop pulmonary and cardiac dysfunction, which might be related to the release of various mediators such as thromboxane A2, C5a, and C3a anaphylatoxins. The involvement of PAF-acether (PAF), a potent vasoactive thrombocytopenic and leukoneutropenic agent, has not been determined. Therefore, 10 patients were studied during and after CABG. The release of PAF, lipo PAF (PAF bound to blood lipoproteins), and lyso PAF (PAF precursor and metabolite) was measured in blood from the left atrium, radial artery, and pulmonary artery before and after CABG. PAF, lipo PAF, and lyso PAF were also determined during ECC at the entry and exit points of the oxygenator. Hemodynamic parameters, platelet, and leukocyte counts in the pulmonary artery were measured simultaneously. PAF did not increase significantly during ECC; it showed a transitory six-fold increase immediately after CABG in the radial artery (0.18 +/- 0.13 v 1.09 +/- 0.36 ng/mL, P < 0.05), but not in the pulmonary artery (0.10 +/- 0.03 v 0.56 +/- 0.21 ng/mL, P > 0.05). Blood PAF amounts in the radial artery were significantly higher than in the left atrium following ECC (1.09 +/- 0.36 v 0.06 +/- 0.04, P < 0.05), probably indicating PAF production in the heart. No variation of blood lipo PAF and lyso PAF was observed. No correlation was seen between PAF amounts and blood cell count.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of platelet-activating factor in pulmonary edema after coronary ligation in dogs

To evaluate whether PAF is related to the precipitation of pulmonary edema after myocardial ischemia, we studied the effect of a specific PAF antagonist, CV-6209, on the extravascular lung water level measured by the thermal-dye double indicator dilution method, ETV, after coronary ligation in dogs. Eight dogs served as sham control animals (group 1). The proximal left anterior descending coronary artery was ligated for 45 min in eight dogs (group 2), and the coronary artery was ligated after pretreatment with CV-6209 (1 mg/kg) in eight dogs (group 3). The ETV increased significantly after coronary ligation in groups 2 and 3. The amount of increase in ETV in group 2 was significantly larger than in group 3. Thus, CV-6209 can prevent the accumulation of extravascular lung water after coronary ligation without producing changes in pulmonary vascular dynamics, indicating that PAF may play an important role in pulmonary edema after myocardial ischemia.

Endothelin-1 enhances vascular permeability in conscious rats: role of thromboxane A2

The purpose of the present experiments was to study the effects of endothelin-1 (ET-1) on vascular permeability and the involvement of the cyclooxygenase metabolites in the vascular responses to ET-1. Bolus intravenous injection of ET-1 (0.1-1.0 nmol/kg) into conscious rats induced immediate hypotension lasting for 30 s followed by sustained dose-dependent hypertension. A low dose of ET-1 (0.1 nmol/kg) did not modify the hematocrit value but the 1.0-nmol/kg dose increased the hematocrit value from 39.7 to 44.4%. Pretreatment of the animals with BM-13505 (1 mg/kg), a thromboxane A2 (TxA2) receptor antagonist, prolonged the duration of the hypotensive response to ET-1 (1.0 nmol/kg) but had no effect on the pressor response. Pretreatment with OKY-046 (10 mg/kg), a TxA2 synthesis inhibitor, or indomethacin (10 mg/kg), a cyclooxygenase inhibitor, had no significant effect on ET-1-induced changes in blood pressure. Evans blue dye extravasation, a marker of vascular permeability, increased up to 235% over control levels in specific vascular beds including the upper and lower bronchi, stomach, duodenum and kidney of ET-1 (1.0 nmol/kg)-treated animals. Pretreatment of the animals with BM-13505, OKY-046 or indomethacin reduced by 60-100% the Evans blue extravasation in these tissues. These results suggest that the effect of ET-1 on vascular permeability is partly mediated and/or modulated by the secondary release of TxA2, whereas its action on arterial blood pressure appears to be independent from prostanoid release in conscious rats.

Variations in blood platelet-activating-factor levels after protamine reversal of heparin in humans

The potent inflammatory mediator PAF-acether (PAF = platelet-activating factor) can produce the same hemodynamic and hematological effects as protamine infusion. In 10 patients, blood PAF and precursor levels were measured in the left atrium, the pulmonary and the radial artery before and after protamine reversal of heparin during coronary artery bypass graft. Blood PAF level in the left atrium increased 6-fold (17 +/- 12 pg.ml-1 vs 98 +/- 46 pg.ml-1, P = 0.03) after protamine infusion. By contrast, a 4-fold decrease was observed in the pulmonary artery blood (130 +/- 48 pg.ml-1 vs 31 +/- 23 pg.ml-1, P = 0.03) and a 9-fold decrease was noted in the radial artery blood (285 +/- 104 pg.ml-1 vs 31 +/- 15 pg.ml-1, P = 0.01). No cardiovascular impairment was observed but all patients exhibited thrombocytopenia. After protamine, PAF in the left atrium reached lower levels than those observed in the pulmonary and radial artery before protamine infusion. Moreover, no significant correlation was observed between platelet counts and PAF levels. Thus PAF seems not to mediate the platelet drop induced by heparin-protamine complexes. A positive correlation was obtained between leukocyte counts in the pulmonary artery and PAF levels in the left atrium (r = 0.78, P = 0.02). Protamine infusion may stimulate PAF biosynthesis by leukocytes in the lung, on the one hand, and accelerate the disappearance of PAF in the arterial bed, on the other hand.

Platelet-activating factor causes neutrophil accumulation and neutrophil-mediated increased vascular permeability in canine trachea

Platelet-activating factor (PAF) has potent effects on the respiratory airways that may be mediated through its ability to act as an inflammatory stimulant. To study its inflammatory properties in the airways, we infused PAF into the vasculature of the canine trachea and examined (1) the kinetics of neutrophil transit through the tracheal microcirculation, (2) accompanying changes in vascular permeability, and (3) the dependence of vascular permeability changes on neutrophil accumulation. Neutrophil kinetics were assessed by measuring the transit times of fluorescein isothiocyanate-labeled canine neutrophils by in vivo microscopy. Changes in vascular permeability were measured by the extravascular leakage of radiolabeled albumin and comparison of wet-to-dry weight ratios. The importance of neutrophils in increasing vascular permeability was assessed by perfusing the trachea with either autologous blood depleted of its leukocytes, or leukocyte-depleted blood replenished with neutrophils. Our data indicate that PAF causes rapid and prolonged neutrophil accumulation in the canine trachea and an increase in vascular permeability that is partially mediated by neutrophils.

Mechanism of action of platelet activating factor in the pulmonary circulation: an investigation using a novel isotopic system in rabbit isolated lung

1. Rabbit isolated lungs were perfused via the pulmonary artery with Tyrode solution containing 4.5% Ficoll and 0.1% bovine serum albumin at a constant rate of 20 ml min-1. Lung perfusate was drawn for alternating 5 min periods from two reservoirs, one containing 125I-albumin and the other unlabelled albumin to wash out the intravascular label. Microvascular 125I-albumin leakage was determined from the count remaining at the end of the washout phase with an external gamma scintillation probe. In addition, perfusion pressure was monitored continuously. Each experiment comprised 6 cycles over a total period of 60 min. 2. Infusion of platelet activating factor (PAF, 3 nmol min-1 for 10 min) resulted in microvascular 125I-albumin leakage, whereas lyso-PAF was without effect. During PAF infusions there was also an increase in perfusion pressure. Both the permeability and pressor effects of PAF were inhibited by the PAF antagonist L-652731. 3. Infusion of the thromboxane analogue U-46619 (0.6 nmol min-1 for 10 min) caused an increase in perfusion pressure but protein accumulation was not significantly different from that observed with control infusions. 4. Bolus injections of PAF (1 nmol) caused increases in perfusion pressure which were reduced by indomethacin, dazmegrel and BW 755C. Bolus injections of PAF, repeated at 30 min intervals caused reproducible pressor responses; however, repeated injections at 60 min intervals resulted in augmented responses. This augmentation did not occur in the presence of indomethacin. 5. Retrograde perfusion of PAF via the pulmonary vein induced increased perfusion pressure and microvascular 125I-albumin leakage. The observed increase in leakage when compared with forward perfusion suggests that PAF produces predominantly arteriolar constriction i.e. proximal to the site of leakage during forward perfusion. 6. These results indicate that PAF is a vasoconstrictor in the rabbit pulmonary circulation and augmented responses occur with repeated injections at 60 min intervals. Cyclo-oxygenase inhibition abolished this vascular hyperresponsiveness induced by PAF. PAF also caused protein accumulation in the lungs. Both these actions of PAF appear to be receptor-mediated because they were inhibited by PAF antagonists. Another pulmonary vasoconstrictor, U-46619 did not cause protein accumulation suggesting that the extravasation of protein with PAF is not merely secondary to changes in vascular tone.

The role of plasma proteins in formation of obstructive protamine complexes

Formation of complexes between heparin and protamine (in saline), or heparin, plasma proteins, and protamine (in plasma) was assessed by measurements of light transmission through different test solutions. To examine the formation of these complexes, 125I-labeled protamine was used. Addition of 125I-protamine to plasma or blood resulted in the sedimentation of 125I-protamine in the form of insoluble complexes. This complex formation was not affected by the presence of heparin, suggesting that protamine-plasma protein interaction may be primarily responsible for precipitation of 125I-protamine. To assess the capability of these complexes to obstruct the pulmonary circulation, an in vitro experimental model was developed. Citrated serum, plasma, blood, or saline were allowed to flow through a glass bead column with the help of a peristaltic pump. A pressure transducer positioned before the column allowed pressure measurements at a constant flow rate during the experiment. Mixing of protamine with plasma or blood prior to their passage through the glass bead column resulted in a significant increase in pressure suggesting that the column was being clogged with insoluble complexes. The increase in pressure occurred both in the presence and absence of heparin in plasma or blood. Under identical experimental conditions, the increase in pressure was insignificant when protamine was added to saline or serum regardless of whether heparin was present or absent. This was further confirmed by the use of 125I-protamine. These observations suggest that protamine forms insoluble complexes with certain plasma proteins. Based on these observations, it is hypothesized that following intravenous administration, protamine immediately forms complexes in circulating blood.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein kinase C regulates the synthesis of platelet-activating factor by human monocytes

Human peripheral blood monocytes synthesize the potent lipid autacoid platelet-activating factor (PAF) following appropriate stimulation. We examined the role of protein kinase C (PKC) in regulating the synthesis of PAF by stimulated monocytes. 4 beta-phorbol 12-myristate 13-acetate (PMA) and 1,2-dioctanoyl-sn-glycerol, which directly activate PKC, stimulated the synthesis of PAF. Sphingosine, a long-chain amine that inhibits PKC, blocked both the binding of phorbol esters to monocytes and the synthesis of PAF in response to PMA (half-maximal inhibition at 5 to 10 microM and complete inhibition at 10 to 30 microM sphingosine). Thus, the activation of PKC was necessary and sufficient for PAF synthesis in response to phorbol ester. Sphingosine also blocked PAF synthesis in response to the calcium ionophore A23187 and opsonized zymosan particles by specific inhibition of PKC. Two other PKC inhibitors, stearylamine and staurosporine, also blocked PAF synthesis following A23187 or opsonized zymosan stimulation. These experiments demonstrated that PKC activation was required for PAF synthesis in response to the calcium signal generated by A23187 or a receptor-mediated agonist, opsonized zymosan. The synthesis of PAF and leukotriene B4 were temporally coupled following cell stimulation. Further, production of these two lipid mediators, and the release of arachidonic acid, were inhibited in parallel by sphingosine. Thus, PKC regulate the synthesis of both PAF and leukotriene B4 at a common step, probably phospholipase A2.

Role of eicosanoids in PAF-induced increases of the vascular permeability in rat airways

1. Platelet activating factor (PAF; 1.0 and 5.0 micrograms kg-1) injected in the tail vein of unanaesthetized rats dose-dependently increased the vascular permeability of the trachea, upper and lower bronchi (up to 400%) as measured by the extravasation of Evans blue dye. The permeability of the parenchyma was not affected by PAF treatment. 2. Pretreatment of the animals with an intravenous injection of the PAF antagonist BN-52021 (10 mg kg-1) abolished almost totally the vascular permeability changes elicited by PAF injection (5.0 micrograms kg-1). 3. Pretreatment of the animals with intravenous injections of inhibitors of thromboxane formation, indomethacin (10 mg kg-1) and compound OKY-046 (10 mg kg-1), and thromboxane antagonist, compound L-655,240 (5 mg kg-1), partially reduced PAF effects in the airways (from 28 to 69%). The thromboxane mimic U-44069 (5.0 micrograms kg-1) did not modify the vascular permeability of rat airways. The effect of a low dose of PAF (0.1 microgram kg-1) on the vascular permeability of the trachea and bronchi (but not of the parenchyma) was potentiated by compound U-44069 (5.0 micrograms kg-1) or noradrenaline (400 ng kg-1) whereas the effect of a high dose of PAF (5.0 micrograms kg-1) was not affected. 4. Neither the peptidoleukotriene antagonist MK-571 (10 mg kg-1) nor the 5-lipoxygenase inhibitor, L-663,536 (10 mg kg-1) given before the injection of PAF (5.0 micrograms kg-1) affected the protein extravasation in rat lung tissues. 5. These data suggest that the effect of PAF on rat vascular permeability is partly modulated by thromboxane formation although thromboxanes have no direct effect on the permeability. Thromboxane may act via a vasoconstriction that increases hydrostatic pressure and potentiates the extravasation elicited by PAF effect on endothelial cells. 6. Leukotrienes do not appear to be involved in the changes of rat airway permeability induced by PAF.

Circulating plasma platelet activating factor in persistent pulmonary hypertension of the newborn

Platelet activating factor (PAF) is an endogenous phospholipid mediator that causes pulmonary hypertension and thrombocytopenia in experimental animal models. To investigate circulating PAF in persistent pulmonary hypertension of the newborn (PPHN), we studied PAF and its degradative enzyme, acetylhydrolase. Thirteen neonates with PPHN, diagnosed by routine clinical methods including echocardiography, were compared to six age-matched control patients with respiratory distress. Overall, plasma PAF levels were elevated in patients with PPHN compared to control patients (20.1 +/- 3.9 versus 1.6 +/- 0.7 ng/ml, p less than 0.01). In addition, plasma PAF concentrations in patients with PPHN correlated with the severity of disease as defined by the delta AaPO2 (r = 0.65, p = 0.015). In three patients with elevated PAF levels, as the clinical status improved, the plasma PAF values decreased. Acetylhydrolase activity was similar in both groups (3.96 +/- 0.90 versus 3.78 +/- 1.44 nmol/ml/min, p = NS). We conclude that PAF production is increased in PPHN and that abnormal production of PAF may be associated with pulmonary hypertension.

The effects of neutrophils and phospholipase A2 on transvascular albumin flux in isolated rabbit lungs

In this study, addition of phospholipase A2 (PLA2) to salt-perfused isolated rabbit lungs containing rabbit polymorphonuclear leukocytes leads to an increase in pulmonary capillary permeability. We add 1.5 X 10(8) polymorphonuclear leukocytes to the perfusate. Next, indomethacin is added to the perfusate and 40 units of PLA2 are infused into the pulmonary arterial inflow of the lungs. At the end of the study, a lung sample is removed for measurement of transvascular albumin flux using I125-albumin as a measure of the permeability-surface area product. Control studies demonstrate no increase in transvascular albumin flux. Addition of a dual cyclooxygenase and lipoxygenase inhibitor, BW755C, to the perfusate prevents the increase in transvascular albumin flux. We conclude that PLA2 interacts with polymorphonuclear leukocytes to increase protein permeability. Since PLA2 can release endogenous arachidonic acid and platelet-activating factor from cells, this suggests that release of such products may contribute to an increase in pulmonary capillary permeability from polymorphonuclear leukocytes. The ability of BW755C to prevent the increase suggests the possibility that lipoxygenase products contribute.

Platelet activating factor receptor antagonist improves survival and attenuates eicosanoid release in severe endotoxemia

Exogenous platelet activating factor (PAF) causes hypotension, plasma extravasation, metabolic acidosis, and death. These effects are similar to those of endotoxin as well as the eicosanoids. A specific PAF receptor antagonist, BN52021, was used to determine its effects on the hemodynamic events, the eicosanoid production, and on survival in severe rat endotoxemia. Endotoxin alone significantly produced hypotension, prostaglandins (TxB2, PGE2) release, and death. In contrast pretreatment with BN52021, a specific PAF receptor antagonist, significantly altered the hypotension, significantly attenuated the eicosanoid release, and improved the survival rate (p less than 0.01). These findings suggest that PAF receptor activation is an early event in endotoxemia. Eicosanoid release in endotoxemia could be related to PAF synthesis and PAF receptor activation. These findings support the hypothesis that there may be an intimate relationship between PAF and the eicosanoids and that in endotoxemia some of the effects of PAF may be mediated via the cyclo-oxygenase pathway.

Pulmonary hypertensive response to foreign body microemboli

Pulmonary hypertension and foreign body granulomas are recognized sequelae of chronic intravenous drug abuse. We have recently described the development of transient pulmonary hypertension and increased permeability pulmonary edema after the intravenous injection of crushed, suspended pentazocine tablets in both humans and dogs. To determine the role of vasoactive substances in the development of this transient pulmonary hypertension, we measured pulmonary hemodynamics and accumulation of arachidonic acid metabolites in dogs during the infusion of indomethacin, a cyclooxygenase inhibitor, diethylcarbamazine (DEC), a lipoxygenase inhibitor, and FPL 55712, a receptor antagonist for leukotriene C4/D4 (LTC4/D4). Following the intravenous administration of crushed, suspended pentazocine tablets (3-4 mg/kg of body weight), mean pulmonary artery pressure increased from 14 +/- 2 mmHg to 30 +/- 6 mmHg (p less than 0.05) at 60 secs with a concomitant increase in plasma concentrations of 6-keto-PGF1 alpha from 187 +/- 92 pg/ml to 732 +/- 104 pg/ml and thromboxane B2 from 206 +/- 83 pg/ml to 1362 +/- 117 pg/ml (both p less than 0.05). Indomethacin prevented the increase in both cyclooxygenase metabolites, but had no effect on the pulmonary hypertension. In contrast, DEC had no effect on the increase in cyclooxygenase products, but blocked the pulmonary hypertension. FPL 55712 did not effect either the increase in cyclooxygenase metabolites or the pulmonary hypertension. We conclude that the transient pulmonary hypertension, induced by the intravenous injection of crushed, suspended pentazocine tablets, is not mediated by cyclooxygenase products but may be mediated by lipoxygenase product(s) other than LTC4/D4.

Angiopathic consequences of saturating the plasma scavenger system for actin

Two plasma proteins, vitamin D-binding protein (actin monomer sequestrant) and gelsolin (actin polymer severing), have been found in association with actin in plasma from ill humans and during experimental injury. In vitro, these are the only plasma proteins that display a high affinity for actin. We infused increasing amounts of globular actin intravenously to rats to evaluate its disposition in plasma and tissues. Intravascular filament formation, microthrombi, and endothelial injury were observed, especially in the pulmonary circulation. These pathological changes were not observed when the globular actin in the infusate had been preincubated with the vitamin D-binding protein in vitro. Complexes of actin with both proteins were found in the plasma, suggesting a saturable, plasma actin-binding system in vivo. Our findings suggest that in vivo saturation of these proteins' actin-binding capacities may serve as a paradigm for pulmonary vascular disorders seen during widespread tissue trauma and cell lysis.

Adult respiratory distress syndrome

The Adult Respiratory Distress Syndrome (ARDS) is a fulminant form of respiratory failure affecting many seriously ill patients. The early manifestations of ARDS are caused by increased permeability of the alveolo-capillary barrier leading to pulmonary edema, stiff lungs, and a large right-to-left intrapulmonary shunt. Polymorphonuclear leukocytes (PMNS) are involved in the pathogenesis of most ARDS, and multiple PMN mechanisms can effect pulmonary injury; interactions between PMN adherence, proteolytic enzyme release, and oxygen radical production are emphasized. ARDS therapy remains largely supportive and has had little impact on mortality. The complications of infection and multiorgan failure play important roles in determining ARDS outcome.

Effects of ethanol on human platelets stimulated with platelet-activating factor, a biologically active ether phospholipid

The interaction between ethanol and 1-0-alkyl-2-acetyl-sn-glycerol-3-phosphocholine (platelet activating factor, PAF) was addressed using platelets obtained from normal nonalcoholic volunteers. Ethanol at concentrations of 20 to 100 mM inhibited PAF activation of human platelets. Ethanol inhibited prominently the second or arachidonic acid metabolite dependent wave of platelet aggregation, which occurs with human platelets in citrated plasma. It also inhibited serotonin release and thromboxane A2 formation associated with this secondary phase of aggregation. Ethanol did not readily inhibit the primary wave of PAF-induced aggregation. The incorporation of PAF into platelets or metabolism of PAF was not influenced by up to 100 mM ethanol. Since ethanol inhibited only the secondary response, a direct interaction between PAF, ethanol, and a platelet PAF receptor is unlikely. The effect of ethanol on PAF-induced platelet aggregation shows a selectivity similar to that demonstrated by other investigators for epinephrine and adenosine diphosphate.

Kinetics of pulmonary platelet deposition and clearance during thrombin-induced microembolism in rabbits

Using 111In-labeled autologous platelets, we studied the kinetics of pulmonary platelet deposition and clearance in relation to hemodynamic and structural events during thrombin-induced pulmonary microembolism in rabbits. Autologous platelets were radiolabeled and returned to animals prior to infusion of thrombin (100 units/kg over 15 min) (n = 20) or saline (n = 6). All animals were pretreated with tranexamic acid, an inhibitor of fibrinolysis. Thrombin-treated animals manifested progressive increases in mean pulmonary platelet activity, reaching a maximum of 38% above baseline (p less than .0001), whereas no change was observed in saline-treated controls. Animals that died during, or immediately following, thrombin infusion manifested significantly greater increases in pulmonary platelet uptake (mean 1.55 +/- 0.47 times baseline), compared to surviving animals (1.14 +/- 0.16; p less than .05 survivors vs. nonsurvivors). In surviving animals, following cessation of thrombin, pulmonary platelet activity cleared gradually, with a half-time of approximately 12 min. Thrombin reduced circulating platelet counts (p less than .001), increased mean pulmonary artery pressure (13 +/- 3 mm Hg to 18 +/- 6 mm Hg; p less than .0001), and reduced mean systemic arterial pressure (55 +/- 10 mm Hg to 44 +/- 7 mm Hg; p less than .001). The time courses of these events approximated that of thrombin-induced pulmonary platelet uptake. Furthermore, the increase in pulmonary artery pressure occurred predominantly in the group of animals in which the increase in pulmonary radiolabeled platelet activity exceeded the median value of 20%. Postmortem histology showed extensive pulmonary thrombus extending from small arterial to capillary levels in animals that died during, or immediately following, thrombin infusion, but not in surviving animals. Our findings suggest that platelet aggregation plays an important role in the pathogenesis of hemodynamic change following thrombin-induced pulmonary embolization.

The role of thromboxane A2 [TxA2] in liver injury in mice

The role of thromboxane A2 (TxA2) in CCl4-induced liver disease was investigated in mice. Significant elevation of TxB2 in the liver was observed 6 hours after the injection of CCl4. Administration of OKY-046, a selective TxA2 synthetase inhibitor (10 and 50 mg/kg) and ONO-3708, a TxA2 receptor antagonist, (0.5, 1 and 2 mg/Kg) suppressed the elevation of serum GOT and GPT levels and histopathological changes of the liver. In addition, OKY-046 inhibited the elevation of TxB2 in the liver. When U-46619, a stable TxA2 mimetic was injected i.v. into the mice, clear elevation of serum GOT and GPT levels and histopathological score of the liver were observed. These results suggest that TxA2 play a role for the onset of CCl4-induced liver injury in mice.

Human platelets modulate edema formation in isolated rabbit lungs

The role of platelet glucose-6-phosphate dehydrogenase (G-6-PD) in mediating the effects of human platelets on oxidant-induced edema in the isolated perfused rabbit lung was investigated using dehydroepiandrosterone, a specific steroidal inhibitor of G-6-PD. Xanthine oxidase (0.003 and 0.012 U/ml) caused lung edema that was attenuated by coinfusion of washed human platelets. Platelets that were incubated with DEA to inhibit G-6-PD activity augmented xanthine oxidase-induced lung edema and pulmonary hypertension at both doses of xanthine oxidase. Infusion of papaverine to maintain stable pulmonary artery (PA) pressures, incubation of G-6-PD-inhibited platelets with acetylsalicylate, or infusion of a thromboxane-prostaglandin endoperoxide receptor site antagonist, SQ 29548, into the lung perfusate prevented augmentation of lung edema and the PA pressor response by G-6-PD-inhibited platelets. It was concluded that antioxidant-intact platelets attenuate oxidant-induced lung edema by preventing increased membrane permeability, and that G-6-PD-inhibited platelets augment lung edema through hydrostatic mechanisms mediated by release of platelet cyclooxygenase products.

Platelet-activating factor (Paf) antagonist, WEB 2086, protects against Paf-induced hypotension in Macaca fascicularis

1. The actions of intravenously administered platelet-activating factor (Paf) (0.1-3.33 nmol kg-1) and the effect of a recently described Paf antagonist, WEB 2086, were investigated in the anaesthetized open-chest monkey, Macaca fascicularis. 2. Paf dose-dependently reduced blood pressure, left ventricular pressure (LVP) and its first differential LV dP/dt. 3. Mean pulmonary artery pressure, recorded in three animals, was essentially unchanged by any dose of Paf. 4. WEB 2086 (0.22 mumol kg-1, i.v.) attenuated the Paf-induced changes in BP, LVP and LV dP/dt. The dose-response curve for fall in BP was shifted to the right by one order of magnitude. 5. Histamine-induced cardiovascular changes (systemic hypotension and tachycardia) were not affected by prior administration of WEB 2086. 6. WEB 2086 should be of value in assessing the role of Paf in pathophysiological conditions.

Occupancy of platelet receptors for platelet-activating factor in patients with septicemia

The possible involvement of platelet-activating factor (PAF) in the pathogenesis of endotoxemia, was investigated by using a binding assay to patients' platelets, complemented with the extraction and chemical characterization of PAF obtained from patients' platelets. Platelets from 12 human volunteers had 281 +/- 63 freely accessible high affinity binding sites (PAF-receptors) per platelet; whereas this number was of 49 +/- 37 PAF-receptors per platelet, n = 14 samples, P less than 0.01, in a group of 13 patients with positive blood culture. A group of patients with respiratory or cardiovascular disturbances and negative blood culture had 253 +/- 74, accessible receptors per platelet (n = 19 samples from 16 patients, P less than 0.01 as compared to septic patients, which was not significantly different when compared to control individuals). Patients with sepsis possessed significant amounts of PAF associated to their platelets, whereas this mediator could not be isolated from platelets of patients with respiratory or cardiovascular disturbances and negative blood culture, nor from platelets of control individuals. PAF was also assayed in whole blood samples and found at high concentrations in sepsis patients. These data indicate that occupancy of PAF receptors in combination with high amounts of platelet-associated PAF, is a common finding in patients with sepsis.

Platelet participation in the increased severity of endotoxin-induced pulmonary injury in aged rats

Recent studies have demonstrated that aged rats are more susceptible to the lethal effects of endotoxin as compared with young rats. The morphogenesis of early endotoxin-induced pulmonary injury in young (6 months) and aged (24 months) rats was examined by combined light and transmission electron microscopy to elucidate cell populations that may be responsible for these effects. Pulmonary endothelial cell injury was of greater severity and occurred at earlier time periods in aged rats as compared with young rats. Platelet sequestration and aggregation were observed only in aged rats in this study, and occurred in conjunction with the initial degenerative changes in the endothelium. Morphological evidence of granulocyte degranulation and fragmentation was also observed only in aged rats. These results suggest that pulmonary endothelial cells of aged rats are more susceptible to endotoxin-induced injury and that platelets may play an important role in the enhancement of initial endothelial damage. Furthermore, the extent of injury to the endothelial cell population may play an important role in accounting for differences in endotoxin-induced mortality between young and aged rats.

Effects of platelet activating factor on airway calibre, airway responsiveness, and circulating cells in asthmatic subjects

The effects of inhaled platelet activating factor were compared with those of inhaled methacholine (control) on airway calibre, airway responsiveness to methacholine and isoprenaline, and circulating cells in eight subjects with mild, stable asthma. Platelet activating factor was given in six doses at 15 minute intervals and airway response measured as change in partial expiratory flow at 30% of vital capacity (Vp30). Platelet activating factor caused a fall in Vp30, the mean (SEM) maximum percentage fall being 28.9 (4.2) five minutes after the first dose (12 micrograms) and 50.9 (8.0) after the second dose (24 micrograms). Tachyphylaxis occurred, however, with the four subsequent doses of inhaled platelet activating factor. There was transient neutropenia after the first dose, from a mean of 3.6 (0.2) x 10(9) to 2.2 (0.5) x 10(9) neutrophils/l; this response also showed tachyphylaxis with subsequent doses. The mean PC40 (the concentration of methacholine needed to cause a 40% fall in Vp30) was unchanged one, three, and seven days after administration of platelet activating factor. There was no significant correlation between baseline PC40 methacholine and the maximal fall in Vp30 after either the first (12 micrograms) or the second dose (24 micrograms) of platelet activating factor. The control challenge with methacholine produced a degree of bronchoconstriction similar to that of platelet activating factor but was not associated with any significant change in bronchial responsiveness or in circulating cells. The bronchodilator response to inhaled isoprenaline measured three days after inhalation of platelet activating factor and of methacholine was similar after the two challenges. Thus asthmatic subjects who are hyperresponsive to methacholine show a similar bronchoconstrictor response to platelet activating factor, as has been observed in normal subjects; overall this did not cause airway hyperresponsiveness to methacholine.

Hydrogen peroxide stimulates the synthesis of platelet-activating factor by endothelium and induces endothelial cell-dependent neutrophil adhesion

Oxidant-induced damage to the intima of pulmonary and systemic vessels is thought to be an important mechanism of injury in a variety of syndromes of vascular damage. Hydrogen peroxide (H2O2) is an active oxygen metabolite that may induce intimal injury by cytolytic attack or by inducing biochemical and functional alterations in the endothelial cells (EC); however, mechanisms involved in noncytolytic perturbation of EC are largely unknown. We found that H2O2 stimulated the synthesis of platelet-activating factor (PAF) by primary cultures of bovine pulmonary artery endothelium (BPAEC) and by human umbilical vein endothelium (HUVEC). In each cell type the incorporation of [3H]acetate into [3H-acetyl]PAF was concentration- and time-dependent and was temporally dissociated from severe plasma membrane disruption and cytolytic cell injury; the newly synthesized PAF remained associated with the EC. H2O2 caused permeabilization of EC to 45Ca2+ and an increase in intracellular Ca2+, suggesting that a transmembrane Ca2+ flux is the signal that initiates PAF synthesis. H2O2 also induced the endothelial cell-dependent adhesion of neutrophils to HUVEC monolayers. This response was rapid, with an onset within minutes and a subsequent time course that paralleled the time course of PAF accumulation, and was dependent on extracellular Ca2+ but not on de novo protein synthesis. These studies demonstrate that H2O2 can induce two rapid activation responses of endothelium, PAF synthesis and EC-dependent neutrophil adhesion, events that may be important in physiologic and pathologic inflammation.

Characterization of serum platelet-activating factor (PAF) acetylhydrolase. Correlation between deficiency of serum PAF acetylhydrolase and respiratory symptoms in asthmatic children

Platelet-activating factor (PAF) acetylhydrolase has been recognized as an enzyme that inactivates PAF. We developed a convenient and reproducible method for determining human serum PAF acetylhydrolase activity. The assay was based on measurement of [14C]acetate produced from 1-O-alkyl-2-[14C]-acetyl-sn-glycero-3-phosphocholine upon precipitation of the complex of radioactive substrate and albumin with TCA. The apparent Km value of PAF acetylhydrolase (near the physiological concentration of serum protein) was 1.5 X 10(-4) M PAF. 32 subjects with serum PAF acetylhydrolase deficiency were found among 816 healthy Japanese adults. The low PAF acetylhydrolase activity in the deficient serum might not be due to the presence of enzyme inhibitor. Both the sensitivity to PAF and the metabolism of PAF in platelets from PAF acetylhydrolase-deficient subjects were almost the same as those of normal subjects. Deficiency in serum PAF acetylhydrolase appeared to be transmitted by autosomal recessive heredity among five Japanese families. Among healthy adults, healthy children, and asthmatic children, who were grouped into five classes on the basis of respiratory symptoms (remission, wheezy, mild, moderate, and severe groups), the probability of PAF acetylhydrolase deficiency was significantly higher in groups with severe symptoms (moderate and severe) (P less than 0.01). These results suggest that deficiency of serum PAF acetylhydrolase might be one of the factors leading to severe respiratory symptoms in asthmatic children.

PAF increases vascular permeability in selected tissues: effect of BN-52021 and L-655,240

The effect of the potent inflammatory mediator, platelet activating factor (PAF) was studied on the vascular permeability of selected rat tissues using the extravasation of Evans blue dye (EB) as a marker. EB (20 mg/kg) was injected in the caudal vein together with increasing doses of PAF (0.1, 1.0 and 5.0 micrograms/kg). The animals were killed and the dye was extracted in selected organs using formamide (4 ml/g wet weight tissues) and the content was expressed as EB micrograms/g dry weight. Extravasation of EB varied markedly from one tissue to another and increased as a function of time (from 0 to 60 min). PAF (5.0 micrograms/kg) increased the pancreas and duodenum vascular permeability by 15 and 5 fold respectively. At the doses of 0.1 and 1.0 microgram/kg, PAF induced a slight increase (P less than 0.01) of the vascular permeability of the heart 5 min after the injection. The PAF antagonist BN-52021 (2 and 10 mg/kg) produced a dose-dependent inhibition of the PAF effects on the pancreas, heart and duodenum. Maximum inhibition (approximately 100%) was achieved at the dose of 10 mg/kg. This antagonist given in the absence or the presence of PAF reduced the lung plasma extravasation below control levels. A thromboxane antagonist, L-655,240 (1.0 and 5.0 mg/kg) also inhibited PAF-induced increases in vascular permeability in heart, duodenum and pancreas. It also reduced below control levels the EB extravasation in kidneys, spleen and lungs. Maximum inhibition (50% for the duodenum, and 40% for the pancreas) was achieved at the dose of 5.0 mg/kg.

Cerebrovascular and cerebrometabolic effects of intracarotid infused platelet-activating factor in rats

Platelet-activating factor has been implicated in a variety of disease processes including ischemic brain injury and endotoxic shock, but its effects on cerebral blood flow (CBF) and metabolism in normal brain have not been described. The effects of platelet-activating factor on global CBF (hydrogen clearance) and the global cerebral metabolic rate for oxygen (CMRO2) were studied in halothane-N2O anesthetized Wistar rats. Hexadecyl-platelet-activating factor infused into the right carotid artery (67 pmol/min) for 60 min decreased mean arterial pressure (MAP) from 122 +/- 4 (x +/- SEM) to 77 +/- 6 mm Hg and CBF from 159 +/- 12 to 116 +/- 14 ml/100 g/min (p less than 0.002). In contrast, CMRO2 increased from 9.7 +/- 0.9 to 11.7 +/- 1.1 ml/100 g/min after 15 min (p less than 0.05). In controls rendered similarly hypotensive by blood withdrawal and infused with the platelet-activating factor vehicle, CMRO2 was unchanged, whereas CBF transiently decreased then returned to baseline at 60 min. These cerebrovascular and cerebrometabolic effects of PAF are reminiscent of and may be relevant to hypoperfusion and hypermetabolism observed after global brain ischemia and in endotoxic shock.

Pulmonary endothelial and alveolar epithelial lesions induced by O,O,S-trimethyl phosphorothioate in rats

The morphogenesis of pulmonary injury induced by an impurity present in a commercially important organophosphorus insecticide, O,O,S-trimethyl phosphorothioate (OOS-TMP), was studied by combined light and transmission electron microscopy. Weanling female WAG/Rij rats received OOS-TMP dissolved in corn oil by gavage and were studied at intervals from 6 to 168 h after treatment. Sequestration of neutrophils was initially observed at 12 h after treatment and was accompanied by interstitial oedema. Plasmalemma alterations in endothelium lining capillaries and small arteries and veins were observed from 12 to 120 h after treatment and were accompanied by endothelial cell detachment and separation from the basal lamina. Abundant aggregates of fibrin were sequentially observed in intravascular, interstitial, and alveolar spaces. Platelet aggregation and degranulation were occasionally observed in capillaries as early as 12 h after treatment, and frequently observed in capillaries and small vessels from 24 to 96 h after treatment. Significant increases in wet lung weight and lung water content occurred at the same time that morphologic changes were observed in pulmonary endothelium. Alterations in type I alveolar epithelial cells were initially observed at 24 h after treatment. Cell swelling, fragmentation, and necrosis were observed in both type I and type II cells and resulted in a bare basal lamina. Marked attenuation, hypertrophy, and proliferation of type II epithelial cells followed alveolar epithelial cell injury and loss. Minimal changes were observed in non-ciliated bronchiolar epithelial (Clara) cells; predominant changes included the loss of surface microvilli and apical cytoplasmic bulge. The results of this study indicate that the endothelium and alveolar epithelium are the predominant cell types in the rat lung injured following OOS-TMP administration.(ABSTRACT TRUNCATED AT 250 WORDS)