Lack of platelet-activating factor release on acute myocardial ischemia in the isolated interventricular septum of rabbit heart.

The effects of platelet-activating factor (PAF) on myocardial injury after 1 h global ischemia-30 min reperfusion were investigated in isolated arterially perfused interventricular septum of rabbit heart. PAF did not significantly affect developed tension, +/- dT/dtmax, resting tension and the times of active state in non-ischemic septa. The recovery of developed tension was significantly reduced by PAF (100 nM), after an ischemia-reperfusion challenge, from the control value of 20.9 +/- 3.5% to 10.5 +/- 1.8%, without a change in the resting tension (15.7 +/- 2.8 vs. 15.6 +/- 1.3 g). BN 52021 (20 microM), alone did not modify either parameter of ischemic damage, but antagonized the aggravating effect of PAF. Evidence of PAF activity was not found in any of the samples of the effluent perfusate obtained from ischemic control experiments. On the basis of the present results, we suggest a direct role for PAF in aggravating the myocardial damage induced by ischemia, and discard heart cells as the source of PAF in this state.

Effect of immunological stimulation on the production of platelet-activating factor by rat peritoneal cells: its relevance to anaphylactic reactions.

The production of platelet-activating factor (PAF) by rat peritoneal cells was studied using as stimuli either monoclonal IgE, IgG1 or IgG2b anti-DNP (2,4-dinitrophenyl), and DNP-BSA. Peritoneal cells sensitized in vitro with any of these antibodies at concentrations higher than 10 nM and challenged with 1 microM DNP-BSA produced PAF. PAF production was also elicited by preformed IgE/ and IgG2b/DNP-BSA immune complexes, preferentially at a large antigen/antibody ratio. The production of PAF was unrelated to the activation of mast cells, since it occurred in populations depleted of mast cells by adherence to plastic dishes. Moreover, the release of [3H]serotonin from IgE-sensitized mast cells showed a time-course more rapid than PAF production and occurred in cells sensitized with IgE at concentrations lower than those required for PAF formation. In contrast, peritoneal cells sensitized with IgG1 and IgG2b failed to release [3H]serotonin. Rat peritoneal cells showed a significant ability to catabolize PAF by intracellular PAF-acetylhydrolase in view of both the amounts of enzyme activity assayed in cellular homogenates, and the 15-fold increase on controls of PAF quantities detected in peritoneal cells treated with phenylmethylsulfonyl fluoride (PMSF), a known inhibitor of PAF-acetylhydrolase. The PAF activity produced upon PMSF addition showed a retention time on reverse-phase HPLC which suggests structural identity to PAF produced by either immunological challenge or ionophore A23187. These data suggest that PAF formed during rat passive anaphylaxis reactions depends on the activation of mononuclear phagocytes. This production may be triggered by two types of low affinity receptors: Fc epsilon RII/CD23 and Fc gamma R. The ability of peritoneal cells to catabolize PAF by intracellular acetylhydrolase seems unaffected by immunological stimulation.

Involvement of tyrosine kinase and protein kinase C in platelet-activating-factor-induced c-fos gene expression in A-431 cells.

In A-431 cells, platelet-activating factor (PAF) induces the expression of c-fos and TIS-1 genes in both the absence and the presence of cycloheximide in a structurally specific and receptor-coupled manner. We have now investigated the molecular mechanisms of this response, particularly in relation to the role of protein kinases. Pretreatment of cells with genistein or methyl-2,5-dihydroxycinnamate (tyrosine kinase inhibitors) or staurosporine (a protein kinase C inhibitor) for 20 min abolished the c-fos expression induced by PAF. Interestingly, when genistein was added 90 s after addition of PAF, no inhibition was observed. Similarly, staurosporine did not inhibit c-fos expression when added 8 min after PAF addition to the cells. These inhibitions were dose-dependent (IC50 for staurosporine was 180 nM, and for genistein 50 microM). Simultaneous addition of PAF and phorbol 12-myristate 13-acetate (PMA) did not give a synergistic effect on c-fos expression. Pretreatment of cells with PMA had no effect on [3H]PAF binding, but abolished the PAF-induced gene expression. PAF-stimulated gene expression was desensitized if cells were pretreated with PAF. Interestingly, epidermal growth factor was able to stimulate c-fos expression in PAF-desensitized cells, and thus indicated involvement of distinct mechanisms for the two stimuli. Forskolin, an activator of adenylate cyclase, did not induce c-fos expression and had no effect on the PAF response. Exposure of cells to PAF for as little as 1 min, followed by its removal, was sufficient to activate the gene expression and demonstrated the rapidity and the exquisite nature of the signalling involved in this process. It is concluded that activation of PAF receptor (a proposed G-protein-coupled receptor) causes rapid production of signals which induce the expression of c-fos gene and that this is mediated via tyrosine kinase and protein kinase C.

The role of platelet-activating factor and peptidoleukotrienes in the vascular changes of rat passive anaphylaxis.

1. The role of platelet-activating factor (PAF) and peptidoleukotrienes as putative mediators of some of the vascular changes triggered by antigen was investigated in rats passively sensitized with monoclonal anti-DNP (2,4-dinitrophenyl) IgE. 2. Lethal anaphylaxis with respiratory distress, systemic hypotension, detachment of the intestinal mucosa, leukopenia and extravasation of protein-rich plasma was observed after antigen challenge of rats sensitized with partially purified monoclonal IgE at concentrations of 15 mg protein kg-1. 3. Analysis of the peritoneal fluid obtained after i.v. challenge with DNP-BSA (bovine serum albumin) showed the presence of significant amounts of PAF (101 +/- 8 pg/rat), whereas this mediator was undetectable in control animals. Leukotriene D4 was the predominant peptidoleukotriene that could be recovered after antigen challenge, and showed an extremely high concentration (92 +2- 15 ng/rat) as compared to PAF levels. 4. Extravasation of protein-rich plasma was observed shortly after challenge and reached a maximum at 30 min. Treatment of animals with i.v. PCA 4248 (1-2 mg kg-1) and WEB 2086 (1 mg kg-1), two chemically unrelated compounds which are antagonists of the PAF-receptor, produced a significant reduction of the extravasation of protein-rich plasma. 5. The same degree of protection could be afforded by MK-886, an inhibitor of leukotriene biosynthesis. Combined treatment with WEB 2086 and MK-886 provided greater inhibition of protein-rich plasma extravasation than either compound alone. PCA 4248 was also found to inhibit in a dose-dependent manner the systemic hypotension observed upon DNP-BSA challenge.6. These data indicate that the lipid mediators PAF and peptidoleukotrienes are major effectors of the vascular disturbances observed in rat passive IgE-mediated anaphylaxis.

Platelet-activating factor antagonists do not protect against the development of experimental autoimmune encephalomyelitis.

There is evidence suggesting the involvement of the platelet-activating factor (PAF) in central nervous system (CNS) functions. The possibility exists that PAF may be relevant in eliciting cell-mediated autoimmune phenomena in CNS. To assess the role of PAF in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), male Lewis rats were primed with whole spinal cord from guinea pig, emulsified in Freund's adjuvant supplemented with 10 mg/ml of Mycobacterium tuberculosis, H37Ra strain. Treatment with two different PAF antagonists (PCA 4248, WEB 2170) was applied starting from day 1 or day 5 postinoculation on a twice-daily basis. Neither PCA 4248 nor WEB 2170 suppressed the clinical signs of EAE. PAF concentration was measured in CNS tissue from the 9th day after inoculation to the 15th day, and no differences were found between control and EAE animals. These results suggest that PAF is not involved in the mediation of EAE.

Metabolism of platelet-activating factor in human haematopoietic cell lines. Differences between myeloid and lymphoid cells.

The binding and metabolism of platelet-activating factor (PAF) was studied in human cell lines resembling myeloid cells (HL60 and U937) and B and T lymphocytes (Daudi and Jurkat). All of the cell lines were found to bind and catabolize exogenous [3H]PAF in a time- and temperature-dependent manner. PAF binding could also be demonstrated in isolated membrane fractions, which provides further evidence of the existence of true membrane receptors. Myeloid cell lines contained numbers of receptors at least 10-fold higher than in lymphoid cell lines. Biosynthesis of PAF upon challenge by ionophore A23187 could be demonstrated in HL60 and U937 cells. In contrast, lymphoid cell lines were unable to produce PAF. Incubation with [14C]acetate showed incorporation of the label into three main fractions: neutral lipids, phosphatidylcholine and PAF, but the distribution of the label varied depending on the cell line. Significant incorporation into phosphatidylcholine was observed in uninduced myeloid cell lines. A phospholipase A2 acting on 1-O-hexadecyl-2-arachidonoyl-sn-glycero-3-phosphocholine and an acetyl-CoA:lyso-PAF acetyltransferase were expressed in the HL60 cell line and showed variations in specific activity with granulocytic differentiation. In contrast, these enzyme activities were not expressed in Daudi and Jurkat cell lines. These data indicate (1) the occurrence of PAF binding and catabolism in both myeloid and lymphoid cell lines; (2) the restriction of PAF biosynthesis to myeloid cell lines, especially HL60 cells; (3) the occurrence of differentiation-elicited changes in the specific activities of the enzymes involved in PAF biosynthesis by the remodelling pathway; and (4) the central role played by the disposal of lyso-PAF, a product of the phospholipase A2 reaction, in PAF biosynthesis.

Pharmacological actions of PCA 4248, a new platelet-activating factor receptor antagonist: in vivo studies.

The ability of PCA 4248 [2-(phenylthio)ethyl-5-methoxycarbonyl- 2,4,6-trimethyl-1,4-dihydropyridine-3-carboxylate] to block PAF-induced systemic hypotension and protein-rich plasma extravasation in rats, and PAF-induced death in mice, was tested. These studies were complemented with experiments using soluble aggregates of immunoglobulin G (A-IgG), bacterial endotoxin and the cytokine tumor necrosis factor as putative inducers of the generation of endogenous PAF. Significant inhibition of PAF-induced systemic hypotension was observed with i.v. PCA 4248 at doses of 0.3 to 1 mg/kg (IC50 value, 0.45 mg/kg, with PAF 0.33 micrograms/kg). Reversal of the hypotension was rapidly observed when PCA 4248 was administered after PAF. The extravasation induced by 1 microgram/kg PAF was also blocked by PCA 4248 (IC50 value, 0.36 mg/kg). Inhibition of the extravasation induced by A-IgG and endotoxin was also provided by PCA 4248 at the dose of 1 mg/kg, and lasted for at least 1 hr in the experiments carried out with endotoxin, which caused extravasation with a temporal pattern more protracted than that of PAF and A-IgG. Intradermal extravasation induced by PAF reached a maximum at 30 min after injection, and was also inhibited by PCA 4248. In contrast, PCA 4248 caused a less remarkable, but statistically significant reduction of the intradermal extravasation caused by tumor necrosis factor. Pretreatment of mice with an oral dose of 30 mg/kg PCA 4248, 5 min before challenge with PAF (LD84 = 80 micrograms/kg PAF, i.v.) increased the survival rate from 16% to 68%. These data indicate that compounds containing a 1,4-dihydropyridine structure can antagonize PAF effects on experimental animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Biosynthesis of platelet-activating factor (PAF) in human polymorphonuclear leucocytes. The role of lyso-PAF disposal and free arachidonic acid.

Theophylline and 1-methyl-3-isobutylxanthine (MIX), compounds that block eicosanoid formation and modulate phospholipase A2 activity, inhibited in a dose-dependent manner the formation of both leukotriene B4 (LTB4) and platelet-activating factor (PAF) by human polymorphonuclear leucocytes (PMN) in response to ionophore A23187. Theophylline and MIX lacked any inhibitory effect on acetyl-CoA: lyso-PAF acetyltransferase activity, which is the rate-limiting step for PAF biosynthesis in PMN. The effect of theophylline and MIX on PAF formation could be reversed by incubating the cells in the presence of 1-10 microM exogenous lyso-PAF. Incubation of PMN homogenates in the presence of unsaturated non-esterified fatty acids resulted in dose-dependent inhibition of the acetyltransferase. This effect was linked to the presence of a free carboxyl group, since both arachidonic acid methyl ester and palmitoyl-arachidonoyl phosphatidylcholine lacked inhibitory activity. This inhibitory effect was also dependent on the number of double bonds, since arachidonic acid (C20:4) and eicosapentaenoic acid (C20:5) displayed maximal effect. Kinetic analysis showed that the effect of arachidonic acid was consistent with competitive inhibition, with a Ki value of about 19 microM. Oxidative metabolites of arachidonic acid showed a lesser inhibitory effect with the following order of potency: arachidonic acid greater than 15-HETE (15-hydroxy-6,8,11,14-eicosatetraenoic acid) greater than LTB4 greater than 5-HETE (5-hydroxy-6,8,11,14-eicosatetraenoic acid) greater than lipoxin A4. Examination of enzymes involved in CoA-dependent acylation revealed a low activity of both arachidonoyl-CoA synthetase and arachidonoyl-CoA: lyso-PAF arachidonoyltransferase. These data indicate a strong influence on PAF biosynthesis of the products of the phospholipase A2 reaction, with lyso-PAF disposal being a critical event for PAF formation, and unsaturated fatty acids acting as feed-back inhibitors. The conversion of arachidonic acid via oxidative metabolism into less active inhibitors of acetyl-CoA:lyso-PAF acetyltransferase seems to be an additional mechanism of modulation of this enzyme activity, linked to the function of lipoxygenases. Finally, the enzyme activities involved in arachidonoyl-CoA-dependent acylation of lyso-PAF show a low efficiency in capturing arachidonic acid.

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.

Role of complement-derived peptides in thrombocytopenia elicited by soluble aggregates of immunoglobulin G in the rat.

The variations in platelet counts upon intravenous challenge with soluble aggregates of IgG were assessed in normal rats. A time- and dose-dependent thrombocytopenia, followed by recovery to preinfusion values after 30 minutes was observed. Rats injected with immune aggregates showed an increase in plasma levels of immunoreactive thromboxane B2, however, this increase was delayed as compared with the peak level of the thrombocytopenia. Previous treatment of rats with either indomethacin or aspirin, inhibited thromboxane B2 release, but did not affect thrombocytopenia. Pretreatment of the animals with BN 52021, a potent antagonist of platelet-activating factor binding to its receptor, also failed to block thrombocytopenia. Complement depletion by prior treatment with cobra venom factor, caused a significant reduction of the thrombocytopenia, whereas DL-2-mercaptomethyl-3-guanidinoethylthiopropanoic acid, an inhibitor of carboxypeptidase N, potentiated the thrombocytopenia elicited by submaximal doses of either IgG aggregates or a homogeneous preparation of rat anaphylatoxin containing C5a. In addition, rats challenged with doses of IgG aggregates higher than 5 mg/kg showed a massive complement consumption coincident with the onset of thrombocytopenia. "In vitro" aggregation/secretion experiments with rat platelets showed little platelet-stimulating activity either by aggregated IgG through the Fc receptor or through the CR1 receptor. By contrast, a preparation of rat serum anaphylatoxins containing C5a, showed a high platelet-secreting activity. These data suggest that a complement-derived peptide(s), most probably C5a, is one of the effector substances for platelet activation in response to soluble aggregates of IgG.

Biosynthesis of platelet-activating factor in glandular gastric mucosa. Evidence for the involvement of the 'de novo' pathway and modulation by fatty acids.

The biosynthesis of platelet-activating factor (PAF), a phospholipid autocoid with potent ulcerogenic properties that is produced in secretory exocrine glands by physiological secretagogues, was assessed in microsomal preparations of glandular gastric mucosa. For this purpose, 1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine (lyso-PAF):acetyl-CoA acetyltransferase (EC 2.3.1.67); the enzymes of the 'de novo' pathway: 1-O-alkyl-2-lyso-sn-glycero-3-phosphate (alkyl-lyso-GP):acetyl-CoA acetyltransferase and 1-O-alkyl-2-acetyl-sn-glycerol (alkylacetyl-G):CDP-choline cholinephosphotransferase (EC 2.7.8.16); and some enzymes involved in the catabolism of PAF and lyso-PAF were assayed. Only the enzymes of the 'de novo' pathway and small amounts of PAF acetylhydrolase, phospholipase A2 and a lysophospholipase D acting on either lipids could be detected in the gastric preparations, whereas lyso-PAF:acetyl-CoA acetyltransferase activity was undetectable. The specific activity of alkyl-lyso-GP:acetyl-CoA acetyltransferase in the gastric mucosa was about one-tenth of that found in spleen microsomes and its apparent Km for acetyl-CoA was 454 microM compared with 277 microM in spleen microsomes. Glandular mucosa homogenates contained preformed PAF at a concentration of 2.7 +/- 0.7 ng equivalents of PAF (hexadecyl)/mg of protein. When gastric microsomes were incubated with micromolar concentrations of fatty acids (arachidonic, palmitic and oleic) prior to the assay of dithiothreitol (DTT)-insensitive cholinephosphotransferase, a dose-dependent reduction in the formation of PAF was observed, arachidonic acid being the most potent inhibitor, followed by linoleic acid (only tested on spleen microsomes) and oleic acid. By contrast, 1,2-diolein and phosphatidylcholine (dipalmitoyl) showed no or little effect. These results indicate that glandular gastric mucosa can produce PAF through the 'de novo' pathway, and that fatty acids, especially unsaturated, can reduce that synthesis by modulating the expression of DTT-insensitive cholinephosphotransferase.

Role of paf-acether in the mediation of pathophysiological responses to aggregated immunoglobulins. Studies with the platelet-activating factor receptor antagonist BN 52021.

Sprague-Dawley rats were challenged with an intravenous (i.v.) infusion of soluble aggregates of immunoglobulin G. Animals receiving a dose of aggregates of 40 mg/kg showed a significantly reduced time of lysis of diluted blood clot, which paralleled the appearance in plasma of tissue-type plasminogen activator. These changes occurred about 5-10 min after the challenge, which is a more protracted time-course than that observed in response to paf-acether. A significant increase in serum levels of N-acetylglucosaminidase was also observed in the animals several minutes after challenge. Blood neutrophil count showed a 50% reduction that reached its maximum at 10 min and was followed by an overshoot after 30 min. In experiments in rats previously depleted of circulating PMN by treatment with vinblastine, no significant differences were observed in N-acetylglucosaminidase release as compared to non-treated animals. Since prior evidence indicated that endogenously generated paf-acether could be a mediator responsible for these changes, at least to some extent, the compound BN 52021, a specific antagonist of the paf-acether receptor was given to these animals prior to the challenge with the complexes. All the above mentioned responses were significantly reduced by BN 52021, which is in keeping with the hypothesis involving endogenous paf-acether release in the mediation of these changes. By contrast, BN 52021 did not interfere with the clearance of the aggregates from the circulation, which seems to be a beneficial mechanism to reduce immune-mediated tissue injury. These data extend the number of paf-acether mediated pathophysiological changes that can be observed in response to immune aggregates.

Increased levels of platelet-activating factor in blood from patients with cirrhosis of the liver.

The levels of platelet-activating factor (paf-acether) were measured in blood and ascitic fluid from cirrhotic patients and in blood from a group of controls, using a recently described technique for extraction and measurement. In addition, activity of acetylhydrolase, the main catabolic enzyme for paf-acether, was also measured. The highest levels of paf-acether in blood were found in decompensated cirrhotics (1.78 +/- 0.62 ng ml-1; mean +/- SD, n = 8). Compensated cirrhotics showed lower blood values (0.79 +/- 0.21, n = 4), but higher than controls (0.20 +/- 0.04, n = 12). Paf-acether levels in ascitic fluid were similar to those of blood. Values of acetylhydrolase in serum were similar in all the groups studied (3.0 +/- 0.4 in cirrhotics vs. 2.3 +/- 0.4 nmol min-1 mg-1 of protein in controls). These data suggest an enhanced production of paf-acether in cirrhotic patients rather than a decreased catabolism. High levels of paf-acether in blood could be involved in the impaired haemodynamics of cirrhotic patients and in their renal function alterations.

Evidence of a role for PAF-acether in the pathophysiology of the shock state.

The pathophysiology of the shock state includes a variety of hemodynamic changes such as systemic hypotension, pulmonary hypertension and increased vascular permeability leading to the extravasation of protein rich plasma. These changes can be initiated by different etiological factors, but many of them have been related to the stimulation of activation systems (complement, kinins, etc.) or to the generation of inflammatory mediators. The purpose of the present study has been to obtain evidence of the involvement of paf-acether in the pathogenesis of the shock state initiated in rat and mouse by Gram-negative bacteria and soluble aggregates of immunoglobulin G. The injection of 1-2 MDa aggregates of immunoglobulin G to normal Sprague-Dawley rats, induced a dose-dependent systemic hypotension which appeared about five minutes after completion of the intravenous challenge. Simultaneously, extravasation of protein-rich plasma occurred as judged from the finding of an increased clearance of 125I-BSA. In similar experiments in mice, a reduction of the vascular volume was observed using 51Cr-labelled homologous red blood cells. Under these conditions, a lipid compound analogous to paf-acether was obtained from the liver and the spleen of these animals. The generation of this compound preceded the development of blood volume depletion and could be suppressed by either quinacrine or depletion of mononuclear phagocytes by total irradiation with 700 rads. The previous treatment of the rats with the compound BN 52021 (a specific antagonist of the paf-acether receptor) at a dose of 5mg/kg, i.v., prevented the appearance of hypotension and extravasation in response to an i.v. challenge with soluble aggregates of immunoglobulin G. Interestingly, the reversal of hypotension was also observed when BN 52021 was infused after the immunoaggregates (5mg/kg). The possible involvement of paf-acether in the hemodynamic changes of Gram-negative sepsis was studied in rats which had received an intraperitoneal inoculation of E. coli. The animals inoculated with the doses of bacteria which produced mortality showed a time- and dose-dependent increase of vascular permeability as judged from the presence of abundant peritoneal exudate and the reduction of the circulating volume. Simultaneously, significant amounts of paf-acether could be obtained from the peritoneal exudate and from the spleen preceding to the development of the circulating volume depletion.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of the platelet-activating factor antagonist BN 52021 on the hemodynamics of rats with experimental cirrhosis of the liver.

Previous studies from this laboratory have shown that rats with experimental cirrhosis of the liver induced by the combined administration of oral phenobarbital and inhaled carbon tetrachloride show an hyperdynamic status with enhanced cardiac output (CO), and decreased mean arterial pressure (MAP) and peripheral vascular resistance (PVR). Cirrhotic rats also showed an increased vascular permeability. All these phenomena are similar to some of the known effects of the systemic infusion of low doses of synthetic platelet-activating factor into the systemic circulation of normal rats. The measurement of the levels of platelet-activating factor in samples of blood demonstrated significantly higher levels in cirrhotic (2.65 +/- 0.39; n = 10) than in control rats (1.50 +/- 0.57 ng/ml; n = 10; p less than 0.05). The hemodynamic changes induced by the intravenous injection of the platelet-activating factor receptor antagonist BN 52021 (5 mg/kg body weight) have been measured in 10 control and 10 cirrhotic male Wistar rats, using a radioactive microsphere technique. BN 52021 induced no significant hemodynamic changes in control animals. However, in cirrhotic animals it induced a significant decrease in CO with increase in PVR. MAP increased slightly but not significantly. From these data it can be deduced that platelet-activating factor plays a role in the hemodynamic derangement shown by cirrhotic rats and that these derangement can be reversed by BN 52021, a highly selective antagonist of the platelet-activating factor receptor.

Inhibition of the vascular actions of IgG aggregates by BN 52021, a highly specific antagonist of paf-acether.

The effect of BN 52021, a selective antagonist of paf-acether (Braquet GB patent 8, 418, 424 July 19, 1984), was studied in normotensive rats challenged with different doses of paf-acether. Sudden death was observed in animals receiving an i.v. dose of 10 micrograms/kg of paf-acether and this was prevented by prior treatment with BN 52021 (5 mg/kg, i.v.). Animals receiving 2.5 micrograms/kg of paf-acether had a fall of mean arterial pressure of 92.5 +/- 4.7 mmHg which recovered to the prechallenge level 20.5 +/- 0.2 min thereafter. Previous treatment with BN 52021 (5 mg/kg, i.v.) reduced the mean arterial pressure fall to 47 +/- 0.9 mmHg and the time of recovery to 5.7 +/- 1.7 min. The extravasation of 125I-bovine serum albumin under the above conditions was reduced by BN 52021 from 36 +/- 3 to 18 +/- 3%. A lower dose of BN 52021 (1 mg/kg, i.v.) was also effective in reducing later extravasation, but was unable to prevent the extravasation which appears up to 10 min after the injection of paf-acether. To extend these findings to a model of endogenous production of paf-acether, other animals were challenged with soluble aggregates of human IgG (40 mg/kg, i.v.; Iñarrea et al., Immunopharmacology 6:7, 1983).(ABSTRACT TRUNCATED AT 250 WORDS)

Presence of platelet-activating factor in blood from humans and experimental animals. Its absence in anephric individuals.

Blood from humans and experimental animals was examined for the presence of platelet-activating factor. The procedure included a rapid extraction of the samples and a purification of the lipid content by thin layer chromatography. The chemical characterization was performed by phospholipases' treatment and high performance liquid chromatography. Rats contained the highest concentrations of platelet-activating factor and rabbits the lowest. Five anephric patients undergoing support hemodialysis had undetectable blood levels and the same finding was observed in six rats in which surgical nephrectomy was performed. Based on these data we suggest: 1) Low amounts of platelet-activating factor can be present in blood under normal conditions. 2) Kidney tissue seems to play a role in the formation of the platelet-activating factor that can be detected in blood under these conditions.