Interference of the PAF-acether antagonist BN 52021 with endotoxin-induced hypotension in the guinea-pig

Because of the potential role of PAF-acether in the pathogenesis of endotoxin shock, we examined the preventive and curative effects of BN 52021, a new PAF-acether antagonist in guinea-pig challenged with S. Typhimurium endotoxin. A biphasic reduction of mean arterial pressure was elicited by i.v. endotoxin (300 micrograms/kg) in control animals, with a rapid drop of blood pressure (maximal decrease within 10 min), partial recovery at 20 min and a second gradual decrease after 30 min. Treatment with BN 52021 injected 15 min prior to endotoxin reduced the initial rapid drop of blood pressure from 38.5 +/- 5 mmHg in vehicle-treated controls (n = 15) to 17 +/- 3 mmHg (p less than 0.01) in animals treated with 1 mg/kg BN 52021(n = 10) and to 9.5 +/- 8 mmHg (p less than 0.01) in guinea-pigs treated with 6 mg/kg BN 52021 (n = 5). The early hypotensive phase was associated with severe thrombocytopenia-leukopenia; only the thrombocytopenia was reduced by BN 52021. The prolonged secondary phase of hypotension was reduced by BN 52021 pretreatment whereas a small increase of hematocrit persisted. The two phases of the arterial pressure profile during endotoxic shock were not observed in animals previously made thrombopenic by rabbit and anti-platelet serum and only the late hypotensive phase persisted. This late hypotension induced by endotoxin in thrombopenic animals was suppressed by BN 52021 pretreatment suggesting that BN 52021 may act via a platelet-independent mechanism. The intravenous injection of BN 52021 during the prolonged secondary phase of shock was followed by an immediate increase of the depressed blood pressure. This increase of blood pressure was dose-dependent, maximum at 6 mg/kg BN 52021, and observed in normal and thrombopenic animals. The interference of BN 52021 with endotoxin shock may be related to its PAF-acether antagonist properties and suggests that PAF-acether is an important participant in endotoxic shock.     

Free Radicals Scavengers Attenuate Platelet-Activating Factor (PAF)-And Endotoxin-Induced Intestinal Myoelectric Disturbances in Rats

Pretreatment with radical scavengers significantly reduced the intestinal myoelectric disturbances following either E. coli endotoxin or platelet-activating factor (PAF) injection in the rat indicating that free radicals might be involved in the intestinal motor alterations observed in endotoxin shock and that PAF acts partially via free radical production. Moreover, dimethylsulfoxide (DMSO) was found to be more effective in inhibiting the endoxotin-induced intestinal motor alterations, than superoxide dismutase (SOD) and allopurinol. BN 52021, a specific PAF antagonist, was able to reduce the effects of endotoxin on intestinal motility, However, when BN 52021 was combined with free radical scavengers, no additive effect was observed. It is concluded that free radicals involved in endotoxin-induced intestinal motility alterations are at least in part produced in response to PAF.     

Pharmacological modulation of the bronchopulmonary action of the vasoactive peptide, endothelin, administered by aerosol in the guinea-pig

Administration by aerosol for 1 min of solutions of endothelin (ENDO; 1, 5 or 10 micrograms/ml) to anaesthetized and ventilated guinea-pigs induced a dose-dependent bronchopulmonary response (BR) which was maximal within 4 to 5 min. In contrast, no significant change of the mean arterial blood pressure was observed. Pretreatment of guinea-pigs with propranolol (1 mg/kg, i.v.), mepyramine (1 mg/kg, i.v.), nifedipine (50 mg/kg, i.p.) or verapamil (0.3 mg/kg, i.v.) did not significantly affect the BR induced by an aerosol of a solution of 10 micrograms/ml ENDO. In contrast, BR was significantly reduced when the animals were pretreated with the cyclooxygenase inhibitor, indomethacin (10 mg/kg, i.v.) or the platelet-activating factor (PAF) receptor antagonist, BN 52021 (10 mg/kg, i.v.). These results indicate that aerosolized ENDO induces a BR via the generation of secondary mediators such as cyclooxygenase products and PAF in a process which is unaffected by the blockers of the voltage-dependent calcium channels.     

Interference of the PAF-acether antagonist BN 52021 with passive anaphylaxis in the guinea-pig

PAF-acether may be involved in anaphylaxis and asthma. We tested the new PAF-acether antagonist BN 52021 against the effects of antigen in passively sensitized guinea-pigs. Bronchoconstriction by ovalbumin administered i.v. (1 mg/kg) or by aerosol (1 or 10 mg/ml for a period of 1 min) was significantly reduced by BN 52021 (1-10 mg/kg), which did not inhibit drop of leukocyte counts after the i.v. challenge. In both cases, when the guinea-pigs were pretreated by propranolol, high amounts of BN 52021 became ineffective against shock. The reduction of the anaphylactic bronchoconstriction, induced by the combination of mepyramine, aspirin and FPL 55712 was not improved by BN 52021. Tested on isolated lung strips from passively sensitized guinea-pig, BN 52021, at a concentration which inhibits PAF-induced contraction (0.1 mM), did not inhibit the anaphylactic contraction triggered by the administration of ovalbumin (10 micrograms/ml) nor the accompanying release of histamine and thromboxane. In contrast, BN 52021 (30 microM) significantly reduced the anaphylactic release of histamine and of thromboxane from perfused lungs of passively sensitized guinea-pigs. The results with the isolated lung strips and the propranolol-treated guinea-pigs in vivo suggest a dissociation between the anti-anaphylactic and the anti-PAF-acether properties of BN 52021.     

Interactions between platelet activating factor and eicosanoids during endotoxic shock in anaesthetized pigs

The effects of platelet activating factor (PAF) on eicosanoid release during endotoxic shock was investigated in anaesthetized pigs receiving 5 mug kg(-1) Escherichia coli endotoxin (LPS) into the superior mesenteric artery over a 60 min period, by measuring plasma levels of a variety of mediators. Fifteen of the 31 animals infused with LPS and not treated with BN 52021, a PAF receptor antagonist, died within 30 min after the commencement of LPS infusion (non-survivors), while the other 16 survived the experimental period of 3 h, though in a state of shock (survivors). No alterations were observed in plasma concentrations of eicosanoids in the non-survivors. A significant, though transient, increase in eicosanoid concentrations occurred only in the survivors. Treatment with BN 52021 (4 mg kg-1, i.v.) injected 5 min prior to LPS infusion, failed to exert any effect on the survival rate. However, pretreatment with BN 52021 prevented circulatory collapse in the survivors and reduced the concentration of cyclooxygenase enzyme products, without affecting LTB(4) release. Exogenous administration of PAF (0.01 mug kg(-1)) caused hypotension and increased TXB(2) levels although 6-keto PGF(1alpha) and LTB(4) concentrations were unchanged. The data suggest that prostanoid formation may be secondary to PAF release in circulatory collapse evoked by LPS infusion in survivors, and give further support to the suggestion that PAF prostanoid interaction is important during endotoxic shock. However, their role in early death seems to be negligible, indicating the importance of other mediators.     

Effect of long-term treatment with platelet-activating factor on IL-1 and IL-2 production by rat spleen cells

To study the effect of the in vivo administration of platelet-activating factor (PAF) on cytokine production, alzet minipumps loaded with the mediator or solvent alone were connected to the jugular vein and placed under the skin of Sprague-Dawley rats. Over 7 days the animals received total doses of 0.5, 1, 4.5, 9, or 28 micrograms PAF or the solvent alone. The spleen mononuclear cells isolated from Ficoll gradients and the adherent cell fraction were separated before determination of basal and mitogen-stimulated IL-1 and IL-2 production, respectively. Adherent splenocytes from rats having received 28 micrograms PAF exhibited a decreased capability to produce IL-1, as compared to those from vehicle-treated animals. In contrast, adherent splenocytes from rats having received 9 and 4.5 micrograms PAF yielded higher amounts of released and cell-associated IL-1 activity upon LPS stimulation, as compared to those from solvent-treated animals. The PAF antagonist, BN 52021, given orally (5 mg/kg, twice a day throughout the experiments) inhibited the in vivo effect of 28 micrograms PAF. Statistically significant 144 +/- 43% (p less than 0.001, n = 5) and 73 +/- 33%, (p less than 0.01, n = 3) increases in IL-2 production were observed when whole spleen mononuclear cells from rats administered with 1 and 4.5 micrograms PAF, respectively, were stimulated with Con A. BN 52021 markedly inhibited the in vivo effect of 1 microgram PAF on the IL-2 release. Our study demonstrates that PAF can modulate immune functions in vivo and suggests that the specific PAF antagonist, BN 52021, may be used as an immunomodulatory agent.     

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.     

Pharmacologic profile of BN 50739, a new PAF antagonist in vitro and in vivo

The effect of a new PAF antagonist BN 50739 was studied on PAF-induced [3H]-serotonin release from washed rabbit platelets in vitro and on PAF-induced hypotension in vivo. BN 50739 competitively inhibited PAF-induced [3H]-serotonin release from the platelets in a dose-dependent manner. In the presence of 4, 10 and 50 nM of BN 50739, the concentration of PAF inducing 50% maximal [3H]-serotonin release from the platelets (EC50) increased from 2.15 nM to 5.10, 45.10 and 900 nM, respectively. The IC50 of BN 50739 for PAF (10 nM) induced [3H]-serotonin release was 3.67 nM. Under the same experimental condition, the IC50s of BN 50726, BN 50730, BN 50741, WEB 2086, SRI 63-441 and BN 52021 were 5.40, 4.61, 6.88, 5.98, 40.90 nM and 14.90 microM, respectively. PAF-induced hypotension in conscious rats was also inhibited dose-dependently by i.p. pretreatment of BN 50739 (3 and 10 mg/kg). PAF-induced hypotension was diminished both in magnitude and duration in rats pretreated with BN 50739. These data taken together indicate that BN 50739 is a most potent PAF antagonist in vitro and in vivo.     

The effect of platelet-activating factor and its antagonist--BN 52021--on immune reactions in vivo in mice and in vitro

The effect produced by the injection of platelet activation factor (PAF) and its antagonist BN 52021 on the intensity of humoral immune response in (CBA x C57BL)F1 mice was studied. PAF was found to stimulate the formation of antibodies to sheep red blood cells. In addition PAF stimulated the phagocytic activity of mouse peritoneal macrophages. The stimulation of immune response under the action of PAF may be attributed to an increase in the phagocytic activity of macrophages. The stimulating effect of PAF on immune response in vivo was abolished by the injection of BN 52021, the antagonist of PAF. At the same time the dose-dependent decrease of immune response was observed after the injection of BN 52021. Indomethacin, an inhibitor of prostaglandin synthesis, when administered to mice treated with BN 52021, abolished the BN 52021-induced suppression of humoral immune response. Mouse peritoneal macrophages, treated in vitro with BN 52021, were found to produce significantly more prostaglandin E than control macrophages. Thus, BN 52021 induced the suppression of humoral immune response in vivo; this suppression was probably due to the action of prostaglandin E2, a messenger of the second order. Besides, the PAF antagonist BN 52021 significantly decreased leukotriene B4 production by macrophages in vitro. BN 52021 may be supposed to switch over the synthesis and/or secretion of arachidonic acid from the lipoxygenase pathway to the cycloxygenase one.     

Effect of Platelet-activating Factor on in vitro and in vivo Interleukin-6 Production

The aim of the present study was to investigate the possible effect of platelet-activating factor (PAF), by comparison with interleukin-1beta and polyriboinositic/polyribocytidylic (poly I-C) acid, on IL-6 production by L 929 mouse fibroblasts. At concentrations above 1 muM PAF, the production of IL-6 by mouse fibroblasts was enhanced in a dose dependent fashion. At 5 muM PAF, the peak increase (60.1 +/- 19.4 U/ml) was similar to that induced by 50 mug/ml poly I-C (60.0 +/- 35.0 U/ml) and higher than the one evoked by 100 U/ml IL-1beta (3.8 +/- 1.8 U/ml). The increase of 11-6 activity induced by 5 muM PAF was maximal after a 22 h incubation period with L 929 cells. Lyso-PAF (5 muM) also increased IL-6 activity from fibroblasts to a similar extent compared with 5 muM PAF. In addition, the IL-6 activity induced by 5 muM PAF was still observed when the specific PAF antagonist, BN 52021 (10 muM), was added to the incubation medium of L 929 cells. The result suggests that the production of IL-6 by L 929 cells evoked by PAF in vitro is not receptor mediated. The in vivo effect of PAF on IL-6 production was also investigated in the rat. Two hours after intravenous injection of PAF (2 to 4 mug/kg), a dramatic increase of IL-6 activity in rat serum was observed, this effect being dose dependent. The increase of IL-6 induced by 3 mug/kg PAF was not observed when the animals were treated with the PAF antagonist, BN 52021 (1 to 60 mg/kg0. These results demonstrate that PAF modulates IL-6 production and that the in vivo effect is receptor mediated.     

Relationship between PAF-acether and thromboxane A2 biosynthesis in endotoxin-induced intestinal damage in the rat

PAF-receptor antagonists are known to inhibit gastrointestinal damage induced by endotoxin. In the present study, the interaction between the biosynthesis of PAF and thromboxane (TX) A2, as putative mediators of the acute intestinal damage induced by endotoxin, has been investigated in the anaesthetised rat. Bolus intravenous administration of lipopolysaccharide from E. coli (5-50 mg/kg) induced dose-related jejunal damage, assessed using both macroscopic and histological techniques. This damage was accompanied by significant increases in the jejunal formation of PAF determined by bioassay, and of TXB2, determined by radioimmunoassay. Pretreatment with the structurally-unrelated thromboxane synthase inhibitors, 1-benzyl imidazole (10-50 mg/kg) or OKY 1581 (25 mg/kg) substantially reduced both jejunal damage and TXB2 formation, but did not inhibit PAF formation. Likewise, pretreatment with indomethacin (5 mg/kg) or BW 755C (50 mg/kg) reduced jejunal damage and TXB2 formation but did not affect PAF formation. Pretreatment (2h) with dexamethasone (4 mg/kg) reduced jejunal damage and the formation of both TXB2 and PAF. Intravenous infusion of PAF (100 ng/kg/min for 10 min) induced jejunal damage and significantly increased the formation of TXB2, whereas non-specific jejunal damage induced by oral administration of ethanol did not augment PAF formation. The present findings that inhibition of jejunal thromboxane formation is associated with a substantial reduction in jejunal damage, with no corresponding inhibition in PAF formation, therefore suggests a complex interaction or sequential release of these tissue destructive mediators underlying the intestinal damage induced by endotoxin.     

Effect of cyclosporin A and the platelet-activating factor (PAF) antagonist, BN 52021, on PAF- and antigen- induced bronchoconstriction in the guinea-pig

The effects of the PAF antagonist, BN 52021, and cyclosporin A (CsA), either alone or in combination, on PAF- and antigen- induced bronchoconstriction were investigated in control and passively sensitized guinea-pigs, respectively. Although single administration of CsA alone has no effect on the PAF-induced bronchoconstriction, a marked inhibition of this phenomenon is observed when the drug is given along with an inactive dose of BN 52021. This effect of the association of the two drugs on the bronchoconstriction is also related to an action on the PAF-induced alterations in the number of leukocytes and platelets. In addition, administration of CsA for 48 hrs, which alone does not influence PAF-induced bronchoconstriction, markedly increases the inhibition evoked by BN 52021. Although bolus administration of CsA has no effect on the antigen -induced bronchoconstriction, a marked inhibition of this phenomenon is observed when the drug is given for 2 days. This inhibition by CsA is not further enhanced when the animals are also treated with BN 52021. These results strengthen the hypothesis that PAF and the immune system are involved in the regulation of bronchopulmonary reactions.     

Interference of the PAF-acether antagonist BN 52021 with passive anaphylaxis in the guinea-pig

PAF-acether may be involved in anaphylaxis and asthma. We tested the new PAF-acether antagonist BN 52021 against the effects of antigen in passively sensitized guinea-pigs. Bronchoconstriction by ovalbumin administered i.v. (1 mg/kg) or by aerosol (1 or 10 mg/ml for a period of 1 min) was significantly reduced by BN 52021 (1–10 mg/kg), which did not inhibit drop of leukocyte counts after the i.v. challenge. In both cases, when the guinea-pigs were pretreated by propranolol, high amounts of BN 52021 became ineffective against shock. The reduction of the anaphylactic bronchoconstriction, induced by the combination of mepyramine, aspirin and FPL 55712 was not improved by BN 52021. Tested on isolated lung strips from passively sensitized guinea-pig, BN 52021, at a concentration which inhibits PAF-induced contraction (0.1 mM), did not inhibit the anaphylactic contraction triggered by the administration of ovalbumin (10 μg/ml) nor the accompanying release of histamine and thromboxane. In contrast, BN 52021 (30 μM) significantly reduced the anaphylactic release of histamine and of thromboxane from perfused lungs of passively sensitized guinea-pigs. The results with the isolated lung strips and the propranolol-treated guinea-pigs in vivo suggest a dissociation between the anti-anaphylactic and the anti-PAF-acether properties of BN 52021.     

Failure of platelet-activating factor (PAF-acether) to induce decidualization in mice and failure of antagonists of PAF to inhibit implantation

The possible role of platelet-activating factor (PAF) in the uterine responses associated with implantation was investigated. Attempts to trigger a decidual cell response in the uteri of hormonally sensitized, ovariectomized mice by instilling PAF-acether (1-1000 ng) intraluminally were unsuccessful. The effect of PAF antagonists on implantation was investigated in females ovariectomized on Day 3 of pregnancy and treated with progesterone. Implantation was induced in these females by injection of 10 ng oestradiol-17 beta on Day 8. Hourly intraperitoneal injections of three PAF antagonists (WEB 2086, CV 3988 and BN 52021 at doses of 1.2-1.4 mg/kg) given over a 24-h period starting 1 h before the injection of oestradiol-17 beta had no significant effect on the occurrence of implantation sites. Intraluminal injection of WEB 2086 (15 micrograms) or BN 52021 (5 micrograms) either 3 h before or 6 h after the nidatory oestradiol also had no significant inhibitory effect on implantation. SRI 63-441 given once daily over the first 4 days of pregnancy at a dose of 40 micrograms/30 g body weight had no inhibitory effect on the establishment of pregnancy. These results are not consistent with a critical role for PAF in implantation in mice.     

Role of platelet-activating factor (PAF) in the initiation of the decidual reaction in the rat

Injection of PAF into the left uterine horn induced a dose-dependent decidua-like reaction in the pseudopregnant rat. This reaction was maximal when PAF was injected at Day 5 of pseudopregnancy and was blocked by the specific PAF antagonist, BN 52021. BN 52021 did not interfere with the decidual reaction induced by prostaglandin E-2 or insertion of a cotton thread in the uterine horn. In contrast, a decidua-like reaction was not evoked by the inactive lyso-PAF, demonstrating the specificity of the action of PAF. The decidua-like reaction induced by PAF involves the generation of cyclooxygenase metabolites of arachidonic acid since it was inhibited by indomethacin. The histological alterations induced by PAF were similar to those observed after embryo implantation, strengthening the postulate for a role of the autacoid in the early stages of pregnancy.     

Characterization of specific binding sites for PAF in the iris and ciliary body of rabbit

The protective effect exerted by BN 52021 a specific PAF-receptor antagonist in experimentally induced ocular inflammatory disorders led us to investigate the possible presence of specific receptors for PAF in rabbit iris and ciliary body. Two classes of PAF binding sites were found in isolated iris and ciliary process of pigmented rabbit eyes: a high affinity site Kd1 congruent to 4.9 +/- 0.47 nM, Bmax1 congruent to 3.17 +/- 0.50 pmoles/mg protein, a low affinity sites Kd2 congruent to 11.6 +/- 0.33 nM, Bmax2 congruent to 12.46 +/- 2.3 pmoles/mg protein for iris. The specific binding was not affected by lyso-PAF the biologically inactive precursor and metabolite of PAF, up to 10(-6) M; inhibition by unlabelled PAF demonstrated a biphasic curve partially antagonized by BN 52021. The present results demonstrate the presence of specific binding sites for PAF in rabbit eyes which could mediate the action of this mediator in eye inflammatory processes and explain the protective effect observed with BN 52021.     

Superoxide Dismutase (SOD) and the Paf-Antagonist (BN 52021) Reduce Small Intestinal Damage Induced by Ischemia-Reperfusion

Oxygenated free-radicals appear to play a prominent role in mediating damage associated with gastrointestinal diseases. Production of reactive oxygen metabolites in ischemia-reperfusion involves oxidases found in resident phagocytic cells and microvascularand mucosal epithelial cells. Platelet activating factor (PAF), a phospholipid associated with inflammatory disorders, has been shown to both prime and amplify the release of superoxide anion and hydrogen peroxide from polymorphonuclear neutrophils and macrophages stimulated by FMLP or PMA. To further elucidate the involvement of free radicals in intestinal damage and the potential role of PAF in their production, we examined the effect of superoxide dismutase (SOD) and BN 52021 (ginkgolide B) on ischemia-reperfusion induced damage in the small intestine.

The study involved 32 Sprague-Dawley rats (100–200 g) divided into four groups. Three of these groups were subjected to occlusion of the mesenteric artery 30 mins followed by 24 h reperfusion. On 2 groups SOD (15,000 U/kg/iv) and BN 52021 (20 mg/kg/po) were administered 45 mins before arterial occlusion. Following the 24 h reperfusion, the rats were sacrificed after overnight fasting. The jejunum and ileon were removed and fixed for morphological examination. Lesions in the small intestine were quantified.

The results showed extensive necrosis, hemorrhage, oedema and neutrophil invasion in the jejunal and ileal mucosa. This injury was significantly reduced by SOD (15.000 U/kg/iv) and BN 52021 (20 mg/kg/po) pretreatment. In conclusion, free-oxygenated radicals appear to mediate reperfusion damage in the small intestine and PAF appears to be involved in the genesis of these toxic products. Thus, SOD and BN 52021 may be considered as protectors against ischemic disorders.     

Effects of platelet activating factor (PAF) and its receptor antagonist BN 52021 on isolated perfused guinea-pig heart

The cardiac effects of PAF and its antagonist BN 52021 have been investigated on the isolated perfused guinea-pig heart maintained at a constant hydrostatic perfusion pressure of 80 cm water. In this model, PAF (1 x 10(-11) to 1 x 10(-7) moles) induced a dose-dependent coronary vasoconstriction, a decrease in heart rate and a fall in contractile force. BN 52021 (1 x 10(-6) to 2 x 10(-4) M) dose-dependently inhibited the vasospasm induced by PAF (1 x 10(-10) moles). BN 52021 also antagonized the decrease in coronary flow and heart rate, but not that of contractile force induced by a high dose of PAF (1 x 10(-7) moles). This dose of PAF also significantly (p less than 0.001) provoked a marked release of TxB2 but did not alter the generation of 6 Keto PGF1 alpha, PGE2 or LTC4. The PAF-induced increase in TxB2 release was completely abolished by BN 52021.     

Antagonism of PAF-induced death in mice

The ability of three platelet activating factor (PAF) antagonists, BN52021, L652, 731 and 48740RP, and the leukotriene antagonist FPL55712 to block iv PAF-induced death was tested in mice. PAF-induced sudden death was been previously characterized as a model of systemic anaphylaxis and circulatory shock related its hypotensive actions. Of the drugs, BN52021 and L652, 731 provided dose-dependent protection against PAF toxicity, whereas the others had no effect. 48740RP was, however active against PAF-induced rabbit platelet aggregation. BN52021 was inactive in three other mouse sudden death models in which arachidonic acid, U46619 or collagen combined with epinephrine is injected iv to provoke a thrombotic/ischemic sudden death. In contrast, the TXA₂ antagonist SQ29548 inhibited the acute toxicity of two of these latter challenges (arachidonic acid and thromboxane agonist U46619), but was inactive against PAF lethality.These results suggest that PAF toxicity in mice is a specific model for PAF agonism, and is not mediated by TXA₂ or peptido-leukotrienes. Further, PAF-induced mortality should be a simple and useful technique for testing potential PAF antagonists for activity by various routes of administration.     

A study with BN 52021 demonstrates the involvement of PAF-acether in IgE-dependent anaphylactic bronchoconstriction

The involvement of platelet activating factor (PAF) in anaphylaxis was examined by recording the pulmonary responses of anesthetized passively sensitized guinea-pigs to the aerosolization of ovalbumin. Animals were tested with and without BN 52021 (a ginkgolide B, PAF receptor antagonist) pretreatment. Aerosolization of ovalbumin produced a bronchoconstriction (BC) which could be made refractory to additional challenges with the antigen. In animals desensitized to ovalbumin, aerosolization of PAF produced an unattenuated BC. Guinea pigs desensitized by repeated aerosolizations of PAF subsequently showed reduced responses to aerosolized antigen suggesting that PAF may be involved in the BC. Animals pretreated with BN 52021, were protected against the effects of systemically administered PAF and also showed reduced responses to aerosolized antigen. Aerosolization of the leukotriene antagonist, FPL 55712, was ineffective against anaphylactic BC under conditions where catecholamine and histamine release were blocked.