Thrombus induction by endogenic PAF-acether and its inhibition by Ginkgo Biloba extracts in the guinea pig

The anti-thrombotic effects of specific paf-acether antagonist BN 52021 were compared to the effects of Ginkgo Biloba extracts A, B, (A+B), and C local superfusion of BN 52021 over an experimentally injured arterial segment embolizes an existent paf-acether induced platelet thrombus. When applied before paf-acether, BN 52021 prevents local thromboformation in this model. Applied intravenously, BN 52021 reduces local thromboformation in a significant way. As compared to this BN 52021 standard, only Ginkgo Biloba B and the (A+B)-mixture present major thromboreductive activity.     

The effect of 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (paf-acether) on the arterial wall

The effect of a topical paf-acether superfusion over an injured arterial segment was assessed in the guinea-pig, using an opto-electronic in vivo thrombosis model allowing on-line quantification of small platelet thrombus dynamics. As compared to control, ADP-induced, thromboformation and behaviour, exogenous paf-acether causes a large, dense platelet thrombus, invaded and surrounded by numerous leukocytes, spreading widely over the adjoining, vacuolized, endothelium. Its embolization has to be forced with prostanoids, mepacrine, EDTA, or with a specific paf-acether antagonist (BN 52021). A few minutes after such forced embolization, a new thrombus starts growing at the same site, without renewal of the paf-acether superfusion. This phenomenon of spontaneous reappearance after forced embolization can be followed during several hours. Experiments with labelled paf-acether and the paf-acether antagonist indicate a possible endogenous paf-acether (or paf-acether-like) production triggered by superfusion with exogenous paf-acether.     

The effect of 1-O-alkyl-2-acetyl-Sn-glycero- 3-phosphocholine (paf-acether) on the arterial wall

The effect of a topical paf-acether superfusion over an injured arterial segment was assessed in the guinea-pig, using an opto-electronic in vivo thrombosis model allowing on line quantification of small platelet thrombus dynamics.As compared to control, ADP-induced, thromboformation and behaviour, exogenous paf-acether causes a large, dense platelet thrombus, invaded and surrounded by numerous leukocytes, spreading widely over the adjoining, vacuolized, endothelium. Its embolization has to be forced with prostanoids, mepacrine, EDTA, or with a specific paf-acether antagonist3 (BN 52021). A few minutes after such forced embolization, a new thrombus starts growing at the same site, without renewal of the paf-acether superfusion. This phenomenon of spontaneous reappearance after forced embolization can be followed during several hours. Experiments with labelled paf-acether and the paf-acether antagonist indicate a possible endogenous paf-acether (or paf-acether-like) production triggered by superfusion with exogenous paf-acether.     

Involvement of platelet-activating factor (PAF) in cerebral post-ischemic phase in Mongolian gerbils

Platelet-activating factor (PAF) is a potent mediator of anaphylaxis and shock. In addition, evidence for PAF participation in gastric, intestinal and heart post-ischemic phase has been recently demonstrated. Ginkgo biloba extracts improve cerebral metabolism and protect brain against hypoxic damage in various models of cerebral ischemia. Potent and specific antagonists of PAF have been found in Ginkgo biloba and termed Ginkgolides: BN 52020, BN 52021, BN 52022, BN 52024. We therefore undertook the investigation of the role of Ginkgolides in cerebral ischemia obtained by bilateral ligature of the common carotid for 10 min and 6 h of recirculation in male Mongolian adult gerbils. Given preventively (one week treatment 10 mg/kg/day orally) or at the time of clamping, BN 52021 and related Ginkgolides dose-dependently antagonize morbidity assessed by the stroke-index. Similarly the mitochondrial respiration evaluated by the respiratory control ratio is significantly improved. In both determinations, the range of activity: BN 52021 greater than, BN 52020 greater than BN 52022 greater than BN 52024 shows that the effect of Ginkgolides in cerebral ischemia are correlated with their PAF antagonistic properties. Given curatively, 1 h after declamping, BN 52021 is able to reverse the cerebral impairment trend. Kadsurenone and brotizolam, two other chemically unrelated PAF antagonists led to similar recovery. Therefore PAF appears to play an important role in the post-ischemic phase after bilateral carotid ligation in Mongolian gerbils.     

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.     

Inhibition by BN 52021 (ginkgolide B) of the binding of [3H]-platelet-activating factor to human neutrophil granulocytes

The inhibitory effect of BN 52021, a specific antagonist of platelet-activating factor (PAF) on PAF-induced activation of human polymorphonuclear granulocytes (PMNL) and on the binding of [3H]-PAF to neutrophils were examined. BN 52021 over the range of 10(-9)-10(-4) M inhibited PAF-induced degranulation and superoxide production of PMNLs in a dose-dependent manner with Kd values of 0.6 +/- 0.1 x 10(-6) M and 0.4 +/- 0.1 x 10(-6) M, respectively. BN 52021 (up to 1 mM) did not show any agonistic activity and it did not affect neutrophil responses to N-formyl-methionyl-leucyl-phenylalanine or leukotriene B4. The Ki value of BN 52021 for the specific binding of [3H]-PAF to neutrophils was 1.3 +/- 0.5 x 10(-6) M versus a Ki of 1.1 +/- 0.3 x 10(-7) M for PAF itself. BN 52021 did not affect metabolism of PAF by PMNL. These studies indicate that BN 52021 inhibits neutrophil responses to PAF by inhibiting binding of PAF to its specific PMNL receptor.     

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.     

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.     

Effects of a platelet activating factor antagonist (BN 52021) on free fatty acids, diacylglycerols, polyphosphoinositides and blood flow in the gerbil brain: inhibition of ischemia-reperfusion induced cerebral injury

The effects of a platelet activating factor antagonist (BN 52021) on cerebral ischemia-reperfusion was studied in the gerbil. Following ten minutes of bilateral carotid artery ligation, gerbils were reperfused and injected intraperitoneally with either BN 52021 or vehicle-dimethylsulfoxide. Cerebral blood flow and systemic arterial pressure were monitored until 90 minutes of reperfusion. Free fatty acids, diacylglycerols and polyphosphoinositides were then analyzed in forebrains and midbrains. BN 52021 inhibited the maturation of ischemic injury. Cerebral blood flow increased following 60 to 90 minutes of reperfusion. Free fatty acid levels were reduced likely by inhibition of phospholipase A. Phospholipase activity may likely be decreased since there was a tendency to increase phosphatidylinositol-4',5'-bisphosphate and diacylglycerols in BN 52021-treated animals.     

Inhibition of hippocampal LTP by ginkgolide B is mediated by its blocking action on PAF rather than glycine receptors

Platelet-activating factor (PAF), a biologically active lipid (1-O-alkyl-2-acetyl-sn-glycero-3-phosphoholine), is identified in different regions of brain, including hippocampus. Specific PAF-activated receptors (PAFRs) are expressed in corresponding brain areas. PAF has been proposed to be a retrograde messenger of long-term potentiation (LTP): the antagonist of PAFRs, ginkgolide B (or BN52021) prevents induction of LTP. Recently it has been found that ginkgolide B is also an efficient blocker of the glycine receptor (GlyR) operated chloride channels (IC(50)=270+/-10 nM in hippocampal pyramidal neurons). The question is as follows: is the alteration of LTP by BN52021 due to the PAF antagonism or to the inhibition of glycine-gated chloride channels? We have studied the effects of ginkgolides B and J on LTP induced in the CA1 area of rat hippocampus. Ginkgolide J which is the weakest blocker of PAFR (IC(50)=54 microM, as compared to IC(50)=2.5 microM for ginkgolide B) inhibits GlyR-operated channels with IC(50)=2.0 microM. This assures a convenient concentration window which allows to inhibit GlyR-operated channels without affecting PAFRs. An amount of 5 microM of ginkgolide J did not prevent the induction of LTP, while ginkgolide B (5 microM) completely inhibited this phenomenon. The effect of ginkgolide B on LTP did not alter considerably if GlyRs were blocked by strychnine (2 microM). Strychnine itself had no significant effect on the induction of LTP. Both ginkgolides and strychnine significantly facilitated short-term potentiation (STP). Our data support a hypothesis according to which ginkgolides affect LTP by inhibiting PAFRs.     

Ginkgo biloba attenuated hepatotoxicity induced by combined exposure to cadmium and fluoride via modulating the redox imbalance,Bax/Bcl-2 and NF-kB signaling pathways in male rats

Molecular Biology Reports - Aim of this study was to investigate the efficacy of Ginkgo Biloba (G.B) hydro-ethanolic extract against hepatotoxicity induced by combined exposure to cadmium (Cd) and...     

Involvement of monoamine oxidase inhibition in neuroprotective and neurorestorative effects of Ginkgo biloba extract against MPTP-induced nigrostriatal dopaminergic toxicity in C57 mice.

The present study investigated the neuroprotective and neurorestorative effects of Ginkgo biloba extract (EGb 761) and its two components ginkgolides A (BN52020) and B (BN52021) in mice. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (30 mg/kg/d i.p. for six days) significantly reduced striatal dopamine (DA) levels in C57 mice measured by high performance liquid chromatography with electrochemical detection (HPLC-EC). When C57 mice were pretreated with EGb 761 (20, 50, 100 mg/kg/d i.p.) for 7 days and then treated with the same extract 30 min before MPTP injection for 6 days, the neurotoxic effect of MPTP was antagonized in a dose-dependent fashion. Similar treatment with ginkgolides A and B (5, 10, 50 mg/kg/d i.p.) showed no protective effect. When C57 mice were treated with EGb 761 (50 mg/kg/d i.p.) after MPTP-lesion, the recovery of striatal dopamine (DA) levels was accelerated. However, similar treatment with ginkgolides A or B (10 mg/kg/d i.p.) did not show any effect. EGb 761, but not ginkgolides A and B, nonselectively inhibited mouse brain MAO activity in vitro (IC50 = 36.45 +/- 1.56 microg/ml) tested by an improved fluorimetric assay. The results demonstrate that EGb 761 administered before or after MPTP treatment effectively protects against MPTP-induced nigrostriatal dopaminergic neurotoxicity and that the inhibitory effect of EGb 761 on brain MAO may be involved in its neuroprotective effect.     

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.     

BN52021, a platelet activating factor antagonist, is a selective blocker of glycine-gated chloride channel

We have found that the platelet activating factor antagonist (BN52021) is an effective blocker of the glycine (Gly) receptor-mediated responses in the hippocampal pyramidal neurons of rat. Using the whole-cell voltage clamp and concentration clamp recording techniques, we investigated the mechanism underlying the inhibitory action of this terpenoid on the glycine-induced chloride current. BN52021 selectively and reversibly inhibits glycine current in a non-competitive and voltage-dependent fashion. The antagonistic effect of this substance is more pronounced at positive membrane potentials. At holding potential −70 mV and in the presence of 200 μM glycine IC₅₀ value for the blocking action of BN52021 was 270±10 nM. Repetitive applications of BN52021 reveal the use-dependence of its blocking action. When co-applied with strychnine (STR), a competitive glycine receptor antagonist, BN52021 does not alter the IC₅₀ value for strychnine. The inhibitory effect of BN52021 on gamma-aminobutyric acid (GABA) current is at least 25 times less potent than the effect on glycine current. This substance fails to affect AMPA and NMDA responses. It may be concluded that BN52021 inhibits glycine-gated Cl⁻ channels by interacting with the pore region and does not compete for the strychnine-binding centre.     

Inhibition of transmembrane movement and metabolism of platelet activating factor (PAF-acether) by a specific antagonist, BN 52021

Incorporation of 1-[3H]-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine ([3H] PAF-acether) into rabbit platelet phosphatidylcholine (PC) was inhibited by a specific antagonist, BN 52021 (IC50 5.6 X 10(-6) M, maximal effect, i.e 70% inhibition, at 10(-4) M). Under the same conditions, [3H] lyso-PAF-acether incorporation remained 9 fold lower, compared to PAF-acether, without any effect of BN 52021. Upon cell lysis, both phospholipids attained the same rate of metabolic conversion, corresponding to a 1.15-fold and a 12-fold increase for PAF-acether and lyso-PAF-acether, respectively. In none of these cases was BN 52021 effective. It is concluded that transmembrane movement of the two phospholipids represents the limiting step of their metabolism. The higher rate of PAF-acether conversion by intact platelets could involve its binding to a membrane receptor, as suggested by the inhibitory effect of BN 52021, the significance of which is discussed.     

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.     

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.     

Platelet-Activating Factor Antagonist BN52021 Decreases Accumulation of Free Polyunsaturated Fatty Acid in Mouse Brain During Ischemia and Electroconvulsive Shock

We have investigated the effects of the specific platelet-activating factor (PAF; 1-alkyl-2-acetyl-glycerophosphocholine) antagonist BN52021 on free fatty acid (FFA) and diacylglycerol (DG) accumulation and on the loss of fatty acids from phosphatidylinositol-4,5-bisphosphate (PIP2) in mouse brain. Mice were pretreated with BN52021 (10 mg/kg, i.p.) 30 min before electroconvulsive shock (ECS) or postdecapitation ischemia. These procedures cause rapid breakdown of PIP2 and accumulation of FFA and DG. Lipid extracts were prepared from microwave-fixed cerebrum and fractionated by TLC, and the fatty acid methyl esters were prepared by methanolysis and quantified by capillary GLC. In saline or vehicle (dimethyl sulfoxide)-treated mice, ECS caused marked accumulation of FFA and DG and loss of mainly stearic (18:0) and arachidonic (20:4) acids from PIP2. BN52021 pretreatment of ECS-treated mice decreased the accumulation of free palmitic (16:0), 18:0, 20:4, and docosahexaenoic (22:6) acids with no effect on the fatty acids in DG or the loss of PIP2. BN52021 had no effect on basal levels of FFA, DG, or PIP2. One minute of postdecapitation ischemia induced PIP2 loss and accumulation of FFA and DG. BN52021 attenuated the accumulation of free 20:4 and 22:6 acids, decreased the content of oleic (18:1), 20:4, and 22:6 acids in DG, but had no effect on PIP2 loss. These data indicate that BN52021 reduces the injury-induced activation of phospholipase A2 and lysophospholipase, which mediate the accumulation of FFA in brain, while having a negligible effect on phospholipase C-mediated degradation of PIP2.     

BN52021 stabilizes the oxidant-antioxidant equilibrium in peritoneal lavage fluid in experimental hemorrhagic shock

The overproduction of highly reactive oxygen metabolites initiates and contributes to the damage to abdominal organs in hemorrhagic shock (HS). Peritoneal environment including free cells located in peritoneal cavity may interact with the inflammatory processes occurring in abdominal organs during HS. Peritoneal lavage was carried out in 48 rats divided into following groups: (1) control, (2) untreated HS for 75 minutes, (3) HS + restoration of blood volume with polyelectrolyte solution (PES) 60 minutes after blood withdrawal, and (4) HS + platelet activating factor (PAF) receptor antagonist BN52021 directly after bleeding + PES after 60 minutes of HS. Peritoneal lavage fluid (PLF) was examined for Cu-, Zn-superoxide dismutase (SOD) activity, sulfhydryl compound (-SH) concentration, and malondialdehyde (MDA) level measured as thiobarbituric acid reactive substances (TBARS). The untreated shock (group 2) as well as HS + PES (group 3), resulted in significant increase in cell numbers in PLF. In groups 2 and 3, the SOD activities were not detected while -SH group levels were significantly higher, than those in the control. The group of shocked rats after blood volume restoration with PES was the only group where the MDA in PLF was found. The highest -SH group concentrations and detectable SOD activities were recorded in shocked rats treated with BN52021 and PES. Systemic hemorrhage may cause significant alterations in the oxidant-antioxidant (O-A) balance in peritoneal cavity, accompanied by significant elevation of number of cells lavaged from peritoneal cavity. There is an escalation of disturbances in O-A balance in peritoneal lavage fluid due to restoration of blood volume. BN52021 may exert beneficial effects stabilizing peritoneal antioxidant system in the hemorrhagic shock.     

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.