Injection Of Platelet-activating Factor Research Articles

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.

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-1β and polyriboinositic/polyribocytidylic (poly I–C) acid, on IL-6 production by L 929 mouse fibroblasts. At concentrations above 1 μM PAF, the production of IL-6 by mouse fibroblasts was enhanced in a dose dependent fashion. At 5 μM PAF, the peak increase (60.1 ± 19.4 U/ml) was similar to that induced by 50 μg/ml poly I–C (60.0 ± 35.0 U/ml) and higher than the one evoked by 100 U/ml IL-1β (3.8 ± 1.8 U/ml). The increase of 11-6 activity induced by 5 μM PAF was maximal after a 22 h incubation period with L 929 cells. Lyso-PAF (5 μM) also increased IL-6 activity from fibroblasts to a similar extent compared with 5 μM PAF. In addition, the IL-6 activity induced by 5 μM PAF was still observed when the specific PAF antagonist, BN 52021 (10 μM), 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 μg/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 μg/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.

Renal vascular and sympathetic nerve responses to hypotension induced by platelet-activating factor in anesthetized dogs

This experiment was designed to determine renal sympathetic and renal vascular responses to platelet-activating factor (PAF)-induced hypotension in anesthetized dogs with and without systemic baroreceptor denervation. The left kidney was perfused at a constant flow, and renal perfusion pressure and efferent left renal sympathetic nerve activity were measured simultaneously. Intrarenal injection of PAF (1.25−5.0×10 −2 μg/kg, n = 6) produced a dose-dependent increase in renal perfusion pressure without any change in systemic blood pressure. An intravenous injection of PAF (10 μg/kg) to intact animals ( n = 7) caused an initial increase in renal nerve activity (157±14%) followed by a gradual reduction below baseline (72±7%) with concomitant systemic hypotension (from 116±7 to 46±6 mmHg). Renal perfusion pressure increased significantly from 84±2 to 161±33 mmHg concomitant with an increase in renal nerve activity at 1 min and was maintained at this elevated level throughout the experiment. Similar responses of renal nerve activity and renal perfusion pressure were found in animals with complete systemic baroreceptor denervation ( n = 7). These renal suggest that renal vascular response during PAF-induced hypotension may presumably be mediated by a direct vasoconstrictor effect of PAF on the renal vasculature and that baroreceptor reflex is not involved in either renal sympathetic or renal vascular changes.

Role of prostaglandins and nitric oxide in acute inflammatory reactions in guinea‐pig skin

1. Oedema formation in skin is dependent on a synergism between mediators that increase vascular permeability and mediators that enhance local blood flow. Leukocyte accumulation is also enhanced by mediators that increase local blood flow. In this study, we have investigated whether nitric oxide (NO), an important endogenous vasodilator, could modulate oedema formation and leukocyte accumulation in guinea-pig skin. 2. Local administration of the NO synthesis inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), dose-dependently inhibited the oedema formation induced in response to intrademal injection of bradykinin or histamine. L-NAME, but not NG-nitro-D-arginine methyl ester (D-NAME); also inhibited oedema formation in response to i.d. injection of platelet-activating factor (PAF), zymosan-activated plasma (ZAP) and in a passive cutaneous anaphylactic (PCA) reaction. 3. N-iminoethyl-L-ornithine (L-NIO) was less effective and about 100 times less potent than L-NAME in inhibiting bradykinin-induced oedema formation. The cyclo-oxygenase inhibitor, ibuprofen, had little effect on oedema responses induced by bradykinin, PAF and in a PCA reaction. On the other hand, histamine-induced oedema formation was significantly suppressed by ibuprofen. 4. The inhibition by L-NAME of bradykinin-induced oedema formation was reversed by co-injection of sodium nitroprusside (SNP) or prostaglandin E1 (PGE1). 5. L-NAME inhibited 111In-eosinophil and 111In-neutrophil accumulation induced by i.d. injection of ZAP. 111In-eosinophil accumulation induced by PAF and in the PCA reaction was also inhibited by L-NAME but not by D-NAME. 6. Co-injection of SNP or PGE1, reversed the inhibition by L-NAME of ZAP-induced oedema formation and 111In-neutrophil accumulation. SNP, but not PGE1, also reversed the effects of L-NAME on ZAP-induced 111In-eosinophil accumulation.7. L-NAME caused a significant decrease in basal cutaneous blood flow when injected alone or with bradykinin. Again, SNP or PGE, reversed the effects of L-NAME suggesting that the inhibitory action of L-NAME on oedema formation and cell accumulation was due to an inhibition of vasodilator tone in the microcirculation.8. Thus, it appears that in guinea-pig skin the inhibition of the production of endogenous NO inhibits both leukocyte accumulation and oedema formation induced by different mediators of inflammation.Since administration of L-NAME also causes a local decrease in basal blood flow, we suggest that this is the mechanism by which it exerts anti-inflammatory effects in this model.

In vivo responses of mouse blood cells to platelet-activating factor (PAF): Role of the mediators of anaphylaxis

Intravenous injection of platelet-activating factor (PAF) (0.36 mumol/kg b.w.) in mice induced severe hemoconcentration, leucopenia, thrombocytopenia and finally the death of 85% of the tested animals. Combined inhibition of histamine and serotonin by promethazine and chlorpromazine, 6.24 and 3.12 mg/kg b.w. subcutaneously, protected the mice from PAF in part, reducing the death rate to 43%. These drugs did not protect the mice against the PAF-induced hemoconcentration, leucopenia and thrombocytopenia. Sulfinpyrazone (100 mg/kg b.w.) intravenously was the most effective both in protecting mice from PAF-induced death, reducing the death rate to 17%, and from thrombocytopenia, although hemoconcentration persisted. These results indicated that an important component of the PAF-induced systemic effects is mediated by reactions which can be inhibited by sulfinpyrazone. Furthermore, PAF-induced thrombocytopenia is not a direct PAF effect since it can be inhibited by sulfinpyrazone.

Prostaglandin F2 alpha mediates platelet-activating factor-stimulated atrial natriuretic factor release from the isolated rat heart.

Platelet-activating factor (PAF) and the prostaglandins have recently been shown to stimulate atrial natriuretic factor (ANF) secretion from the heart. As PAF also potentiates the release of cyclooxygenase products from isolated hearts, the role of these substances in PAF-induced ANF secretion was investigated. Using an isolated perfused rat heart preparation, cyclooxygenase inhibition by indomethacin or meclofenamic acid (10 microM for each) significantly attenuated the rise in ANF associated with PAF administration (2.5 nmol). Prostaglandin F2 alpha (PGF) produced an immediate and dose-dependent increase in ANF secretion, which was significant at 0.01 mumol and reached 348 +/- 66% over baseline values after a 1-mumol injection. Prostaglandin E2 (PGE) generated a much smaller 98 +/- 25% increase after a 1-mumol administration. Furthermore, PGF but not PGE was released from isolated hearts immediately after PAF administration. PGF release reached a maximum of 0.06 nmol/min g Heart-1 1 min after PAF stimulation and had returned to undetectable baseline values by 6 min. Cyclooxygenase inhibition abolished the release of PGF after PAF, in addition to attenuating (by 60-70%) the increased secretion of ANF after PAF injection. These results demonstrate very clearly that PGF is the major mediator for PAF-stimulated ANF secretion. Such an interaction may provide an alternative mechanism to atrial distension for the secretion of ANF in pathologies such as myocardial infarction, where autacoids such as PAF and the PGs are released from damaged cardiac muscle and elevated plasma levels of ANF are observed.

Platelet-activating factor-induced ischemic bowel necrosis: the effect of platelet-activating factor acetylhydrolase.

In the present investigation, the rat model of necrotizing enterocolitis (NEC) was further developed by injection of platelet-activating factor (PAF) in the descending aorta. The role of the plasma PAF-acetylhydrolase (PAF-AH) was examined in the prevention of this disease. PAF (0.35 micrograms) caused ischemic intestinal necrosis when administered intraaortically. The effects of PAF injection on the small intestine were examined histologically in samples of the duodenum, jejunum, and ileum. The administration of PAF resulted in extensive hemorrhagic damage in all regions of the small bowel and a marked hemoconcentration. Pretreatment of the rats with dexamethasone or medroxyprogesterone significantly increased plasma PAF-AH activity. Dexamethasone and medroxyprogesterone prevented the gross and histologic features of NEC as well as the hemoconcentration. In contrast, lower amounts of PAF were sufficient to cause bowel necrosis and hemoconcentration when decreased activities of plasma PAF-AH were induced by 17 alpha-ethynylestradiol or 4-aminopyrazolopyrimidine administration. We have recently reported that PAF-AH is present in human milk. The beneficial effect of breast feeding in preventing the development of NEC in the newborn is discussed and a mechanism proposed to explain this finding. It is suggested that PAF may play an important role in the pathogenesis of NEC and that the increased plasma activity of PAF-AH caused by dexamethasone and the presence of this enzyme, of milk origin, in the lumen of the small bowel may prove to be beneficial in the prevention of this disease.

Intererence of the PAF receptor antagonist, PCA 4248, with the rat pleurisy evoked by inflammatory mediators or allergen

This study investigated the effect of the platelet-activating factor (PAF) receptor antagonist, PCA 4248, on the rat pleurisy caused by PAF, serotonin, bradykinin, histamine or allergen. The pleurisy was assessed by measuring liquid extravasation and eucocyte infiltration. Oral pretreatment with PCA 4248 (2.5–20 mg/kg) completely inhibited the pleural exudation caused by intrattoracic (i.t.) injection of PAF (1 μg/cavity) (ED 50 = 6.1 mg/kg), partially (42% reduction) the one induced by serotonin (100 μg/cavity), but was inactive against histamine (200 μg/cavity) or bradykinin (50 μg/cavity). PCA 4248 blocked the increase in the number of neutrophils, eosinophils and mononuclear cells observed 6 h after the i.t. injection of PAF, as well as the selective eosinophil accumulation noted 24 h later. In actively sensitized rats, PCA 4248 (20 mg/kg) failed to modify the increase in the total leucocyte counts noted 4 h after ovalbumin (12 μg/cavity), but dose dependently inhibited the pleural exudation observed within 1 h and the late eosinophil infiltration noted 24 h post-antigen. These observations led us to suggest that PCA 4248 is a potent PAF antagonist with anti-serotoninergic properties. Its interference with exudation and eosinophil infiltration caused by allergen is consistent with the interpretation that PCA 4248 may be useful in the management of allergic dysfunctions.

Role of PAF in the allergic pleurisy caused by ovalbumin in actively sensitized rats.

Selective platelet-activating factor (PAF) antagonists and autodesensitization to this lipid were used to investigate the role of PAF in antigen-induced pleurisy in the rat. Pleural inflammation was triggered by the intrathoracic (i.t.) injection of ovalbumin (12 micrograms/cavity) into animals actively sensitized 14 days before. Successive daily i.t. injections of PAF (1 microgram/cavity) led to selective autodesensitization, which was apparent after the third injection and maximal after the fifth. The PAF antagonists BN 52021 and WEB 2086 inhibited the late pleural eosinophil accumulation caused by antigen but, as also noted with WEB 2170, failed to modify the early antigen-induced plasma exudation and leukocyte infiltration. In contrast to the antagonists, desensitization to PAF was clearly effective against these early alterations. To further investigate this discrepancy, the antigenic challenge was performed 24 h after a single prestimulation with PAF, when sensitivity to the lipid was still intact. Under this condition, plasma exudation and cellular influx triggered by the antigen were also abrogated, indicating that this protective effect was accounted for by a mechanism other than refractoriness to PAF. Because 24 h after PAF injection only eosinophil counts remained elevated, an alternative eosinophilotactic substance was used to further study the mechanism of PAF versus antigen-induced pleural inflammation. Prior treatment with the peptide Ala-Gly-Ser-Glu (ECF-A, 20 micrograms/cavity) also inhibited the allergic pleurisy, whereas the noneosinophilotactic substances histamine (200 micrograms/cavity) and serotonin (100 micrograms/cavity) were inactive. Furthermore, drugs that share the ability to impair PAF-induced eosinophilia, including azelastine and cetirizine, prevented the inhibitory effect of PAF on the antigen-induced pleurisy. These findings suggest that PAF may account for the late eosinophilia, but not for the acute phase of the rat allergic pleurisy, which is clearly attenuated by PAF or ECF-A pretreatment.

Pulmonary vascular reactivity: effect of PAF and PAF antagonists.

We investigated the effects of two different platelet-activating factor (PAF) antagonists, SRI 63-441 and WEB 2086, on PAF-, angiotensin II-, and hypoxia-induced vasoconstrictions in isolated rat lungs perfused with a physiological salt solution. Bolus injection of PAF (0.5 micrograms) increased pulmonary arterial and microvascular pressures and caused lung edema. Both SRI 63-441, a PAF-analogue antagonist, and WEB 2086, a thienotriazolodiazepine structurally unrelated to PAF, completely blocked PAF-induced vasoconstriction and lung edema at 10(-5) M. At a lower concentration (10(-6) M), WEB 2086 was more effective than SRI 63-441. WEB 2086 also blocked the pulmonary vasodilation induced by low-dose PAF (15 ng) in blood-perfused lungs preconstricted with hypoxia. SRI 63-441 and CV 3988 (another PAF analogue antagonist), but not WEB 2086, caused acute pulmonary vasoconstriction at 10(-5) M and severe lung edema at a higher concentration (10(-4) M). PAF-induced but not SRI- or CV-induced pulmonary vasoconstriction and edema were inhibited by WEB 2086. In addition, SRI 63-441 potentiated angiotensin II- and hypoxia-induced vasoconstrictions. This effect of SRI 63-441 is not due to PAF receptor blockade because 1) addition of PAF (1.6 nM) to the perfusate likewise potentiated angiotensin II-induced vasoconstriction and 2) WEB 2086 did not cause a similar response. We conclude that both SRI 63-441 and WEB 2086 are effective inhibitors of PAF actions in the rat pulmonary circulation. However, antagonists with structures analogous to PAF (SRI 63-441 and CV 3988) can have significant pulmonary vasoactive side effects.

Platelet-activating factor causes hypoketonaemia in starved rats.

1. The aim of this work was to examine whether platelet-activating factor could mimic the hypoketonaemia seen in septic and endotoxic experimental animals. Platelet-activating factor was administered either by the intraperitoneal (high dose) or intravenous (jugular vein, low dose) routes. 2. Intraperitoneal injection of platelet-activating factor (25 micrograms/kg body weight) decreased the blood ketone body concentration (acetoacetate plus 3-hydroxybutyrate) transiently (30 min after injection) in starved rats. Continuous intravenous infusion of platelet-activating factor (40 ng min-1 kg-1 for 5 h) caused comparable hypoketonaemia. 3. The hepatic acetoacetate concentration also decreased transiently after injection of platelet-activating factor and there was an increase in the 3-hydroxybutyrate/acetoacetate ratio. The hepatic ATP concentration decreased at 15 and 30 min after injection of platelet-activating factor. Infusion of platelet-activating factor caused a similar decrease in hepatic ketone body concentration, but no significant change in the 3-hydroxybutyrate/acetoacetate ratio or adenine nucleotide concentrations. 4. Platelet-activating factor administered by infusion, but not by injection, decreased the plasma non-esterified fatty acid concentration. The plasma glycerol concentration also decreased after infusion of platelet-activating factor, suggesting decreased lipolysis in adipose tissue. 5. Changes in plasma insulin concentration or white adipose tissue blood flow did not appear to contribute to the decrease in the plasma non-esterified fatty acid concentration after infusion of platelet-activating factor. However, there was a significant decrease in blood flow to interscapular brown adipose tissue in both the infused and injected groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Prolonged pulmonary hypertension caused by platelet-activating factor and leukotriene C4 in the rat lung.

Platelet-activating factor (PAF) and leukotrienes (LTs) are potent pulmonary hypertensive and inflammatory mediators produced by the lung. Previously we showed that a rapid injection of PAF into the pulmonary artery of an isolated rat lung produced an extended elevation in mean pulmonary arterial pressure (PAP). The objective of the present study was to determine whether the extended pressor response induced by PAF was caused by prolonged activation of the 5-lipoxygenase pathway or slow clearance of LTs from the lung parenchyma. Rat lungs were perfused with a nonrecirculating physiological salt solution that contained indomethacin and albumin. Five minutes after a rapid injection of PAF into the pulmonary artery catheter, the following elevations (mean % above baseline) were observed: PAP (83%), LTB4 (3,260%), LTC4 (1,490%), LTD4 (970%), and LTE4 (1,500%). At 20 min these levels declined but were still significantly elevated above baseline. The 5-lipoxygenase inhibitor diethylcarbamazine (DEC), administered before the PAF injection, inhibited the elevations of PAP and all LTs. DEC administration that began 5 min after PAF reduced PAP and only LTC4 levels at 20 min in comparison to lungs with no DEC. The 5-lipoxygenase-activating protein inhibitor MK886, administered orally 2-6 h before perfusion, also inhibited the pressor response to PAF as well as LT production, as did DEC. We conclude that 1) the extended pulmonary hypertension induced by PAF was caused mainly by prolonged activation of 5-lipoxygenase with LTC4 production, 2) the relative overall lung clearance of LTB4, LTD4, and LTE4 was slower than that of LTC4, and 3) LTB4, LTD4, and LTE4 had no appreciable pressor effect.

Endothelin-1 inhibits PAF-induced paw oedema and pleurisy in the mouse.

1. The current study analyses the effects of endothelin-1 (ET-1) on paw oedema and pleurisy induced by platelet activating factor (PAF) and other inflammatory agents in the mouse. 2. Combined subplantar injection of ET-1 (0.5 pmol/paw) did not modify oedema caused by histamine (1 to 100 mumol/paw), 5-hydroxytryptamine (1 to 100 mumol/paw) or bradykinin (1 to 100 nmol/paw) but markedly inhibited the response to PAF (0.95 to 3.8 nmol/paw). The selective action of ET-1 against PAF-induced (1.9 nmol/paw) oedema was dose-dependent, reaching a maximum at 0.5 pmol/paw and lasted up to 2 h. 3. ET-1 (0.5 pmol/paw) also inhibited paw oedema (3-4 h) caused by zymosan (500 micrograms/paw). In contrast, it did not modify either the early (1-4 h) or late (48-72 h) phases of the oedematogenic response to carrageenin (300 micrograms/paw), when given either together with or 24 h after the carrageenin. 4. Intrathoracic injection of PAF (1.9 nmol/cavity) induced pleurisy characterized by an increase in pleural exudate volume, and in accumulation of Evans Blue which was maximal at 30 min and lasted up to 4 h. When injected together with PAF, ET-1 (0.5 pmol/cavity) virtually abolished PAF-induced pleurisy. 5. It is concluded that ET-1 is a potent inhibitor of PAF-induced inflammation in the mouse. Its mechanism of anti-inflammatory action in this species, in contrast to what has been found in other species, does not appear to derive from its potent vasoconstrictor properties as ET-1, at the doses used, failed to affect oedematogenic responses to other inflammatory mediators.

Analysis of pulmonary and systemic vascular responses to platelet-activating factor in the cat.

Pulmonary and systemic vascular responses to platelet-activating factor (PAF) were investigated in the anesthetized cat. Intravenous injections of PAF decreased arterial pressure, increased pulmonary arterial pressure, and caused small but significant decreases in right and left atrial pressures. A transient increase in cardiac output was followed by a secondary decrease, and heart rate was increased. Pulmonary vascular resistance (PVR) was increased, systemic vascular resistance (SVR) was reduced, and changes in PVR and SVR in response to PAF were blocked by the novel PAF receptor antagonist, BN 50730. Under constant-flow conditions PAF dilated the hindlimb vascular bed in a dose-related manner, whereas in the pulmonary lobar vascular bed, PAF caused dose-related increases in perfusion pressure. Hindlimb and lobar vascular responses to PAF were blocked by BN 50730 in a selective manner, whereas cyclooxygenase inhibitors had no effect on responses to the phospholipid mediator. Hindlimb vasodilator responses to PAF were reduced by N omega-nitro-L-arginine in a dose that blocked the response to acetylcholine but did not decrease responses to prostaglandin E1 or nitroprusside. Increases in lobar arterial pressure in response to PAF were not altered by treatment with a thromboxane receptor antagonist, when the lung was perfused with a low-molecular-weight dextran solution, or when ventilation to the lobe was interrupted. These data suggest that the release of cyclooxygenase products, activation of thromboxane A2 receptors, cellular aggregation, release of leukocyte or platelet mediators, or changes in bronchomotor tone do not contribute to the pulmonary vasoconstrictor response to PAF and that the hindlimb vasodilator response to the phospholipid mediator is dependent in part on the release of endothelium-derived relaxing factor.

Effect of human recombinant interleukin-5 on in vitro responsiveness to PAF of lung from actively sensitized guinea-pigs.

1. The intra-tracheal (i.t.) administration of human recombinant interleukin-5 (rhIL-5; 100 or 300 ng) to isolated perfused lungs from guinea-pigs actively sensitized to ovalbumin induced an increased bronchoconstriction and release of thromboxane A2 (TXA2) and histamine into the lung effluent following the subsequent (10 min) intra-arterial injection of platelet-activating factor (PAF). Lung responses to 5-hydroxytryptamine were unaffected by rhIL-5. 2. Hyperresponsiveness to PAF was observed when the lungs were obtained from guinea-pigs used 2 or 7 days after a booster injection of the antigen and, to a lower extent, when they were from animals sensitized by a single antigen administration. By contrast, rhIL-5 did not modify the responses to PAF of lungs from passively sensitized or from adjuvant-treated guinea-pigs, suggesting that immunological stimulation is required to allow the expression of synergism between rhIL-5 and PAF. 3. Guinea-pigs killed 2 and 7 days after the booster injection of the antigen exhibited a marked increase in the number of eosinophils in the bronchoalveolar lavage fluid (BAL), as compared to non-sensitized animals. 4. Our results demonstrate that rhIL-5 and PAF act synergistically to induce enhanced bronchoconstriction and mediator release exclusively when lungs are obtained from guinea-pigs sensitized once to ovalbumin and then boosted. Since recruitment of eosinophils into the airways and the development of hyperresponsiveness to PAF are concomitant, it is suggested that eosinophils are the target cells for interaction between rhIL-5 and PAF.

Inflammatory effects of platelet activating factor (PAF) in equine skin.

Intradermal administration of PAF (0.001-1 micrograms/site), but not lyso-PAF (10 micrograms/site), in the horse caused an increase in cutaneous vascular permeability which was maximal by 32 min. Responses to PAF and histamine were reduced by coadministration of the histamine 1 receptor antagonist chlorpheniramine, although only the inhibition of histamine-induced responses was dose-related and statistically significant. The cyclo-oxygenase inhibitor indomethacin was without effect on PAF-induced increases in vascular permeability. These findings suggest that the actions of PAF on equine skin microvasculature may be partly due to histamine release but not to prostanoid formation. Coadministration of prostaglandin (PG) E2 enhanced the oedematous responses to both PAF and histamine, although PGE2 failed to exert direct permeability-increasing activity. In addition, and in contrast to PAF and histamine, PGE2 increased cutaneous blood flow and skin surface temperature. PAF, but not lyso-PAF, also caused neutrophil infiltration into the skin which was maximal at 2 h. No significant effects on eosinophil or mononuclear cell numbers were apparent up to 24 h after injection of PAF. These results are consistent with the concept that PAF may be a mediator of inflammatory disorders of the skin in the horse.

Platelet-activating factor (PAF) plays an important role in the immediate asthmatic response in guinea-pig by augmenting the response to histamine.

1. To investigate the role of platelet activating factor (PAF) in the immediate asthmatic response, we examined the bronchial reactivity to histamine after administration of PAF to guinea-pigs or antigen challenge to passively sensitized guinea-pigs. 2. A bolus injection of PAF (20-40 ng kg-1), which did not cause a significant increase in intrathoracic pressure (ITP), augmented the bronchial response to histamine almost 8 fold. This airway hyperreactivity was observed even 1 min after PAF treatment. 3. A subthreshold dose of antigen (0.01 mg kg-1, i.v.) also provoked hyperreactivity to histamine, which became significant 6 and 11 min after the antigen treatment. 4. The specific PAF-antagonists, SM-10661 and CV-6209 (i.v.) dose-dependently inhibited both PAF- and antigen-induced airway hyperreactivities to histamine. 5. These results suggest that PAF plays an important role in antigen-induced acute airway responses by augmenting the activities of spasmogens.

Suppression of the Arthus reaction by Y-24180, a potent and specific antagonist of platelet-activating factor.

A novel and potent antagonist of platelet-activating factor (PAF), Y-24180 (4-(2-chlorophenyl)-2-[2-(4-isobutylphenyl)ethyl]-6,9-dimethyl-6H- thieno[3,2-f][1,2,4]triazolo[4,3-a][1,4] diazepine) was investigated for the effects on the skin reactions induced by chemical mediators and the Arthus reactions. In the rat dorsal skin, Y-24180 (0.1-10 mg/kg, p.o.) inhibited increase in vascular permeability by the intradermal PAF injection in a dose dependent manner and the inhibitory activity was 60 times more potent than that of WEB 2086. While even at doses as large as 10 mg/kg, p.o., it had no effect on vascular permeability in the rat skin induced by histamine, serotonin, bradykinin and leukotriene D4. On a reversed passive Arthus reaction in rat dorsal skin, Y-24180 (0.1-1 mg/kg, p.o.) markedly inhibited vascular permeability in a dose dependent manner and the inhibitory activity was 15 times more potent than that of WEB 2086. Y-24180 also inhibited the Arthus dermal reaction in rabbits (0.03-0.3 mg/kg, p.o.) and guinea pigs (0.1-1 mg/kg, p.o.). In addition, Y-24180 (0.1-10 mg/kg, p.o.) significantly reduced the exudate volume and the number of infiltrated inflammatory cells in the reversed passive Arthus pleural reaction in rats. Furthermore, in rat passive Arthus pancreatitis, Y-24180 (0.3-10 mg/kg, p.o.) significantly inhibited the dye extravasation from the pancreas. These results provide strong evidence that endogenous PAF plays an important role as a mediator in the type III allergic inflammation.

Nedocromil sodium prevents in vivo generation of the eosinophilotactic substance induced by PAF but fails to antagonize its effects.

1 The intrathoracic injection of platelet activating factor (PAF) into rats induced a decrease in the pleural leucocyte numbers within 15 min, accompanied by a marked exudation, maximal 1 h later. After 6 h, concomitantly with the reduction of exudation, a marked increase in the number of mononuclear cells, neutrophils and eosinophils was observed. Within 24 h, the pleural eosinophil accumulation peaked and persisted up to 96 h. 2 Topical treatment with nedocromil sodium affected pleural exudation by PAF under conditions where systemic meclizine was ineffective. Nedocromil sodium blocked, dose-dependently, the increase in the pleural content of mononuclear cells, neutrophils and eosinophils, observed 6 h after PAF administration, as well as the eosinophilia 24 h later. Moreover, the co-incubation of peritoneal eosinophils with nedocromil sodium did not interfere with the migration triggered by PAF. 3 The transfer of the 6 h-PAF pleural washings from donor to recipient rats caused a selective pleural eosinophilia, which was clearly inhibited when nedocromil sodium was administered to donor, but not to recipient animals, showing that this drug interferes with the generation rather than with the expression of the eosinophilotactic activity(ies). 4 These findings indicate that the nedocromil sodium interferes with PAF-induced exudation and leucocyte accumulation, by a mechanism other than its ability to reduce the local effects of histamine and which may relate to suppression of the eosinophilotactic principle generation.

Effects of antihistamines on cutaneous reactions and influx of eosinophils after local injection of PAF, kallikrein, compound 48/80 and histamine in patients with chronic urticaria and healthy subjects.

The effects of one week's daily treatment with dexchlorpheniramine (3 + 3 mg x 2) and loratadine (10 mg x 2) on the cutaneous reactions to putative mediators of urticarial reactions were studied in healthy subjects and in patients with chronic urticaria. Biopsy specimens were taken from skin with delayed reactions and studied immunohistochemically for the presence of eosinophilic cationic protein (ECP). In healthy subjects both antihistamines significantly decreased the weal and flare induced by histamine and the histamine releaser compound 48/80. They also reduced the flare seen after injection of PAF (platelet activating factor) and kallikrein. In patients with chronic urticaria the delayed reactions to PAF and kallikrein were larger than in healthy subjects. The immediate flare seen after injection of histamine, 48/80 and PAF, and the delayed reaction to 48/80, were significantly decreased by treatment with loratadine. No correlation was found between the clinical response and test reactions. In the group of healthy subjects, eosinophils were increased in the skin of all subjects after intradermal injection of 100 micrograms of PAF and in 50% after 1 microgram of PAF, but no eosinophils were seen after injection of 1 ng of PAF. In patients with chronic urticaria the eosinophils were increased at all sites where 1 ng of PAF had been injected and also at a limited number of sites of injection of histamine, 48/80, kallikrein and saline. Treatment with the antihistamines had no effect on the influx of eosinophils in the skin.