1The mechanisms underlying oedema formation induced in a reversed passive Arthus (RPA) reaction and, for comparison, in response to zymosan in rabbit skin were investigated. 2 Oedema formation at skin sites was quantified by the accumulation of intravenously-injected '25I-labelled human serum albumin. 3 Recombinant soluble complement receptor type 1 (sCRI), administered locally in rabbit skin, suppressed oedema formation induced in the RPA reaction and by zymosan. 4 The platelet-activating factor (PAF) antagonists, WEB 2086 and PF10040 administered locally, inhibited oedema formation induced in the RPA reaction and by PAF but not by zymosan. 5 A locally administered leukotriene B4 (LTB4) antagonist, LY-255283, inhibited oedema formation induced by LTB4 but did not inhibit oedema responses to PAF, zymosan or the RPA reaction. 6 The results demonstrate a role for complement in oedema formation in both the RPA reaction and in response to zymosan. An important contribution by PAF is indicated in the RPA reaction but not in response to zymosan whereas no evidence was obtained to suggest a role for LTB4 in either inflammatory response.

1 The effect of a single intratracheal dose (10 mg) of phenoxymethyl] quinoline hydrochloride, a specific inhibitor of the 5-lipoxygenase pathway of arachidonic acid metabolism and a leukotriene D4 antagonist) on airway changes induced in response to Alternaria tenuis aerosol challenge was assessed in adult rabbits neonatally immunized. Leukotriene generation was determined in vivo by measuring leukotriene B4 (LTB4) levels in bronchoalveolar lavage (BAL) fluid and ex vivo by measuring calcium ionophore-stimulated production of LTB4 in whole blood. 2 While PF 5901 (10 mg) had no significant effect on the acute bronchoconstriction induced by antigen, this dose was sufficient to inhibit significantly the increase in airway responsiveness to inhaled histamine 24 h following antigen challenge (P<0.05). 3 Total leucocyte infiltration into the airways induced by antigen, as assessed by bronchoalveolar lavage, was significantly inhibited by pretreatment with PF 5901 (10 mg). However, the pulmonary infiltration of neutrophils and eosinophils induced by antigen was unaltered by prior treatment with PF 5901 (10 mg). 4 PF 5901 (1O mg) had no effect on ex vivo LTB4 synthesis in whole blood. However, the antigeninduced increase in LTB4 levels in BAL 24 h following challenge was significantly inhibited (P<0.05). 5 We suggest from the results of the present study that the antigen-induced airway hyperresponsiveness to inhaled histamine in immunized rabbits is mediated, at least in part, by products of the 5-lipoxygenase metabolic pathway, and is not dependent on the extent of eosinophil or neutrophil influx into the airway lumen.

1 Aerosol administration of platelet activating factor (PAF) (80pjgml' for 60min) to neonatally immunized rabbits caused bronchoconstriction which was far in excess of that produced by a comparable aerosol of bovine serum albumin (BSA) D4 antagonist, at a dose of 10 mg (direct intratracheal administration) significantly inhibited the airway resistance (RL) component of the bronchoconstriction induced by PAF in neonatallyimmunized rabbits. Doses of 10 mg, 3 mg and 1 mg PF 5901 (direct intratracheal administration) were sufficient to inhibit significantly the PAF-induced increase in airways responsiveness to inhaled histamine in immunized rabbits. PF 5901 however, failed to alter the pulmonary cell infiltration induced by PAF, as assessed by BAL. 5 We suggest from the results of the present study that PAF induces consistent and long-lasting increases in airways responsiveness to histamine in immunized rabbits, which is mediated, at least in part, by products of the 5-lipoxygenase metabolic pathway. Furthermore, the inability of PF5901 to inhibit the influx of inflammatory cells into the airway lumen following PAF challenge may suggest that bronchial hyperresponsiveness and cellular infiltration are not strictly associated events.

1 Peritoneal mast cells from rat were co-incubated in vitro in a platelet aggregometer cuvette with washed rabbit platelets. In response to stimulation with calcium ionophore (A23187; 1-5 ,UM), the mast cells released a substance which stimulated the platelets to aggregate. These concentrations of ionophore did not stimulate platelet aggregation in the absence of mast cells, nor affect the responsiveness of the platelets to aggregation induced by thrombin or PAF. Release of a PAF-like substance was also observed in response to stimulation of the mast cells with antigen. 2 This pro-aggregatory activity is attributable to the release of PAF by the mast cells, since the activity could be abolished by preincubating the platelets with a specific PAF receptor antagonist (WEB 2086; 10M). Furthermore, the platelet-aggregating factor co-migrated with PAF on thin-layer chromatographs and could be abolished by incubation with phospholipase A2 (20,ugml-1)

No abstract