PLATELET-ACTIVATING-FACTOR - AN INFLAMMATORY MEDIATOR IN THE ACUTE-PHASE OF ALLERGIC CONJUNCTIVITIS IN A GUINEA-PIG MODEL

THE role of platelet-activating factor (PAF) as a mediator of increase d conjunctival vascular permeability was investigated in a guinea-pig model of immediate hypersensitivity. Vascular permeability of the conj unctiva was determined by measuring the albumin content in lavage flui d (LF) after topical challenge with either PAF or ovalbumin. PAF produ ced a dose-dependent increase of the vascular permeability within minu tes. Topical pretreatment with levocabastine, a potent histamine H-1-a ntagonist demonstrated no effect towards the vascular permeability in response to PAF provocation. Pretreatment with eyedrops containing the specific PAF antagonist BN 52021 (1%) showed a significant inhibition of the vascular permeability (60.2%) and the clinical score (27.5%) a fter PAF challenge. In sensitized guinea-pigs, levocabastine showed a marked inhibition of both the vascular permeability (80.5%) and the cl inical score (70%) after topical challenge with ovalbumin. BN 52021, a lthough to a lesser extent, showed a similar effect towards the vascul ar permeability (26.8%) and the clinical score (28%) after antigen pro vocation. When BN 52021 and levocabastine were administered in combina tion, the vascular permeability was significantly decreased after anti gen challenge in comparison with eyes pretreated with levocabastine al one. These results indicate that PAF plays a role in the acute phase o f allergic conjunctivitis in the guinea-pig.