THE ROLE OF PLATELET ACTIVATING FACTOR (PAF) BRONCHIAL IN AIRWAY HYPERRESPONSIVENESS

PAF is a biologically active lipid mediator of inflamation when given by inhalation it causes bronchoconstriction, airway epithelial damage and increases vascular permeability. PAF also activates eosinophils to release the major basic protein and eosinophils cationic protein (ECP). Inhaled PAF has been reported to increase airway responsiveness to methacholine in normal subjects over several weeks. We have examined the effect of inhaled PAF (96ug) on bronchial responsiveness to methacholine at day 1, 3 and 7 after PAF challenge in 6 non-atopic and 7 atopic healthy volunteers. PAF challenge and methacholine responsiveness was repeated on 2 more occasions allowing at least 4 weeks between cycles. The maximum mean (sent) % falls in SGaw in the 1st , 2nd and 3rd PAF challenge in non-atopic subjects were 47.3 (8.7), 49.5 (9.3) and 47.2 (8.2) Respectively, and in atopic subjects 41.7 (6.2), 48.0 (6.1) and 49.3 (6.3) respectively.The changes in SGaw were comparable in 3 cycles in both groups. The geometric mean PC SGaw was 9.2/mg/ml in non-atopic subjects and 1.16mg/ml in atopic subjects before PAF inhalation. However PAF did not alter the mean PC SGaw in both groups. Our results suggests that PAF is a potent bronchoconstrictor but does not induce airways hyper responsiveness in non atopic and atopic subjects.