Actions of PAF receptor antagonists in horses with the allergic skin disease sweet itch.

Platelet activating factor (PAF) mimics the effects of Culicoides antigen by inducing oedema and inflammatory cell accumulation in the dermis of horses with the allergic skin disease, sweet itch. PAF could therefore contribute to antigen-induced inflammatory changes in these horses. We now report that intravenous administration of the PAF receptor antagonist WEB 2086 (3 mg kg-1), at a dose that inhibited the vascular and cellular responses to PAF in sweet itch horses, reduced Culicoides antigen-induced oedema at 1 h by 73% and at 8 h by 71% (p < 0.05). Neutrophil accumulation and eosinophil recruitment were not significantly reduced by WEB 2086 or a second hetrazepine PAF receptor antagonist WEB 2170 (0.1 mg kg-1). These findings suggest a key role for PAF in oedema formation, but not inflammatory cell accumulation, induced by Culicoides antigen in the skin of sweet itch horses.