ACTIONS OF PAF RECEPTOR ANTAGONISTS IN HORSES WITH THE ALLERGIC SKIN-DISEASE SWEET ITCH

Platelet activating factor (PAF) mimics the effects of Culicoides anti gen by inducing oedema and inflammatory cell accumulation in the dermi s of horses with the allergic skin disease, sweet itch. PAF could ther efore contribute to antigen-induced inflammatory changes in these hors es. We now report that intravenous administration of the PAF receptor antagonist WEB 2086 (3 mg kg(-1)), at a dose that inhibited the vascul ar and cellular responses to PAF in sweet itch horses, reduced Culicoi des antigen-induced oedema at 1 h by 73% and at 8 h by 71% (p < 0.05). Neutrophil accumulation and eosinophil recruitment were not significa ntly reduced by WEB 2086 or a second hetrazepine PAF antagonist WEB 21 70 (0.1 mg kg(-1)). These suggest a key role for PAF in oedema formati on, but not inflammatory cell accumulation, induced by Culicoides anti gen in the skin of sweet itch horses.