The inhibition of adenylate cyclase in equine platelets by collagen and by platelet-activating factor

Equine platelet aggregation was stimulated by collagen fibres or platelet-activating factor. The action of both ligands was blocked by forskolin or prostaglandin E₁ agents which are known to activate adenylate cyclase. Equine platelet membranes were found to contain adenylate cyclase activity which was inhibited in dose-dependent fashion by both collagen and platelet-activating factor. Platelet-activating factor-induced inhibition was antagonised by WEB2086.