Aspirin, salicylate and prostaglandins.

The effects of aspirin, salicylic acid and gentisic acid on the paw swellings in the arachidonic acid-potentiated and in the conventional carrageenan-induced oedema tests as well as on the content of prostaglandin-like activity and leucocyte migration in the exudate of inert implanted sponges in the rat have been studied. It is concluded that aspirin exerts two separate inhibitory effects on prostaglandin formation in vivo, a rapid action of the intact molecule on easily accessible tissues and a later action due to its metabolic conversion to salicylic acid. Salicylic acid inhibits prostaglandin biosynthesis in vivo as the salicylate ion itself and there is no formation of a subsequent 'active' metabolite.