Acute anti-inflammatory effects of aspirin and dexamethasone in rats deprived of endogenous prostaglandin precursors.

Paw oedema, induced by carrageenan, was potentiated in normal rats by arachidonic acid and bishomo-gamma-linoleic acid, but not by 5,8,11-eicosatrienoic acid. The latter is not an endogenous prostaglandin precursor, but replaces the other two in essential fatty acid deficient (EFAD) rats. Carrageenan oedema was partially suppressed in these EFAD rats. Aspirin exhibited equal suppression of carrageenan oedema in both normal and EFAD rats, despite the fact that, in the latter, prostaglandins are of negligible importance. The anti-inflammatory effect of dexamethasone was also identical in both normal and EFAD rats. The view that interference with the prostaglandin-system explains the acute anti-inflammatory effects of the two drugs, is discussed, in relation to the present results.