Products derived from arachidonic acid (AA) via both the cyclo-oxygenase and lipoxygenase pathways play a role in inflammation: prostaglandins (PGs), particularly PGE2, contribute to the formation of oedema, erythema and hyperalgesia whereas leukotriene B4 (LTB4), a product of the 5' lipoxygenase, may modulate the recruitment of leukocytes.

We have previously reported that supplementation of a standard rat diet with eicosapentaenoic acid (EPA) caused a significant increase in the formation of LTB5, which is less active biologically than LTB4, and a decrease in the synthesis of LTB4 by stimulated leukocytes. Now we have assessed the effects of administration of highly purified EPA ethyl ester (79% pure), in two models of acute inflammation.

Supplementation of a standard rat diet with 240 mg/kg/day EPA for 4 weeks significantly decreased the concentration of PGE2 and TXB2 in inflammatory exudate derived from implantation of carrageenin impregnated sponges: neither the concentration of LTB4 nor the cell number were reduced significantly. Triene prostaglandins were not detected in the exudate, however, significant levels of LTB5 were present.

In the second model, oedema induced by injection of carrageenin into rat paws was significantly reduced in animals fed an EPA-rich diet. Supplementation of the diet with EPA could, by mainly reducing the synthesis of prostaglandins, offer a novel and non-toxic approach to the modulation of an inflammatory response.