Arachidonic acid, an in vivo inhibitor of carrageenin induced granulomas in the rat.

Arachidonic acid (AA) injected locally into carrageenin/sponge granulomas, but not if given orally, inhibited granuloma growth. Granuloma macrophage (M0) infiltration was inhibited, and prostaglandin E2 (PGE2) synthesis (ng/100 mg granuloma dry weight) stimulated, by AA treatment. M0 adenosine 3',5'-cyclic monophosphate (cAMP) levels and granuloma exudate volume were not affected. Granuloma M0s incubated in vitro with arachidonic acid synthesised thromboxane B2 (Txb2), 6-ketoprostaglandin F1 alpha (6-ketoPGF1 alpha), and preferentially, PGE2. The AA inhibition of granuloma growth was possibly mediated via the synthesis of PGE2.