We have already demonstrated that arachidonic acid (AA) inhibits carrageenin-induced granuloma growth in vivo and that this effect is related to an increase in prostaglandin E2 formation. As prostaglandin E1 has been shown to be more effective in inhibiting granuloma growth than prostaglandin E2 we investigated the effect of linoleic acid (LA) (18:2 omega 6) and dihomo-gamma-linolenic acid (DHGLA) (20:3 omega 6), potential precursors of prostaglandin E1, in this model. LA and DHGLA inhibited the development of carrageenin-induced granulomas in the rat when injected locally. Both fatty acids (FA) stimulated the release of prostaglandin (PG) E1 from granuloma macrophages (M phi) in vitro, DHGLA being most effective. LA had little effect on the release of PGE2, 6 keto PGF1 alpha, the stable product of prostacyclin (PGI2) or thromboxane (Tx) B2, the stable metabolite of TxA2. DHGLA had no effect on the release of 6 keto PGF1 alpha, but inhibited PGE2 and, to a lesser extent, TxB2 synthesis.
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