Modulation of prostaglandin synthesis in rat peritoneal macrophages with omega-3 fatty acids

In view of the findings that omega 3 fatty acids inhibit the synthesis of prostaglandins (PG) from arachidonic acid (20:4 omega 6) and that among immunologically active cells, the macrophage is a major producer of PG, we undertook a study of the effect of dietary alpha-linolenic acid (18:3 omega 3) on PG synthesis in the macrophage. Rats were fed purified diets containing either 10% corn oil (CO) or linseed oil (LO), providing either a low (1/32) or high (3.5/1) ratio of 18:3 omega 3 to 18:2 omega 6, respectively, for 6 weeks. Fatty acid analysis of macrophage phospholipids showed that there was an appreciable increase in the percentage of omega 3 fatty acids and a decrease in the omega 6 fatty acids in macrophages from rats fed the LO diet. The changes in fatty acid composition were associated with a significant decrease in the synthesis of prostaglandin E (PGE) by macrophages from rats fed the LO diet. Macrophages from rats fed the 2 dietary oils did not differ in their ability to degrade PG, thus the difference in PG production appeared to be a consequence of decreased synthesis only. The dietarily induced changes in PGE synthesis were readily overcome in vitro by culturing macrophages with complexes of fat-free bovine serum albumin and either 20:4 omega 6 or 20:5 omega 3.