1. Colonic mucosa from 19 patients with ulcerative colitis, eight with Crohn's disease and 14 controls were analysed for arachidonic acid (C20:4), linoleic acid (C18:2), oleic acid (C18:1), stearic acid (C18:0) and palmitic acid (C16:0).
2. Gas–liquid chromatography of lipid extracts showed that arachidonic acid was significantly higher in ulcerative colitis (19 ± 4) and Crohn's disease (20 ± 3) than in controls (13 ± 5 μg/mg of protein) (means ± sd). Neither the degree of inflammation nor treatment with sulphasalazine or prednisolone appeared to influence the fatty acid concentrations.
3. Seventy-five to ninety-five per cent of the arachidonic acid was found in the phospholipid fraction after separation by thin-layer chromatography. There were no significant changes in the concentrations of the other fatty acids measured, although oleic acid was lower in inflammatory bowel disease. The ratios of oleic acid to stearic acid and to palmitic acid were lower in inflammatory bowel disease.
4. The alteration in the fatty acid profile may partly explain the increased synthesis of eicosanoids in colonic mucosa in inflammatory bowel disease.