1. Platelet-activating factor can be synthesized by two distinct biochemical pathways and is degraded by a number of enzymes, the first step of which is deacetylation by a specific acetyl hydrolase.

2. The biochemical pathway of platelet-activating factor synthesis de novo and the first step in platelet-activating factor degradation have been investigated for the first time in incubates of normal human colon mucosa and in inflamed mucosa from patients with inflammatory bowel disease.

3. In the presence of 100 μmol/l CDP-choline and 100 μmol/l hexadecyl acetyl glycerol, homogenates from inflamed mucosa synthesized significantly greater platelet-activating factor [851 ± 574 pmol/mg of protein (mean ± SEM) in 90 min incubation] than normal mucosa [105 ± 61 pmol/mg of protein in 90 min incubation] (P < 0.05).

4. Under the same conditions of assay, the percentage turnover to inactive lyso-platelet-activating factor was similar in inflamed mucosa (35.5 ± 9.4%) and normal mucosa (42.7 ± 8.5%) in 90 min (P > 0.05).

5. The identity of platelet-activating factor was confirmed by HPLC, by its mobility on TLC and by the ability of WEB 2170, a selective platelet-activating factor receptor antagonist, to block its platelet-aggregatory action.

6. These findings confirm the presence of the pathway for the synthesis de novo of the potently proinflammatory platelet-activating factor in human colon mucosa in inflammatory bowel disease.

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