Occurrence of platelet‐activating factor (PAF) in normal rat stomach and alteration of PAF level by water immersion stress

We detected platelet‐activating substance in gastrointestinal areas, which was confirmed to be platelet‐activating factor (PAF) on the basis of the following findings: 1 ) it comigrated with authentic PAF on thin‐layer chromatography; 2 ) it did not aggregate PAF‐desensitized platelets; and 3 ) its activity was completely antagonized by the receptor antagonists CV3988 and L‐652,731. The level of PAF was determined with a bioassay method based on the release of [ 3 H] serotonin from washed rabbit platelets. In the normal rat stomach, the level of PAF was high in the antrum (940 ± 200 nmol PAF/mol phosphorus of original phospholipids), especially in the antral mucosa (1801 ± 426 nmol/mol phosphorus of original phospholipids). The stomach PAF level was significantly altered by water immersion stress. Stress for a period of 1 h was associated with a decrease in the antral PAF level to 39 ± 7% of that of untreated controls. This low PAF level persisted during stress. On the other hand, in the corpus, stress for periods of 1 and 3 h was associated with decreases in the PAF content, and further stress (7 h) resulted in restoration of the PAF level to normal. Furthermore, 7 h of stress was associated with distinct hemorrhagic lesions, which were prevented by CV3988 infused i.v. before the stress. This is the first report of an association between a decrease of the endogenous PAF level in animal tissues and tissue damage.—S ugatani , J.; F ujimura , K.; M iwa , M.; M izuno , T.; S ameshima , Y.; S aito , K. Occurrence of platelet‐activating factor (PAF) in normal rat stomach and alteration of PAF level by water immersion stress. FASEB J. 3: 65‐70; 1989.