Production of platelet-activating factor in inflammatory exudate.

Platelet-activating factor (PAF) demonstrated a considerable increase in vascular permeability in the skin of several experimental animals, suggesting its role in inflammatory exudation. To verify the role of PAF in exudation, we also examined the effect of PAF antagonists on the exudation of rat pleurisy, and found that PAF antagonists significantly inhibited exudation induced by PAF, phorbol ester and zymosan. Furthermore we observed PAF activity in the exudate of these types of pleurisy. 50% of the PAF activity found in the exudate was of the released form and might be the cause of the increase in vascular permeability. In an in vitro study, synthesized PAF was mostly retained in the cells and less was released, suggesting that it might constitute a transient reservoir or resultant scavengers for lysophospholipids.