Platelet activating factor in surfactant-TA is inhibited by coexisting inhibitors.

To clarify whether or not the platelet activating factor (PAF) present in surfactant-TA (calf-lung extract) is harmful, we investigated the activity and inhibitory activity of PAF in a surfactant preparation using a bioassay with washed rabbit platelets. The surfactant-TA contained PAF at 11-21 pmol/vial. The fractions of lysophosphatidylcholine, sphingomyelin, phosphatidylserine plus phosphatidylinositol, and phosphatidylglycerol dose-dependently inhibited the aggregation of washed rabbit platelets induced by PAF. Surfactant-TA contained sufficient amounts of these phospholipids to inhibit the PAF activity completely. These results suggest that coexisting PAF inhibitors protect the lung from the harmful effects of PAF in surfactant-TA.