Platelet-activating factor in the inflammatory exudate in the anaphylactic phase of allergic inflammation in rats

Using a model of allergic inflammation of air pouch type in rats, the platelet-activating factor (PAF) in the pouch fluid in the anaphylactic phase was analyzed. Anaphylactic reaction was induced by injecting an antigen (azobenzene-arsonate-conjugated acetyl bovine serum albumin) solution into a subcutaneous air pouch preformed on the dorsum of immunized rats. The pouch fluid was collected 30 min after the antigenic challenge, and chloroform extract was subjected to normal phase high-performance liquid chromatography to isolate two fractions, PAF and lyso-PAF. In the pouch fluid, however, there was little activity of PAF as examined by the aggregation of guinea pig platelets. The lyso-PAF fraction obtained was acetylated to PAF chemically with pyridine and acetic anhydride. This acetylated lyso-PAF fraction induced the aggregation of guinea pig platelets, which was inhibited dose-dependently by a PAF antagonist, CV-3988. The amount of lyso-PAF in the pouch fluid of the immunized group in the anaphylactic phase was significantly higher than that of the nonimmunized group. When (3H-)PAF was incubated with the supernatant fraction of the pouch fluid it was metabolized into lyso-PAF time-dependently. The significance of the higher level of lyso-PAF in the pouch fluid in the anaphylactic phase of allergic inflammation is discussed.