PRESENCE OF IMMUNOREACTIVE PLATELET-ACTIVATING-FACTOR IN PERITONEAL-EXUDATE INDUCED BY ZYMOSAN IN RATS

The presence of the platelet-activating factor (PAF) in peritoneal exu date, induced by zymosan, was investigated in rats. Intraperitoneal in jection of zymosan induced an extravasation of plasma proteins and an accumulation of polymorphonuclear leukocytes in the peritoneal cavity. Zymosan induced a release of immunoreactive PAF in peritoneal exudate which reached maximum levels at 30 min and then declined slowly. Immu noreactive PAF was evenly distributed in the fluid and cellular fracti ons of the exudate. A PAF-acetyltransferase activity was found as well in the exudate as in plasma. Histamine levels, measured by bioassay, increased after injection of zymosan, reached a peak at 15 min and dec lined to a normal level within 4 hr. Protein extravasation was inhibit ed by WEB 2086, a PAF antagonist, during the 6 hours of the study, whe reas the accumulation of leukocytes was suppressed at 2 hour by WEB 20 86 and SM 12502, two PAF antagonists. PAF is present in the peritoneal exudate induced by zymosan in rats, and plays a role in the developme nt of the inflammatory response. Its main origin might be resident mac rophages and polymorphonuclear leukocytes.