Extracellular phospholipase A2 activity in peritoneal cavity of casein-treated rats.

An extracellular phospholipase A2 was detected in the peritoneal cavity of rats injected intraperitoneally with casein. This activity required Ca2+ ion and had a pH optimum of 9. The increase of phospholipase A2 activity in the peritoneal fluid as a function of time roughly paralleled the increase in the number of polymorphonuclear (PMN) leukocytes found in the peritoneal cavity. Phospholipase A2 activity was also observed in rat PMN homogenates, and its characteristics were similar to those of the enzyme found in cell-free peritoneal fluid fraction. PMN leukocytes may release non-lysozomal phospholipase A2 into the extracellular space as 'inflammation reactions' proceed.