Extracellular phospholipase A2 activity in two in vivo models of inflammation

Two "in vivo" models of inflammation have been used to investigate the role of phospholipases A2 (PLA2) in inflammation. These models are casein-induced peritonitis in the rat and zymosan-induced peritonitis in the mouse. The extracellular PLA2 activities from peritoneal lavage fluid in these two models are similar: they are calcium dependent and have broad neutral pH optima. However, the relationship between extracellular PLA2 activity and cell influx in these models are not identical. In zymosan peritonitis, PLA2 activity preceded peak cell influx, reaching a maximum within 15 min after zymosan injection, while cell influx peaked by 8 hr. In casein-induced peritonitis, the PLA2 activity peaked at 24 hr, while cell influx continued through 48 hr. The origins of the PLA2 activities in both models remain unclear; one potential source is the plasma. Understanding the role of extracellular PLA2 activity in "in vivo" models, and investigating specific inhibitors in these models may aid in our understanding of the role of extracellular PLA2 in diseases such as rheumatoid arthritis, endotoxin shock and pancreatitis.