Peritoneal permeability to fluorescein-isothiocyanate-conjugated (FITC) dextran, mol wt 10,000 was studied in acute experimental pancreatitis (AEP) in rats. The aim of the study was to elucidate the role of the pancreatitis ascites and its phospholipase A2 activity on the observed peritoneal permeability increase during AEP. Phospholipase A2 activity of ascites was 40 U/microL 1 h after the induction of AEP and decreased during the next 3 h gradually to a plateau of about 20 U/microL, where it remained to the end of the experiment at 24 h. A similar pattern was seen for protein, amylase, and lipase although the initial peak was most pronounced for lipase. Pancreatitis ascites did not--irrespective of its age (1 or 20 h) or incubation time (3-20 h)--affect the peritoneal transport of FITC dextran 10,000 in healthy rats. Similarly, intravenously-administered ascites and intraperitoneal instillation of pancreatic phospholipase A2 dissolved in saline were without effects. On the other hand, in another group of healthy animals, phospholipase dissolved in fresh pancreatitis ascites caused a statistically significant increase of peritoneal transport, as defined. In rats with pancreatitis, the addition of phospholipase A2 to the peritoneal fluid increased peritoneal transport of FITC dextran 10,000 as well as phospholipase A2 itself. We conclude that phospholipase A2 when instilled into the peritoneal cavity in the presence of pancreatitis ascites, has the ability to increase peritoneal permeability to FITC dextran 10,000 in healthy, as well as in pancreatitis rats. However, the phospholipase A2 activity of rat pancreatitis ascites is not sufficient for this mechanism to work. This, however, does not exclude its existence in other species, including humans.