Hyperstimulation of the exocrine pancreas with cerulein causes acute pancreatitis, characterized by intensive interstitial edema, acinar vacuolization, leukocytic infiltration, and hyperamylasemia. Whereas the pathogenesis of cerulein-induced pancreatitis is not well-defined, a local inflammatory response may contribute to the full expression of acute pancreatitis. Platelet-activating factor (PAF) seems to be an important mediator of the inflammatory response. The present evidence includes: 1) pancreatic PAF levels increased in rats in which cerulein-induced pancreatitis was initiated, concomitant with an increase in calcium concentrations in the pancreatic tissue; 2) treatment of rats exposed to cerulein with WEB2170, a PAF receptor antagonist, was shown to reduce inflammatory injury, as demonstrated by decreases in pancreatic weight, Evan's blue extravasation, and myeloperoxidase activity and an improvement in pancreatic histology. In an idealized in vitro experiment mimicking cerulein-induced acute pancreatitis, in which pancreatic acini were employed, cerulein induced amylase release, an increase in [Ca2+]i, and an increase in PAF synthesis. Whereas amylase release was induced by low concentrations of cerulein (10(-11) mol/L), relatively high concentrations of cerulein (10(-9) mol/L) were required for the observed increases in PAF synthesis and the [Ca2+]i, indicating that these two responses may not occur under physiological conditions. The present study suggests that the pancreatic accumulation of PAF coupled with Ca2+ overload are important biochemical components of the pathophysiology of cerulein-induced acute pancreatitis. In fact, PAF production may serve as a primary mediator of inflammation observed during pancreatic hyperstimulation. This is an important observation that will allow a more detailed characterization of the molecular basis of cerulein-induced acute pancreatitis.