Cholecystokinin (CCK) has been suggested to be a contributory mediator in acute pancreatitis (AP). The aim of the present study was to assess the role of CCK in the development of oxidative stress at different stages of AP induced by pancreatic duct obstruction (PDO) in rats, using L364,718 (a potent CCK-receptor antagonist) to block CCK action. Intra-acinar oxygen free radical (OFR) generation was analysed by flow cytometry using dihydrorhodamine-123 as a fluorogenic dye. Parallel measurements of pancreatic levels of reduced glutathione (GSH) and of several parameters for the diagnosis of AP were performed in both untreated PDO rats and PDO rats receiving L364,718 (0.1 mg·12 h-1·kg-1). Diagnosis parameters indicated a greater severity of AP in rats treated with the CCK antagonist. The increase in OFR generation observed in acinar cells up to 12 h after inducing AP was triggered at an earlier stages and reached higher values when L364,718 was administered. Accordingly, greater pancreatic GSH depletion was observed in rats with AP treated with the CCK antagonist. Two populations of acinar cells that were differentiated by flow cytometry, R1 and R2, showed similar behaviour with regard to OFR generation in PDO rats; however, R1 cells showed greater sensitivity to L364,718 administration, and thus OFR production was increased in R1 cells earlier than in R2 cells. In conclusion, CCK blockade anticipates and enhances the amount of OFR produced in acinar cells as a consequence of AP, thus leading to earlier development of and more severe disease. The detrimental effect of L364,718 in AP induced by PDO suggests that plasma CCK does not play a major role in the development of this AP model.

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