Pancreatic lysosomal enzyme secretion via gut-hormone-regulated pathway in rats

To explore the secretory profiles of lysosomal enzyme in pancreatic juice, we stimulated the secretion of lysosomal enzyme by intravenous pancreatic secretagogues and intraduodenal instillation of liquid meals in rats. Lysosomal hydrolases, such as cathepsin B, are secreted from the apices of pancreatic acinar cells via a hormone-regulated pathway, as in the secretion of pancreatic digestive enzymes. The intravenous infusion of the cholecystokinin analogue caerulein, or the intraduodenal administration of nutrients results in a closely related secretion of both amylase and cathepsin B from the apices of acinar cells, suggesting that they are discharged from the same presecretory compartment (zymogen granules). Lysosomal enzymes appear to enter into the secretory compartment as a result of malsorting, but the cause of this anomaly is not known. We found small amounts of lysosomal enzymes colocalized with digestive enzymes within zymogen granules in normal acinar cells and in normal pancreatic juice, suggesting some physiological roles of lysosomal enzymes in pancreatic ducts. Furthermore, lysosomal enzymes appear to play important roles in the pathogenesis of pancreatic disease, such as pancreatitis, from both inside and outside the pancreas, since cathepsin B can probably activate trypsinogen.