Background & aims: Pancreatitis-associated protein (PAP), which is overexpressed in pancreatic acinar cells, appears in pancreatic juice and serum after acute pancreatitis. The aim of this study was to examine intracellular localization of PAP and amylase in healthy rat pancreas and pancreatitis pancreas to ascertain PAP transport from the rough endoplasmic reticulum to the zymogen granules into the acinar lumen.
Methods: Control rats and rats with taurocholate-induced pancreatitis were killed after 24 hours. Pancreata prepared for light and electron microscopy were used for amylase and PAP detection with specific antibodies.
Results: Induced acute pancreatitis disturbed the gross histology and ultrastructure of the acinar cells with the formation of new intracellular fibrous material into the cytoplasm, which was also found into the acinar lumen. PAP is almost absent from normal acinar cells; after acute pancreatitis, it appears in rough endoplasmic reticulum, it is strongly present in normal and abnormal zymogen granules, and it remains an important component of the fibrous material. Except for its exclusive presence in fibrous material, PAP is always colocalized with amylase in the other cell compartments.
Conclusions: These observations show that the accumulated PAP into the acinar cells in response to acute pancreatitis behaves like all the other secretory proteins with the exception that it also accumulates in a new fibrillous cellular structure also found in the acinar lumen.