Localized necrohemorrhagic pancreatitis in the rat after pancreatic interstitial trypsin injection. Regressive pseudochronic lesions.

Different materials dissolved in 0.9% NaCl were injected into the connective, interlobular tissue of the duodenal part of the rat pancreas. Activated rat pancreatic juice or trypsin were able to induce localized necrohemorrhagic pancreatitis. Only mild edema and leukocytic infiltration were observed after injecting bovine albumin, chinese ink, trypsinogen or nonactivated pancreatic juice. The progression of histological changes was followed for 2 weeks in the trypsin-induced pancreatitis. Limited foci of severe hemorrhage, liquefaction and coagulative necrosis were observed in the first 24 h. Acinar cell degeneration and regeneration were observed 48 h after the operation, fibroblasts appearing in the interlobular spaces. Four days after injection, inter- and intralobular fibrosis, acinar cell degeneration and tubular complexes were observed, presenting a picture characteristic of chronic pancreatitis. Some minimal changes were still seen in the pancreas 1 week after injection, but by the end of the 2nd week the pancreatic histology was normal. These results demonstrate the significance of active trypsin in the pancreatic interstitium with respect to the induction of pancreatitis. This model of localized necrohemorrhagic pancreatitis is highly reproducible and without significant mortality. Following the acute process, histological changes resembling chronic pancreatitis can be observed, but they are completely reversible.