Manju Saluja

Pancreatic duct obstruction triggers acute necrotizing pancreatitis in the opossum

BACKGROUND The common channel theory suggests that bile reflux, through a common biliopancreatic channel, triggers acute pancreatitis. In the present study, this controversial issue was evaluated using an experimental model of hemorrhagic necrotizing pancreatitis. METHODS American opossums underwent ligation of the pancreatic duct alone, bile and pancreatic duct separately, or common biliopancreatic duct; the severity of pancreatitis was evaluated at selected times after ligation. RESULTS Animals in all three experimental groups developed hemorrhagic necrotizing pancreatitis; the severity of pancreatitis was similar in each group, although only those subjected to common biliopancreatic duct ligation experienced bile reflux. CONCLUSIONS Bile reflux into the pancreatic duct, via a common biliopancreatic channel, is not necessary for the development of pancreatitis and does not worsen the severity of pancreatitis associated with pancreatic duct obstruction in this model.

Pancreatic duct obstruction in rabbits causes digestive zymogen and lysosomal enzyme colocalization.

The pancreatic duct of anesthetized rabbits was cannulated and, in some animals, flow of pancreatic exocrine secretions was blocked by raising the cannula to a vertical position. Blockage for 3-7 h caused a rapid and significant rise in serum amylase activity and an increase in amylase activity within the pancreas. The concentration of lysosomal enzymes in the pancreas was not altered but they became redistributed among subcellular fractions and, as a result, an increased amount was recovered in the 1,000-g, 15-min pellet, which was enriched in zymogen granules. Immunofluorescence studies indicated that lysosomal enzymes become localized within organelles which, in size and distribution, resemble zymogen granules. They also contain digestive enzyme zymogens. Blockage of pancreatic secretions also caused lysosomal enzyme-containing organelles to become more fragile and subject to in vitro rupture. These changes noted after short-term pancreatic duct obstruction are remarkably similar to those previously noted to occur during the early stages of diet and secretagogue-induced experimental pancreatitis, observations that have suggested that colocalization of digestive enzyme zymogens and lysosomal hydrolases might result in intracellular digestive enzyme activation and be an important early event in the evolution of those forms of experimental acute pancreatitis.

Acute necrotizing pancreatitis in the opossum : earliest morphological changes involve acinar cells

Acute pancreatitis was induced by ligating the opossum common biliopancreatic duct immediately proximal to its entry into the duodenum, and macroscopic as well as microscopic changes were evaluated during the subsequent 24 hours. Transient pancreatic edema and progressive hyperamylasemia were noted within 6 hours of pancreatic and bile duct ligation. Light microscopic evidence of pancreatic injury including acinar cell necrosis, hemorrhage, fat necrosis, and inflammatory cell infiltration was noted within 12 hours of duct obstruction. Electron microscopic changes included massive dilatation of the rough endoplasmic reticulum and disruption of the apical plasmalemma of acinar cells during the initial 3 hours. These observations indicate that pancreatic and bile duct ligation in the opossum results in the rapid (less than 24 hours) appearance of changes consistent with acute hemorrhagic and necrotizing pancreatitis and that the initial lesion in this model of experimental pancreatitis involves acinar cells.

The effect of chloroquine administration on two experimental models of acute pancreatitis

BACKGROUND Recent experimental findings have suggested that activation of trypsinogen by cathepsin B within acidic pancreatic acinar cell cytoplasmic vacuoles may be a critical early event in both secretagogue and diet-induced pancreatitis. The weak base chloroquine accumulates within acidic intracellular compartments, raises their pH, and can inhibit proteolysis as well as cathepsin B. METHODS We have investigated the effect of in vivo chloroquine administration on both secretagogue and diet-induced experimental pancreatitis to determine if raising the pH of cytoplasmic vacuoles in these models of pancreatitis would have a protective effect. RESULTS Infusion of chloroquine (5 mg.kg-1.h-1) resulted in the uptake and concentration of chloroquine in the pancreas, an increase in the pH of acinar cell acidic compartments, and interference with the pH-dependent sorting of lysosomal hydrolases from digestive enzyme zymogens. However, chloroquine administration did not have a protective effect against the hyperamylasemia, the pancreatic edema, the morphological changes or the mortality that is associated with these models of pancreatitis. CONCLUSIONS These observations lead us to conclude that raising the pH of acinar cell acidic compartments by in vivo administration of chloroquine does not prevent either secretagogue or diet-induced pancreatitis.

Apical secretion of lysosomal enzymes in rabbit pancreas occurs via a secretagogue regulated pathway and is increased after pancreatic duct obstruction.

Lysosomal hydrolases such as cathepsin B are apically secreted from rabbit pancreatic acinar cells via a regulated as opposed to a constitutive pathway. Intravenous infusion of the cholecystokinin analogue caerulein results in highly correlated apical secretion of digestive and lysosomal enzymes, suggesting that they are discharged from the same presecretory compartment (zymogen granules). Lysosomal enzymes appear to enter that compartment as a result of missorting. After 7 h of duct obstruction is relieved, caerulein-stimulated apical secretion of cathepsin B and amylase is increased, but the ratio of cathepsin B to amylase secretion is not different than that following caerulein stimulation of animals never obstructed. These findings indicate that duct obstruction causes an increased amount of both lysosomal and digestive enzymes to accumulate within the secretagogue releasable compartment but that duct obstruction does not increase the degree of lysosomal enzyme missorting into that compartment. Pancreatic duct obstruction causes lysosomal hydrolases to become colocalized with digestive enzymes in organelles that, in size and distribution, resemble zymogen granules but that are not subject to secretion in response to secretagogue stimulation. These organelles may be of importance in the development of pancreatitis.

Intravenous contrast medium does not increase the severity of acute necrotizing pancreatitis in the opossum

Contrast-enhanced computed tomography provides diagnostic and prognostic information in patients with acute pancreatitis. To evaluate whether contrast medium may worsen the severity of acute pancreatitis, we have used a model of necrotizing pancreatitis induced by ligating the common bile-pancreatic duct in opossums. Animals were infused with either saline or an ionic contrast agent 48 and 96 hr after induction of pancreatitis. Hyperamylasemia, pancreatic edema, acinar cell fragility, and macroscopic evidence of pancreatitis were comparable in both experimental groups. The microscopic extent of inflammation was similar in both groups, whereas acinar cell injury/necrosis was less in the contrast group. We conclude that administration of this ionic contrast agent during early stages of necrotizing pancreatitis in the opossum does not worsen the disease severity. The concept that administration of contrast medium during early stages of pancreatitis is dangerous should not be accepted until additional experimental and clinical studies support its validity.

The role of oxygen-derived free radicals in two models of experimental acute pancreatitis: Effects of catalase, superoxide dismutase, dimethylsulfoxide, and allopurinol

SummaryThe role of oxygen-derived free radicals was evaluated in two models of experimental acute pancreatitis by testing the effects of agents which either reduce oxygen-derived free radical generation or scavenge those free radicals. Those agents (catalase, superoxide dismutase, polyethylene glycol-superoxide dismutase, dimethylsulfoxide, and allopurinol) were evaluated using the choline-deficient ethionine-supplemented diet-induced model of acute hemorrhagic pancreatic necrosis and the supramaximal caerulein stimulation model of acute interstitial edematous pancreatitis. In both models, the only effect associated with administration of the test agents was a reduction in the degree of pancreatic edema. These results suggest that oxygen-derived free radicals may play an important role in the development of pancreatic edema during pancreatitis but that those free radicals do not play an important role in the development of acinar cell injury.

A plasma protease which is expressed during supramaximal stimulation causes in vitro subcellular redistribution of lysosomal enzymes in rat exocrine pancreas.

The complex events by which digestive enzyme zymogens and lysosomal hydrolases are segregated from each other and differentially transported to their respective membrane-bound intracellular organelles in the pancreas have been noted to be disturbed during the early stages of several models of experimental pancreatitis. As a result, lysosomal hydrolases such as cathepsin B are redistributed to the subcellular zymogen granule-rich fraction and lysosomal hydrolases as well as digestive enzyme zymogens are colocalized within large cytoplasmic vacuoles. The current study was designed to create an in vitro system that would reproduce this redistribution phenomenon. Our results indicate that cathepsin B redistribution occurs when rat pancreatic fragments are incubated with a supramaximally stimulating concentration of the cholecystokinin analogue caerulein along with plasma from an animal subjected to in vivo supramaximal caerulein stimulation. Neither the plasma nor a supramaximally stimulating concentration of caerulein, alone, is sufficient to induce in vitro cathepsin B redistribution. The ability of the plasma to induce in vitro cathepsin redistribution is dependent upon its content of a 10,000-30,000-D protein and is lost by exposure to protease inhibitors. In vitro cathepsin B redistribution also occurs when rat pancreatic fragments are incubated with plasma obtained from opossums with hemorrhagic necrotizing pancreatitis caused by bile/pancreatic duct ligation.