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The pathological activation of zymogens within the pancreatic acinar cell plays a role in acute pancreatitis. To identify the processing site where activation occurs, antibodies to the trypsinogen activation peptide (TAP) were used in immunofluorescence studies using frozen sections from rat pancreas. Saline controls or animals receiving caerulein in amounts producing physiological levels of pancreatic stimulation demonstrated little or no TAP immunoreactivity. However, after caerulein hyperstimulation (5 micrograms. kg-1. h-1) for 30 min and the induction of pancreatitis, TAP immunoreactivity appeared in a vesicular, supranuclear compartment that demonstrated no overlap with zymogen granules. The number of vesicles and their size increased with time. After 60 min of hyperstimulation with caerulein, most of the TAP reactivity was localized within vacuoles >/=1 micrometer that demonstrated immunoreactivity for the granule membrane protein GRAMP-92, a marker for lysosomes and recycling endosomes. Pretreatment with the protease inhibitor FUT-175 blocked the appearance of TAP after hyperstimulation. These studies provide evidence that caerulein hyperstimulation stimulates trypsinogen processing to trypsin in distinct acinar cell compartments in a time-dependent manner.

Stimulation of the exocrine pancreas with cholecystokinin analogues leads to a variety of intraacinar processes, many coupled to energy consumption. It was hypothesized that extensive ATP depletion could play a role in the pathophysiology of acute pancreatitis, especially in the hyperstimulation (cerulein) model. Mice received seven intraperitoneal injections of cerulein at hourly intervals, at doses ranging from physiological (0.1 micrograms/kg) to pharmacological (50 micrograms/kg). A single dose of cerulein induced a 28-33% decrease in ATP, whereas a complete course of injections led to a nadir as low as 45% of the control value. The overall pattern of ATP tissue content during the observed time course was surprisingly similar in all four groups and statistically not different at any time point. Until 12 h, ATP levels in all groups remained below the control value. In contrast, serum amylase and light microscopy reflected a degree of pancreatitis in a close dose-response pattern to the administered cerulein dose. These findings suggest that ATP depletion--although probably facilitating acinar damage--does not seem to play a causal or primary role in the pathophysiology of acute pancreatitis.

In order to reproduce what might occur during the initial phase in some cases of acute alcohol-induced pancreatitis, rabbits were infused with diluted ethanol and low-dose cerulein. The duct permeability was assessed by recovery of fluoresceinated dextran (molecular weight 19,500) in central venous blood following orthograde duct perfusion with this substance in the anesthetized animal. Serum ethanol, lipase, and amylase were measured; pancreatic duct morphology was examined by light microscopy and electron microscopy. ATP and glutathione were measured, as were amylase, trypsinogen/trypsin, cathepsin B, and DNA levels in differential centrifugates. As expected, acinar amylase and trypsinogen showed a significant decrease in the experimental group; cathepsin B activity was similarly diminished. Compared with the control group, the activity of serum amylase and lipase in the experimental group demonstrated a significant increase. However, no differences between saline-infused control animals and the treated group regarding pancreatic duct permeability, continuity of lumen-lining epithelium, ATP and glutathione levels, and the relative subcellular distribution of pancreatic digestive and lysosomal enzymes were observed. Thus, our findings do not support the relevance of some of the most common hypotheses on the pathophysiology of acute pancreatitis in its early stage for at least a certain subgroup of patients with acute alcohol-induced pancreatitis.

Acute pancreatitis (AP) is believed to result from intraparenchymal activation of trypsin and other digestive enzymes within the pancreas followed by autodigestion of the gland. Gabexate mesilate (FOY), a synthetic guanidino acid ester exhibiting potent and versatile inhibitory actions on a number of proteinases (e.g., trypsin, kallikrein, C1-r, C1 esterase, plasmin, thrombin, phospholipase A2), was examined for its ability to protect the rat pancreas against development of AP induced by pharmacological doses of ceruletide (CRT). Rats were i.v. infused for 6 h with either CRT (5 micrograms/kg/h) or CRT + FOY (50 mg/kg/h). In FOY-treated rats the serum amylase and trypsinogen concentrations were reduced by 60 and 80%, respectively, compared to rats infused with CRT alone. Histologically, the extent of acinar cell vacuolization in the pancreas was significantly reduced and interstitial edema, although not assessed by quantitative morphometric techniques, appeared to be qualitatively lessened in the FOY-treated rats. The ability of FOY to inhibit significantly AP produced by supramaximal doses of CRT, coupled with its inhibitory properties on components of the coagulation and complement cascades, stress the importance of continued research on this compound as a potential therapeutic agent for treatment of AP and its systemic sequelae.

The onset, course, and regression of the biochemical and structural alterations associated with pancreatitis induced by various doses of caerulein were studied in the mouse. In addition, the protective effect of secretin was compared with that of the cholecystokinin-receptor antagonists proglumide and benzotript. Subcutaneous or intraperitoneal injections of caerulein induced increases in serum amylase concentration and pancreatic weight and histologic evidence of acute pancreatitis, all effects being dose-related. Cytoplasmic vacuoles were the earliest histologic alterations. As the pancreatitis progressed these vacuoles increased to an enormous size. Interstitial inflammation and acinar cell necrosis were prominent after 6 h, reached a maximum after 12 h, and mostly disappeared after 4 days. During the course of pancreatitis approximately 40% of the acinar cells showed signs of severe degeneration or necrosis at the most effective doses of caerulein. Electron microscopy showed both intact and degenerating granules inside the vacuoles. Signs of basolateral exocytosis of zymogen granules were not observed. During the regression of pancreatitis, focal atrophy was a remarkable histologic finding. Repetitive initiation of pancreatitis (six courses of caerulein injections over 5 wk) produced marked focal atrophy and early fibrosis. High doses of proglumide or benzotript markedly ameliorated both the biochemical and structural alterations induced by caerulein. Secretin, even at very high doses, had only minor protective effects. This study presents a model of acute necrotizing pancreatitis in which the severity of the induced pancreatitis ranges dose-dependently from mild interstitial inflammation to severe necrosis. The ultrastructural alterations described herein support the hypothesis that the trigger mechanism of acute pancreatitis appears to be a primary intracellular event rather than an interstitial event that secondarily damages the acinar cells.