Effects of in vivo cholinergic stimulation of rat exocrine pancreas

Experimental Acute Pancreatitis Models: History, Current Status, and Role in Translational Research

Acute pancreatitis is a potentially severe inflammatory disease that may be associated with a substantial morbidity and mortality. Currently there is no specific treatment for the disease, which indicates an ongoing demand for research into its pathogenesis and development of new therapeutic strategies. Due to the unpredictable course of acute pancreatitis and relatively concealed anatomical site in the retro-peritoneum, research on the human pancreas remains challenging. As a result, for over the last 100 years studies on the pathogenesis of this disease have heavily relied on animal models. This review aims to summarize different animal models of acute pancreatitis from the past to present and discuss their main characteristics and applications. It identifies key studies that have enhanced our current understanding of the pathogenesis of acute pancreatitis and highlights the instrumental role of animal models in translational research for developing novel therapies.

Anterior Gradient 2 (AGR2) Induced Epidermal Growth Factor Receptor (EGFR) Signaling Is Essential for Murine Pancreatitis-Associated Tissue Regeneration

A recently published study identified Anterior Gradient 2 (AGR2) as a regulator of EGFR signaling by promoting receptor presentation from the endoplasmic reticulum to the cell surface. AGR2 also promotes tissue regeneration in amphibians and fish. Whether AGR2-induced EGFR signaling is essential for tissue regeneration in higher vertebrates was evaluated using a well-characterized murine model for pancreatitis. The impact of AGR2 expression and EGFR signaling on tissue regeneration was evaluated using the caerulein-induced pancreatitis mouse model. EGFR signaling and cell proliferation were examined in the context of the AGR2^-/-null mouse or with the EGFR-specific tyrosine kinase inhibitor, AG1478. In addition, the Hippo signaling coactivator YAP1 was evaluated in the context of AGR2 expression during pancreatitis. Pancreatitis-induced AGR2 expression enabled EGFR translocation to the plasma membrane, the initiation of cell signaling, and cell proliferation. EGFR signaling and tissue regeneration were partially inhibited by the tyrosine kinase inhibitor AG1478, but absent in the AGR2^-/-null mouse. AG1478-treated and AGR2^-/-null mice with pancreatitis died whereas all wild-type controls recovered. YAP1 activation was also dependent on pancreatitis-induced AGR2 expression. AGR2-induced EGFR signaling was essential for tissue regeneration and recovery from pancreatitis. The results establish tissue regeneration as a major function of AGR2-induced EGFR signaling in adult higher vertebrates. Enhanced AGR2 expression and EGFR signaling are also universally present in human pancreatic cancer, which support a linkage between tissue injury, regeneration, and cancer pathogenesis.

Animal models for investigating chronic pancreatitis

Chronic pancreatitis is defined as a continuous or recurrent inflammatory disease of the pancreas characterized by progressive and irreversible morphological changes. It typically causes pain and permanent impairment of pancreatic function. In chronic pancreatitis areas of focal necrosis are followed by perilobular and intralobular fibrosis of the parenchyma, by stone formation in the pancreatic duct, calcifications in the parenchyma as well as the formation of pseudocysts. Late in the course of the disease a progressive loss of endocrine and exocrine function occurs. Despite advances in understanding the pathogenesis no causal treatment for chronic pancreatitis is presently available. Thus, there is a need for well characterized animal models for further investigations that allow translation to the human situation. This review summarizes existing experimental models and distinguishes them according to the type of pathological stimulus used for induction of pancreatitis. There is a special focus on pancreatic duct ligation, repetitive overstimulation with caerulein and chronic alcohol feeding. Secondly, attention is drawn to genetic models that have recently been generated and which mimic features of chronic pancreatitis in man. Each technique will be supplemented with data on the pathophysiological background of the model and their limitations will be discussed.

The lysosomal hydrolases in the rat pancreas after maximal or supramaximal stimulation with cerulein

The decompartmentation of lysosomal compartment in pancreatic acinar cells with consecutive activation of zymogens might play an important role as a "trigger mechanism" in acute pancreatitis. The admixture of lysosomal hydrolases to secretory enzymes in pancreatic juice was found, but their role in pancreatic secretion remains obscure. The aim of the present study was to assess the fragility of pancreatic lysosomal structure after maximal (optimal) or supramaximal stimulation of rats with cerulein during 3, 6, 12 h, and after recovery. In the mitochondrial-lysosomal (M-L) and in the supernatant (S) of pancreases free (F) total (T), and fractional free (%F/T) activities of beta-glucuronidase (beta G), acid phosphatase (AcP), cathepsins (Cs), and beta-N-acetyl-hexosaminidase (NAH) were estimated. In edematous pancreatitis following supramaximal stimulation with cerulein, a significant increase of %F/T of beta G in whole homogenate began at 6 h of hyperstimulation in comparison to the control (93 vs 42% p < 0.01). This increment persisted until 12 h of hyperstimulation and declined after 24 and 48 h of recovery to 67-69%. The changes of %F/T of beta G in M-L followed those in whole homogenate, and additionally the increase free activity in S after 6 h of hyperstimulation and after 24 h recovery occurred. The respective activities of other hydrolases showed a similar pattern of changes. It is of interest that fragility of lysosomal membranes increases significantly also after maximal stimulation when inflammatory changes were absent. Our results suggest that the increase of lysosomal fragility of the pancreas is most unlikely pathological in itself, but also occurs during stimulated pancreatic secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

In-vivo stimulation of rat pancreatic acinar cells by infusion of secretin. I. Changes in enzyme content, pancreatic fine structure and total rate of protein synthesis

Infusion of synthetic secretin in conscious unrestricted rats for periods up to 24 h was used to study the structural and functional adaptation of pancreatic acinar cells to this secretagogue. Initial dose-response studies established 16 clinical units (CU) per kg and h (corresponding to 4.64 micrograms X kg-1 X h-1) as optimal dose for persistent stimulation of enzyme discharge. Infusion of this dose led to a slow but progressive depletion of enzyme stores with minimal content by 12 h stimulation. As a result of persistent stimulation total protein synthesis in the acinar cells increased after a lag period of 3 h and reached maximal values 90% above controls by 6 and 12 h secretin infusion. No structural equivalent for pronounced fluid and bicarbonate secretion was observed for either acinar or duct cells over the entire dose range (1 to 64 CU X kg-1 X h-1) and infusion period (1-24 h), except an increased number of coated vesicles in duct cells. Discharge of enzymes from acinar cells was paralleled by a high frequency of exocytotic images at the luminal plasma membrane and was accompanied by the occurrence of membrane fragments in the luminal space, especially after 3 and 6 h secretin infusion. An increased number of lysosomal bodies at these time points especially in the vicinity of the Golgi complex was interpreted in relation to membrane recycling following massive exocytosis. This pattern of structural and functional adaptation of acinar cells following secretin infusion corresponds to previously described changes following caerulein and carbamylcholine stimulation.