Table II. Summary of the advantages, disadvantages and clinical relevance of invasive experimental models of acute pancreatitis.

Model	Advantages	Disadvantages	Clinical relevance	References
Closed duodenal loop (CDL)	Relatively simple Reproducible Useful for studying the role of duodenal reflux in the pathogenesis of acute pancreatitis in humans Suitable for experiments on small animals (i.e. rats) and thus economical	Requires surgical intervention, the non-physiologic pressure levels created in the closed duodenal compartment and the pancreatic duct, and the controversial role of bacterial infection Not widely used	Closely resembles the few patients who develop acute pancreatitis in association with afferent loop obstruction after Billroth II gastrectomy	108,109,110,112,113,114,115
Antegrade pancreatic duct perfusion	Useful for studying early pathophysiology and subsequent progression of acute pancreatitis Reliable Reproducible Pancreatitis severity may be varied within well-defined time intervals according to the volumes and perfusion pressures Ideal for assessing potential therapeutic agents (i.e. cholecystokinin antagonists, somatostatin, fibrinolytic agents and cytokine antagonists) Perfusion of an isolated segment of the rat pancreatic duct with bile salt increases its permeability; therefore smaller and cheaper animals can be used (i.e. rats)	Complex (ductal cannulation and perfusion) Often requires large animals (i.e. cats) which are expensive and difficult to maintain	Aetiology and morphological changes closely resemble the human situation	126,127,128,129
Biliopancreatic duct injection	Suitable for studying systemic issues of acute pancreatitis Useful for studying pseudocyst formation, pancreatic abscess and fatty tissue necrosis Reproducible model for creating a severe, rapidly evolving, and lethal variety of acute haemorrhagic pancreatitis	Technically challenging to control constant pressure recordings and hence produce a standard degree of injury Difficult to establish the degree of variation regarding tissue necrosis and survival in animal groups Surgery is restricted to simulate the type of obstruction that would take place during the passage of gallstones via the papilla of Vater	Clinical and pathogenetic relevance unclear Limited evidence to support the role of bile reflux in the human condition where the bile concentration in the general tissue is higher than the pancreatic tissue concentration	131,136,137,138
Combination of secretory hyperstimulation with minimal intraductal bile acid exposure	Combined action of low-dose intraductal GDOC with intravenous caerulein causes acute pancreatitis more reliably than induction by either component alone Accelerated detergent effect is not elicited when using very low dose of GDOC (5 or 10 mmol/l); the bile salt is dispersed throughout the periphery of the pancreas Relatively easy to perform Reproducible Relatively inexpensive Mortality rates vary between 6% and 42% at 24 h Pancreatic cell injury is progressive over at least 24 h Produces homogeneous injury of intermediate rate of onset suitable for scoring and testing treatments Pancreatic injury can be manipulated by controlling the amount and time of infusion of intraductal low-dose GDOC	High concentrations of bile acids produce extensive acinar necrosis too rapidly and the resulting lesions show substantial heterogeneity Applying very low concentrations of GDOC (5 or 10 mmol/l) produces non-remarkable acute pancreatitis, with no death	Homogeneous injury has a moderately severe acute pancreatitis that impairs all regions of the gland, resembling human acute pancreatitis	139
Vascular-induced	Microcirculatory disturbance Acute haemorrhagic necrotizing pancreatitis can be reproduced by using microspheres of diameters < 20 µm Induction of hypovolaemic shock significantly lowers pancreatic blood flow, thus may potentially be used to study pancreatic damage in cardiac surgery Useful for studying coagulopathy and thrombosis of microvessels caused by acute pancreatitis Allows the study of endothelin receptor antagonists (i.e. ET-RA, PAF-RA, ICAM-1-AB); ET-RA is most effective Pancreatic artery occlusion May potentially be used to study pancreatic damage in cardiac surgery Allows relative preservation of islet cell function Pancreatic venous occlusion May be used to study acute splenic vein or portal vein thrombosis in acute pancreatitis Overall Vascular-induced models are relatively inexpensive	Microcirculatory disturbance Maintaining the normality of other organs during the cannulation of pancreatic vessels is difficult Pancreatic artery occlusion Limited reproducibility Pancreatic venous occlusion Not suitable for investigating local changes in the pancreas Not easily reproducible Overall Vascular-induced models do not reliably induce equivalent severity of acute pancreatitis Reproducibility sometimes limited due to extensive collateral network of pancreatic circulation Require large experimental animals Surgical procedures are time-consuming Minimal histological changes of acute pancreatitis May eventually progress to chronic pancreatitis	In a clinical setting, acute pancreatitis caused by occlusion of a main artery is not a common event; it is sometimes observed in patients with arteritis Microcirculatory disturbance models increase capillary permeability, similar to clinical situation	149,150,152,153,154,155,156
Ischaemia/reperfusion	Hoffman's model allows complete and reversible interruption of arterial blood supply to the pancreas Intravital fluorescence microscopy enables the parameters of microcirculation during the entire reperfusion period to be assessed repetitively and quantitatively	Current models – incomplete ischaemia and inability to quantitate the remaining blood supply to the pancreas; irreversible ischaemia, making it unsuitable for reperfusion studies; and complete and reversible ischemia, limited to ex vivo models Quantitative analysis of post-ischaemic reperfusion failure at the microcirculation level is difficult to achieve Various methods, i.e. methylene blue or India ink injection, radioactive microspheres injection, light and electron microscopic analysis of microangiographic architecture or laser Doppler flowmetry cannot be used	Ultrastructural changes after 2 h of ischaemia simulate acinar structural changes in pancreas grafts following transplantation in human	154,163
Duct ligation	Avoids artificial drug usage that may produce unwanted systemic effects and the theory relating to clinical acute biliary acute pancreatitis with biliary pancreatic reflux	Cannot induce acute pancreatitis by surgical ligation of pancreatic duct alone Most laboratory animals develop chronic lesions in the pancreas characterized by atrophy and apoptosis of acinar and ductal tissue, but not significant necrosis or inflammation Technically difficult to perform Expensive Limited reproducibility Analogous to chronic pancreatitis	Ligation of the common biliopancreatic duct in the rat causes a clinical syndrome resembling the multiple organ failure seen in humans Main clinical correlation of duct ligation-induced pancreatitis is the acute pancreatitis seen after Polya gastrectomy	108,113,171,177,178,184
Duct-ligated Opossum/possum	Opossum Ligation of the pancreatic duct alone, bile and pancreatic duct separately, or the common biliopancreatic duct leads to severe acute pancreatitis Mortality rates approach 100% within 2 weeks of induction Useful for investigating pathophysiology of biliary acute pancreatitis Necrosis is the primary mechanism; apoptosis is only present in the early stages of acute pancreatitis	Opossum	Opossum Closely simulates the mechanical events that occur during or after gallstone passage	179,180,181,182,184,186
	Possum Well characterized Useful for studying the motility of the sphincter of Oddi (SO); it functions as a variable resistor in modulating bile and pancreatic secretion Suitable for investigating the role of SO motility in other forms of acute pancreatitis, i.e. gallstone pancreatitis, and pancreatitis secondary to alcohol, scorpion envenomation, organophosphate poisoning, and octreotide treatment Does not require gastroduodenostomy Readily available	Possum Co-existing duodenal wall necrosis, and pancreatic peritoneal sepsis often add complexity to the model; this complicates interpretation of results	Possum The arrangement of the pancreatic and bile ducts come together and are controlled by an SO complex, resembling those of humans Responses to hormonal and drug stimuli are similar to humans