Characteristics of in vivo and in vitro experimental models

In this chapter, in vivo and in vitro experimental models for the study of the exocrine pancreas in various animal species are reviewed. For the intact animal models, some anatomical details of the pancreatic duct system, which are important for the surgical preparation necessary for collection of pancreatic juice, are explained. Several techniques for collecting pancreatic juice are described, with their relevance to specific animal species. The advantages and disadvantages of various materials used for cannulas and catheters for collecting pancreatic juice are presented. For the vascular perfused models, some anatomical details of the vascular supply system are described, and the techniques used for preparation and perfusion, including the apparatus and composition of perfusates. As models for the study of cellular mechanisms, the characteristics of pancreatic segments, dispersed acinar cells and dispersed acini preparations are presented, as well as the techniques used. Systematic research into the functions of the exocrine pancreas, i.e. the pancreatic acini (synthesis and release of pancreatic enzymes and secretion of chloride-rich fluid) and ducts (secretion of bicarbonate-rich fluid), only began in the last hundred years using whole animal preparations. These preparations were necessary to study the secretory response of pancreatic juice to changes in various conditions: diets, stages of life, environments, diseases etc. and the role of pancreatic juice in the nutrition. The factors found to regulate pancreatic secretions in intact animals were investigated to see whether they acted directly on the pancreas or not. To simplify the interpretation by excluding interference from other organs, isolated perfused preparations or pancreatic segment preparations were developed. However, isolated pancreas and pancreatic segments still contain the endocrine portion, which regulates exocrine functions, as later became known. To study direct effects on acinar cells, preparations of dispersed single acinar cells and acini were developed. The development of these experimental models led to significant progress in animal and human pancreatology. The purpose of this chapter is to review and characterise experimental models for studying the functions of the exocrine pancreas.