|ISSN No. 1606-7754 Vol.12 No.3 December 2004|
Effects of insulin and glucose metabolism on pancreatic exocrine function
3rd Department of Internal Medicine, MAV Hospital, Budapest,1062, Hungary
Glucose metabolism is highly dependent on hormones secreted by the islets of Langerhans, and most notably on insulin. Moreover, the endocrine and exocrine pancreas has a complex anatomical and functional interaction. The exocrine part of the pancreas is influenced by the islet hormones mainly through an islet-acinar portal system, for example, the periinsular acinar cells are larger and contain more zymogen and amylase. The insulo-acinar axis is also indicated by morphological evidences. Hypoinsulinemia causes pancreatic atrophy with fat replacement of the exocrine pancreas in different species. These results indirectly show the significant role of insulin on pancreatic exocrine function. However, direct evidence is also available to highlight the key role of insulin. Both endogenous and exogenous insulin evoke increases in pancreatic enzyme synthesis and growth. Insulin is not only important in healthy conditions, but is also involved in the regenerative processes during pancreatitis. Human studies have also proved the necessity of insulin in pancreatic exocrine function. In conclusion, insulin has long term effects on the regulation of the biosynthesis of pancreatic digestive enzymes and short term effects on the stimulation of pancreatic secretion. Other peptides, such as pancreatic polypeptide, glucagon and somatostatin seem to inhibit pancreatic secretion, although more experiments are needed to clarify this hypothesis. Despite our current knowledge, many other hypotheses and questions remained unanswered concerning the effects of hormones secreted by different cells of the islets of Langerhans, therefore, it seems to be of great importance to explore the effects of these hormones on pancreatic exocrine function.
The endocrine and exocrine pancreas has a complex anatomical and functional interaction.1 It is well documented, that intact islets of Langerhans is necessary for the normal pancreatic exocrine function.2,3 Moreover, the exocrine pancreas is influenced by the islet hormones not only systemically but also through a direct islet-acinar portal system.4 The insulo-acinar axis is also indicated by other morphological evidences. The acinar cells around the islets, termed periinsular acini, can be distinguished from teleinsular acini by their histological characteristics. These periinsular cells are bigger in size, contain larger nuclei and nucleoli, and have more abundant zymogen granules5,6,7 and amylase.8 This heterogeneity of the acinar cells plays an important role in non-parallel secretion and adaptation of pancreatic secretion to the carbohydrate rich diet.9 In this review key roles of insulin and normal glucose level on pancreatic exocrine function are highlighted.
Key words: pancreas, diabetes, insulin, exocrine function, pancreatitis