Tissue renin-angiotensin system: its expression, localization, regulation and potential role in the pancreas

The classical concept of the renin-angiotensin system (RAS) is that of a bl ood-borne cascade, whose final and bioactive product, angiotensin II, plays an important endocrine role in the maintenance of blood pressure and elect rolyte as well as fluid balance. In addition to this circulating RAS, there are an increasing number of studies to suggest the existence of a local an giotensin-generating system in several tissues. The so-called tissue RAS ca n act locally as a paracrine and/or autocrine factor in meeting specific ne eds fur individual tissues and it can operate, in whole or ill part, indepe ndently of the circulating counterpart. Recent studies on the expression an d localization of key RAS components, particularly angiotensinogen and reni n, have provided solid evidence for the existence of an intrinsic, angioten sin-generating system in the pancreas. The tissue RAS has a potential role in finely regulating exocrine and endocrine functions of the pancreas such as ductal anion secretion and islet hormonal secretion. Some of these effec ts may be exerted via the markedly vasoconstrictive effects of RAS. Of part icular interest in this contest are the recent epidemiological data showing that administration of angiotensin-converting enzyme inhibitors appears to be protective against the development of diabetes in hypertensive patients . Moreover, the upregulation of pancreatic RAS has been shown to occur duri ng chronic hypoxia. The significance of changes in pancreatic RAS could hav e a potential role in acute pancreatitis, islet transplantation and in diff erent shuck states, by causing a further decrease of blood perfusion in the pancreas.