Implications of integrated pancreatic microcirculation: Crosstalk between endocrine and exocrine compartments

Abstract

The endocrine and exocrine pancreas have been studied separately by endocrinologists and gastroenterologists as two organ systems. The pancreatic islet, consisting of 1–2% mass of the whole pancreas, has long been be-lieved to be regulated independently from the surround-ing exocrine tissues. Particularly, islet blood flow has been consistently illustrated as one-way flow from arte-riole(s) to venule(s) with no integration of the capillary network between the endocrine and exocrine pancreas. It is likely linked to the long-standing dogma that the rodent islet has a mantle of non–β-cells and that the islet is completely separated from the exocrine compartment. A new model of islet microcirculation is built on the basis of analyses of in vivo blood flow measurements in mice and an in situ three-dimensional structure of the capillary network in mice and humans. The deduced integrated blood flow throughout the entire pancreas suggests direct interactions between islet endocrine cells and sur-rounding cells as well as the bidirectional blood flow between the endocrine and exocrine pancreas, not necessarily a unidirectional blood flow as in a so-called insuloacinar portal system. In this perspective, we discuss how this conceptual transformation could po-tentially affect our current understanding of the bio-logy, physiology, and pathogenesis of the islet and pancreas.