Microvascular development: learning from pancreatic islets.

Microvascular development is determined by the interplay between tissue cells and microvascular endothelial cells. Because the pancreatic islet is an organ composed mainly of endothelial and endocrine cells, it represents a good model tissue for studying microvascular development in the context of a tissue. In this review, we will describe the special morphology of islet capillaries and its role in the physiologic function of islets: secretion of insulin in response to blood glucose levels. We will speculate on how islet-secreted VEGF-A generates a permeable endothelium that allows insulin to pass quickly into the blood stream. In addition, we speculate on how endothelial cells might form a capillary lumen within the islets. At the end, we look at the islet microvasculature from a medical point of view, thus describing its critical role during type I diabetes and islet transplantation.