To discuss the controversy of the current concept of islet microcirculation, an international symposium was held at the Long Beach Veterans Administration Regional Medical Education Center (Long Beach, CA) and broadcast over the Internet via the World Wide Web to 14 international stations. Studies concerning three models of islet microcirculation, mantle-to-core, core-to-mantle, and polar, were presented. One presentation, including an interactive question and answer session, was broadcast from the Massachusetts Institute of Technology (Cambridge, MA) and received by the symposium participants in Long Beach, as well as by the 14 stations. The fundamental differences between the models, ie, the relationship of the microcirculation flow pattern and the islet cell composition, were discussed in an open forum with critiques of techniques, results, and interpretations.

Each islet has from one to five arterioles, which penetrate into the islet and divide into numerous capillaries (1),(2),(3),(4). The capillaries, resembling a glomerulus, course through the islet in a tortuous fashion that is ideal for cell-blood and blood-cell interactions. The [alpha]-,[beta]-,[delta]-, and PP-cells, which secrete glucagon, insulin, somatostatin, and pancreatic polypeptide, respectively, are nestled between the capillaries and receive their nutrient, hormonal, and neurohormonal regulatory signals across the capillary endothelium, as well as through the interstitial space (5),(6). Since the cell types have specific locations within the islet, the pattern of blood flow through the islet should have a significant impact on the ability of cells to intercommunicate within the islet. It is this relationship that represents the controversial topic that was the focus of the symposium. The following is a review of the three models of islet microcirculation discussed at the symposium.