Close association of centroacinar/ductular and insular cells in the rat pancreas.

Close contacts between endocrine insular cells and exocrine acinar, centroacinar and ductular cells occur frequently in the rat pancreas as seen by both light and electron microscopy. Islets of Langerhans are surrounded incompletely by a thin connective tissue capsule or mantle but numerous exocrine-endocrine cell contacts occur at the periphery, which is irregular with considerable "intermingling" of the two cell types. Centroacinar and ductular cells are seen to be in contact with all endocrine cell types but most commonly insulin-secreting B-cells. The basal surface of centroacinar cells in the region of contact may be extensive, sometimes with overlap of basal processes of these cells and their lateral extension between acinar and insular cells. The areas of contact contain no connective tissue or basal lamina and show no surface specializations. The presence of both the "open" and "closed" type of enteroendocrine cells within acini is confirmed, some also being in contact with centroacinar cells. The functional significance of these exo-endocrine cell contacts is discussed in terms of the endocrine-acinar portal system, possible direct paracrine secretion, compartmentalization within the islet, and the known effects of islet hormones on exocrine secretion. Also relevant is the developmental origin of islets from ductal tissue and the cellular origin of some tumours, e.g., insulinomas, from duct cells.