The pancreatic ductal system of the rat: cell diversity, ultrastructure, and innervation

The morphological features and innervation of the pancreatic ductal epithelium of the rat was investigated. For the purposes of this study, pancreatic ducts were classified as either intercalated, intralobular, interlobular, or main. Epithelial cells of these different classes were classified as either principal or specialized. Principal cells make up the majority of epithelial cells in all classes of ducts. Ultrastructural analysis indicated that cytoplasmic vesicles, some containing amorphous material, were often seen in the apical portion of principal cells. Similarly, a common feature of these cells was the appearance of apical membrane projections containing various cytoplasmic organelles. These vesicles and apical membrane projections became larger as one progressed through the ductal system to the main duct. Junctional complexes contained well-developed tight junctions that, when analyzed by freeze-fracture analysis, were found to consist of three to five sealing strands in a parallel arrangement. Specialized cells could be morphologically divided into five categories: light cells, basal cells, goblet cells, endocrine cells, and brush cells. Light cells, which only differed from principal cells by their clear, lightly staining cytoplasm, were found in all classes of ducts. Basal cells, which were attached to the basement membrane of the ductal epithelium but did not extend to the lumen, were found in all classes of ducts except the intercalated ducts. Goblet cells and endocrine cells were observed in the main and interlobular ducts, while cells very similar in morphologic appearance to the brush cells of the lung were found restricted to the interlobular ducts. Localization of biogenic amines by histofluorescence indicated that adrenergic nerve fibers were associated with the main ducts and interlobular ducts. Histochemical localization of acetylcholinesterase activity indicated that cholinergic fibers were also associated with the main and interlobular ducts. These results indicate that in the rat, the pancreatic ductal system is composed of a number of cell types that are differentially distributed in the various classes of ducts, and pancreatic ducts are associated with adrenergic and cholinergic nerves.