Acino-insular cells in normal rat pancreas.

The possibility that one specialized cell could be transformed into a distinctly different type of cell has long been a controversial issue in the fields of embryology and histology. Most investigators have assumed that islet cells in the pancreas are derived from primordial duct epithelium in that organ. The possibility that islet cells might also arise from exocrine tissue, however, is still a matter of great dispute. In several light microscopic investigations' the presence of cells containing cytologic characteristics of both exocrine and endocrine cells have been noted. This brief report presents electron microscopic evidence for the presence of both zymogen and beta-cell granules in the same cell in rat pancreas.