Regeneration of rat submandibular gland following partial extirpation. A light and electron microscopic study

A wedge of parenchymal tissue was excised from the left submandibular gland of six week old male Sprague‐Dawley rats. The animals were randomly grouped by body weight and killed at intervals of one day to five weeks following the operation. Tissue from and adjacent to the site of injury was removed and prepared for routine light and electron microscopy. Light microscopic findings consisted of degeneration and necrosis of the parenchymal tissue during the first 24 hours, followed by hyperemia and endothelial as well as epithelial proliferation from one to three days. Extensive epithelial proliferation occurred during the next two weeks, followed by regeneration of new lobules, beginning at the periphery of the injured lobes. Ultrastructurally, the new parenchymal tissue appeared to have regenerated from residual duct cells. Dedifferentiated epithelial cells gave rise to two different cell lines: one line which transformed into terminal tubules and acinar cells, and another which became striated ducts. These differentiating cells were organizing into lobules as early as three weeks after the operation. Because of their proximity to cells of regenerating striated ducts as well as intercalated ducts and acini, the myoepithelial cells appeared to be of epithelial origin.