[Experimental studies on regeneration of myoepithelial cells--the rat submandibular gland autografted in the tongue].

The regeneration process of myoepithelial cells in the injured salivary gland was studied. Fragments of the rat submandibular gland autografted in the tongue were examined from 12 hours to 14 days after implantation by means of the methods of autoradiography, histochemistry and electron microscopy. Two days after implantation, the central area of the fragments showed necrosis and parenchymal regeneration was, on the other hand, revealed at the remaining periphery. It was demonstrated by [3H] thymidine autoradiography that the regeneration of the intralobular parenchyma took place at the remaining intercalated and striated portions of the duct, but never did at the secretory endpieces. Initially, solid cell clusters were composed of regenerating uniformly immature polygonal epithelial cells. Four days after implantation, intracytoplasmic filaments running parallel to the plasma membrane of the cell, measured 50-70 A in diamter, were detected in some cells of the cluster. These filaments were accompanied by dense bodies characteristic of those of smooth muscle cells, and were thereby identified with myofilaments. Based on the findings, the regenerating cells with myofilaments were recognized as immature myoepithelial cells. Showing mosaic arrangement, they intermingled with the other kind of regenerating epithelial cells in the cluster. Each regenerating cell cluster formed gradually tubular structure with epithelial stratification. Ten days after implantation, most tubular structures were consisted of the single layer of columnar or cuboidal cells. Fourteen days after implantation, alkaline phosphatase activity characteristic of mature myoepithelial cells was observed in the spindle cells located between tubular epithelium and basal lamina. Ultrastructurally these spindle cells were identified with mature myoepithelial cells because of furnishing myofilaments with dense bodies. The results of this experiment suggest that, in case of tissue injury, the epithelial regeneration in the intralobular portion of the salivary gland is initiated at the intercalated and/or striated portions of the duct, and followed by myoepithelial differentiation of some of the regenerating epithelial cells.