Myoepithelial cells after duct ligation and de-ligation of rat submandibular gland, light and electron microscopic study

ABSTRACT

Myoepithelial cells are observed in several exocrine glands. They are star-shaped cells that lie in between the basal lamina and the acinar and ductal cells [Ogawa et al., 1999][30]. These cells have the structural features and function of both smooth muscle cells and epithelium [Frank et al., 1980][31]. They contract when the gland is stimulated to secret. They aid expulsion of glandular secretion through compressing or reinforcing the underlying parenchymal cells. It was suggested that the major function of myoepithelial cells in salivary glands is to support the glandular structure through isometric contraction [Segawa et al., 1995][36]. They also display the characteristics of epithelium in that they are situated within the glandular epithelium between secretory cells and the basement membrane [Tandler, 1965; Harrop, 1968; Leeson and Leeson, 1971][45, 19, 26]. Myoepithelial cells have speculated to play an important role in histogenesis of some salivary gland tumors, such as pleomorphic adenoma, Myoepith-elloma, adenoid cystic carcinoma and certain other tumors [Batsakis et al., 1983; Dardick and Buford-Mason, 1993; Redman, 1994][2,9,33]. Studies of the responses of SMG to ligation of the main excretory duct have established that both acinar cells and cells of the granular ducts are markedly altered morphologically and functionally [Kasai, et al., 1993; Kern, 1993] [24, 25]. Moreover, ligation of the main excretory duct of the rat submandibular gland [SMG] produces a pronounced atrophy that is reversed upon ligature removal. The altered morphology and function of ligated salivary glands recover toward the normal state after removal of ligature [Junqueira and Rabinovitch, 1954; Harrison and Garrett, 1976; Randriamampita and Tsien, 1993; Ahn et al., 2000][23, 17,32,1]. However, it is not established whether myoepithelial cells are able to proliferate in atrophic rat submandibular gland, which differ histologically from parotid glands. Burgess et al. [1996][6] observed that atrophy of the rat parotid glands which induced by duct ligation was associated with proliferation of myoepithelid cells. However, Bataskis et at. [1989][3] found low proliferation in myoepithelial cells in atrophied rat salivary glands. Therefore, the present study was undertaken to clarify the effects of duct ligation and ligature removal on the myoepithelial cells of rat SMG. Also, it is an attempt to determine the crucial role of myoepithelial cells upon the integrity of acinar cells in both ligated and de-ligated ducts of SMG of rat