DIFFERENTIATING MYOEPITHELIAL AND ACINAR-CELLS IN RAT NEONATAL PAROTID-GLAND AND HISTOGENETIC CONCEPTS FOR SALIVARY-GLAND TUMORS

Histogenetic concepts for salivary gland tumors are predicated on the presence of reserve or undifferentiated cells in normal glands, presum ably the source for cell renewal and induction of tumors. Developing r at parotid gland, which remains fetal-like at birth, provides the oppo rtunity to study differentiation and observe whether cytologically und ifferentiated cells do or do not have functional indicators of specifi c differentiation pathways. Immunohistochemistry and immunoelectron mi croscopy, when applied to parotid gland at birth, at 1' days of age an d in the adult gland, indicate that commitment to myoepithelial cell d ifferentiation occurs prior to development of structural changes chara cteristic of these cells. Conversely, secretory granules are evident i n differentiating acinar cells prior to synthesis of amylase. The resu lts suggest that an appearance of undifferentiation does not confer re serve cell status either in the normal salivary gland or their tumors.