Spontaneous hyperplastic and metaplastic duct epithelium in the sublingual salivary glands of Wistar rats

Focal epithelial hyperplasia and metaplasia were observed in the intralobular ducts of the sublingual salivary glands of 302 out of 1142 Wistar rats. These rats (aged 16-145 weeks) served as controls in toxicological experiments. The ductal changes varied from small groups of irregular cylindrical cells with basophilic cytoplasm and vesicular nuclei, with often prominent nucleoli, to large areas of non-keratinized stratified squamous epithelium with marked mitotic activity and necrotic superficial cells being released in the lumen. Mononuclear inflammatory cells were often present in fibrous tissue surrounding altered ducts. Within certain limits the degree and incidence of the changes increased with increasing age; their aetiology is unknown.