Stereological analysis of nasal mucosa. III. Stepwise alterations in cellular and subcellular components of pseudostratified, metaplastic and dysplastic epithelium in nickel workers.

Nasal mucosal biopsies taken primarily for diagnostic purposes were graded as pseudostratified, metaplastic (consisting of stratified cuboidal, non-keratinizing and keratinizing stratified squamous epithelium) or dysplasic, and were analysed by simple stereological procedures at the electron microscopic level. For biological and methodological reasons the evaluation was focused on the basal cells of the epithelium. The transition of pseudostratified to metaplasic and dysplasic epithelium was accompanied by significant alterations in the karyoplasm and cytoplasm. The main changes in the karyoplasm were a gradual reduction of heterochromatin and an enlargement of the nucleoli. In the cytoplasm the main changes involved: (i) the mitochondria, with a threefold increase in size and a corresponding reduction in number. In addition the surface density of their cristae was reduced by 32%. (ii) The surface density of rough endoplasmic reticulum, which increased by 100%, (iii) the volume fraction of tonofilaments which decreased by 60%, and (iv) the number of desmosomes which increased by 60%. The morphologic changes, especially those involving the mitochondria and endoplasmic membranes, suggest that biochemical differences also exist between the original, and metaplasic and dysplasic epithelia. The stepwise alterations of several independent cellular and subcellular components support the hypothesis of a gradual transformation of pseudostratified epithelium to stratified squamous epithelium and dysplasia.