Comparative light and scanning electron microscopic observations of nasal cavity carcinogenesis in rats treated with 1,4-dinitrosopiperazine.

Epithelial lesions in the nasal cavity of male F344 rats appeared as papillary and nodular hyperplasias progressing to invasive carcinomas during administration of 1,4-dinitrosopepirazine (DNP) at a dose of 0.01% in the drinking water. Observations with specific attention to the cells covering the luminal surface of the mucosa were made by scanning electron microscopy at 10-week intervals. After administration of DNP for 20 and 30 weeks three different types of light microscopically identifiable focal lesions, i.e., papillary hyperplasia, nodular hyperplasia and papilloma, of the epithelium in the nasal cavity were distinguished, and after 40 and 50 weeks areas of squamous cell carcinomas were also observed. In the scanning electron microscope, papillary hyperplasia appeared as a nodular elevation of the surface with a smoother appearance than the surrounding nonnodular areas. Areas of nodular (inverted) hyperplasias had irregularly shaped indentions of the surface. Papillomas appeared as pedunculated projections of the surface. Carcinoma presented as a protrusion of irregular cell masses. The surface cells in the areas of papillary and nodular hyperplasias and of papilloma had numerous short microvilli rather uniform in shape (short-uniform microvilli), unlike the normal epithelium in the nasal cavity, which possesses cilia or olfactory vesicles. The microvilli of carcinoma cells were more irregular in shape and size than those of hyperplastic cells (pleomorphic microvilli).