[Morphogenesis and micromorphology of epithelial tumors induced in the rat kidney by nitrosomorpholine. IV. Tubular lesions and basophilic tumors (author's transl)].

The genesis of basophilic cell kidney tumors was investigated stepwise by light and electron microscopy in rats treated with N-nitrosomorpholine for a limited time (stop experiment). Seven weeks after the beginning of the experiment the kidney tubules sometimes showed unusually large "chromophobic" and basophilic cells. After a lag period of 22-97 weeks more than 60% of the animals had developed these atypical tubules. Parallel to the appearance of chromophobic tubules 50% of the carcinogen-treated animals developed basophilic cell kidney tumors. All intermediate stages between chromophobic or basophilic cell tubules and tumors were found. During the neoplastic transformation chromophobic epithelia appeared to change into basophilic cells. Some of the chromophobic renal tubules and most of the renal tubules which consisted of chromophobic and basophilic epithelia stored acid mucopolysaccharides as demonstrated by histochemical methods. The fine structure of the basophilic epitheliomas was relatively uniform. The basophilia observed under the light microscope correlated with abundant membrane-bound and free ribosomes as seen under the electron microscope. The frequent appearance of brush borders and microbodies indicated the origin of the basophilic cell tumors from proximal renal tubules. In some tumor cells many mitochondria were found. These cells resembled oncocytes. However, in contrast to typical oncocytes the mitochondria of these cells were poor in cristae or showed tubular formations of the inner membrane. In some mitochondria homogeneous condensations could be detected in the intracristal space and tooth-like formations were seen on the surface of the cristae. In perpendicular sections these cristae resembled saw blades. Acute tubular lesions and cellular regeneration, as described earlier by other authors in early stages of the development of kidney tumors, were not found. It is suggested that the storage of acid mucopolysaccharides observed in many tubules and in some renal tumors indicates a disturbance of the cellular metabolism which plays an important role in tumor development.