Ultrastructure of streptozotocin-induced renal tumours in mice.

Streptozotocin-induced tumours in the kidneys of experimental animals have been shown to be histologically similar to human renal cell carcinoma. We report the ultrastructural features of renal tumours induced in 15 mice by a single intravenous bolus of 2.5% streptozotocin administered in a dose of 250 mg streptozotocin/kg mouse body weight. Animals were sacrificed 232-361 days after the administration of streptozotocin. On examination both kidneys from each animal contained 1-4 dysplastic tubules and 1-3 discrete tumours per kidney. Twelve dysplastic proximal convoluted tubules showing varying degrees of epithelial atypia and nine tumours exhibiting either a papillary or solid architecture were examined. Dysplastic epithelial cells and tumours of papillary and solid type exhibited complex cell borders with well-developed junctional complexes. The majority of cells contained surface microvilli, and in some cells microvilli-lined intracytoplasmic lumina were observed. Occasional dysplastic epithelial cells and tumour cells contained double-membrane vesicles 120-200 nm in diameter. These were similar to the intracytoplasmic vesicles characteristic of human chromophobe renal cell carcinoma. Intracytoplasmic collections of glycogen granules and flocculant protein were identified in both dysplastic and neoplastic cells, and where prominent they resulted in compression of cytoplasmic organelles. Coated vesicles were commonly observed. These were free within the cytoplasm and were also seen budding from strands of rough endoplasmic reticulum. The distribution of these vesicles suggested a role in protein transport from the rough endoplasmic reticulum. It is concluded that while streptozotocin-induced renal tumours have some ultrastructural features in common with human chromophobe renal cell carcinoma, the overall ultrastructural morphology differs significantly from that described for the various histological types of human renal cell carcinoma.