Cellular origin of rat renal oncocytoma.

The cellular origin of the rat renal oncocytoma was studied by light and electron microscopy in rats treated with N-nitrosomorpholine. The oncocytomas which appeared as small solid masses or cysts developed from tubules lined by oncocytes. Rats treated with N-nitrosomorpholine showed a number of oncocytomas and many oncocytic tubules, the incidence of which increased with time. A small number of oncocytic tubules but no oncocytomas were observed in the oldest control rats. Two major types of oncocytes were detected in the oncocytic lesions. Whereas some oncocytes contain only small round mitochondria, most oncocytes exhibited both small and unusually large pleomorphic mitochondria. The tubular origin of the oncocytic lesions was established precisely in serial sections. Numerous transitions of both oncocytomas and oncocytic tubules into renal tubules of normal appearance indicated that oncocytic lesions developed frequently from the cortical collecting duct system, including the connecting tubule, and occasionally from the outer medullary collecting duct. Mitochondrial changes similar to those of fully developed oncocytes were recognized in principal and intercalated cells of these segments, indicating the involvement of these cell types in the genesis of the renal oncocytoma.