Sodium saccharin has previously been demonstrated to induce hyperplasia and tumors of the urothelium of the rat urinary bladder. It was fed as 5% of the diet to male F344 rats for 2 years. In the present experiment, mild simple hyperplasia of the urinary bladder epithelium was again frequently observed, and a marked nodular and papillary hyperplasia of the urothelium of the kidney pelvis was also found in approximately half of the sodium saccharin-fed rats. This was infrequently associated with focal calcification of the renal papilla and pelvis. In contrast, rats fed sodium saccharin had a significantly reduced incidence of the interstitial nephritis frequently observed in older rats. No significant incidence was observed of lesions of tissues other than those of the urinary tract.
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