The distribution of intracellular
keratin proteins was examined in a variety of urinary bladder lesions of the rat using the immunoperoxidase staining technique. In
ethanol-fixed sections, the normal epithelium was strongly positive for
keratin staining. Focal regenerative
hyperplasia of the bladder epithelium induced by freezing exhibited relatively weak staining. However, diffuse regenerative
hyperplasia induced by a single
intraperitoneal injection of
cyclophosphamide (CP) showed an intensely positive reaction throughout the epithelium. Of the sections fixed with
Bouin's solution, the staining reaction was drastically reduced in the normal bladder and the staining was totally negative in the regenerative
hyperplasia caused by freezing. Simple
hyperplasia induced by a 4-week feeding of N-[4-(5-nitro-2-furyl)-2-thiazolyl]
formamide (
FANFT) as 0.2% of the diet exhibited strong reactivity, and nodular and papillarly
hyperplasia induced by a 10-week feeding of
FANFT was also positive for
keratin throughout the lesions. In contrast to the preneoplastic lesions,
FANFT-induced
transitional cell carcinoma showed differential staining within the
tumors. These results suggest that different
keratin expression is involved in the proliferative bladder lesions induced mechanically by freezing and chemically by CP or by the
carcinogen FANFT.