Scanning electron microscopy of changes in the urinary bladder in dogs treated with N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN).

The fine structures of the bladder mucosa during BBN carcinogenesis and of bladder tumors induced by BBN in dogs were examined by scanning electron microscopy. Normal dog bladder mucosa was covered with polygonal superficial cells with peaked microridges, but no microvilli. Microridges and uniform microvilli were observed in hyperplastic mucosa. In low grade papillary tumors induced by low doses of BBN, pleomorphic microvilli predominated. In dogs which received high doses of BBN, bizarre pleomorphic microvilli and blebs were observed in papillary lesions, whereas bumpy surfaces with thick short microvilli were observed in non-papillary lesions. These sequential changes which were observed in dog bladder mucosa during BBN carcinogenesis parallelled the changes that occurred in the process of chemical carcinogenesis in rodents, and dog bladder tumors were similar to those of rodents and of human bladder cancers.