The number of nucleolar organizer regions (NORs) stained by the one-step
silver colloid method was measured in preneoplastic and neoplastic bladder lesions induced by
N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in rats. Male ACI/N rats, 6 weeks of age, were given 0.05% BBN in
drinking water for 5, 8, 12, 18 and 30 weeks to induce preneoplastic and neoplastic transitional cell lesions. The mean numbers of
silver-stained NORs (
AgNORs) in such lesions were as follows: untreated transitional epithelium (n = 6), 1.26 +/- 0.09; transitional cell epithelium outside focal lesions (n = 10), 1.75 +/- 0.10; simple
hyperplasia (n = 10), 2.01 +/- 0.15; papillary or nodular (PN)
hyperplasia (n = 10), 2.15 +/- 0.19; transitional cell
papilloma (n = 5), 2.37 +/- 0.12;
transitional cell carcinoma (n = 5), 3.52 +/- 0.23. Thus, the mean number of
AgNORs showed a step-wise increase from untreated and treated, histologically normal transitional epithelium through simple
hyperplasia and PN
hyperplasia to transitional cell
papilloma and
carcinoma. These results suggest that the mean number of
AgNORs may reflect the proliferative nature of bladder lesions induced by BBN, as reported in preneoplastic and neoplastic lesions in other organs. PN
hyperplasias were classified into two types based upon the mean number of
AgNORs, indicating that they include reversible and irreversible changes in contrast with simple
hyperplasia which is reversible change.