Alterations of the nucleolar organizer regions during 4-nitroquinoline 1-oxide-induced tongue carcinogenesis in rats.

The number of silver-stained nucleolar proteins (AgNORs) was enumerated in preneoplastic and neoplastic rat tongue lesions induced by 4-nitroquinoline 1-oxide (4-NQO). Male ACI/N rats were given 0 to 10 p.p.m. 4-NQO for 12, 20 or 36 weeks to induce hyperplasia, dysplasia and neoplasm in tongue. The mean numbers of AgNORs stained by a modified one-step silver colloid method in various epithelial lesions were as follows: normal squamous epithelium (n = 5), 1.52 +/- 0.03; non-lesional squamous epithelium (n = 5), 1.58 +/- 0.04; hyperplasia (n = 20), 1.84 +/- 0.15; dysplasia (n = 20), 2.32 +/- 0.12; papilloma (n = 6), 2.23 +/- 0.10; and squamous cell carcinoma (n = 4), 3.06 +/- 0.26. Thus, the mean number of AgNORs showed a stepwise increase from untreated and treated, histologically normal squamous epithelium through hyperplasia and dysplasia to squamous cell papilloma and carcinoma, although the value of severe dysplasia was between those of papilloma and carcinoma. These results indicate that the mean number of AgNORs may reflect the proliferative nature of tongue lesions, as suggested in carcinogenesis of other organs, and also suggest that severe dysplasia is a direct precursor lesion for squamous cell carcinoma of the tongue induced by 4-NQO.