Quantification of oral epithelial hyperplasia in rats after topical application of the carcinogen 4-nitroquinoline...

Hyperplasia of the palatal epithelium was quantified in two groups of rats exposed thrice weekly to the carcinogen 4NQO for 2 weeks and 2 months, respectively. The lengths and areas of the epithelial layers were measured with a computerized line-following device. In the group treated for 2 weeks the maximum area of the nuclear layer was nearly three times and the maximum length of the epithelial/connective tissue interface almost twice the normal at the end of the carcinogen application period. The maximum area of the cornified layer was three times and the maximum lengths of the epithelial surface and the keratin/nuclear layer interface almost one and a half times the normal 1 week after painting with 4NQO. Thereafter the lengths and areas decreased gradually in both experimental groups. The area of the cornified layer and the length of the epithelial/connective tissue interface in the group treated for 2 months were significantly larger than those in animals treated for 2 weeks. These variables may be two of several indicators of prognostic significance in the assessment of dose-related premalignant epithelial hyperplasia.