The effect of intraperitoneal N-methyl-N-nitrosourea on hamster palatal gingiva and intermolar mucosa.

Fifty 4- to 6-week-old male random-bred golden hamsters were injected intraperitoneally with a weight-related dose (12.5 mg/kg body weight) of N-methyl-N-nitrosourea (NMU) three times a week for 4 weeks. Groups of seven animals were killed 10, 16 and 22 weeks after the first injection. The palatal gingiva from six animals and the intermolar mucosa from 21 animals was examined. Seven male age-matched untreated control animals were killed at each period. Although all NMU-treated hamsters showed dysplastic and neoplastic changes similar to those in human oral squamous-cell carcinoma, other changes such as acantholytic dyskeratosis, invading cysts, duct-like structures and basaloid islands and cords were not. The extent and severity of the changes increased with time so that by 22 weeks there was extensive involvement of the palatal bone and marrow spaces, the molar periodontal ligament and the greater palatine neurovascular bundle by neoplastic epithelium. The invading epithelium was derived from the junctional, crevicular and palatal gingival and intermolar epithelium. The latent period for the crevicular and junctional epithelia was shorter than that for the palatal gingival and intermolar epithelium. The invasive changes from the latter epithelium were often preceded by exophytic changes such as epithelial projections, papillae and papillomas. Such changes were infrequent for the gingival, crevicular and junctional epithelia. The study shows that intraperitoneal NMU acts as a complete carcinogen on the palatal gingival and intermolar epithelium in hamsters.