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 inje ction. 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 or al squamous-cell carcinoma, other changes such as acantholytic dyskera tosis, invading cysts, duct-like structures and basaloid islands and c ords were not. The extent and severity of the changes increased with t ime so that by 22 weeks there was extensive involvement of the palatal bone and marrow spaces, the molar periodontal ligament and the greate r palatine neurovascular bundle by neoplastic epithelium. The invading epithelium was derived from the junctional, crevicular and palatal gi ngival and intermolar epithelium. The latent period for the crevicular and junctional epithelia was shorter than that for the palatal gingiv al and intermolar epithelium. The invasive changes from the latter epi thelium were often preceded by exophytic changes such as epithelial pr ojections, papillae and papillomas. Such changes were infrequent for t he gingival, crevicular and junctional epithelia. The study shows that intraperitoneal NMU acts as a complete carcinogen on the palatal ging ival and intermolar epithelium in hamsters.