Neurogenic tumors in rats induced by ethylnitrosourea

Ethylnitrosourea (ENU) was injected intravenously into Sprague-Dawley rats on day 15 of gestation at doses of 0, 2.50, 6.25 and 10.00 mg/kg. The resulting 1980 progeny were observed for up to 24 months in a life-time study (900 rats) or for periods of 171-325 days in a serial sacrifice study (1080 rats). The rats in both studies were randomized into three groups, one exposed to a radiofrequency, one sham-exposed and one cage control. Since no effects of the radiofrequency were observed on the ENU-induced tumors, the exposure groups were combined to facilitate study of the tumors by dose rate over time. All rats were necropsied and major organs were examined histologically including the brain, entire spinal cord, trigeminal nerves and all tumors. A total of 48 spinal cord tumors (SCT), 251 spinal nerve tumors, 264 cranial nerve tumors and 1058 brain tumors were studied. The tumors were characterized by incidence, histologic type, volume, malignancy and multiplicity. Ethylnitrosouria, as given in this study, was determined to be an effective carcinogen reliably inducing (in order of frequency) brain, cranial nerve, spinal nerve and SCT. Dose of ENU correlated positively with the frequency, multiplicity, volume, malignancy, and negatively with latency of brain tumors and to a lesser extent with nerve tumors.