High susceptibility of analbuminemic rats to neurogenic tumor induction by transplacental administration of N-ethyl-N-nitrosourea

Low susceptibility to N-ethyl-N-nitrosourea-induced transplacental carcinogenesis in Long-Evans Cinnamon (LEC) rats

The Long-Evans Cinnamon (LEC) rat, an animal model of Wilson's disease, is resistant to a variety of chemical carcinogenesis except liver and colon. In the present study, N-ethyl-N-nitrosourea (ENU)-induced transplacental carcinogenesis was examined in male and female LEC, Long-Evans Agouti (LEA), a sibling line of the LEC rat, and F344 rats (n=21). ENU was administered to pregnant rats as a single s.c. injection at a dose of 60 mg/kg body weight on the 17th day after conception. Cerebral/spinal gliomas and trigeminal/spinal nerve schwannomas developed in both LEA and F344 rats at 30 weeks of age, but no nervous system tumors developed in LEC rats, the difference being statistically significant. Lung adenomas also developed in LEA and F344 rats, but not in LEC rats. Semiquantitative RT-PCR demonstrated that metallothionein (MT)1a, MT2 and O(6)-methylguanine-DNA methyltransferase (MGMT) mRNA levels in the liver of LEC rats were higher than those in F344 and LEA rats. In addition, Western blot analysis showed that MT (MT1 plus MT2) in the liver of LEC rats was also higher than that in other strains. Present results suggest that high levels of MT and/or MGMT contribute to the resistance to nitrosamine-induced carcinogenesis in LEC rats.

Testing electromagnetic fields for potential carcinogenic activity: a critical review of animal models

In order to assess the potential of electromagnetic fields (EMF) to influence the process of carcinogenesis, it will be necessary to supplement epidemiological studies with controlled laboratory studies in animals. There are now a number of suitable assays available that focus on different histopathological forms of cancer and on different stages of carcinogenesis--induction, promotion, progression. In this review we discuss eight major systems in the context of this generalized carcinogenesis paradigm. Our aim is to bring together what is currently known about the biology of carcinogenesis in these systems in order to provide a context for evaluating EMF results as they become available. We also critically discuss EMF test results that have so far been obtained in the animal models reviewed. Most of the 19 completed studies identified were negative. However, suggestive positive results were reported in three promotion assays (in rat mammary gland, in rat liver, and in mouse skin), and in one multigeneration study in mice. Results in the rat liver assay and in the multigeneration study have only been reported in abstract form and cannot be adequately evaluated. Positive results reported in both the rat mammary gland and the mouse skin systems are of weak statistical significance and have not been independently replicated. However, it may be of interest that effects in both systems appear primarily to involve the progression stage of carcinogenesis. We suggest that more definitive conclusions as to the carcinogenic potential of EMF may require expanded test protocols that reinforce traditional carcinogenesis end points with biochemical or other parameters reflective of biological processes known to be associated with carcinogenesis in the different systems.

Increasing development of pepsinogen-altered pyloric glands and adenocarcinoma in glandular stomach of analbuminemic rats

The susceptibility of pepsinogen-altered pyloric glands (PAPG) and neoplastic glandular stomach lesions induced by N-methyl-N-nitro-N-nitrosoguanidine (MNNG) and catechol or sodium cholate in Nagase analbuminemic rats (NAR) was compared to Sprague-Dawley rats (SD). Male NAR and SD rats were given a single dose of 80 mg/kg body weight of MNNG by gastric intubation and, 2 weeks later, fed basal diet containing 0.8% catechol or 0.3% sodium cholate for 18 weeks. The animals were killed at the end of week 20 or after maintenance on basal diet at week 60. The number of pepsinogen-altered pyloric glands at week 20 was significantly (P < 0.001) higher in NAR fed either catechol or sodium cholate compared with SD rats. At week 60, adenomatous hyperplasias and adenocarcinomas were observed in 7 (88%; P < 0.01) and 3 (38%; P < 0.01) of 8 NAR fed catechol and in 4 (22%) and 0 of 18 SD rats, respectively. The results show that the frequency of PAPG in NAR and SD rats is related to the susceptibility to glandular stomach carcinoma. PAPG is a useful endpoint lesion for evaluation of gastric carcinogenicity in a 20-week carcinogenicity test, and NAR are sensitive for glandular stomach carcinogenesis.