Estrous cycle modification of rat uterine DNA alkylation by N-methyl-N-nitrosourea

Dietary lignin, and insoluble fiber, enhance uterine cancer but did not influence mammary cancer induced by N-methyl-N-nitrosourea in rats

Previous investigations suggested potential breast cancer-preventive properties of dietary fiber from cabbage. The purpose of the present investigation was to determine whether lignin, a component of cabbage fiber, would protect against mammary carcinogenesis by N-methyl-N-nitrosourea (MNU) in Sprague-Dawley rats. A six-week study was conducted using diets containing 0.5-5% dietary wood lignin (a readily available, purified source). These diets were well tolerated by the rats, and a carcinogenesis study using 5 mg MNU/100 g body wt i.v. at 50 days of age was conducted, with the 2.5% lignin diet fed from 6 through 8 weeks of age followed by 5% lignin diet until 20 weeks after MNU. Dietary lignin and MNU treatment increased food consumption (p < 0.05), and body weight was slightly reduced at 10 and 20 weeks after MNU in the MNU-5% lignin diet group (p < 0.05). Serum estradiol was not altered by dietary lignin or MNU treatment, but uterine weights were highest in the MNU-control diet group 4 and 12 weeks after MNU. Expression of creatine kinase B, and estrogen-responsive gene, was lower in eh uteri of the MNU-lignin diet group than in other groups at 20 weeks. Mammary carcinogenesis was not altered by dietary lignin. However, uterine endometrial adenocarcinoma was observed only in the MNU-lignin diet group (4 carcinomas/40 effective rats) (p < 0.05).

Estrous cycle dependence of nitrosomethylurea (NMU)-induced preneoplastic lesions in rat mammary gland

Virgin 50-55-day-old rats exhibiting regular estrous cycles were injected i.v. with the direct acting carcinogen 1-nitroso-1-methylurea (NMU) on the morning of proestrus, estrus, or diestrus. Rats were killed at weekly intervals following NMU administration to identify source and number of microscopically identifiable dysplasias. Terminal end bud (TEB) abnormalities appeared within 1 week following NMU administration, with a significantly greater number of abnormal TEBs in mammary glands of rats injected on proestrus (PE) and estrus (E) than on diestrus (DE). Ductal (DH) and ductal alveolar hyperplasias (DAH) and hyperplastic alveolar nodules (HAN) appeared during week 3, with significantly more of each type of lesion appearing by 6 weeks after NMU injection. HAN were most numerous in glands from rats injected on estrus. Adenocarcinomas arose from both the proximal and distal ductal network; at 10 and 12 weeks post NMU, significantly more tumors were found in rats injected on proestrus than diestrus and estrus. These results support the theory that the hormonal environment at the time of NMU administration significantly alters early development of mammary tumors in the rat.