[Effects of light deprivation on carcinogenesis induced by N-nitrosomethylurea in female rats]

One month-old female rats were blinded by surgery and received single intravenous injections of 50 mg/kg body weight of N-nitrosomethylurea (NMU) two weeks later. Simultaneously, normal animals were injected an identical dose of NMU. The frequency of NMU-induced neoplasms in blind rats was 33% vs. 75% in control (P < 0.05), with neoplastic development latency being longer as compared with controls. The frequency of mammary gland adenocarcinoma, leukemia and adenoma of the pituitary and thyroid gland in blind rats was significantly lower while mammary gland fibroadenoma was more frequent than in intact animals. Carcinogen-treated blind animals survived much longer (448 +/- 21 days) than normal controls (284 +/- 22 days) (P < 0.001). The frequency of spontaneous neoplasms in blind and normal rats was identical. The inhibitory effect on carcinogenesis seems to be due to enhanced functional activity of the pineal gland in blind animals.