Influence of light and 9,10-dimethylbenz(a) anthracene on rat ovarian steroidogenesis: phenolic steroids

Effect of exposure to light-at-night on life span and spontaneous carcinogenesis in female CBA mice

The effect of constant illumination on the development of spontaneous tumors in female CBA mice was investigated. Fifty female CBA mice starting from the age of 2 months were kept under standard light/dark regimen (12 hr light:12 hr dark; LD) and 50 CBA mice of similar age were kept under constant illumination (24 hr a day, 2,500 Lux, LL). Exposure to the LL regimen decreased food consumption but did not influence body weight, significantly accelerated age-related disturbances in estrous function, and was followed by a significant increase in spontaneous tumor incidence in female CBA mice. Tumor incidence as well as the number of total or malignant tumors was significantly increased in the LL group compared to the LD group (p < 0.001). The incidence of lung adenocarcinomas, leukemias and hepatocarcinomas was 7/50; 6/50 and 4/50 in the LL group and 1/50; 0/50 and 0/50 in the LD group. Mice from the LL groups had shorter life spans then those from the LD group. The data demonstrate, for the first time, that exposure to constant illumination was followed by increases in the incidence of spontaneous lung carcinoma, leukemias and hepatocarcinoma in female CBA mice.

Effect of light/dark regimen on N-nitrosoethylurea-induced transplacental carcinogenesis in rats

Pregnant females were randomly subdivided into three groups (24 rats per group) and kept at the 12:12 h light/dark regimen (group 1), at the constant light illumination (24 h a day, group 2) or at the continuous darkness (group 3). N-nitrosoethylurea (NEU) has been injected into the tail vein of all rats (80 mg/kg) on the 18-19th day of the pregnancy. After the delivery the lacting dams and their progeny during the lactation period (1 month after delivery) were kept also at the three different light/dark regimens. Then all offspring from each group was kept at the 12:12 h light/dark regimen, males and females separately, and were observed until natural death. The exposure to constant light significantly promoted the transplacental carcinogenesis whereas the exposure to constant darkness inhibited it. The incidence of total tumors, tumors of both a peripheral nervous system and kidney was 2.6; 2.5 and 8.5 times higher, and survival significantly shorter, correspondingly, in rats from the group 2 exposed to the constant light regimen as compared to the group 1 (12:12 h light/dark regimen) (P<0.05). On the other hand, the exposure to the continuous darkness during the pregnancy and the lactation period significantly inhibited the transplacental carcinogenesis in the offspring of rats treated with NEU. The incidence of total tumors, tumors of a peripheral nervous system was by 2.4 and 2.7 times less, and survival longer, respectively, in exposed to the darkness rats from the group 3 as compared to the group 1 (12:12 h light/dark regimen) (P<0.05). Thus, our data firstly have shown the modifying effect of light-dark regimen on the realization of the transplacental carcinogenesis induced by NEU in rats.