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Comparative Study
. 2000 Feb 1;148(2):121-6.
doi: 10.1016/s0304-3835(99)00320-1.

Effect of constant light on DMBA mammary tumorigenesis in rats

L E Anderson  1 , J E Morris, L B Sasser, R G Stevens
Affiliations
Comparative Study

Effect of constant light on DMBA mammary tumorigenesis in rats

L E Anderson et al. Cancer Lett. .

Abstract

A study of light, and mammary tumorigenesis was conducted in rats. One-hundred female Sprague-Dawley rats were divided by weight into two groups. One group was exposed to constant light (LL) from 26 days of age, and the second group was exposed to 8 h light and 16 h dark per day (LD). Both groups received an 8 mg dose of a chemical carcinogen, dimethylben-zanthracene (DMBA) at 52 days of age. At 13 weeks post-DMBA, there were significantly fewer mammary tumors in the LL group compared with the LD group. Constant light was clearly demonstrated to have a profound effect on mammary tissue development. Although virgin, the majority of the LL rats (29/50) had gross evidence of lactation at 141 days of age. None of the LD rats (0/50) showed evidence of milk production. These results suggest that constant light not only substantially accelerated mammary gland development, but pushed development of the tissue past the stage normally observed in virgin animals (to the lactation stage).

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Figures

Fig. 1
Fig. 1
Average body weight (mean±SE) of rats exposed to constant light beginning at 26 days of age, LL group (- - - ○- - -); or to normal lighting, 8:16, LD group (□). Both groups were gavaged with DMBA (8 mg) at 52 days of age. The growth curves of the two groups were not statistically different (P>0.05).
Fig. 2
Fig. 2
Number of rats with palpable masses exposed to constant light beginning at 26 days of age, LL group (- - - ○- - -); or to normal lighting, 8:16, LD group (□). Both groups were gavaged with DMBA (8 mg) at 52 days of age. The number of rats confirmed with tumors at necropsy in the LL group (○) and LD group (□). The groups were significantly different (P<0.05) by analysis of variance.
Fig. 3
Fig. 3
Total palpable masses in rats exposed to constant light beginning at 26 days of age, LL group (- - - ○- - -); or to normal lighting, 8:16, LD group (□). Both groups were gavaged with DMBA (8 mg) at 52 days of age. The total number of confirmed tumors at necropsy in the LL group (○) and LD group (□). The groups were significantly different (P<0.01) by analysis of variance.
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