The effects of short light/dark cycle in mice

光/暗循环是生物体内最基本和最重要的环境因素之一，它决定了动物生理或行为的昼夜节律。昼夜周期的变化影响着各种生理功能的昼夜节律，如激素分泌、细胞周期、行为等。并且，这种昼夜节律现在被用于确定药物给药的时间。本研究比较了短光/暗周期对6hr -6hr暗周期小鼠肺和肝脏DNA合成和肿瘤生长的影响，并与长时间12hr -12hr暗标准周期小鼠进行了比较。用聚氨酯或二乙基亚硝胺处理CD-1、A/J和C3H/He小鼠，维持在短光/暗循环（6小时亮，6小时暗）下，其肺肿瘤或肝癌的大小明显大于标准光/暗循环（12小时亮，12小时暗）下的小鼠，说明短而频繁的光/暗循环促进了肿瘤的生长。注射3h标记胸苷并测量肺组织的放射性掺入，在短光/暗循环下，肺内DNA合成在一天内出现两个峰，且两个峰都在亮周期，而在标准光/暗循环下，在暗周期只观察到一个峰。虽然短光/暗周期下肺组织中3h -胸苷的掺入水平低于标准周期，但频繁或不平衡的DNA合成可能促进了肺肿瘤的生长。

The light/dark cycle is one of the most essential and important environmental element in the organism, and this determines the physiological or behavioral circadian rhythm in animals. The change of daily light/dark cycle is known to influence the circadian rhythm of various physiological functions such as secretion of hormone, cell cycle, behavior, etc. And, such circadian rhythm is now utilized for determining the timing of drug administration.In the present study, it was examined that the effects of short light/dark cycle on the DNA synthesis and tumor growth in the mouse lung and liver when mice were nursed in the 6hr light-6hr dark cycle in comparison with 12hr light-12hr dark standard cycle for long period.CD-1, A/J and C3H/He mice, which were treated with urethane or diethylnitrosamine and maintained under the short light/dark cycle (6hr light, 6hr dark), developed significantly larger sizes of lung tumors or hepatoma than the mice maintained under standard light/dark cycle (12hr light, 12hr dark), indicating that short and frequent light/dark cycle enhanced tumor growth. When 3H-labeled thymidine was injected and incorporated radioactivities in the lung tissue were measured, two peaks of DNA synthesis in the lung were observed in a day under the short light/dark cycle, and both peaks were during light periods, while only one peak was observed during the dark period under the standard light/dark cycle. Although the level of 3H-thymidine incorporation into the lung tissue in the short light/dark cycle is lower than that in the standard one, frequent or unbalanced DNA synthesis may have promoted the growth of lung tumors.