Iversen O H, Kauffman S L
Int J Chronobiol. 1981;8(1):49-62.
Groups of hairless nice were given a single topical application of each of two highly-reactive carcinogens (methylnitrosourea and beta-propiolactone) at 12(00) and 00(00). The tumor yield was as follows: for methylnitrosourea there was a slightly higher yield of skin tumours in the animals painted at 12(00); for animals painted with beta-propiolactone, there was a significantly higher skin tumour yield in those painted at 12(00). When the groups painted with the two carcinogens are considered together, there was a significantly higher number of animals with all types of tumours in the group painted at 12(00). Hence, there seems to be a circadian variation in the sensitivity of a tissue to a single contact with a chemical carcinogen. This may be related to the proliferative state of the tissue involved: at 12(00), DNA and cell division takes place at a more rapid rate than at 00(00).
将无毛小鼠分为几组，分别在中午12点和午夜0点单次局部涂抹两种高活性致癌物（甲基亚硝基脲和β-丙内酯）。肿瘤发生率如下：对于甲基亚硝基脲，中午12点涂抹的动物皮肤肿瘤发生率略高；对于涂抹β-丙内酯的动物，中午12点涂抹的动物皮肤肿瘤发生率显著更高。当将涂抹两种致癌物的组放在一起考虑时，中午12点涂抹组中出现各类肿瘤的动物数量显著更多。因此，组织对单次接触化学致癌物的敏感性似乎存在昼夜变化。这可能与所涉及组织的增殖状态有关：中午12点时，DNA和细胞分裂的速度比午夜0点时更快。
