抄録
Circadian timing system and the cell division cycle are frequently deregulated in cancer. We examined the differences of carcinogenicity and circadian activity rhythmicity by the time of day after the injection of carcinogen. Diethylnitrosamine (DEN), which is widely used to promotes hepatic carcinoma, was injected (i.p., 200 mg/kg) on rats kept under the light-dark cycle at zeitgeber time (ZT) 3:00, 9:00, 15:00 and 21:00. Before and after the injection of DEN, locomotor activity rhythm was recorded until 10th week. After the activity recording, livers of same specimens were histochemically analyzed using H-E and GST-P immunostaining, early detection marker of carcinogenicity, positive cells. After the DEN injection, decrease of activity mass on the next day was common in any of the injection time. The GST-P positive cells were abundant when the DEN was injected at 9:00 and 21:00 compared that at 15:00 and 3:00. The ratio of activity during the dark and light was greatest when the DEN was injected at 3:00. The effect of DEN on carcinogenicity and locomotor activity rhythm are not uniform by the administration time in a day. The activity levels during the dark period might relate with the hepatic carcinogenicity. [J Physiol Sci. 2008;58 Suppl:S90]
