Thorud E, Clausen O P, Kauffman S L
Cell Tissue Kinet. 1984 Nov;17(6):549-56. doi: 10.1111/j.1365-2184.1984.tb00614.x.
Circadian rhythms in epidermal basal cell-cycle progression in hairless mouse skin have been repeatedly demonstrated. A dose of 10 mg/animal hydroxyurea (HU), given to inhibit DNA synthesis was injected intraperitoneally to two groups of hairless mice. One group was injected at 10.00 hours MET, when the cell-cycle progression and cell division rate are relatively high, and another group was injected at 20.00 hours, when the same variables are at minimum values. Various cell kinetic methods--[3H]TdR autoradiography, DNA flow cytometry and the stathmokinetic method (Colcemid)--were used to study HU-induced alterations in cell kinetics. Hydroxyurea (HU) immediately reduced the labelling index (LI) to less than 10% of controls when injected at both times of the day, and higher then normal values were observed 8 hr later. A subsequent decrease towards normal values was steeper in the 20.00 hours injected group. The proportion of cells with S-phase DNA content was transiently reduced in both series, but the reduction was less pronounced and control values were reached earlier in the series injected at 10.00 hours. The observed alterations in LI and fraction of cells in S phase were followed by comparable alterations in the fraction of cells in G2 and in the mitotic rate. Hence the changes in G2 and mitotic rate are easily explained as consequences of the previous perturbations in the S phase. The time-dependent differences in the cell kinetic perturbations caused by HU in the S phase may be explained by a circadian-phase-dependent action of HU on the influx and efflux of cells to and from the S phase, respectively. At 10.00 hours the efflux of cells from S is most heavily inhibited; at 20.00 hours the influx is predominantly blocked. Hence, when physiological flux is high HU mainly blocks the efflux from S, but when flux normally is low, HU mainly blocks the entrance to S. Within 20 hours after the HU injection, the cell kinetic variables had approached the unperturbed circadian pattern.
无毛小鼠皮肤表皮基底细胞周期进程中的昼夜节律已得到反复证实。向两组无毛小鼠腹腔注射剂量为10mg/动物的羟基脲（HU）以抑制DNA合成。一组在中部欧洲时间10:00注射，此时细胞周期进程和细胞分裂率相对较高；另一组在20:00注射，此时相同变量处于最小值。使用了各种细胞动力学方法——[3H]TdR放射自显影术、DNA流式细胞术和有丝分裂阻断法（秋水仙酰胺）——来研究HU诱导的细胞动力学变化。当在一天中的这两个时间点注射时，羟基脲（HU）立即将标记指数（LI）降低至对照组的10%以下，8小时后观察到高于正常值。随后向正常值的下降在20:00注射组中更为陡峭。两个系列中具有S期DNA含量的细胞比例均短暂降低，但在10:00注射的系列中降低不太明显且更早达到对照值。观察到的LI和S期细胞比例的变化之后，G2期细胞比例和有丝分裂率也出现了类似变化。因此，G2期和有丝分裂率的变化很容易解释为先前S期扰动的结果。HU在S期引起的细胞动力学扰动的时间依赖性差异可能是由于HU对细胞进出S期的流入和流出分别具有昼夜节律依赖性作用。在10:00，细胞从S期的流出受到最严重抑制；在20:00，流入主要被阻断。因此，当生理通量高时，HU主要阻断从S期的流出，但当通量正常较低时，HU主要阻断进入S期。在HU注射后20小时内，细胞动力学变量已接近未受扰动的昼夜节律模式。
