| Abstract: | Recent studies have suggested the possibility that nocturnal light exposure affects manybiological processes in rodents, especially the circadian rhythm, an endogenousoscillation of approximately 24 h. However, there is still insufficient information aboutthe physiological effects of nocturnal light exposure. In this study, we examined thechanges in gene expression and serum levels of plasminogen activator inhibitor-1 (PAI-1),a major component of the fibrinolytic system that shows typical circadian rhythmicity, inC3H/He mice. Zeitgeber time (ZT) was assessed with reference to the onset of light period(ZT0). Exposure to fluorescent light (70 lux) for 1 h in the dark period (ZT14) caused asignificant increase in hepatic Pai-1 gene expression at ZT16. SerumPAI-1 levels also tended to increase, albeit not significantly. Expression levels of thetypical clock genes Bmal1, Clock, andPer1 were significantly increased at ZT21, ZT16, and ZT18,respectively. Exposure to nocturnal light significantly increased plasma adrenalin levels.The effects of nocturnal light exposure on Pai-1 expression disappearedin adrenalectomized mice, although the changes in clock genes were still apparent. Inconclusion, our results suggest that nocturnal light exposure, even for 1 h, altershepatic Pai-1 gene expression by stimulating the adrenal pathway.Adrenalin secreted from the adrenal gland may be an important signaling mediator of thechange in Pai-1 expression in response to nocturnal light exposure. |
