The role of clock gene on cardiovascular regulation

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Circadian rhythm is an endogenous rhythm controlled by a master oscillator in the supra-chiasmatic nucleus of hypothalamus. Recent developments in our understanding of the genetic mechanisms of circadian system have led to a transcriptional feedback loop contains both positive and negative components. In order to clarify the role of Clock gene, which is one of the main positive components, we recorded blood pressure (BP) and heart rate (HR) in the Clock mutant mice on Jcl : ICR background (Clockj) and wild-type mice (WT) using telemetry system (TA11PA-C20 ; DSI). BP in the Clockj was significantly higher than WT during the light period. HR in the Clockj was significantly lower than WT during the dark period. Daily mean of BP in the Clockj was significantly higher, and that of HR was significantly lower in comparison to WT. We hypothesized that Clockj has some impairment of water balance controlled by adreno-cortical hormones. After adrenalectomy, the amplitude of BP and HR lost the significant difference between the Clockj and WT, although the acrophase did not change. It is possible that the altered function of adrenal gland, which is caused by the lack of normal Clock gene, may induce non-dipping circadian profile of BP and HR.