Abstract
BackgroundDiurnal variations in the incidence of events such as heart attack and stroke suggest a role for circadian rhythms in the etiology of cardiovascular disease. The aim of this study was to assess the influence of the suprachiasmatic nucleus (SCN) circadian clock on cardiovascular function.Methodology/Principal FindingsHeart rate (HR), blood pressure (BP) and locomotor activity (LA) were measured in circadian mutant (Vipr2 −/−) mice and wild type littermates, using implanted radio-telemetry devices. Sleep and wakefulness were studied in similar mice implanted with electroencephalograph (EEG) electrodes. There was less diurnal variation in the frequency and duration of bouts of rest/activity and sleep/wake in Vipr2 −/− mice than in wild type (WT) and short “ultradian” episodes of arousal were more prominent, especially in constant conditions (DD). Activity was an important determinant of circadian variation in BP and HR in animals of both genotypes; altered timing of episodes of activity and rest (as well as sleep and wakefulness) across the day accounted for most of the difference between Vipr2 −/− mice and WT. However, there was also a modest circadian rhythm of resting HR and BP that was independent of LA.Conclusions/SignificanceIf appropriate methods of analysis are used that take into account sleep and locomotor activity level, mice are a good model for understanding the contribution of circadian timing to cardiovascular function. Future studies of the influence of sleep and wakefulness on cardiovascular physiology may help to explain accumulating evidence linking disrupted sleep with cardiovascular disease in man.
Highlights
Mammals exhibit daily rhythms in many aspects of their physiology, metabolism and behavior, such as sleep and wakefulness, the secretion of stress hormones, body temperature, heart rate and blood pressure
The time spent in rest periods less than 3 h in duration was a measure of ultradian activity, which robustly distinguished the behavior of Vipr22/2 mice from wild type (WT)
Using the squared correlation coefficient (R2) measure for explained variance [28] we found that the day/night cycle explained less of the variability in heart rate and blood pressure in WT mice than locomotor activity in all conditions (Table S2); in Vipr22/2 mice the contribution of the day/night cycle was very small
Summary
Mammals exhibit daily rhythms in many aspects of their physiology, metabolism and behavior, such as sleep and wakefulness, the secretion of stress hormones, body temperature, heart rate and blood pressure. These rhythms are coordinated by a master circadian clock, situated in the suprachiasmatic nuclei (SCN) of the hypothalamus, which is synchronized to the external environment primarily by signals from the visual system, providing information about the 24-hr light-dark environment. There are two mechanisms by which the SCN may impose rhythmicity: directly, by imposing circadian timing through neural or hormonal signals and indirectly, through effects on rhythms of behavior, such as feeding and the sleep-wake cycle [2]. The aim of this study was to assess the influence of the suprachiasmatic nucleus (SCN) circadian clock on cardiovascular function
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
