Circadian rhythms of cardiovascular functions are modulated by the baroreflex and the autonomic nervous system in the rat.
BACKGROUND
We assessed the hypothesis that the baroreflex and the autonomic nervous system are important in the control of the circadian rhythms of cardiovascular functions.


RESULTS
We continuously measured blood pressure (BP), heart rate (HR), and locomotor activity in sinoaortic denervated (SAD), sympathectomized, and atropine-injected rats by use of a radiotelemetry system. The circadian rhythm of mean blood pressure (MBP) was selectively disrupted in SAD rats under 12-hour light-dark (LD12:12) cycles as a result of an increase in MBP during the light period and disappeared under constant darkness (DD). The locomotor activity and HR were not remarkably affected by SAD. The circadian rhythm of MBP was suppressed in sympathectomized rats by a decrease in the MBP during the dark period, and the abrupt changes in MBP when the lighting was altered were not seen under LD. Under DD, an MBP rhythm similar to that observed under LD was obtained. Sympathectomized rats also showed lower HR levels during the dark period than intact rats under LD cycles. In atropine-injected rats, the MBP and HR increased, especially during the light period, resulting in a reduction of light-dark differences in MBP and HR. The locomotor activity showed an apparent 24-hour variation in the sympathectomized and atropine-injected rats.


CONCLUSIONS
The disruption of the baroreflex selectively eliminates the circadian rhythm of BP, and the circadian rhythms of BP and HR are modulated by the autonomic nervous system in rats. The circadian rhythms of BP and HR are regulated by different mechanisms involving the autonomic nervous system.
Makino
M
M
First Department of Internal Medicine, Nagoya University School of Medicine, Japan.
Hayashi
H
H
Takezawa
H
H
Hirai
M
M
Saito
H
H
Ebihara
S
S
D000818:Animals; D001341:Autonomic Nervous System / Q000502:physiology*; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D002320:Cardiovascular Physiological Phenomena; D002940:Circadian Rhythm; D003714:Denervation; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology; D009407:Nerve Block; D010275:Parasympathetic Nervous System / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012850:Sinus of Valsalva / Q000294:innervation; D013563:Sympathectomy, Chemical