Suprachiasmatic lesions eliminate 24-h blood pressure variability in rats.

To evaluate whether the suprachiasmatic nuclei (SCN) control 24-h rhythmicity in cardiovascular function, rats were subjected to computerized recording of 24-h blood pressure (BP) and heart rate (HR) following SCN lesions. In sham- and nonlesioned rats, circadian patterns of BP and HR ran in phase with those in feeding behavior. In SCN-lesioned rats circadian rhythmicity in BP, HR and food intake were abolished. Minute-to-minute variation of BP and HR was similar as in sham- and nonlesioned rats. We conclude that long-term but not short-term variability of blood pressure and heart rate is largely determined by SCN-controlled activity levels.