Effects of suprachiasmatic lesions on circadian rhythms of blood pressure, heart rate and locomotor activity in the rat.

To determine whether the circadian rhythms in blood pressure (BP), heart rate (HR) and locomotor activity are controlled by an internal biological clock located in the suprachiasmatic nucleus (SCN), we continuously measured these parameters in SCN-lesioned rats using a newly developed implantable radiotelemetry device and a computerized data collecting system. Although SCN-lesioned rats showed a weak but significant 24-h periodicity in BP and HR under light-dark (LD) cycles, BP, HR and locomotor activity became completely aperiodic under constant dark (DD) conditions. The amount of locomotor activity was significantly reduced in SCN-lesioned rats compared to that in intact rats. BP tended to be higher in SCN-lesioned rats, but the differences were significant only in the comparison of systolic blood pressure (SBP) under LD and DD (p < 0.05) and of mean blood pressure (MBP) under LD (p < 0.05). HR in SCN-lesioned rats was significantly lower under LD (p < 0.05), but not under DD. The standard deviation and the variation coefficient of MBP, as indices of short-term variability of this parameter, were significantly larger in SCN-lesioned rats than in intact rats, while those of HR and locomotor activity did not differ significantly between SCN-lesioned and intact rats. These results indicate that the SCN is important not only for generating circadian rhythms of BP, HR and locomotor activity, but also for buffering the short-term variability of BP in rats.