CIRCADIAN AND SHORT-TERM VARIABILITIES IN BLOOD-PRESSURE AND HEART-RATE MEASURED BY TELEMETRY IN RABBITS AND RATS

Blood pressure (BP) and heart rate (HR) were measured by telemetry in conscious unrestrained rabbits to clarify the profile of their variabi lities. The variabilities were assessed for two periods, 24 h (circadi an rhythm) and 1 h (short-term variability), and compared with those i n rats. BP and HR in rabbits were lower than those in rats but the cir cadian rhythms in rabbits showed nocturnal patterns as is the case in rats. In contrast, short-term variabilities in BP in rabbits were cons iderably larger than those in rats. The short-term variability in BP i n rabbits was suppressed by alpha-adrenergic blocking without changes in basal values but not by beta-adrenergic blocking or angiotensin con verting enzyme inhibition. These results demonstrate the need to take the unique characteristics of short-term variability in BP in rabbit i nto consideration when the circadian rhythm is focused on and that the short-term variability in BP in rabbits is caused mainly by activatio n of alpha-adrenergic receptors.