Alterations in blood pressure and heart rate variability in transgenic rats with low brain angiotensinogen

To study whether the brain renin-angiotensin system plays a role in the lon g-term and short-term control of blood pressure and heart rate variability, we examined in transgenic rats [TGR(ASrAOGEN)] with low brain angiotensino gen levels the 24-hour variation of blood pressure and heart rate. Telemetr y recordings were made during basal and hypertensive conditions induced by a low-dose subcutaneous infusion of angiotensin IT for 7 days. Short-term b lood pressure and heart rate variability were evaluated by spectral analysi s, and as a measure of baroreflex sensitivity, the average transfer gain be tween the pressure and heart rate variations was calculated. During the ang iotensin II infusion in control but not TGR(ASrAOGEN) rats, the 24-hour rhy thm of blood pressure was inverted (5.8+/-2 versus -0.4+/-1.8 mm Hg/group o f day-night differences of blood pressure P<0.05, respectively). In both th e control and TGR(ASrAOGEN) rats, the 24-hour heart rate rhythms remained u naltered and paralleled those of locomotor activity. The transfer gain betw een 0.3 to 0.6 Hz was significantly higher in TGR(ASrAOGEN) than in control rats during control (0.71+/-0.1 versus 0.35+/-0.06, P<0.05) but not during angiotensin II infusion (0.6+/-0.07 versus 0.4+/-0.1, P>0.05). These resul ts demonstrate that the brain renin-angiotensin system plays an important r ole in mediating the effects of angiotensin II on the circadian variation o f blood pressure. Furthermore, these data indicate that a permanent deficie ncy in the brain renin-angiotensin system alters the reflex control of hear t rate in rats.