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 long-term and short-term control of blood pressure and heart rate variability, we examined in transgenic rats [TGR(ASrAOGEN)] with low brain angiotensinogen levels the 24-hour variation of blood pressure and heart rate. Telemetry recordings were made during basal and hypertensive conditions induced by a low-dose subcutaneous infusion of angiotensin II for 7 days. Short-term blood pressure and heart rate variability were evaluated by spectral analysis, and as a measure of baroreflex sensitivity, the average transfer gain between the pressure and heart rate variations was calculated. During the angiotensin II infusion in control but not TGR(ASrAOGEN) rats, the 24-hour rhythm of blood pressure was inverted (5.8±2 versus −0.4±1.8 mm Hg/group of day-night differences of blood pressure, P P P >0.05). These results demonstrate that the brain renin-angiotensin system plays an important role in mediating the effects of angiotensin II on the circadian variation of blood pressure. Furthermore, these data indicate that a permanent deficiency in the brain renin-angiotensin system alters the reflex control of heart rate in rats.