Abstract 14634: Central Angiotensin II Induces Sympathoexcitation and Attenuates the Open Loop Baroreflex Gain without Altering Central Baroreflex Characteristics
Backgrounds: The arterial baroreflex system is one of the most important and powerful negative-feedback mechanisms that stabilize arterial pressure (AP). Central angiotensin II (AngII) induces sympathoexcitatory hypertension. However, how AngII impacts on the AP stabilization function of baroreflex remains unknown.
Methods: In 7 anesthetized rats, we examined the acute effects of intracerebroventricular (icv) infusion of AngII (2 ng/kg/min) on the open loop baroreflex characteristics. We altered the intra-carotid sinus pressure (CSP) stepwise from 60 to 170 mmHg, while measuring AP and splanchnic sympathetic nerve activity (SNA) with or without icv infusion of AngII. We characterized the baroreflex arc by the CSP-SNA relation (neural arc), the SNA-AP relation (peripheral arc) and the CSP-AP relation (total arc).
Results: Central AngII markedly shifted the central arc upward (ΔSNA=79.6±14.6%, p<0.01) with little changes in the contour of the response curves (left panel). In the peripheral arc, AngII significantly increased AP (ΔAP=49.8±10.4 mmHg, p<0.01). The SNA-AP relation, however, remains on the same curve linear line and plateaued in the high SNA range (middle panel). In the total arc, AngII shifted the CSP-AP relationship upward while flattened the response curve in the high CSP (maximum gain: -1.42±0.12 vs. -0.68±0.16, p<0.01) and narrowed the response range (66.9±4.7 vs. 39.0±8.8 mmHg, p<0.01). Since the baroreflex operates under the closed loop condition, i.e., AP=CSP, AngII decreased the gain at the operating AP (right panel, -1.41±0.15 vs. -0.63±0.13, p<0.01).
Conclusions: Central AngII induces significant sympathoexcitation with baroreflex resetting. The fact that AngII induced excessive sympathoexcitation saturated the peripheral response and decreased the open loop gain at the operating point indicates that AngII induces central resetting impairs AP stabilizing function of baroreflex.
- © 2012 by American Heart Association, Inc.