Background: Sympathetic nervous hyperactivity as well as the cardiovascular abnormality (arterial atherosclerosis and cardiac hypertrophy) has long been suspected to contribute to the pathogenesis of hypertension. However, quantitative, simultaneous and individual assessment of the neural and the peripheral characteristics responsible for increased arterial pressure has been difficult.
Methods: We investigated the open-loop characteristics of baroreflex function in anesthetised spontaneously hypertensive rats (SHR, n = 7) and normotensive Wistar Kyoto rats (WKY, n = 6) by isolating the carotid sinus baroreceptor. Carotid sinus pressure (CSP) was controlled at various pressures and the sympathetic nervous activity (SNA) and arterial pressure (AP) responses were recorded simultaneously. The transfer function from CSP to SNA [neural arc], and from SNA to AP [peripheral arc] were described in a baroreflex equilibrium diagram. Peripheral characteristics were additionally estimated by measuring plasma norepinephrine concentrations (NE) before and after autonomic blockade, and by examining AP response to phenylephrine administration.
Results: Although slope and offset of the baroreflex peripheral arc (linear relation) were similar, the neural arc response (inverted sigmoid curve) range was attenuated in SHR (71 ± 2% vs. 91 ± 3%, P < 0.01). The operating-point AP was higher in SHR than in WKY (144 ± 6 mm Hg vs. 109 ± 5 mm Hg, P < 0.01).
Although NE was higher in SHR at baseline condition (403.1 pg/ml vs. 203.2 pg/ml, P < 0.01), AP response to phenylephrine was similar (linear relation), suggesting preserved peripheral response to sympathetic activity.
Conclusion: The baroreflex equilibrium diagram indicates that baroreflex regulation of SNA rather than the cardiovascular response to SNA plays a critical role in the development of hypertension in SHR.
© 2011 Published by Elsevier Inc.