Document Detail

Resetting of the arterial baroreflex increases orthostatic sympathetic activation and prevents postural hypotension in rabbits.
MedLine Citation:
PMID:  15878944     Owner:  NLM     Status:  MEDLINE    
Since humans are under ceaseless orthostatic stress, the mechanism to maintain arterial pressure (AP) under orthostatic stress against gravitational fluid shift is of great importance. We hypothesized that (1) orthostatic stress resets the arterial baroreflex control of sympathetic nerve activity (SNA) to a higher SNA, and (2) resetting of the arterial baroreflex contributes to preventing postural hypotension. Renal SNA and AP were recorded in eight anaesthetized, vagotomized and aortic-denervated rabbits. Isolated intracarotid sinus pressure (CSP) was increased stepwise from 40 to 160 mmHg with increments of 20 mmHg (60 s for each CSP level) while the animal was placed supine and at 60 deg upright tilt. Upright tilt shifted the CSP-SNA relationship (the baroreflex neural arc) to a higher SNA, shifted the SNA-AP relationship (the baroreflex peripheral arc) to a lower AP, and consequently moved the operating point to marked high SNA while maintaining AP. A simulation study suggests that resetting in the neural arc would double the orthostatic activation of SNA and increase the operating AP in upright tilt by 10 mmHg, compared with the absence of resetting. In addition, upright tilt did not change the CSP-AP relationship (the baroreflex total arc). A simulation study suggests that although a downward shift of the peripheral arc could shift the total arc downward, resetting in the neural arc would compensate this fall and prevent the total arc from shifting downward to a lower AP. In conclusion, upright tilt increases SNA by resetting the baroreflex neural arc. This resetting may compensate for the reduced pressor responses to SNA in the peripheral cardiovascular system and contribute to preventing postural hypotension.
Atsunori Kamiya; Toru Kawada; Kenta Yamamoto; Daisaku Michikami; Hideto Ariumi; Kazunori Uemura; Can Zheng; Syuji Shimizu; Takeshi Aiba; Tadayoshi Miyamoto; Masaru Sugimachi; Kenji Sunagawa
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2005-05-05
Journal Detail:
Title:  The Journal of physiology     Volume:  566     ISSN:  0022-3751     ISO Abbreviation:  J. Physiol. (Lond.)     Publication Date:  2005 Jul 
Date Detail:
Created Date:  2005-07-04     Completed Date:  2005-09-16     Revised Date:  2013-06-09    
Medline Journal Info:
Nlm Unique ID:  0266262     Medline TA:  J Physiol     Country:  England    
Other Details:
Languages:  eng     Pagination:  237-46     Citation Subset:  IM; S    
Department of Cardiovascular Dynamics, National Cardiovascular Centre Research Institute, Osaka 565-8565, Japan.
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MeSH Terms
Adaptation, Physiological / physiology
Blood Pressure*
Dizziness / complications,  physiopathology*
Hypotension / physiopathology*
Hypotension, Orthostatic / etiology,  physiopathology*
Sympathetic Nervous System*

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