Resetting of the arterial baroreflex increases orthostatic sympathetic activation and prevents postural hypotension in rabbits

Atsunori Kamiya, Toru Kawada, Kenta Yamamoto, Daisaku Michikami, Hideto Ariumi, Kazunori Uemura, Can Zheng, Syuji Shimizu, Takeshi Aiba, Tadayoshi Miyamoto, Masaru Sugimachi, Kenji Sunagawa

Research output: Contribution to journalArticlepeer-review

23 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)237-246
Number of pages10
JournalJournal of Physiology
Issue number1
Publication statusPublished - Jul 1 2005
Externally publishedYes

ASJC Scopus subject areas

  • Physiology


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