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1 Department of Cardiovascular Dynamics, National Cardiovascular Center Research Institute, Suita, Osaka, Japan
2 Department of Cardiovascular Dynamics, National Cardiovascular Center Research Institute, Suita, Osaka, Japan; Japan Association for the Advancement of Medical Equipment, Bunkyoku, Tokyo, Japan
* To whom correspondence should be addressed. E-mail: kentay{at}ri.ncvc.go.jp.
The effects of the muscle mechanoreflex on the arterial baroreflex neural control have not previously been analyzed over the entire operating range of the arterial baroreflex. In anesthetized, vagotomized, and aortic-denervated rabbits (n = 8), we isolated carotid sinuses and changed intra-carotid sinus pressure (CSP) from 40 to 160 mmHg in increments of 20 mmHg per minute while recording renal sympathetic nerve activity (SNA) and arterial pressure (AP). Muscle mechanoreflex was induced by passive muscle stretch (5 kg tension) of the hindlimb. Muscle stretch shifted the CSP-SNA relationship (neural arc) to a higher SNA, whereas did not affect the SNA-AP relationship (peripheral arc). SNA was almost doubled (from 63 ± 15 to 118 ± 14 a.u., P < 0.05) at the CSP level of 93 ± 8 mmHg, and AP was increased approximately 50% by muscle stretch. When the baroreflex negative feedback loop was closed, muscle stretch increased SNA from 63 ± 15 to 81 ± 21 a.u. (P < 0.05) and AP from 93 ± 8 to 109 ± 12 mmHg (P < 0.05). In conclusion, the muscle mechanoreflex resets the neural arc to a higher SNA, which moves the operating point towards a higher SNA and AP under baroreflex closed-loop conditions. Analysis of the baroreflex equilibrium diagram indicated that changes in the neural arc induced by the muscle mechanoreflex might compensate for pressure falls resulting from exercise-induced
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