title: Muscle mechanoreflex augments arterial baroreflex-mediated dynamic sympathetic response to carotid sinus pressure.
abstract: Although the muscle mechanoreflex is one of the pressor reflexes during exercise, its interaction with dynamic characteristics of the arterial baroreflex remains to be quantitatively analyzed. In anesthetized, vagotomized, and aortic-denervated rabbits (n = 7), we randomly perturbed isolated carotid sinus pressure (CSP) using binary white noise while recording renal sympathetic nerve activity (SNA) and arterial pressure (AP). We estimated the transfer functions of the baroreflex neural arc (CSP to SNA) and peripheral arc (SNA to AP) under conditions of control and muscle stretch of the hindlimb (5 kg of tension). The muscle stretch increased the dynamic gain of the neural arc while maintaining the derivative characteristics [gain at 0.01 Hz: 1.0 +/- 0.2 vs. 1.4 +/- 0.6 arbitrary units (au)/mmHg, gain at 1 Hz: 1.7 +/- 0.6 vs. 2.7 +/- 1.4 au/mmHg; P < 0.05, control vs. stretch]. In contrast, muscle stretch did not affect the peripheral arc. In the time domain, muscle stretch augmented the steady-state response at 50 s (-1.1 +/- 0.3 vs. -1.7 +/- 0.7 au; P < 0.05, control vs. stretch) and negative peak response (-2.1 +/- 0.5 vs. -3.1 +/- 1.5 au; P < 0.05, control vs. stretch) in the SNA step response. A simulation experiment using the results indicated that the muscle mechanoreflex would accelerate the closed-loop AP regulation via the arterial baroreflex.
authors.affiliation: Consolidated Research Institute for Advanced Science and Medical Care, Waseda University, 513 Wasedatsurumakicho, Tokyo 162-0041, Japan. kenta@aoni.waseda.jp
authors.forename: Kenta
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Toru
authors.initials: T
authors.lastname: Kawada
authors.forename: Atsunori
authors.initials: A
authors.lastname: Kamiya
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Takaki
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Shishido
authors.forename: Kenji
authors.initials: K
authors.lastname: Sunagawa
authors.forename: Masaru
authors.initials: M
authors.lastname: Sugimachi
mesh_terms: D000465:Algorithms; D000818:Animals; D001158:Arteries / Q000294:innervation / Q000502:physiology*; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D002346:Carotid Sinus / Q000294:innervation / Q000502:physiology*; D003714:Denervation; D007668:Kidney / Q000000981:diagnostic imaging / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D009470:Muscle Spindles / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D011311:Pressoreceptors / Q000502:physiology*; D011817:Rabbits; D011877:Radionuclide Imaging; D012023:Reflex, Monosynaptic / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology*; D014628:Vagotomy