Sympathetic Neural Regulation of Heart Rate Is Robust against High Plasma Catecholamines

Kawada, Toru; Miyamoto, Tadayoshi; Miyoshi, Yukiko; Yamaguchi, Sayo; Tanabe, Yukiko; Kamiya, Atsunori; Shishido, Toshiaki; Sugimachi, Masaru

doi:10.2170/physiolsci.rp006006

Cited by 9 publications

(3 citation statements)

References 27 publications

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“…However, intravenous infusion of angiotensin II did not affect the transfer function of baroreflex peripheral arc [18]. Moreover, intravenous infusion of catecholamine had no effects on the transfer function from sympathetic stimulation to heart rate [19]. These studies are consistent with the predominance of sympathetic neural control on cardiovascular pressor function [20].…”

Section: Discussionsupporting

confidence: 68%

Upright Tilt Resets Dynamic Transfer Function of Baroreflex Neural Arc to Minify the Pressure Disturbance in Total Baroreflex Control

et al. 2008

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Maintenance of arterial pressure (AP) under orthostatic stress against gravitational fluid shift and pressure disturbance is of great importance. One of the mechanisms is that upright tilt resets steady-state baroreflex control to a higher sympathetic nerve activity (SNA). However, the dynamic feedback characteristics of the baroreflex system, a hallmark of fastacting neural control, remain to be elucidated. In the present study, we tested the hypothesis that upright tilt resets the dynamic transfer function of the baroreflex neural arc to minify the pressure disturbance in total baroreflex control. Renal SNA and AP were recorded in ten anesthetized, vagotomized and aorticdenervated rabbits. Under baroreflex open-loop condition, isolated intracarotid sinus pressure (CSP) was changed according to a binary white noise sequence at operating pressure ± 20 mmHg, while the animal was placed supine and at 60° upright tilt. Regardless of the postures, the baroreflex neural (CSP to SNA) and peripheral (SNA to AP) arcs showed dynamic highpass and low-pass characteristics, respectively. Upright tilt increased the transfer gain of the neural arc (resetting), decreased that of the peripheral arc, and consequently maintained the transfer characteristics of total baroreflex feedback system. A simulation study suggests that postural resetting of the neural arc would significantly increase the transfer gain of the total arc in upright position, and that in closed-loop baroreflex the resetting increases the stability of AP against pressure disturbance under orthostatic stress. In conclusion, upright tilt resets the dynamic transfer function of the baroreflex neural arc to minify the pressure disturbance in total baroreflex control.Key words: baroreflex, blood pressure, sympathetic nervous system.Since human beings are often under orthostatic stress, the maintenance of arterial pressure (AP) under orthostatic stress against gravitational fluid shift is of great importance. During standing, a gravitational fluid shift directed toward the lower part of the body would cause severe postural hypotension if not counteracted by compensatory mechanisms [1]. Arterial baroreflex has been considered to be the major compensatory mechanism [1-3], since denervation of baroreceptor afferents causes profound postural hypotension [4].The baroreflex system consists of two subsystems: the neural arc that represents the input-output relationship between baroreceptor pressure and sympathetic nerve activity (SNA), and the peripheral arc that represents the relationship between SNA and systemic AP. Recently, we investigated the steady-state functional structure of these systems under orthostatic stress [5], and reported that upright tilt shifted the baroreflex peripheral arc to a lower AP for a given SNA. However, upright tilt reset the baroreflex neural arc to a higher steady state SNA. The resetting compensated for the blunted responsiveness of the peripheral arc and contributed to prevent postural hypotension [5].In addition to the steady s...

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Section: Discussionsupporting

confidence: 68%

Upright Tilt Resets Dynamic Transfer Function of Baroreflex Neural Arc to Minify the Pressure Disturbance in Total Baroreflex Control

et al. 2008

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“…The input power spectral density was relatively constant up to 0.25 Hz, which covered the upper frequency range of interest with respect to the sympathetic transfer function in rabbits (15).…”

Section: Methodsmentioning

confidence: 97%

Angiotensin II disproportionally attenuates dynamic vagal and sympathetic heart rate controls

Kawada

Mizuno²,

Shimizu

et al. 2009

American Journal of Physiology-Heart and Circulatory Physiology

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To better understand the pathophysiological role of angiotensin II (ANG II) in the dynamic autonomic regulation of heart rate (HR), we examined the effects of intravenous administration of ANG II (10 microg.kg(-1).h(-1)) on the transfer function from vagal or sympathetic nerve stimulation to HR in anesthetized rabbits with sinoaortic denervation and vagotomy. In the vagal stimulation group (n = 7), we stimulated the right vagal nerve for 10 min using binary white noise (0-10 Hz). The transfer function from vagal stimulation to HR approximated a first-order low-pass filter with pure delay. ANG II attenuated the dynamic gain from 7.6 +/- 0.9 to 5.8 +/- 0.9 beats.min(-1).Hz(-1) (means +/- SD; P < 0.01) without affecting the corner frequency or pure delay. In the sympathetic stimulation group (n = 7), we stimulated the right postganglionic cardiac sympathetic nerve for 20 min using binary white noise (0-5 Hz). The transfer function from sympathetic stimulation to HR approximated a second-order low-pass filter with pure delay. ANG II slightly attenuated the dynamic gain from 10.8 +/- 2.6 to 10.2 +/- 3.1 beats.min(-1).Hz(-1) (P = 0.049) without affecting the natural frequency, damping ratio, or pure delay. The disproportional suppression of the dynamic vagal and sympathetic regulation of HR would result in a relative sympathetic predominance in the presence of ANG II. The reduced high-frequency component of HR variability in patients with cardiovascular diseases, such as myocardial infarction and heart failure, may be explained in part by the peripheral effects of ANG II on the dynamic autonomic regulation of HR.

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“…For instance, 2-Hz cardiac sympathetic nerve stimulation is comparable to increasing a plasma noradrenaline concentration to approximately tenfold in its effects on a myocardial interstitial noradrenaline concentration and ventricular contractility in anesthetized cats [ 171 ]. The sympathetic HR response is robustly observed even when plasma catecholamine levels are increased to approximately tenfold by intravenous catecholamine infusion in anesthetized rabbits [ 172 ]. These results imply that the concentration of sympathetic blockers at the synaptic clefts may not be sufficiently increased to antagonize high levels of SNA in patients with drug-resistant hypertension.…”

Section: Recent Topics In Relation To Chronic Arterial Pressure Regulmentioning

confidence: 99%

Open-loop static and dynamic characteristics of the arterial baroreflex system in rabbits and rats

Kawada

Sugimachi

2015

J Physiol Sci

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The arterial baroreflex system is the most important negative feedback system for stabilizing arterial pressure (AP). This system serves as a key link between the autonomic nervous system and the cardiovascular system, and is thus essential for understanding the pathophysiology of cardiovascular diseases and accompanying autonomic abnormalities. This article focuses on an open-loop systems analysis using a baroreceptor isolation preparation to identify the characteristics of two principal subsystems of the arterial baroreflex system, namely, the neural arc from pressure input to efferent sympathetic nerve activity (SNA) and the peripheral arc from SNA to AP. Studies on the static and dynamic characteristics of the two arcs under normal physiological conditions and also under various interventions including diseased conditions are to be reviewed. Quantitative understanding of the arterial baroreflex function under diseased conditions would help develop new treatment strategies such as electrical activation of the carotid sinus baroreflex for drug-resistant hypertension.

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Sympathetic Neural Regulation of Heart Rate Is Robust against High Plasma Catecholamines

Cited by 9 publications

References 27 publications

Upright Tilt Resets Dynamic Transfer Function of Baroreflex Neural Arc to Minify the Pressure Disturbance in Total Baroreflex Control

Upright Tilt Resets Dynamic Transfer Function of Baroreflex Neural Arc to Minify the Pressure Disturbance in Total Baroreflex Control

Angiotensin II disproportionally attenuates dynamic vagal and sympathetic heart rate controls

Open-loop static and dynamic characteristics of the arterial baroreflex system in rabbits and rats

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