Brain angiotensin II tonically modulates sympathetic baroreflex in rabbit ventrolateral medulla

Saigusa, Takeshi; Iriki, Masami; Ai, Jun

doi:10.1152/ajpheart.1996.271.3.h1015

Cited by 33 publications

(48 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Head and colleagues (21,33,34) showed in anesthetized and conscious rabbits that RVLM microinjection of ANG II increases, whereas microinjection of saralasin attenuates, the sensitivity of the baroreflex control of renal sympathetic activity. These data suggest an endogenous role for ANG II in the modulation of the sympathetic, but not the parasympathetic, component of the baroreceptor reflex at the RVLM (33)(34)(35).…”

Section: Discussionmentioning

confidence: 71%

“…The only data in the literature regarding the baroreflex control refer to the effect of ANG II or its antagonists on renal sympathetic nerve activity (RSNA). It has been shown that ANG II induces facilitation of the baroreflex at the RVLM (33-35) and inhibition of the baroreflex at the CVLM (35,40).It is becoming clear that ANG-(1-7) can act as a counterregulatory peptide of the RAS, because ANG-(1-7) has several effects that are opposite to those of ANG II (16,36). Centrally, lateral ventricular infusion (8,10,29) or microinjection into the NTS (12) of ANG-(1-7) facilitates the baroreflex control of HR, in contrast to the well-known inhibitory effect induced by ANG II (4, 32).…”

mentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Baroreflex modulation by angiotensins at the rat rostral and caudal ventrolateral medulla

Alzamora¹,

Santos²,

Campagnole‐Santos³

2006

American Journal of Physiology-Regulatory, Integrative and Comp

View full text Add to dashboard Cite

-We determined the effect of microinjection of ANG-(1-7) and ANG II into two key regions of the medulla that control the circulation [rostral and caudal ventrolateral medulla (RVLM and CVLM, respectively)] on baroreflex control of heart rate (HR) in anesthetized rats. Reflex bradycardia and tachycardia were induced by increases and decreases in mean arterial pressure produced by intravenous phenylephrine and sodium nitroprusside, respectively. The pressor effects of ANG-(1-7) and ANG II (25 pmol) after RVLM microinjection (11 Ϯ 0.8 and 10 Ϯ 2 mmHg, respectively) were not accompanied by consistent changes in HR. In addition, RVLM microinjection of these angiotensin peptides did not alter the bradycardic or tachycardic component of the baroreflex. CVLM microinjections of ANG-(1-7) and ANG II produced hypotension (Ϫ11 Ϯ 1.5 and Ϫ11 Ϯ 1.9 mmHg, respectively) that was similarly not accompanied by significant changes in HR. However, CVLM microinjections of angiotensins induced differential changes in the baroreflex control of HR. ANG-(1-7) attenuated the baroreflex bradycardia (0.26 Ϯ 0.06 ms/mmHg vs. 0.42 Ϯ 0.08 ms/mmHg before treatment) and facilitated the baroreflex tachycardia (0.86 Ϯ 0.19 ms/mmHg vs. 0.42 Ϯ 0.10 ms/mmHg before treatment); ANG II produced the opposite effect, attenuating baroreflex tachycardia (0.09 Ϯ 0.06 ms/mmHg vs. 0.31 Ϯ 0.07 ms/mmHg before treatment) and facilitating the baroreflex bradycardia (0.67 Ϯ 0.16 ms/mmHg vs. 0.41 Ϯ 0.05 ms/mmHg before treatment). The modulatory effect of ANG II and ANG-(1-7) on baroreflex sensitivity was completely abolished by peripheral administration of methylatropine. These results suggest that ANG II and ANG-(1-7) at the CVLM produce a differential modulation of the baroreflex control of HR, probably through distinct effects on the parasympathetic drive to the heart. baroreflex control of heart rate; renin-angiotensin system; arterial pressure THE BARORECEPTOR AFFERENTS terminate primarily in the intermediate portion of the nucleus of the solitary tract (NTS) subjacent to the area postrema in the dorsal medulla (15, 32). Although many brain stem and forebrain regions participate in the modulation of the sympathetic and parasympathetic outflows, regions inside the ventrolateral medulla (VLM) are essential for the effectiveness of the baroreceptor reflex (32). The caudal VLM (CVLM) has been functionally defined as a tonically active sympathoinhibitory vasodepressor region (15,32,44) that contains a synaptic relay within the baroreflex circuit, connecting the NTS to a site on the sympathoexcitatory reticulospinal neurons, the rostral VLM (RVLM). The RVLM is known to play an essential role in the tonic and reflex control of sympathetic vasomotor tone (15, 32). Two groups of cardiovascular neurons have been functionally defined in the CVLM: neurons that relay baroreflex inputs from the NTS to the RVLM and neurons that are insensitive to the baroreflex input (14, 44). In addition, the CVLM depressor response, in part, is associated with vagally mediated decrease in h...

show abstract

Section: Discussionmentioning

confidence: 71%

mentioning

confidence: 99%

See 1 more Smart Citation

Baroreflex modulation by angiotensins at the rat rostral and caudal ventrolateral medulla

Alzamora¹,

Santos²,

Campagnole‐Santos³

2006

American Journal of Physiology-Regulatory, Integrative and Comp

View full text Add to dashboard Cite

show abstract

“…Microinjection of Ang II into the region of the A1 noradrenergic cells within the CVLM of the rabbit results in a depressor response (50). The most extensive study was performed by Saigusa and colleagues (51) who found that Ang II infusion into the CVLM of anesthetized rabbits decreased sympathetic activity and inhibited RSNA baroreflex while blockade of CVLM Ang receptors increased the sympathetic baroreflex but did not alter resting blood pressure or RSNA.…”

Section: Ang Actions Within the Caudal Ventrolateral Medullamentioning

confidence: 99%

Angiotensin and baroreflex control of the circulation

Head¹,

Saigusa

Mayorov³

2002

Braz J Med Biol Res

Self Cite

View full text Add to dashboard Cite

There is a close association between the location of angiotensin (Ang) receptors and many important brain nuclei involved in the regulation of the cardiovascular system. The present review encompasses the physiological role of Ang II in the brainstem, particularly in relation to its influence on baroreflex control of the heart and kidney. Activation of AT 1 receptors in the brainstem by fourth ventricle (4V) administration to conscious rabbits or local administration of Ang II into the rostral ventrolateral medulla (RVLM) of anesthetized rabbits acutely increases renal sympathetic nerve activity (RSNA) and RSNA baroreflex responses. Administration of the Ang antagonist Sarile into the RVLM of anesthetized rabbits blocked the effects of Ang II on the RSNA baroreflex, indicating that the RVLM is the major site of sympathoexcitatory action of Ang II given into the cerebrospinal fluid surrounding the brainstem. However, in conscious animals, blockade of endogenous Ang receptors in the brainstem by the 4V AT 1 receptor antagonist losartan resulted in sympathoexcitation, suggesting an overall greater activity of endogenous Ang II within the sympathoinhibitory pathways. However, the RSNA response to airjet stress in conscious rabbits was markedly attenuated. While we found no effect of acute central Ang on heart rate baroreflexes, chronic 4V infusion inhibited the baroreflex and chronic losartan increased baroreflex gain. Thus, brainstem Ang II acutely alters sympathetic responses to specific afferent inputs thus forming part of a potentially important mechanism for the integration of autonomic response patterns. The sympathoexcitatory AT 1 receptors appear to be activated during stress, surgery and anesthesia.

show abstract

“…ANG II receptors are also localized in the RVLM (1,2,4,5,25). Blockade of ANG II receptors in the RVLM decreases the baseline levels of SNA (44,45) and attenuates sympathetic responses evoked by stimulation of the hypothalamic paraventricular nucleus (PVN) (54), which suggests that endogenous ANG II or related peptides are involved in controlling the sympathetic outflow.…”

mentioning

confidence: 99%

ANG II modulates both slow and rapid baroreflex responses of barosensitive bulbospinal neurons in the rabbit rostral ventrolateral medulla

Saigusa

2014

American Journal of Physiology-Regulatory, Integrative and Comp

View full text Add to dashboard Cite

Saigusa T, Arita J. ANG II modulates both slow and rapid baroreflex responses of barosensitive bulbospinal neurons in the rabbit rostral ventrolateral medulla. Am J Physiol Regul Integr Comp Physiol 306: R538 -R551, 2014. First published February 12, 2014 doi:10.1152/ajpregu.00285.2013.-This study investigated the effects of ANG II on slow and rapid baroreflex responses of barosensitive bulbospinal neurons in the rostral ventrolateral medulla (RVLM) in urethane-anesthetized rabbits to determine whether the sympathetic baroreflex modulation induced by application of ANG II into the RVLM can be explained by the total action of ANG II on individual RVLM neurons. In response to pharmacologically induced slow ramp changes in mean arterial pressure (MAP), individual RVLM neurons exhibited a unit activity-MAP relationship that was fitted by a straight line with upper and lower plateaus. Iontophoretically applied ANG II raised the upper plateau without changing the slope, and, thereby, increased the working range of the baroreflex response. An asymmetric sigmoid curve that was determined by averaging individual unit activity-MAP relationship lines became more symmetric with ANG II application. The characteristics of the average curves, both before and during ANG II application, were consistent with the renal sympathetic nerve activity-MAP relationship curves obtained under the same experimental conditions. ANG II also affected rapid baroreflex responses of RVLM neurons that were induced by cardiac beats, as application of ANG II predominantly raised the average unit activities in the downstroke phase of arterial pulse waves. The present study provides a possible explanation for the ANG II-induced sympathetic baroreflex modulation based on the action of ANG II on barosensitive bulbospinal RVLM neurons. Our results also suggest that ANG II changes both static and dynamic characteristics of baroreflex responses of RVLM neurons. angiotensin II; baroreflex; sympathetic nervous system; single-unit recording; medulla oblongata THE ROSTRAL VENTROLATERAL medulla (RVLM) contains a group of neurons that project directly to the sympathetic preganglionic neurons in the spinal cord (8,16,20,38) and that provide an essential source of the sympathetic nerve activity (SNA) to maintain mean arterial pressure (MAP) within normal levels (14,21,43,53). A substantial portion of the bulbospinal neurons in the RVLM receive inhibitory inputs driven by arterial baroreceptor inputs, and, thus, display phasic activities that are synchronized to the cardiac cycle (8,28,55). Since blockade of inhibitory neurotransmission in the RVLM largely interferes with sympathetic baroreflex responses (7), the barosensitive bulbospinal neurons in the RVLM are believed to be a key component of the sympathetic baroreflex mechanism.ANG II is one of the peptides that have been identified in nerve terminals within the RVLM (13). Although the origins of the ANG II-containing axon tracts have not been fully identified, several supramedullary regions, such as the late...

show abstract

Brain angiotensin II tonically modulates sympathetic baroreflex in rabbit ventrolateral medulla

Cited by 33 publications

References 0 publications

Baroreflex modulation by angiotensins at the rat rostral and caudal ventrolateral medulla

Baroreflex modulation by angiotensins at the rat rostral and caudal ventrolateral medulla

Angiotensin and baroreflex control of the circulation

ANG II modulates both slow and rapid baroreflex responses of barosensitive bulbospinal neurons in the rabbit rostral ventrolateral medulla

Contact Info

Product

Resources

About