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Journal of Hypertension Sep 2023Altered baroreflex function is well documented in hypertension; however, the female sex remains far less studied compared with males. We have previously demonstrated a...
BACKGROUND
Altered baroreflex function is well documented in hypertension; however, the female sex remains far less studied compared with males. We have previously demonstrated a left-sided dominance in the expression of aortic baroreflex function in male spontaneously hypertensive rats (SHRs) and normotensive rats of either sex. If lateralization in aortic baroreflex function extends to hypertensive female rats remains undetermined. This study, therefore, assessed the contribution of left and right aortic baroreceptor afferents to baroreflex modulation in female SHRs.
METHOD
Anesthetized female SHRs (total n = 9) were prepared for left, right and bilateral aortic depressor nerve (ADN) stimulation (1-40 Hz, 0.2 ms, 0.4 mA for 20 s) and measurement of reflex mean arterial pressure (MAP), heart rate (HR), mesenteric vascular resistance (MVR) and femoral vascular resistance (FVR). All rats were also matched for the diestrus phase of the estrus cycle.
RESULTS
Reflex (%) reductions in MAP, HR, MVR and FVR were comparable for both left-sided and right-sided stimulation. Bilateral stimulation evoked slightly larger ( P = 0.03) reductions in MVR compared with right-sided stimulation; however, all other reflex hemodynamic measures were similar to both left-sided and right-sided stimulation.
CONCLUSION
These data show that female SHRs, unlike male SHRs, express similar central integration of left versus right aortic baroreceptor afferent input and thus show no laterization in the aortic baroreflex during hypertension. Marginal increases in mesenteric vasodilation following bilateral activation of the aortic baroreceptor afferents drive no superior depressor responses beyond that of the unilateral stimulation. Clinically, unilateral targeting of the left or right aortic baroreceptor afferents may provide adequate reductions in blood pressure in female hypertensive patients.
Topics: Rats; Male; Female; Animals; Baroreflex; Rats, Inbred SHR; Blood Pressure; Aorta; Pressoreceptors; Hypertension; Heart Rate; Electric Stimulation
PubMed: 37382160
DOI: 10.1097/HJH.0000000000003493 -
The Journal of Physiological Sciences :... Jun 2023This study investigated effects of experimental baroreceptor stimulation on bilateral blood flow velocities in the anterior and middle cerebral arteries (ACA and MCA)...
This study investigated effects of experimental baroreceptor stimulation on bilateral blood flow velocities in the anterior and middle cerebral arteries (ACA and MCA) using functional transcranial Doppler sonography. Carotid baroreceptors were stimulated by neck suction in 33 healthy participants. Therefore, negative pressure (- 50 mmHg) was applied; neck pressure (+ 10 mmHg) was used as a control condition. Heart rate (HR) and blood pressure (BP) were also continuously recorded. Neck suction led to reductions in bilateral ACA and MCA blood flow velocities, which accompanied the expected HR and BP decreases; HR and BP decreases correlated positively with the ACA flow velocity decline. The observations suggest reduction of blood flow in the perfusion territories of the ACA and MCA during baroreceptor stimulation. Baroreceptor-related HR and BP decreases may contribute to the cerebral blood flow decline. The findings underline the interaction between peripheral and cerebral hemodynamic regulation in autoregulatory control of cerebral perfusion.
Topics: Humans; Blood Flow Velocity; Pressoreceptors; Middle Cerebral Artery; Blood Pressure; Heart Rate
PubMed: 37312034
DOI: 10.1186/s12576-023-00871-7 -
Pflugers Archiv : European Journal of... Aug 2023Reflex summation in the expression of left and right aortic baroreflex control of hemodynamic functions was investigated. In anesthetized Sprague-Dawley rats, mean...
Reflex summation in the expression of left and right aortic baroreflex control of hemodynamic functions was investigated. In anesthetized Sprague-Dawley rats, mean arterial pressure (MAP), heart rate (HR), and mesenteric vascular resistance (MVR) were recorded following left, right, and bilateral stimulation of the aortic depressor nerve (ADN). Stimulation frequency was varied between low (1 Hz), moderate (5 Hz), and high (20 Hz). At 1 Hz, left and right ADN stimulation evoked similar depressor, bradycardic and MVR responses, whereas bilateral stimulation induced larger MAP, HR, and MVR reductions compared with stimulations of either side. The sum of the separate and combined stimulation effects on MAP, HR, and MVR was similar, indicating an additive summation. A similar additive summation was observed with HR responses at 5 and 20 Hz. Left-sided and bilateral stimulation produced greater depressor and MVR responses than right-sided stimulation, with responses of the bilateral stimulation mimicking those of the left side. The bilateral MAP or MVR response was smaller than the sum of the separate responses, suggesting an inhibitory summation. In conclusion, reflex summation of the left and right aortic baroreceptor afferent input is differentially expressed in relation to the frequency of the input signal. Summation of baroreflex control of HR is always additive and independent of stimulation frequency. Summation of baroreflex control of MAP is additive when the frequency input is small and inhibitory when the frequency input is moderate to high, with MAP changes mainly driven by parallel baroreflex-triggered changes in vascular resistance.
Topics: Rats; Animals; Pressoreceptors; Rats, Sprague-Dawley; Blood Pressure; Electric Stimulation; Reflex; Baroreflex; Heart Rate
PubMed: 37219603
DOI: 10.1007/s00424-023-02820-0 -
International Journal of Molecular... Apr 2023Heart rate variability is a useful measure for monitoring the autonomic nervous system. Heart rate variability measurements have gained significant demand not only in...
Heart rate variability is a useful measure for monitoring the autonomic nervous system. Heart rate variability measurements have gained significant demand not only in science, but also in the public due to the fairly low price and wide accessibility of the Internet of things. The scientific debate about one of the measures of heart rate variability, i.e., what low-frequency power is reflecting, has been ongoing for decades. Some schools reason that it represents the sympathetic loading, while an even more compelling reasoning is that it measures how the baroreflex modulates the cardiac autonomic outflow. However, the current opinion manuscript proposes that the discovery of the more precise molecular characteristics of baroreceptors, i.e., that the Piezo2 ion channel containing vagal afferents could invoke the baroreflex, may possibly resolve this debate. It is long known that medium- to high-intensity exercise diminishes low-frequency power to almost undetectable values. Moreover, it is also demonstrated that the stretch- and force-gated Piezo2 ion channels are inactivated in a prolonged hyperexcited state in order to prevent pathological hyperexcitation. Accordingly, the current author suggests that the almost undetectable value of low-frequency power at medium- to high-intensity exercise reflects the inactivation of Piezo2 from vagal afferents in the baroreceptors with some Piezo1 residual activity contribution. Consequently, this opinion paper highlights how low-frequency power of the heart rate variability could represent the activity level of Piezo2 in baroreceptors.
Topics: Pressoreceptors; Heart Rate; Heart; Autonomic Nervous System; Baroreflex
PubMed: 37108199
DOI: 10.3390/ijms24087038 -
Journal of Hypertension Jul 2023The blood pressure (BP) regulatory impact of the arterial baroreflex has been well established in health and disease. Under normotensive conditions, we have previously...
BACKGROUND
The blood pressure (BP) regulatory impact of the arterial baroreflex has been well established in health and disease. Under normotensive conditions, we have previously demonstrated functional differences in the central processing of the left versus right aortic baroreceptor afferent input. However, it is unknown if lateralization in aortic baroreflex function remains evident during hypertension.
METHOD
We therefore, investigated the effects of laterality on the expression of baroreflex-driven cardiovascular reflexes in a genetic model of essential hypertension, the spontaneously hypertensive rat (SHR). Anesthetized male SHRs (total n = 9) were instrumented for left, right, and bilateral aortic depressor nerve (ADN) stimulation (1-40 Hz, 0.2 ms, and 0.4 mA for 20 s) and measurement of mean arterial pressure (MAP), heart rate (HR), mesenteric vascular resistance (MVR), and femoral vascular resistance (FVR).
RESULTS
Left right, and bilateral ADN stimulation evoked frequency-dependent decreases in MAP, HR, MVR, and FVR. Left and bilateral ADN stimulation evoked greater reflex reductions in MAP, HR, MVR, and FVR compared with right-sided stimulation. Reflex bradycardia to bilateral stimulation was larger relative to both left-sided and right-sided stimulation. Reflex depressor and vascular resistance responses to bilateral stimulation mimicked those of the left-sided stimulation. These data indicate a left-side dominance in the central integration of aortic baroreceptor afferent input. Furthermore, reflex summation due to bilateral stimulation is only evident on the reflex bradycardic response, and does not drive further reductions in BP, suggesting that reflex depressor responses in the SHRs are primarily driven by changes in vascular resistance.
CONCLUSION
Together, these results indicate that lateralization in aortic baroreflex function is not only evident under normotensive conditions but also extends to hypertensive conditions.
Topics: Rats; Animals; Male; Rats, Inbred SHR; Pressoreceptors; Electric Stimulation; Blood Pressure; Baroreflex; Hypertension; Heart Rate; Aorta
PubMed: 37074354
DOI: 10.1097/HJH.0000000000003448 -
Experimental Physiology Oct 2023What is the topic of this review? We review barosensory vessel mechanics and their role in blood pressure regulation across the lifespan. What advances does it... (Review)
Review
NEW FINDINGS
What is the topic of this review? We review barosensory vessel mechanics and their role in blood pressure regulation across the lifespan. What advances does it highlight? In young normotensive men, aortic unloading mechanics contribute to the resting operating point of the vascular sympathetic baroreflex; however, with advancing age, this contribution is removed. This suggests that barosensory vessel unloading mechanics are not driving the well-documented age-related increase in resting muscle sympathetic nerve activity.
ABSTRACT
An age-associated increase in arterial blood pressure is evident for apparently healthy humans. This is frequently attributed to stiffening of the central arteries and a concurrent increase in sympathetic outflow, potentially mediated by a reduced ability of the baroreceptive vessels to distend. This is supported, in part, by a reduced mechanical component of the vascular sympathetic baroreflex (i.e., a reduction in distension for a given pressure). Previous characterization of the mechanical component has assessed only carotid artery distension; however, evidence suggests that both the aortic and carotid baroreflexes are integral to blood pressure regulation. In addition, given that baroreceptors are located in the vessel wall, the change in wall tension, comprising diameter, pressure and vessel wall thickness, and the mechanics of this change might provide a better index of the baroreceptor stimulus than the previous method used to characterize the mechanical component that relies on diameter alone. This brief review summarizes the data using this new method of assessing barosensory vessel mechanics and their influence on the vascular sympathetic baroreflex across the lifespan.
Topics: Male; Humans; Baroreflex; Blood Pressure; Pressoreceptors; Carotid Arteries; Sympathetic Nervous System; Homeostasis; Heart Rate
PubMed: 37031381
DOI: 10.1113/EP089686 -
Obesity (Silver Spring, Md.) Jun 2023Sympathetic nervous system overactivation and abnormal lipid metabolism are featured in obesity and may lead to cardiac remodeling. The effects of carotid baroreceptor...
OBJECTIVE
Sympathetic nervous system overactivation and abnormal lipid metabolism are featured in obesity and may lead to cardiac remodeling. The effects of carotid baroreceptor stimulation (CBS) on cardiac remodeling in obese rats and the underlying mechanisms were explored.
METHODS
An obesity model was induced by 16-week high-fat diet feeding. A CBS device was implanted at the 8th week. Body weight and blood pressure measurements, electrocardiography, echocardiography, and glucose and insulin tolerance tests were conducted before sampling. Plasma analysis and histological and biological analyses of left ventricle were also performed. Neonatal rat cardiomyocytes cocultured with 3T3-L1 in transwell chambers were used to investigate the mechanisms.
RESULTS
CBS alleviated several manifestations of obesity, including increased body weight, high blood pressure, hyperlipidemia, and enhanced sympathetic activity. In obese hearts, norepinephrine levels decreased, and the monoamine oxidase A (MAO-A) and reactive oxygen species level increased; these changes, as well as cardiac fibrosis, lipid metabolic disorders, and heart dysfunction, were inhibited by CBS. Neonatal rat cardiomyocytes incubated with norepinephrine showed MAO-A upregulation, increased reactive oxygen species levels, lipid metabolic disorders, and inflammatory response, which were inhibited by clorgyline, a selective MAO-A inhibitor.
CONCLUSIONS
CBS effectively suppresses sympathetic nervous system activity and oxidative stress mediated by MAO-A and prevents cardiac remodeling in obese rats.
Topics: Rats; Animals; Monoamine Oxidase; Pressoreceptors; Reactive Oxygen Species; Ventricular Remodeling; Oxidative Stress; Obesity; Lipids; Norepinephrine
PubMed: 36998154
DOI: 10.1002/oby.23729 -
Hypertension (Dallas, Tex. : 1979) May 2023
Topics: Humans; Baroreflex; COVID-19; Pressoreceptors; Sympathetic Nervous System; Blood Pressure; Afferent Pathways
PubMed: 36802914
DOI: 10.1161/HYPERTENSIONAHA.123.20316 -
Life Science Alliance Mar 2023Baroreceptors are nerve endings located in the adventitia of the carotid sinus and aortic arch. They act as a mechanoelectrical transducer that can sense the tension...
Baroreceptors are nerve endings located in the adventitia of the carotid sinus and aortic arch. They act as a mechanoelectrical transducer that can sense the tension stimulation exerted on the blood vessel wall by the rise in blood pressure and transduce the mechanical force into discharge of the nerve endings. However, the molecular identity of mechanical signal transduction from the vessel wall to the baroreceptor is not clear. We discovered that exogenous integrin ligands, such as RGD, IKVAV, YIGSR, PHSRN, and KNEED, could restrain pressure-dependent discharge of the aortic nerve in a dose-dependent and reversible manner. Perfusion of RGD at the baroreceptor site in vivo can block the baroreceptor reflex. An immunohistochemistry study showed the binding of exogenous RGD to the nerve endings under the adventitia of the rat aortic arch, which may competitively block the binding of integrins to ligand motifs in extracellular matrix. These findings suggest that connection of integrins with extracellular matrix plays an important role in the mechanical coupling process between vessel walls and arterial baroreceptors.
Topics: Rats; Animals; Pressoreceptors; Mechanotransduction, Cellular; Aorta; Arteries
PubMed: 36625204
DOI: 10.26508/lsa.202201785 -
Kidney360 Dec 2022Heart failure is the most common cardiovascular complication of chronic kidney disease (CKD) and foreshadows a high morbidity and mortality rate. Baroreflex impairment...
BACKGROUND
Heart failure is the most common cardiovascular complication of chronic kidney disease (CKD) and foreshadows a high morbidity and mortality rate. Baroreflex impairment likely contributes to cardiovascular mortality. We aimed to study the associations between CKD, heart failure, and baroreflex sensitivity (BRS) and their association with cardiovascular outcomes.
METHODS
We retrospectively analyzed data from a cohort of 247 individuals with moderate to severe HF. All subjects underwent BRS measurements after intravenous phenylephrine along with electrocardiography, echocardiography, and laboratory measurements. We used logistic regression models to assess the association of CKD (estimated glomerular filtration rate <60 ml/min per 1.73 m) with BRS using iterative models. Cox proportional hazards models were used to assess associations of binary BRS and subgroups according to categorizations of CKD and BRS with cardiovascular mortality.
RESULTS
Median eGFR among individuals with CKD was 52 (IQR 44-56) ml/min per 1.73 m. eGFR was lower in those with depressed BRS (65 [IQR 54-76] ml/min per 1.73 m) compared with those with preserved BRS (73 [IQR 64-87] ml/min per 1.73 m; ≤0.001). The majority of individuals with CKD had depressed BRS compared with those without CKD (60% versus 29%; =0.05). In regression models, CKD and BRS were independently associated. Cardiovascular mortality was significantly increased in individuals with or without CKD and depressed BRS compared with those with preserved BRS and CKD.
CONCLUSIONS
Cardiac BRS is depressed in patients with mild to moderate CKD and HF and associated with cardiovascular mortality. Additional study to confirm its contribution to cardiovascular mortality, particularly in advanced CKD, is warranted.
Topics: Humans; Pressoreceptors; Retrospective Studies; Heart Failure; Kidney; Renal Insufficiency, Chronic
PubMed: 36591344
DOI: 10.34067/KID.0004812022