Sinoaortic-denervated Rats Research Articles

Exercise training improves cardiovascular control in sinoaortic denervated SHR by reducing the elevated angiotensin II and augmenting angiotensin-(1−7) availability within autonomic and neuroendocrine PVN nuclei

Previous studies have shown that baroreceptors- and chemoreceptors-denervated SHR exhibit impaired central autonomic circuitry and worsening of the cardiovascular function. It was also known that exercise training (T) ameliorates the autonomic control of the circulation. In the present study we sought to investigate whether sinoaortic denervation (SAD) is able to modify the expression/activity of the renin-angiotensin system (RAS) within brain autonomic areas and the effects induced by T. SHR submitted to SAD or SHAM surgery were trained or kept sedentary (S) for 8 weeks. Femoral artery and vein were chronically cannulated for hemodynamic/autonomic recordings and baroreflex testing (phenylephrine and sodium nitroprusside, i.v). Ang II and Ang (1−7) protein expression (immunofluorescence assays) were quantified within autonomic and neuroendocrine nuclei of the hypothalamic paraventricular nucleus (PVN). SAD-S vs. SHAM-S exhibited large increase in Ang II availability into the ventromedial, dorsal cap and magnocellular PVN nuclei, which are accompanied by augmented sympathetic activity, elevated arterial pressure variability and higher MAP. There was no change in Ang-(1−7) content within these nuclei. In contrast, T largely augmented Ang-(1−7) immunofluorescence in all nuclei, reduced and normalized Ang II availability and ameliorated the autonomic control of the circulation in SAD rats, but did not reduce MAP levels. Data showed that tonic baroreceptors and chemoreceptors’ activity is essential to maintain lower Ang II levels within PVN nuclei. In the absence of afferent signaling, exercise training is still efficient to alter Ang II/Ang-(1−7) balance thus improving cardiovascular control even in the presence of high-pressure levels.

TRPC6 participates in the development of blood pressure variability increase in sino-aortic denervated rats

Increased blood pressure variability (BPV) has been proved to be associated with cardiovascular morbidity and mortality. It is of great significance to elucidate the mechanism of BPV increase. The cation channel transient receptor potential canonical 6 (TRPC6) is involved in a series of cardiovascular disease. Our experiment aimed to explore the role of TRPC6 in the development of BPV increase. Sino-aortic denervation (SAD) operation was applied to establish the model of BPV increase in rats. The BPV was presented as the standard deviation to the mean of systolic or diastolic blood pressure every 1 h during 12h of the light period. SAD was performed in male Sprague Dawley (SD) rats at the age of 10weeks. At 8weeks after SAD operation, the hemodynamic parameters were determined non-invasively via a Rodent Blood Pressure Analysis System. The TRPC6 expressions in myocardial and thoracic aortic tissue was determined utilizing Western Blot, immunofluorescence and quantitative RT-PCR. The expression of TRPC3 was detected as well. To investigate whether TRPC6 was a causative factor of BPV increase in SAD rats, TRPC6 activator and inhibitor with three progressively increasing doses were intraperitoneally injected to the SAD rats. We found that SAD rats presented significant augmentation of systolic and diastolic BPV with no change of BP level and heart rate. The mRNA and protein expression levels of TRPC6 in myocardial and thoracic aortic tissue in SAD rats were substantially increased, but there was no obvious change in TRPC3 expression. The systolic and diastolic BPV increase were dose-dependently exacerbated after TRPC6 activation with GSK1702934A but were dose-dependently attenuated after TRPC6 inhibition with SAR7334. In Conclusion, the TRPC6 (but not TRPC3) expressions in myocardial and thoracic aortic tissue were substantially increased in SAD rats, and TRPC6 probably played an important role in the development of BPV elevation.

Baroreceptor denervation reduces inflammatory status but worsens cardiovascular collapse during systemic inflammation

Beyond the regulation of cardiovascular function, baroreceptor afferents play polymodal roles in health and disease. Sepsis is a life-threatening condition characterized by systemic inflammation (SI) and hemodynamic dysfunction. We hypothesized that baroreceptor denervation worsens lipopolysaccharide (LPS) induced-hemodynamic collapse and SI in conscious rats. We combined: (a) hemodynamic and thermoregulatory recordings after LPS administration at a septic-like non-lethal dose (b) analysis of the cardiovascular complexity, (c) evaluation of vascular function in mesenteric resistance vessels, and (d) measurements of inflammatory cytokines (plasma and spleen). LPS-induced drop in blood pressure was higher in sino-aortic denervated (SAD) rats. LPS-induced hemodynamic collapse was associated with SAD-dependent autonomic disbalance. LPS-induced vascular dysfunction was not affected by SAD. Surprisingly, SAD blunted LPS-induced surges of plasma and spleen cytokines. These data indicate that baroreceptor afferents are key to alleviate LPS-induced hemodynamic collapse, affecting the autonomic control of cardiovascular function, without affecting resistance blood vessels. Moreover, baroreflex modulation of the LPS-induced SI and hemodynamic collapse are not dependent of each other given that baroreceptor denervation worsened hypotension and reduced SI.

The Role of Autonomic Nervous System and Baroreflex in the Pattern of Heart Rate Fragmentation

Although rapid oscillations of the heart rate (HR) are commonly attributed to vagal modulation of the heart, a pattern of ultra‐rapid HR variation has been recently studied. This type of variation, named HR fragmentation (HRF), has been shown to be increased in aging and coronary diseases and seems to be linked to the risk of death and life‐threatening cardiovascular events. However, the mechanisms behind HRF are unknown. Thus, the aim of this study was to evaluate the influence of the autonomic nervous system (ANS) and arterial baroreceptors on HRF. For this, electrodes for electrocardiogram (ECG) and a catheter into femoral vein were implanted in Wistar rats. On the next day, under ECG recordings, the rats were submitted to selective pharmacological blockade of cardiac autonomic receptors with atenolol (4 mg/kg iv in bolus followed by 0.8 mg/kg/h iv) followed by methylatropine (2 mg/kg in bolus followed by 0.4 mg/kg/h iv) or vice‐versa. Another group underwent sinoaortic denervation (SAD), or sham‐operation, and received a catheter in femoral artery. On the next day, SAD and sham rats had its blood pressure directly recorded. All recordings were performed in freely moving animals. Pulse interval or RR‐interval series were generated and transformed into sequence of symbols "−1”, “0” or “1" when the difference between successive values (transitions) was negative, zero, or positive, respectively. In addition, the transitions between symbols "−1" and "1" were classified as "hard" (H) while those between "−1" (or "1") and "0" were classified as "soft" (S). Next, sequences of 4 consecutive symbols were classified according to the number and type of transition, i.e. S, M or H, where M represents mixed transitions (H and S). The total percentage of inflection points (PIP) was also quantified. PIP increased after sympathetic (66±2 to 73±2), parasympathetic (68±1 to 73±1) and double autonomic blockade (67±1 to 73±1). The percentage of sequences with H transitions was lower after parasympathetic (27±3 vs 74±2) and double blockade (43±4 vs 76±1), while sequences with S and M transitions were higher after parasympathetic (S: 28±3 vs 7±1% and M: 44±2 vs 18±1%) and double blockade (S: 15±2 vs 6±1 and M: 41±2 vs 17±1%). The percentage of sequences with M‐type transitions increased after sympathetic blockade (16±1 to 23±3), while no change was found with H and S‐type transitions. PIP was lower in SAD rats (68±2) when compared to the sham counterparts (88±1). Regarding type, the percentage of H transitions was higher in SAD (90±1 vs 20±1), whereas sham rats showed more S (27±1 vs 2±0.1) and M‐type transitions (53±1 vs 7±1). In conclusion, the ANS, specially its parasympathetic branch, attenuates HRF. Moreover, although the removal of arterial baroreceptors represents the loss of an important cardiocirculatory control system, the denervated rats presented lower overall HRF. Nevertheless, the percentage of H‐type transitions is higher in SAD rats, evidencing that both the amount and type of fragmentation represent important indices under physiological and pathophysiological conditions.Support or Funding InformationCNPq, CAPES and FAPESP

Study on the Formation of Antihypertensive Twin Drugs by Caffeic Acid and Ferulic Acid with Telmisartan.

PurposeThis study aimed to synthesize twin drugs from cinnamic acid compounds, caffeic acid (CFA) and ferulic acid (FLA), which can antagonize endothelin-1 (ET-1) with telmisartan through ester bonds. Moreover, the antihypertensive effect of telmisartan and its influence on blood pressure variability (BPV) were enhanced, and the bioavailability of caffeic acid and ferulic acid was improved.MethodsSix twin drugs, which were the target compounds, were synthesized. Hypertensive rats (SHR) and conscious sinoaortic-denervated (SAD) rats were spontaneously used as models for pharmacodynamic research to study the antihypertensive efficacy of these twin drugs. Wistar rats were employed as pharmacokinetic research models to investigate the pharmacokinetics of the target compounds via intragastric administration. Cellular pharmacodynamic research was also conducted on the antagonistic action on Ang II-AT1, ETA and ETB receptor.ResultsCompound 1a was determined as the best antihypertensive twin drug and thus was further studied for its effect on BPV. Compared with that of telmisartan, the antihypertensive effect of compound 1a was improved (p<0.05), and the BPV was reduced (p<0.05). The bioavailability of caffeic acid and ferulic acid after hydrolysis from twin drugs could be increased to varying degrees, and the differences of the main pharmacokinetic parameters among the different forms of caffeic acid and ferulic acid were statistically significant (p<0.05 or p<0.01). Compound 1a had the best antagonistic effect on the Ang II-AT1 receptor. However, the IC50 of Lps-2 was still two orders of magnitude higher than that of the positive drug telmisartan. Hence, the twin drugs worked by metabolizing and regenerating telmisartan and caffeic acid or ferulic acid in the body.ConclusionThe synthesized twin drugs improved telmisartan’s antihypertensive effects, significantly decreased BPV in SAD rats and increased the bioavailability of caffeic acid and ferulic acid. This study serves as a basis for the development of new angiotensin receptor blocker (ARB) in the future and a reference for the development of new drugs to antagonize ET-1.

Selective denervation of the aortic and carotid baroreceptors in rats.

What is the central question of this study? The traditional surgical approach for sino-aortic denervation in rats leads to simultaneous carotid baroreceptor and chemoreceptor deactivation, which does not permit their individual study in different situations. What is the main finding and its importance? We have described a new surgical approach capable of selective denervation of the arterial (aortic and carotid) baroreceptors, keeping the carotid bodies (chemoreceptors) intact. It is understood that this technique might be a useful tool for investigating the relative role of the baro- and chemoreceptors in several physiological and pathophysiological conditions. Studies have demonstrated that the traditional surgical approach for sino-aortic denervation in rats leads to simultaneous carotid baroreceptor and chemoreceptor deactivation. The present study reports a new surgical approach to denervate the aortic and the carotid baroreceptors selectively, keeping the carotid bodies (peripheral chemoreceptors) intact. Wistar rats were subjected to specific aortic and carotid baroreceptor denervation (BAROS-X) or sham surgery (SHAM). Baroreflex activation was achieved by i.v. administration of phenylephrine, whereas peripheral chemoreflex activation was produced by i.v. administration of potassium cyanide. The SHAM and BAROS-X rats displayed significant hypertensive responses to phenylephrine administration. However, the reflex bradycardia following the hypertensive response caused by phenylephrine was remarkable in SHAM, but not significant in the BAROS-X animals, confirming the efficacy of the surgical procedure to abolish the baroreflex. In addition, the baroreflex activation elicited by phenylephrine increased carotid sinus nerve activity only in SHAM, but not in the BAROS-X animals, providing support to the notion that the baroreceptor afferents were absent. Instead, the classical peripheral chemoreflex hypertensive and bradycardic responses to potassium cyanide were similar in both groups, suggesting that the carotid body chemoreceptors were preserved after BAROS-X. In summary, we describe a new surgical approach in which only the baroreceptors are eliminated, while the carotid chemoreceptors are preserved. Therefore, it is understood that this procedure is potentially a useful tool for examining the relative roles of the arterial baroreceptors versus the chemoreceptors in several pathophysiological conditions, for instance, arterial hypertension and heart failure.

Patterns of cardiovascular variability after long-term sino-aortic denervation in unanesthetized adult rats

Baroreflex dysfunction is a diffuse chronic condition that is expected to be followed by a profound loss of organization of BP and HR variability. Nevertheless, long-term effects of baroreflex withdrawal are still debated. Aim of our work was to study BP and HR changes long term after sino-aortic denervation (SAD). Inter-beat-interval (IBI) and intra-arterial BP were recorded beat-by-beat in 43 Wistar-Kyoto rats (Controls, n = 33; SAD rats, n = 10). Power spectra were calculated in controls and in SAD rats within three days and at seven months from denervation. Compared to controls, chronic SAD rats showed 1) similar mean BP (control vs SAD: 95 ± 16 vs 87 ± 22 mmHg) and IBI (171 ± 22 vs 181 ± 15 ms) values, 2) dramatically higher values of BP variance (12 ± 2 vs 64 ± 2 mmHg2, p < 0.01) and of ultra- (ULF) and very-low-frequency (VLF) BP oscillations, 3) dramatically higher values of IBI variability (24 ± 2 vs 71 ± 4 ms2, p < 0.01) and of ULF-IBI oscillations that were synchronized with BP oscillations. Chronic SAD rats reveal a marked change in the pattern of cardiovascular variability characterized by the appearance of synchronized slower oscillations of BP and HR. The cardiovascular system, therefore, retains a high level of organization despite the absence of a reflex control mechanism.

Firing properties of ventral medullary respiratory neurons in sino-aortic denervated rats.

What is the central question of this study? After sino-aortic denervation (SAD), rats present normal levels of mean arterial pressure (MAP), high MAP variability and changes in breathing. However, mechanisms involved in SAD-induced respiratory changes and their impact on the modulation of sympathetic activity remain unclear. Herein, we characterized the firing frequency of medullary respiratory neurons after SAD. What is the main finding and its importance? Sino-aortic denervation-induced prolonged inspiration was associated with a reduced interburst frequency of pre-inspiratory/inspiratory neurons and an increased long-term variability of late inspiratory neurons, but no changes were observed in the ramp-inspiratory and post-inspiratory neurons. This imbalance in the respiratory network might contribute to the modulation of sympathetic activity after SAD. In previous studies, we documented that after sino-aortic denervation (SAD) in rats there are significant changes in the breathing pattern, but no significant changes in sympathetic activity and mean arterial pressure compared with sham-operated rats. However, the neural mechanisms involved in the respiratory changes after SAD and the extent to which they might contribute to the observed normal sympathetic activity and mean arterial pressure remain unclear. Here, we hypothesized that after SAD, rats present with changes in the firing frequency of the ventral medullary inspiratory and post-inspiratory neurons. To test this hypothesis, male Wistar rats underwent SAD or sham surgery and 3days later were surgically prepared for an in situ experiment. The duration of inspiration significantly increased in SAD rats. During inspiration, the total firing frequency of ramp-inspiratory, pre-inspiratory/inspiratory and late-inspiratory neurons was not different between groups. During post-inspiration, the total firing frequency of post-inspiratory neurons was also not different between groups. Furthermore, the data demonstrate a reduced interburst frequency of pre-inspiratory/inspiratory neurons and an increased long-term variability of late-inspiratory neurons in SAD compared with sham-operated rats. These findings indicate that the SAD-induced prolongation of inspiration was not accompanied by alterations in the total firing frequency of the ventral medullary respiratory neurons, but it was associated with changes in the long-term variability of late-inspiratory neurons. We suggest that the timing imbalance in the respiratory network in SAD rats might contribute to the modulation of presympathetic neurons after removal of baroreceptor afferents.

The role of the baroreflex and parasympathetic nervous system in fructose-induced cardiac and metabolic alterations

It is well-established that baroreflex sensitivity is essential for blood pressure control, and also plays a key role in the modulation of disease-induced metabolic alterations. In order to investigate the role of the baroreflex in the cardiometabolic and inflammatory derangements promoted by fructose overload, Wistar rats underwent sinoaortic denervation (SAD) or sham surgery and were studied 90 days after receiving tap water (Den and Ctrl) or a 10% fructose solution (Fruc and Den-Fruc). All experimental groups showed marked and similar degree of baroreflex impairment compared to Ctrl. As expected, fructose overload effectively induced metabolic syndrome; however, when it was associated with SAD, several alterations were attenuated. While Fruc rats displayed increased sympathetic modulation and tone and reduced vagal modulation compared to Ctrl animals, Den-Fruc rats showed greater vagal tone and modulation when compared to the Fruc group. Moreover, the Den-Fruc group showed augmented expression of β1 adrenergic receptors and TNF/IL-10 ratio and reduction of β2 in the left ventricle. The increase in vagal function was correlated with improved insulin sensitivity (r2 = 0.76), and decreased abdominal fat (r2 = −0.78) and β2 receptors (r2 = −0.85). Our results showed that: (1) chronic fructose overload induced severe baroreflex impairment, i.e. in a similar magnitude to that observed in SAD rats, which is accompanied by cardiometabolic dysfunctions; (2) the compensatory enhancement in parasympathetic function in SAD rats submitted to fructose intake may point out the possibility of use of approaches that improve vagal function as therapeutic target to attenuate fructose-induced cardiometabolic dysfunctions.

Possible Breathing Influences on the Control of Arterial Pressure After Sino-aortic Denervation in Rats.

Surgical removal of the baroreceptor afferents [sino-aortic denervation (SAD)] leads to a lack of inhibitory feedback to sympathetic outflow, which in turn is expected to result in a large increase in mean arterial pressure (MAP). However, few days after surgery, the sympathetic nerve activity (SNA) and MAP of SAD rats return to a range similar to that observed in control rats. In this review, we present experimental evidence suggesting that breathing contributes to control of SNA and MAP following SAD.The purpose of this review was to discuss studies exploring SNA and MAP regulation in SAD rats, highlighting the possible role of breathing in the neural mechanisms of this modulation of SNA. Recent studies show that baroreceptor afferent stimulation or removal (SAD) results in changes in the respiratory pattern. Changes in the neural respiratory network and in the respiratory pattern must be considered among mechanisms involved in the modulation of the MAP after SAD.

Effects of losartan on vasomotor function and canonical transient receptor potential channels in the aortas of sinoaortic denervation rats

ABSTRACTIncreased short-term blood pressure variability (BPV) is strongly correlated with target organ damage. However, the molecular mechanisms underlying abnormal BPV-induced organ damage and effective therapeutic targets are poorly understood. The purpose of this study was to investigate the effects of losartan on vasomotor function and canonical transient receptor potential (TRPC) channels in the aortas of rats with arterial pressure lability induced by sinoaortic denervation (SAD). SAD was performed in male Sprague-Dawley rats at the age of 10 weeks. The experiment included sham-operated (Sham), SAD, and losartan-treated SAD (SAD+Los) groups. After 8 weeks of treatment, hemodynamic parameters were measured via catheterization, thoracic aortic vasomotor functions were evaluated using a physiological vascular ring tension recording system, and TRPC1 and 6 mRNA and protein expression levels in the endothelial cells (ECs) and smooth muscle cells (SMCs) of the thoracic aorta were determined via reverse transcription polymerase chain reaction (RT-PCR) and Western-blotting, respectively. Compared with Sham rats, SAD rats exhibited significantly increased BPV, enhanced norepinephrine-induced aortic contraction, and attenuated acetylcholine-induced aortic relaxation. Both the mRNA and the protein expression levels of TRPC1 and 6 were significantly downregulated in the ECs and upregulated in the SMCs of the thoracic aortas of SAD rats. Losartan treatment prevented these SAD-induced changes. In conclusion, losartan efficiently prevented vasomotor function impairment in SAD rats by reducing BPV and regulating TRPC1 and 6 expression levels.

Changes in the inspiratory pattern contribute to modulate the sympathetic activity in sino-aortic denervated rats.

What is the central question of this study? Sino-aortic denervated (SAD) rats present normal levels of sympathetic activity and mean arterial pressure. However, neural mechanisms regulating the sympathetic activity in the absence of arterial baroreceptors remain unclear. Considering that respiration modulates the sympathetic activity, we hypothesize that changes in the respiratory network contribute to keep the sympathetic outflow in the normal range after removal of arterial baroreceptors. What is the main finding and its importance? Despite longer inspiration observed in SAD rats, the respiratory-sympathetic coupling is working within a normal range of variation. These findings suggest that in the absence of arterial baroreceptors the respiratory modulation of sympathetic activity is maintained within the normal range. The activity of presympathetic neurons is under respiratory modulation, and changes in the central respiratory network may impact on the baseline sympathetic activity and mean arterial pressure. It is well known that after removal of baroreceptor afferents [sino-aortic denervation (SAD)], rats present an unexpected normal level of mean arterial pressure. We hypothesized that changes in the respiratory pattern and in the respiratory modulation of the sympathetic activity contribute to keep the sympathetic outflow within a normal range of variation in the absence of arterial baroreceptors in rats. To study these mechanisms, we recorded perfusion pressure and the activities of phrenic and thoracic sympathetic nerves in male juvenile rats using the working heart-brainstem preparation. The time of inspiration significantly increased in SAD rats, and this change was not dependent on the carotid bodies or on the vagal afferents. However, no changes were observed in the perfusion pressure or in the baseline thoracic sympathetic nerves in all phases of the respiratory cycle in SAD rats. Our data show that despite longer inspiratory activity, the baseline sympathetic activity is maintained at a normal level in SAD rats. These findings indicate that the respiratory-sympathetic coupling is normal after SAD and suggest that the respiratory modulation of sympathetic activity is maintained within the normal range after the removal of arterial baroreceptors.

Nonlinearities of heart rate variability in animal models of impaired cardiac control: contribution of different time scales.

Heart rate variability (HRV) has been extensively explored by traditional linear approaches (e.g., spectral analysis); however, several studies have pointed to the presence of nonlinear features in HRV, suggesting that linear tools might fail to account for the complexity of the HRV dynamics. Even though the prevalent notion is that HRV is nonlinear, the actual presence of nonlinear features is rarely verified. In this study, the presence of nonlinear dynamics was checked as a function of time scales in three experimental models of rats with different impairment of the cardiac control: namely, rats with heart failure (HF), spontaneously hypertensive rats (SHRs), and sinoaortic denervated (SAD) rats. Multiscale entropy (MSE) and refined MSE (RMSE) were chosen as the discriminating statistic for the surrogate test utilized to detect nonlinearity. Nonlinear dynamics is less present in HF animals at both short and long time scales compared with controls. A similar finding was found in SHR only at short time scales. SAD increased the presence of nonlinear dynamics exclusively at short time scales. Those findings suggest that a working baroreflex contributes to linearize HRV and to reduce the likelihood to observe nonlinear components of the cardiac control at short time scales. In addition, an increased sympathetic modulation seems to be a source of nonlinear dynamics at long time scales. Testing nonlinear dynamics as a function of the time scales can provide a characterization of the cardiac control complementary to more traditional markers in time, frequency, and information domains.NEW & NOTEWORTHY Although heart rate variability (HRV) dynamics is widely assumed to be nonlinear, nonlinearity tests are rarely used to check this hypothesis. By adopting multiscale entropy (MSE) and refined MSE (RMSE) as the discriminating statistic for the nonlinearity test, we show that nonlinear dynamics varies with time scale and the type of cardiac dysfunction. Moreover, as complexity metrics and nonlinearities provide complementary information, we strongly recommend using the test for nonlinearity as an additional index to characterize HRV.

Sedentary conditions and enhanced responses to GABA in the RVLM: role of the contralateral RVLM.

A sedentary lifestyle is a major risk factor for cardiovascular disease, and both conditions are associated with overactivity of the sympathetic nervous system. Ongoing discharge of sympathetic nerves is regulated by the rostral ventrolateral medulla (RVLM), which in turn is modulated by the primary excitatory and inhibitory neurotransmitters glutamate and γ-amino-butyric acid (GABA), respectively. We reported previously that sedentary conditions enhance GABAergic modulation of sympathoexcitation in the RVLM, despite overall increased sympathoexcitation. Thus the purpose of this study was to test the hypothesis that sedentary conditions increase responsiveness to GABA in RVLM. Male Sprague-Dawley rats performed either chronic wheeling running or remained sedentary for 12-15 wk. Animals were instrumented to perform RVLM microinjections under Inactin anesthesia while mean arterial pressure (MAP) and splanchnic sympathetic nerve activity (SSNA) were recorded. Unilateral microinjections of GABA (30 nl, 0.3-600 mM) into the RVLM produced dose-dependent decreases in MAP and SSNA; however, no group differences were observed. Inhibition of the contralateral RVLM (muscimol, 2 mM, 90 nl) caused decreases in MAP and SSNA that were not different between groups but enhanced decreases in SSNA to GABA in sedentary rats only. In sinoaortic denervated rats, GABA microinjections before or after inhibition of the contralateral RVLM caused decreases in MAP and SSNA that were not different between groups. Our results suggest that the contralateral RVLM plays an important role in buffering responses to inhibition of the ipsilateral RVLM under sedentary but not physically active conditions. Based on these studies and others, sedentary conditions appear to enhance both sympathoinhibitory and sympathoexcitatory mechanisms in the RVLM. Enhanced sympathoinhibition may act to reduce already elevated sympathetic nervous system activity following sedentary conditions.

Role of respiratory changes in the modulation of arterial pressure in rats submitted to sino-aortic denervation.

What is the central question of this study? The arterial baroreflex regulates arterial pressure within a narrow range of variation. After sino-aortic denervation (SAD), rats show a large increase in arterial pressure variability, but mean arterial pressure levels remain similar to those of control rats. Considering that breathing influences the control of arterial pressure, the question is: to what extent does SAD cause changes in breathing? What is the main finding and its importance? Removal of arterial baroreceptors produced changes in breathing in rats, marked by a reduction in respiratory frequency, but not hypertension. These findings are indicative of a possible interaction of respiratory and autonomic neural mechanisms in the regulation of arterial pressure after SAD. Sino-aortic denervated (SAD) rats exhibit a mean arterial pressure (MAP) similar to that of control rats. Given that respiration modulates MAP, we hypothesized that conscious SAD rats show respiratory changes associated with the normal MAP. In this study, we evaluated the cardiovascular and respiratory activities and arterial blood gases in control and SAD rats. Male juvenile Wistar rats (postnatal day19-21) were submitted to SAD, sham surgery or selective removal of the carotid bodies (CBX), and the three groups were evaluated 10 days after the surgery (SAD, n=21; Sham, n=18; and CBX, n=13). The MAP in Sham, SAD and CBX groups was similar (P>0.05), but the variability of MAP was significantly higher in SAD than in Sham and CBX rats (P<0.0001). The duration of expiration and inspiration increased in SAD rats compared with Sham and CBX rats, which resulted in a reduced respiratory frequency and minute ventilation (P<0.05). The arterial partial pressure of O2 and the haemoglobin saturation were reduced in SAD and CBX compared with Sham rats, whereas the arterial partial pressure of CO2 was increased in SAD compared with Sham rats. The short- and long-term respiratory variability were significantly higher in SAD than in Sham and CBX rats (P<0.05). In addition, the reductions in MAP during deep breaths were greater in SAD than in Sham and CBX rats (P<0.0001). The data show that SAD rats exhibit respiratory changes, which may be one of the compensatory mechanisms associated with the maintenance of normal levels of MAP in the absence of arterial baroreceptors.

Characteristic enhancement of blood pressure V-shaped waves in sinoaortic-denervated rats in a conscious and quiet state.

A hemodynamic feature of chronic sinoaortic-denervated (SAD) rats is the increase in blood pressure variability (BPV) without significant changes in the average level of blood pressure (BP). The current study was designed to investigate the changes in BP V-shaped waves (V waves) in SAD rats. Sprague-Dawley (SD) rats were divided into 2 groups: SAD rats and sham-operated rats (n=13). Hemodynamics measurements were obtained in conscious, freely moving rats, four weeks after sinoaortic denervation or sham operation. V wave indices were evaluated in rats in both conscious and quiet states. Additionally, normal and high BPV was simulated by the production of V waves with different amplitudes. The results showed that the V wave amplitude was dramatically increased, with a significantly prolonged duration and reduced frequency in SAD rats. V wave BPV in SAD rats was significantly increased, though BP remained unchanged. The twenty-four hour BPV in all rats was positively correlated with amplitude, duration time and V wave BPV and negatively correlated with frequency. The systolic BP spectral powers in the low frequency range (0.38-0.45 Hz) were significantly reduced in the V waves of SAD rats. Moreover, there was a remarkable increase in mean BPV and a normal mean BP after simulating high BPV in SAD rats. These results suggest that enhancement of V waves might be a waveform character of BP in SAD rats in both the conscious and quiet states. These types of V waves appear to be related to a depression of sympathetic regulation of BP induced by sinoaortic denervation.

Multiscale entropy analysis of heart rate variability in heart failure, hypertensive, and sinoaortic-denervated rats: classical and refined approaches.

The analysis of heart rate variability (HRV) by nonlinear methods has been gaining increasing interest due to their ability to quantify the complexity of cardiovascular regulation. In this study, multiscale entropy (MSE) and refined MSE (RMSE) were applied to track the complexity of HRV as a function of time scale in three pathological conscious animal models: rats with heart failure (HF), spontaneously hypertensive rats (SHR), and rats with sinoaortic denervation (SAD). Results showed that HF did not change HRV complexity, although there was a tendency to decrease the entropy in HF animals. On the other hand, SHR group was characterized by reduced complexity at long time scales, whereas SAD animals exhibited a smaller short- and long-term irregularity. We propose that short time scales (1 to 4), accounting for fast oscillations, are more related to vagal and respiratory control, whereas long time scales (5 to 20), accounting for slow oscillations, are more related to sympathetic control. The increased sympathetic modulation is probably the main reason for the lower entropy observed at high scales for both SHR and SAD groups, acting as a negative factor for the cardiovascular complexity. This study highlights the contribution of the multiscale complexity analysis of HRV for understanding the physiological mechanisms involved in cardiovascular regulation.

Possible Respiratory Modulation of Sympathetic Activity in Rats After Sino‐aortic Denervation

It is well known that several days after sino‐aortic denervation (SAD) rats present normal levels of sympathetic activity and mean arterial pressure (MAP). However, the mechanisms involved in the modulation of the sympathetic activity after SAD remain unclear. Here we hypothesized that the respiratory network may contribute to the modulation of the pre‐sympathetic neurons preventing sustained increase in MAP in SAD rats. To study this mechanism we recorded the activities of phrenic, thoracic sympathetic (tSNA) and cervical vagus nerves (cVN) in male juvenile Wistar rats in the working heart‐brainstem preparation, at high or low respiratory drive induced by hypercapnia or hypocapnia, respectively (SAD, n = 26 and Sham, n = 33). The duration of inspiration significantly increased in SAD rats (1.46 ± 0.05 vs 1.14 ± 0.07 s, P &lt; 0.001). It was also observed that SAD increases cVN inspiratory activity (25 ± 1 vs 32 ± 2%, P &lt; 0.05) and decreases in its post‐inspiratory component (76 ± 1 vs 68 ± 2%, P &lt; 0.05), suggesting an increased upper airway resistance during inspiration in SAD rats. Regarding the baseline tSNA, no changes were observed in the baseline tSNA in all phases of the respiratory cycle in SAD rats, which presented significant reduction in the Traube‐Hering waves magnitude (2.57 ± 0.04 vs 1.19 ± 0.20 mmHg, P = 0.0048). In order to reveal the influence of the respiratory network on the modulation of sympathetic activity rats were exposed to hypercapnia (from 5 to 10 % of CO2) or hypocapnia (from 5 to 3 and 1 % of CO2). High respiratory drive induced by hypercapnia increases tSNA in all phases of respiration in Sham rats (n=13), but in SAD rats (n=14) a significant increase in tSNA was observed only during inspiration (43 ± 3% vs 55 ± 3%, P &lt; 0.01). On the other hand, hypocapnia reduced the respiratory drive and induced sympatho‐inhibition in the SAD (n=8) and in Sham rats (n=10). The data show that in spite of longer inspiratory activity, the baseline sympathetic activity is normal in SAD rats. Whether or not the longer inspiratory activity is driving the sympathetic activity in SAD rats is still matter for further investigation.Support or Funding InformationFAPESP, CAPES and CNPq

Oxidative Stress Is Involved in the Renal Dysfunction Induced by Sinoaortic Denervation in Rats.

The hypothesis that oxidative stress contributes to renal dysfunction in sinoaortically denervated (SAD) rats was investigated. Rats were sinoaortically denervated and received treatment with tempol (0.5 mmol/L in drinking water) for 8 weeks. Although the tempol treatment of the SAD rats had no significant effect on blood pressure or blood pressure viability, it significantly ameliorated the renal dysfunction as indicated by increases in renal blood flow (RBF) and the glomerular filtration rate (GFR) and reductions in plasma creatinine, blood urea nitrogen (BUN), the urine albumin excretion rate (UAE), and the glomerular sclerosis score (GSS). The SAD rats treated with tempol exhibited decreased plasma and renal malondialdehyde (MDA) levels and reduced renal formation of reactive oxygen species (ROS), superoxide (O2-), peroxynitrite (OONO-) and 3-nitrotyrosine. Treatment with tempol suppressed the nuclear concentration of nuclear factor-kappaB (NF-κB) and reduced the renal levels of macrophage chemoattractant protein 1 (MCP-1) and interleukin-6 (IL-6). The tempol-treated SAD rats exhibited decreased renal advanced glycation end product (AGE) levels and decreased receptor for advanced glycation end products (RAGE) protein expression. The tempol treatment of the SAD rats restored mitochondrial adenosine triphosphate (ATP) formation, DNA content, membrane integrity and the renal oxygen consumption rate. Additionally, the activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione S epoxide transferase (GST), and catalase were decreased, and the activities of xanthin oxidase (XO) and reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase were enhanced in the kidneys of the SAD rats. In conclusion, our work firstly provided direct evidence that oxidative stress played an important role in the renal dysfunction of SAD rats.

Involvement of sinoaortic afferents in renal sympathoinhibition and vasodilation induced by acute hypernatremia.

Despite the abundance of evidence that supports the important role of aortic and carotid afferents to short-term regulation of blood pressure and detection of variation in the arterial PO2 , PCO2 and pH, relatively little is known regarding the role of these afferents during changes in the volume and composition of extracellular compartments. The present study sought to determine the involvement of these afferents in the renal vasodilation and sympathoinhibition induced by hypertonic saline (HS) infusion. Sinoaortic-denervated and sham male Wistar rats were anaesthetised with intravenous (i.v.) urethane (1.2g/kg body weight (bw)) prior to the measurement of the mean arterial pressure (MAP), renal vascular conductance (RVC) and renal sympathetic nerve activity (RSNA). In the sham group, the HS infusion (3mol/L NaCl, 1.8mL/kg bw, i.v.) induced transient hypertension (12±4 mmHg from baseline, peak at 10min; P<0.05), an increase in RVC (127±9% and 150±13% from baseline, at 20 and 60min respectively; P<0.05) and a decrease in RSNA (-34±10% and -29±5% from baseline, at 10 and 60min respectively; P<0.05). In sinoaortic-denervated rats, HS infusion promoted a sustained pressor response (30±5 and 17±6mmHg of baseline values, at 10 and 30min respectively; P<0.05) and abolished the increase in RVC (85±8% from baseline, at 10min) and decrease in RSNA (-4±3% from baseline, at 10min). These results suggest that aortic and carotid afferents are involved in cardiovascular and renal sympathoinhibition responses induced by acute hypernatremia.