Exercise and hypertension: a model for central neural plasticity

The Aging GABAergic System and Its Nutritional Support

Aging is associated with a decline in hormones and an associated decline in GABAergic function and calcium and ion current dysregulation. Neurosteroid hormones act as direct calcium channel blockers, or they can act indirectly on calcium channels through their interaction with GABA receptors. The calcium channel dysfunction associated with hormone loss further leads to an excitatory cell state, which can ultimately lead to cell death. The calcium theory of aging posits that cellular mechanisms, which maintain the homeostasis of cytosol Ca2+ concentration, play a key role in brain aging and that sustained changes in Ca2+ homeostasis provide the final common pathway for age-associated brain changes. There is a link between hormone loss and calcium dysregulation. Loss of calcium regulation associated with aging can lead to an excitatory cell state, primarily in the mitochondria and nerve cells, which can ultimately lead to cell death if not kept in check. A decline in GABAergic function can also be specifically tied to declines in progesterone, allopregnanolone, and DHEA levels associated with aging. This decline in GABAergic function associated with hormone loss ultimately affects GABAergic inhibition or excitement and calcium regulation throughout the body. In addition, declines in GABAergic function can also be tied to vitamin status and to toxic chemicals in the food supply. The decline in GABAergic function associated with aging has an effect on just about every body organ system. Nutritional support of the GABAergic system with supportive foods, vitamins, and GABA or similar GABA receptor ligands may address some of the GABAergic dysfunction associated with aging.

Exercise training ameliorates adrenergic control in spontaneously hypertensive rats

The goal of this study was to examine vascular control after sympathetic stimulation by tyramine infusion in hypertensive rats submitted to swimming training. To this end, male rats were assigned to the following groups: sedentary (SN) and trained normotensive (TN), sedentary (SH) and trained hypertensive (TH). Arterial pressure (AP), heart rate (HR), HR variability (HRV), AP variability (APV), and cardiac autonomic function were recorded. Following, infusion of tyramine was administrated. The TN and TH showed a lower resting HR compared with their respective sedentary groups (p < .05). Pressure levels were less in TH than SH (p < .05). The TH showed a higher HRV together with a lower APV in comparison to SH (p < .05). The sympathetic modulation of HRV and APV was lower in TH than in SH (p < .05). Both trained groups presented an increased parasympathetic modulation of HRV compared with their respective sedentary groups (p < .05). The TN and TH groups had a higher vagal effect in comparison with their respective sedentary groups (p < .001). The sympathetic effect was lower in TH than in SH (p < .001). Pressor and HR responses to tyramine in different doses were attenuated in TH (p < .001). Further analysis showed a significant association between infusion of tyramine and normalized LF component of HRV (r = 0.84, p < .001), systolic APV (r = 0.58, p < .001) and diastolic APV (r = 0.49, p < .001). In conclusion, exercise training provokes less pressor response variation by tyramine infusion in hypertensive animals suggesting sympathetic nerve endings adjustments and decrease of the vasoconstrictor effect attenuates injury caused by hypertension improving cardiovascular autonomic dysfunction, which can be associated with sympathetic attenuation.

Swimming training improves cardiovascular autonomic dysfunctions and prevents renal damage in rats fed a high-sodium diet from weaning

NEW FINDINGS

What is the central question of this study? How does swimming exercise training impact hydro-electrolytic balance, renal function, sympathetic contribution to resting blood pressure and cerebrospinal fluid (CSF) [Na⁺ ] in rats fed a high-sodium diet from weaning? What is the main finding and its importance? An exercise-dependent reduction in blood pressure was associated with decreased CSF [Na⁺ ], sympathetically driven vasomotor tonus and renal fibrosis indicating that the anti-hypertensive effects of swimming training in rats fed a high-sodium diet might involve neurogenic mechanisms regulated by sodium levels in the CSF rather than changes in blood volume.

ABSTRACT

High sodium intake is an important factor associated with hypertension. High-sodium intake with exercise training can modify homeostatic hydro-electrolytic balance, but the effects of this association are mostly unknown. In this study, we sought to investigate the effects of swimming training (ST) on cerebrospinal fluid (CSF) Na⁺ concentration, sympathetic drive, blood pressure (BP) and renal function of rats fed a 0.9% Na⁺ (equivalent to 2% NaCl) diet with free access to water for 22 weeks after weaning. Male Wistar rats were assigned to two cohorts: (1) fed standard diet (SD) and (2) fed high-sodium (HS) diet. Each cohort was further divided into trained and sedentary groups. ST normalised BP levels of HS rats as well as the higher sympathetically related pressor activity assessed by pharmacological blockade of ganglionic transmission (hexamethonium). ST preserved the renal function and attenuated the glomerular shrinkage elicited by HS. No change in blood volume was found among the groups. CSF [Na⁺ ] levels were higher in sedentary HS rats but were reduced by ST. Our findings showed that ST effectively normalised BP of HS rats, independent of its effects on hydro-electrolytic balance, which might involve neurogenic mechanisms regulated by Na⁺ levels in the CSF as well as renal protection.

Activity-Dependent Neuroplastic Changes in Autonomic Circuitry Modulating Cardiovascular Control: The Essential Role of Baroreceptors and Chemoreceptors Signaling

Aerobic exercise training improves the autonomic control of the circulation. Emerging evidence has shown that exercise induces neuroplastic adaptive changes in preautonomic circuitry controlling sympathetic/parasympathetic outflow to heart and vessels. The mechanisms underlying neuronal plasticity are, however, incompletely understood. Knowing that sinoaortic denervation blocks training-induced cardiovascular benefits, we investigate whether baroreceptors’ and chemoreceptors’ signaling are able to drive neuronal plasticity within medullary and supramedullary pathways controlling autonomic outflow. Male Wistar rats submitted to sinoaortic denervation (SAD) or dopamine β-hydroxylase-saporin lesion (DBHx) and respective controls (SHAM) were allocated to training (T) or sedentary (S) protocols for 8 weeks. After hemodynamic measurements at rest, rats were deeply anesthetized for brain harvesting. The density of DBH and oxytocin (OT) cell bodies and terminals were analyzed in brainstem and hypothalamic brain areas (double immunofluorescence reactions, optic and confocal microscopy). In SHAM rats training augmented the density of DBH+ neurons in the nucleus of solitary tract, increased the density of ascending NORergic projections and the number of DBH+ boutons contacting preautonomic OT+ neurons into paraventricular hypothalamic preautonomic nuclei, augmented the density of local OTergic neurons and enhanced the density of OT+ terminals targeting brainstem autonomic areas. These plastic changes occurred simultaneously with reduced sympathetic/increased parasympathetic activity, augmented baroreflex sensitivity and reduced resting heart rate. SAD reduced the density of both DBH+ fibers ascending from brainstem to paraventricular nucleus of hypothalamus and preautonomic OT+ neurons projecting to the brainstem, abrogated training-induced plastic changes and autonomic adaptive responses without changing the treadmill performance. Minor neuroplastic changes with preserved baroreflex sensitivity were observed in trained rats after partial selective disruption of ascending NORergic projections. Our data indicated that afferent inputs conveyed by arterial baroreceptors and chemoreceptors are the main stimuli to drive both inactivity-induced and activity-dependent neuroplasticity within the autonomic circuitry.

Maternal physical activity prevents the overexpression of hypoxia-inducible factor 1-α and cardiorespiratory dysfunction in protein malnourished rats

Maternal physical activity attenuates cardiorespiratory dysfunctions and transcriptional alterations presented by the carotid body (CB) of rats. Rats performed physical activity and were classified as inactive/active. During gestation and lactation, mothers received either normoprotein (NP-17% protein) or low-protein diet (LP-8% protein). In offspring, biochemical serum levels, respiratory parameters, cardiovascular parameters and the mRNA expression of hypoxia-inducible factor 1-alpha (HIF-1α), tyrosine hydroxylase (TH) and purinergic receptors were evaluate. LP-inactive pups presented lower RF from 1^st to 14^th days old, and higher RF at 30 days than did NP-inactive and NP-active pups. LP-inactive pups presented with reduced serum protein, albumin, cholesterol and triglycerides levels and an increased fasting glucose level compared to those of NP-inactive and NP-active groups. LP and LP-inactive animals showed an increase in the cardiac variability at the Low-Frequency bands, suggesting a major influence of sympathetic nervous activity. In mRNA analyses, LP-inactive animals showed increased HIF-1α expression and similar expression of TH and purinergic receptors in the CB compared to those of NP groups. All these changes observed in LP-inactive pups were reversed in the pups of active mothers (LP-active). Maternal physical activity is able to attenuate the metabolic, cardiorespiratory and HIF-1α transcription changes induced by protein malnutrition.

Exercise Training Attenuates Sympathetic Activity and Improves Morphometry of Splenic Arterioles in Spontaneously Hipertensive Rats

Background

Alterations in the structure of resistance vessels contribute to elevated systemic vascular resistance in hypertension and are linked to sympathetic hyperactivity and related lesions in target organs.

Objective

To assess the effects of exercise training on hemodynamic and autonomic parameters, as well as splenic arteriolar damages in male Wistar Kyoto (WKY) and Spontaneously Hypertensive Rats (SHR).

Methods

Normotensive sedentary (WKY_S) and trained (WKY_T) rats, and hypertensive sedentary (SHR_S) and trained (SHR_T) rats were included in this study. After 9 weeks of experimental protocol (swimming training or sedentary control), arterial pressure (AP) and heart rate (HR) were recorded in freely moving rats. We assessed the autonomic control of the heart by sympathetic and vagal autonomic blockade. Morphometric analyses of arterioles were performed in spleen tissues. The statistical significance level was set at p < 0.05.

Results

Resting bradycardia was observed in both trained groups (WKY_T: 328.0 ± 7.3 bpm; SHR_T: 337.0 ± 5.2 bpm) compared with their respective sedentary groups (WKY_S: 353.2 ± 8.5 bpm; SHR_S: 412.1 ± 10.4 bpm; p < 0.001). Exercise training attenuated mean AP only in SHR_T (125.9 ± 6.2 mmHg) vs. SHR_S (182.5 ± 4.2 mmHg, p < 0.001). The WKY_T showed a higher vagal effect (∆HR: 79.0 ± 2.3 bpm) compared with WKY_S (∆HR: 67.4 ± 1.7 bpm; p < 0.05). Chronic exercise decreased sympathetic effects on SHR_T (∆HR: -62.8 ± 2.8 bpm) in comparison with SHR_S (∆HR: -99.8 ± 9.2 bpm; p = 0.005). The wall thickness of splenic arterioles in SHR was reduced by training (332.1 ± 16.0 µm² in SHR_T vs. 502.7 ± 36.3 µm² in SHR_S; p < 0.05).

Conclusions

Exercise training attenuates sympathetic activity and AP in SHR, which may be contributing to the morphological improvement of the splenic arterioles.

A randomized controlled trial of exercise training on cardiovascular and autonomic function among renal transplant recipients

BACKGROUND

There are conflicting data regarding the effects of renal transplantation (RT) on uraemic autonomic dysfunction. Moreover, no study has examined the impact of physical training on the cardiac autonomic function in RT patients. Thus, we studied the effects of exercise training on heart rate variability (HRV) and arterial baroreflex sensitivity (BRS), which are sensitive markers of cardiac autonomic outflow, in RT recipients.

METHODS

Eleven patients (Exercise group-aged 52.1 ± 5.6 years) were studied before and after 6 months of exercise training. Twelve age- and sex- matched RT patients (Sedentary) and 12 healthy sedentary individuals (Healthy), who remained untrained, served as controls. At baseline and follow-up, all the subjects underwent cardiopulmonary exercise testing for the evaluation of peak oxygen consumption (VO2peak), a tilt test for the evaluation of BRS and baroreflex effectiveness index (BEI) and an ambulatory 24-h Holter monitoring for time- and frequency-domain measures of HRV.

RESULTS

In the exercise group, VO2peak increased by 15.8% (P < 0.05) and all depressed HRV and BRS indices were significantly improved after training. Specifically, the standard deviation of all normal-to-normal (NN) intervals (SDNN) significantly increased by 92.5%, the root-mean-square of the differences between consecutive NN intervals by 45.4%, the percentage value of NN50 count by 58.2%, the high-frequency by 74.8% and low-frequency spectral power by 41.6%, BRS by 43.7% and BEI by 57.3%. None of the variables studied was altered over time in either control group.

CONCLUSIONS

The increased cardiorespiratory fitness by exercise training was associated with an improved BRS function and a modification of the sympathovagal control of HRV towards a persistent increase in parasympathetic tone. These alterations may lead to a better cardiovascular prognosis in RT recipients.

[Analysis of the control of cardiovascular risk factors in patients with peripheral arterial disease]

INTRODUCTION

The objective was to determine the percentage of patients with peripheral arterial disease (PAD) with good control of their cardiovascular risk factors (CVRF) (LDL cholesterol, blood pressure and smoke cessation).

MATERIAL AND METHODS

Cross-sectional multicentre study. The location was Primary Care and other clinics that typically treat patients with peripheral arterial disease (Internal Medicine, Vascular Surgery, Cardiology, Endocrinology and Nephrology). The first 10 patients with peripheral arterial disease were systematically selected by 440 researchers from all regions.

RESULTS

The study included 4087 patients. Blood pressure was controlled in 29.5% of the cases. The frequency of patients with optimal control was significantly better in primary care (p<.01). There was an optimal control of LDL-C levels in 30.4% of patients. Factors associated with optimal control of LDL-C was, being diabetic, stage I of La Fontaine, and being seen by a doctor that was not the primary care physician. Control was worse in women and in smokers.

CONCLUSIONS

Primary care physicians better manage patients with hypertension. Patients seen in by a specialist as opposed to primary care are more likely to achieve optimal control of CVRF. The situation is far from the ideal, only 6% achieved optimal control of all CVRF.

Interaction of hydrogen sulfide with ion channels

1. Hydrogen sulfide (H(2)S) is a signalling gasotransmitter. It targets different ion channels and receptors, and fulfils its various roles in modulating the functions of different systems. However, the interaction of H(2)S with different types of ion channels and underlying molecular mechanisms has not been reviewed systematically. 2. H(2)S is the first identified endogenous gaseous opener of ATP-sensitive K(+) channels in vascular smooth muscle cells. Through the activation of ATP-sensitive K(+) channels, H(2)S lowers blood pressure, protects the heart from ischemia and reperfusion injury, inhibits insulin secretion in pancreatic beta cells, and exerts anti-inflammatory, anti-nociceptive and anti-apoptotic effects. 3. H(2)S inhibited L-type Ca(2+) channels in cardiomyocytes but stimulated the same channels in neurons, thus regulating intracellular Ca(2+) levels. H(2)S activated small and medium conductance K(Ca) channels but its effect on BK(Ca) channels has not been consistent. 4. H(2)S-induced hyperalgesia and pro-nociception seems to be related to the sensitization of both T-type Ca(2+) channels and TRPV(1) channels. The activation of TRPV(1) and TRPA(1) by H(2)S is believed to result in contraction of nonvascular smooth muscles and increased colonic mucosal Cl(-) secretion. 5. The activation of Cl(-) channel by H(2)S has been shown as a protective mechanism for neurons from oxytosis. H(2)S also potentiates N-methyl-d-aspartic acid receptor-mediated currents that are involved in regulating synaptic plasticity for learning and memory. 6. Given the important modulatory effects of H(2)S on different ion channels, many cellular functions and disease conditions related to homeostatic control of ion fluxes across cell membrane should be re-evaluated.

Arterial baroreflex control of cardiac vagal outflow in older individuals can be enhanced by aerobic exercise training

Maintained cardiac vagal function is critical to cardiovascular health in human aging. Aerobic exercise training has been considered an attractive intervention to increase cardiovagal baroreflex function; however, the data are equivocal. Moreover, if regular exercise does reverse the age-related decline in cardiovagal baroreflex function, it is unknown how this might be achieved. Therefore, we assessed the effects of a 6-month aerobic training program on baroreflex gain and its mechanical and neural components in older individuals (5 women and 7 men, aged 55 to 71 years). We assessed baroreflex function using pharmacological pressure changes (bolus nitroprusside followed by bolus phenylephrine) and estimated the integrated gain (Delta R-R interval/Delta systolic blood pressure) and mechanical (Delta diameter/Delta pressure) and neural (Delta R-R interval/Delta diameter) components via measurements of carotid artery diameter in previously sedentary older individuals before and after 6 months of aerobic training. There was a significant 26% increase in baroreflex gain that was directly related to the amount of exercise performed and that was derived mainly from an increase in the neural component of the arterial baroreflex (P<0.05). We did find changes in the mechanical component, but unlike integrated gain and the neural component, these were not related to the magnitude of the exercise stimulus. These results suggest that exercise training can have a powerful effect on cardiovagal baroreflex function, but a sufficient stimulus is necessary to produce the effect. Moreover, adaptations in the afferent-efferent baroreflex control of cardiac vagal outflow may be crucial for the improvement in arterial baroreflex function in older humans.

Hydrogen sulphide in the hypothalamus causes an ATP-sensitive K+ channel-dependent decrease in blood pressure in freely moving rats

Hydrogen sulfide (H2S) is a naturally occurring gas that may act as an endogenous signaling molecule. In the brain, H2S is mainly produced by cystathionine beta-synthase (CBS) and its cellular effects have been attributed to interactions with N-methyl-D-aspartate (NMDA) receptors and cyclic adenosine 3',5'-monophosphate (cAMP). In contrast, direct vasodilator actions of H2S are most probably mediated by opening smooth muscle ATP-sensitive K+ (K(ATP)) channels. In the hypothalamus, K(ATP) channel-dependent mechanisms are involved in CNS-mediated regulation of blood pressure. In this report, we investigated the hypothesis that H2S may act via K(ATP) channels in the hypothalamus to regulate blood pressure. Mean arterial blood pressure (MAP) and heart rate were monitored in freely moving rats via a pressure transducer placed in the femoral artery. Drugs were infused via a cannula placed in the posterior hypothalamus. Infusion of 200 microM sodium hydrogen sulfide (NaHS), an H2S donor, into the hypothalamus of freely moving rats reduced MAP and heart rate. Infusion of 300 nM to 3 microM gliclazide dose-dependently blocked the effect of 200 microM NaHS. Infusion of the CBS activator, s-adenosyl-L-methionine (0.1 mM and 1 mM), likewise decreased MAP. Infusion of the CBS inhibitors aminooxyacetic acid (10 mM) and hydroxylamine (20 mM) increased MAP but did not block the effects of infusion of 200 microM NaHS. These data indicate that actions of H2S in the hypothalamus decrease blood pressure and heart rate in freely moving rats. This effect appears to be mediated by a K(ATP) channel-dependent mechanism and mimicked by endogenous H2S.

Exercise training and sympathetic nervous system activity: evidence for physical activity dependent neural plasticity

1. It has been generally accepted that regular physical activity is associated with beneficial effects on the cardiovascular system. In fact, the idea that exercise maintains cardiovascular health is evident by the direct links between a sedentary lifestyle and the risk of cardiovascular and other disease states. 2. Cardiovascular diseases, such as hypertension and heart failure, are often associated with sympathetic nervous system (SNS) overactivity. Conversely, exercise has been shown to reduce hypertension and decrease elevated SNS activity. In addition, there is evidence that exercise may reduce resting blood pressure and sympathetic outflow in normal individuals. 3. Although somewhat controversial in humans, evidence from animal studies also indicates that exercise training reduces baroreflex-mediated and other forms of sympathoexcitation in normal individuals. Collectively, these data are consistent with the hypothesis that physical activity may decrease, and physical inactivity may increase, the incidence of cardiovascular disease via alterations in SNS activity. Despite the important clinical implications of this possibility, the mechanisms by which exercise alters control of SNS activity remain to be fully elucidated. 4. Recent evidence suggests that central nervous system (CNS) plasticity occurs under a variety of conditions, including varying levels of physical activity. The purpose of the present brief review is to provide evidence that changes within the CNS contribute importantly to altered regulation of the SNS observed following exercise training. The primary hypothesis is that physical activity versus inactivity produces plasticity within neural networks that regulate SNS activity. This hypothesis is supported by published and preliminary data that suggest that exercise training may reduce sympathoexcitation by reducing activation of neurons within cardiovascular regions of the brain. These mechanisms are likely to be important in disease states of sympathetic overactivity and in normal healthy individuals whose risk of cardiovascular disease is reduced by leading an active versus sedentary lifestyle.

Exercise Training Differentially Affects Intrinsic Excitability of Autonomic and Neuroendocrine Neurons in the Hypothalamic Paraventricular Nucleus

Oxytocinergic and vasopressinergic brain stem projections have been shown to play an important role in mediating cardiovascular adjustments during exercise training (ET). The aim of the present work was to determine whether the intrinsic excitability of hypothalamic neurons giving rise to brain stem peptidergic projections is altered as a consequence of ET. Whole cell patch-clamp recordings were obtained from nucleus of the solitarii tract (NTS)-projecting paraventricular nucleus of the hypothalamus (PVN) neurons and from supraoptic nucleus (SON) and PVN magnocellular cells (MNCs), in hypothalamic slices obtained from sedentary (S) and ET rats. Our results indicate that intrinsic excitability of PVN neurons that innervate the NTS (PVN-NTS) is enhanced by ET, resulting in a more efficient input-output function (increase number of evoked actions potentials, steeper frequency/current relationships and slower decaying frequency/time relationships). Changes in input-output function were accompanied by smaller hyperpolarizing afterpotentials (HAPs) and afterhyperpolarizing potentials (AHPs), during and after trains of spikes, respectively. On the other hand, a decreased efficacy in the input-output function was observed in SON/PVN MNCs during ET. Altogether, our results indicate that ET differentially affects the intrinsic excitability of autonomic and neurosecretory SON and PVN neurons. Increased excitability in PVN-NTS neurons may contribute to enhanced release of OT and VP peptides in the dorsal brain stem, and cardiovascular fine-tuning during exercise training.

Longitudinal studies on the effect of hypertension on circadian hemodynamic and autonomic rhythms in telemetered rats

This study dealt with the long-term effects of hypertension on circadian rhythms of hemodynamic and cardiovascular autonomic functions in radiotelemetered rats. Blood pressure (BP), heart rate (HR), spontaneous locomotor activity, and respiration.were monitored in spontaneously hypertensive rats (SHRs), a model of human hypertension, from 14 to 27 weeks of age and in Wistar-Kyoto rats (WKY) as controls. Cardiovascular autonomic changes were determined by time-domain analysis of the variability of BP (standard deviation of mean arterial pressure, SDMAP) and HR (standard deviation of R-R intervals, SDRR, and the root mean square of successive differences in R-R intervals, rMSSD). Compared with WKY rats, the 24-hr MAP and SDMAP were higher at week 14 in SHRs and showed stepwise increases over the study duration, suggesting progressive increases in vasomotor sympathetic activity in hypertensive rats. Also, higher SDRR, rMSSD, and activity and lower HR and respiration were demonstrated in SHRs. Normal circadian rhythms (higher dark-time values) of MAP, HR, SDMAP, and SDRR were evident in WKY rats at week 20 and continued thereafter. Compared with WKY rats, the circadian BP and HR patterns were abolished and inverted, respectively, in SHRs. Lower dark-time, compared with light-time, SDMAP values were observed in SHRs that were associated with temporal increases in HR variability indices. These findings demonstrate that hypertension elicits significant alterations in circadian autonomic and hemodynamic profiles. Further, the steady increases in BP, average level and oscillations, in SHRs may explain the reported progressive age-related vascular and cardiac hypertrophy in these rats.

Regular voluntary exercise reduces anxiety-related behaviour and impulsiveness in mice

We embarked on a study to delineate the behavioural changes in mice after 4 weeks of voluntary exercise. As an initial behavioural characterization, we exposed the control and exercising mice to a modified hole board and an open field test. As compared to control mice, exercising animals showed clear signs of increased behavioural inhibition (e.g. a longer latency to enter unprotected areas), suggesting increased anxiety in these animals. In addition, the exercising mice were reluctant to spend time in the open field's centre during the beginning of the 30-min open field test, but compensated for this at later times. Paradoxically, the exercising animals showed more rearings on the board of the modified hole board, indicating decreased anxiety. Thus, the behavioural inhibition seen in exercising mice is likely to represent decreased stress responsiveness at the behavioural level which can also be interpreted as reduced impulsiveness. To clarify whether voluntary exercise evolves in more or less anxiety-related behaviour, we exposed animals to the elevated plus-maze and the dark-light box, two selective tests for unconditioned anxiety. Clearly, compared to the control animals, exercising mice spent significantly more time on the open arm of the plus-maze and spent double the amount of time in the light compartment of the dark-light box. Taken together, we conclude that long-term voluntary exercise appears to result in decreased anxiety-related behaviour and impulsiveness. Thus, our observations fit into the concept that regular exercise strengthens endogenous stress coping mechanisms, thereby protecting the organism against the deleterious effects of stress.