Baroreflex sensitivity improvement is associated with decreased oxidative stress in trained spontaneously hypertensive rat

Effectiveness of exercise training on arterial stiffness and blood pressure among postmenopausal women: a systematic review and meta-analysis

BACKGROUND

The acute and long-term benefits of exercise training on cardiovascular health have been well established. The systematic review and meta-analysis aimed to systematically assess the effectiveness of exercise training on arterial stiffness and blood pressure among postmenopausal women with elevated blood pressure.

METHODS

A comprehensive search was conducted on PubMed, Embase, Web of Science, ProQuest, Cochrane Library, Cochrane Central Register of Controlled Trials, and ClinicalTrials.gov website from inception to September 30, 2023, to identify the randomized controlled trials (RCTs), which evaluated the effectiveness of exercise training on arterial stiffness and blood pressure in postmenopausal women. Standardized mean differences (SMD), weighted mean differences (WMD), and 95% confidence intervals (95% CIs) were calculated using random/fixed effects models. Quality assessment was performed using the modified Jadad scale and the Cochrane Risk of Bias Tool. Sensitivity analysis and subgroup analysis were conducted based on drug dosage, treatment duration, and age of administration to further explore potential heterogeneity. Funnel plots were performed to assess publication bias and Begg's regression test was carried out for funnel plot asymmetry.

RESULTS

Twenty-two RCTs involving 1978 participants were included in the quantitative analysis. The mean quality of eligible studies was 4.2 out of 7 based on the modified Jadad scale. The results indicated that exercise training had a significant effect on reducing brachial-ankle pulse wave velocity [MD = - 0.69, 95%CI (- 1.11, - 0.27), P = 0.001], decreasing augmentation index (AIx) [MD = - 6.00, 95%CI (- 6.39, - 5.61), P < 0.00001] and AIx normalized to a heart rate of 75 beats per minute (AIx@75%) [MD = - 7.01, 95%CI - 7.91 to - 6.12, P < 0.00001], lowering systolic blood pressure [MD = - 6.19, 95%CI - 9.24 to - 3.15, P < 0.0001], diastolic blood pressure [MD = - 3.57, 95%CI (- 6.10, - 1.03), P = 0.006) and pulse pressure [MD = - 8.52, 95%CI (- 16.27, - 0.76), P = 0.03]. Subgroup analysis revealed that baseline blood pressure levels had a large impact on the effect of exercise training.

CONCLUSIONS

The systematic review and meta-analysis suggested that exercise training may ameliorate arterial stiffness and reduce blood pressure in postmenopausal women with elevated blood pressure. However, the optimal mode of exercise training that improves arterial stiffness and blood pressure in this population requires further investigation.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42021211268.

Combined Exercise Training Promotes More Benefits on Cardiovascular Autonomic Modulation in Ovariectomized Rats Than Isolated Aerobic or Resistance Training

Introduction

Cardiovascular risk increase after ovarian deprivation has been extensively demonstrated by our research group through cardiovascular autonomic analysis. Interventions involving different types of exercises, such as resistance exercises or combined exercises (aerobic and resistance) have been widely recommended to prevent or minimize neuromuscular decline in postmenopausal women, which is aggravated by a sedentary lifestyle. Experimentally, the cardiovascular effects of resistance or combined training, as well as comparison between aerobic, resistance, and combined training, in ovariectomized animals are scarce.

Purpose

In this study, we hypothesized that the combination of aerobic and resistance training may be more effective in preventing muscle mass loss, as well as improving cardiovascular autonomic modulation and baroreflex sensitivity, than aerobic or resistance training individually in ovariectomized rats.

Animals and Methods

Female rats were divided into 5 groups: sedentary (C); ovariectomized (Ovx); trained ovariectomized submitted to aerobic training (OvxAT); resistance training (OvxRT); combined training (OvxCT). Exercise training lasted 8 weeks, with the combined group alternating between aerobic training and resistance training every other day. At the end of the study, glycemia and insulin tolerance were evaluated. Arterial pressure (AP) was directly recorded. Baroreflex sensitivity was assessed by heart rate response to changes in arterial pressure. Cardiovascular autonomic modulation was evaluated by spectral analysis.

Results

Combined training was the only training regime that increased baroreflex sensitivity for tachycardic response and reduced all systolic blood pressure variability parameters. Furthermore, all animals submitted to exercise training on a treadmill (OvxAT and OvxCT) presented lower systolic, diastolic, and mean pressure, as well as improvements in the autonomic modulation for the heart.

Conclusion

Combined training showed to be more effective than isolated aerobic and resistance training, mixing the isolated benefits of each modality. It was the only modality able to increase baroreflex sensitivity to tachycardic responses, reduce arterial pressure and all parameters of vascular sympathetic modulation.

Benefits of combined exercise training on arterial stiffness and blood pressure in spontaneously hypertensive rats treated or not with dexamethasone

Dexamethasone (DEX)-induced arterial stiffness is an important side-effect, associated with hypertension and future cardiovascular events, which can be counteracted by exercise training. The aim of this study was to evaluate the mechanisms induced by combined training to attenuate arterial stiffness and hypertension in spontaneously hypertensive rats treated or not with dexamethasone. Spontaneously hypertensive rats (SHR) underwent combined training for 74 days and were treated with dexamethasone (50 µg/kg s. c.) or saline solution during the last 14 days. Wistar rats were used as controls. Echocardiographic parameters, blood pressure (BP) and pulse wave velocity (PWV), as well as histological analyses of the heart and aorta, carotid and femoral arteries were performed. At the beginning, SHR had higher BP and PWV compared with Wistar rats. After 60 days, while BP increased in sedentary SHR, combined exercise training decreased BP and PWV. After 74d, the higher BP and PWV of sedentary SHR was accompanied by autonomic imbalance to the heart, cardiac remodeling, and higher arterial collagen deposition. DEX treatment did not change these parameters. On the other hand, trained SHR had reduced BP and PWV, which was associated with better autonomic balance to the heart, reduced myocardial collagen deposition, as well as lower arterial collagen deposition. The results of this study suggest that combined training, through the reduction of aortic collagen deposition, is an important strategy to reduce arterial stiffness in spontaneously hypertensive rats, and these lower responses were maintained regardless of dexamethasone treatment.

Combined effects of angiotensin receptor blocker use and physical training in hypertensive men

PURPOSE

Pharmacological (angiotensin II receptor type 1 receptor blocker use) and non-pharmacological treatment (physical aerobic exercise) are important strategies to reduces blood pressure and control arterial hypertension; however, only few clinical studies have evaluated their combined effects on autonomic cardiovascular control. Therefore, we investigated the effect of a combination intervention that involved losartan administration and physical aerobic training on autonomic cardiovascular control.

METHODS

Thirty-two men (aged 40 to 60 years) were assigned into two groups: normotensive group, without any pharmacological treatment (NG, N = 16), or hypertensive group, with losartan administration (HG, N = 16). They underwent a physical aerobic training for 16 weeks, thrice a week. Hemodynamic parameters, heart rate variability (HRV), blood pressure variability, and spontaneous baroreflex sensitivity (BRS) were measured before and after training.

RESULTS

Before training, both the groups showed similar values of hemodynamic parameters. However, the HG showed decreased BRS and HRV, characterized by reduction in sympathetic (p = .02) and vagal (p < .001) modulation. After training, the NG exhibited decreased heart rate (HR) at rest (p < .001), whereas the HG showed decreased HR at rest (p < .001) and blood pressure (BP) (p = .001). The HG showed decreased sympathetic modulation (p = .02) and increased BRS (p < .001) and vagal modulation (p < .001), but HRV (p < .001) and BRS gain (p < .001) remained significantly lower when compared to the NG.

CONCLUSIONS

Physical aerobic training was essential to improve the BRS and HRV cardiac autonomic modulation in the HG. However, it was not sufficient to normalize the analyzed autonomic parameters.

Loss of Group II Metabotropic Glutamate Receptor Signaling Exacerbates Hypertension in Spontaneously Hypertensive Rats

High blood pressure is a major risk factor of cerebro-cardiovascular outcomes. Blood pressure is partly regulated by the autonomic nervous system and its reflex functions; therefore, we hypothesized that pharmacological intervention in the brainstem that can regulate blood pressure could be a novel therapeutic strategy to control hypertension. We infused a group II metabotropic glutamate receptor (mGluR) antagonist (LY341495, 0.40 μg/day), using a mini-osmotic pump, into the dorsal medulla oblongata in young spontaneously hypertensive rats (SHRs), as this area is adjacent to the nucleus tractus solitarius (NTS), of which the neurons are involved in baroreflex pathways with glutamatergic transmission. Blood pressure was recorded for conscious rats with the tail cuff method. A 6-week antagonist treatment from 6 to 12 weeks of age slightly but significantly increased systolic blood pressure by >30 mmHg, compared to that in SHRs without treatment. Moreover, the effect continued even 3 weeks after the treatment ended, and concurred with an increase in blood catecholamine concentration. However, heart rate variability analysis revealed that LY341495 treatment had little effect on autonomic activity. Meanwhile, mRNA expression level of mGluR subtype 2, but not subtype 3 in the brainstem was significantly enhanced by the antagonist treatment in SHRs, possibly compensating the lack of mGluR signaling. In conclusion, mGluR2 signaling in the dorsal brainstem is crucial for preventing the worsening of hypertension over a relatively long period in SHRs, through a mechanism of catecholamine secretion. This may be a specific drug target for hypertension therapy.

Differential effects of dexamethasone on arterial stiffness, myocardial remodeling and blood pressure between normotensive and spontaneously hypertensive rats

Dexamethasone (DEX)-induced hypertension is observed in normotensive rats, but little is known about the effects of DEX on spontaneously hypertensive animals (SHR). This study aimed to evaluate the effects of DEX on hemodynamics, cardiac hypertrophy and arterial stiffness in normotensive and hypertensive rats. Wistar rats and SHR were treated with DEX (50 μg/kg s.c., 14 d) or saline. Pulse wave velocity (PWV), echocardiographic parameters, blood pressure (BP), autonomic modulation and histological analyses of heart and thoracic aorta were performed. SHR had higher BP compared with Wistar, associated with autonomic unbalance to the heart. Echocardiographic changes in SHR (vs. Wistar) were suggestive of cardiac remodeling: higher relative wall thickness (RWT, +28%) and left ventricle mass index (LVMI, +26%) and lower left ventricle systolic diameter (LVSD, -19%) and LV diastolic diameter (LVDD, -10%), with slightly systolic dysfunction and preserved diastolic dysfunction. Also, SHR had lower myocardial capillary density and similar collagen deposition area. PWV was higher in SHR due to higher aortic collagen deposition. DEX-treated Wistar rats presented higher BP (~23%) and autonomic unbalance. DEX did not change cardiac structure in Wistar, but PWV (+21%) and aortic collagen deposition area (+21%) were higher compared with control. On the other side, DEX did not change BP or autonomic balance to the heart in SHR, but reduced RWT and LV collagen deposition area (-12% vs. SHR_CT ). In conclusion, the results suggest a differential effect of dexamethasone on arterial stiffness, myocardial remodeling and blood pressure between normotensive and spontaneously hypertensive rats.

Impact of an active lifestyle on heart rate variability and oxidative stress markers in offspring of hypertensives

Familial history of hypertension is associated with autonomic dysfunction and increase in blood pressure (BP). However, an active lifestyle has been found to improve a number of health outcomes and reduce all-cause mortality. The aim of the present study was to investigate the effects of an active lifestyle on hemodynamics, heart rate variability (HRV) and oxidative stress markers in offspring of hypertensive parents. One hundred twenty-seven subjects were assigned into four groups: sedentary offspring of normotensives (S-ON) or hypertensives (S-OH); and physically active offspring of normotensives (A-ON) or hypertensives (A-OH). Diastolic BP and heart rate were reduced in the physically active groups when compared to S-OH group. A-ON and A-OH groups presented increased values of RR total variance when compared to the sedentary ones (A-ON: 4,912 ± 538 vs. S-ON: 2,354 ± 159; A-OH: 3,112 ± 236 vs. S-OH: 2,232 ± 241 ms²). Cardiac sympato-vagal balance (LF/HF), systemic hydrogen peroxide and superoxide anion were markedly increased in S-OH group when compared to all other studied groups. Additionally, important correlations were observed between LF/HF with diastolic BP (r = 0.30) and hydrogen peroxide (r = 0.41). Thus, our findings seem to confirm an early autonomic dysfunction in offspring of hypertensive parents, which was associated with a systemic increase in reactive oxygen species and blood pressure. However, our most important finding lies in the attenuation of such disorders in offspring of physically active hypertensives, thus emphasizing the importance of a physically active lifestyle in the prevention of early disorders that may be associated with onset of hypertension.

Ovarian status modulates cardiovascular autonomic control and oxidative stress in target organs

Studies have presented conflicting findings regarding the association between both fluctuation and deprivation of ovarian hormones and cardiovascular autonomic modulation and oxidative stress and their potential impact on resting arterial pressure (AP) and cardiovascular risk. This study aimed to assess cardiovascular autonomic modulation, baroreflex sensitivity (BRS), and oxidative stress in male rats (M) and in female rats during ovulatory (FOV) and non-ovulatory phases (FNOV) of the estrous cycle and after deprivation of ovarian hormones (FO). Direct AP was recorded, and BRS was assessed by using increasing doses of phenylephrine and sodium nitroprusside. AP and heart rate variability were assessed by spectral analysis. Oxidative stress profile was evaluated in cardiac, renal, and muscle tissues. In females, the ovulatory phase and ovarian hormone deprivation induced an increase in AP (FOV and FO ~ 9 mmHg) when compared to the non-ovulatory phase. Ovariectomy promoted increased cardiac sympathovagal balance (~ 17–37%) when compared to other groups. Both FOV and FO groups presented impaired BRS, associated with higher AP variability. In general, antioxidant capacity was higher in the FNOV than in the M group. Ovarian hormone deprivation induced a decrease in catalase activity in cardiac and renal tissues and an increase in lipid peroxidation in all tissues analyzed. Positive correlations (p < 0.05) were found between vascular sympathetic modulation and lipid peroxidation in cardiac (r = 0.60), renal (r = 0.60), and muscle (r = 0.57) tissues. In conclusion, both oscillation and deprivation of ovarian hormones play an important role in cardiovascular autonomic control and oxidative stress profile in target organs, which is reflected in AP changes.

Cardiovascular reactivity to emotional stress: The hidden challenge for pets in the urbanized environment

Emotional stress is currently considered an important risk factor for cardiovascular diseases. Experimental evidence clearly shows robust autonomic cardiovascular effects in animals exposed to stress stimuli. Considering the remarkable variability of stressors, the urban environment can pose a severe challenge to cardiovascular control. Interestingly, pet ownership is indicated as an efficient non-pharmacological therapy to attenuate stress effects that can reduce the risk of cardiovascular disease. However, the risk of cardiovascular diseases in pets themselves living in urban environment has not received attention it deserves. Here, we review the central mechanisms involved in the autonomic cardiovascular response to emotional stress. Next, we discuss experimental evidence showing the cardiovascular effects produced by emotional stressors in animals, aiming to establish a parallel with common urban stressors. Association of additional risk factors such as sedentarism, obesity and ambient temperature are also considered. Our aim is to identify and raise awareness of the risk of cardiovascular disease in pets exposed to quotidian emotional stressors present in the urban environment.

Exercise training initiated at old stage of lifespan attenuates aging-and ovariectomy-induced cardiac and renal oxidative stress: Role of baroreflex

BACKGROUND

The association of aging and menopause is a potent risk factor for cardiometabolic disease. We studied the impact of aerobic exercise training (ET) initiated in the old stage of lifespan in hemodynamics, metabolic, autonomic and oxidative stress.

METHODS

Aged (18 months old) female Wistar rats were divided into: ovariectomized and untrained (AG-OVX), and ovariectomized and trained (AG-OVXt, ET for 8 weeks). Intact aged (AG) and young female rats (3 months old; Y) were also studied. Blood pressure and metabolic parameters were measured. Baroreflex sensitivity (BRS) was studied by bradycardic (BR) and tachycardic (TR) responses to vasoactive drugs. Cardiac and renal lipid peroxidation (LPO), catalase (CAT), superoxide dismutase (SOD) and gluthatione peroxidase (GPx), and gluthatione redox balance (GSH/GSSG) were analyzed.

RESULTS

AG-OVXt group increased aerobic performance in 35%, decreased adipose tissue and triglycerides in 36% and 27%, respectively, and improved insulin tolerance in 50% in comparison to AG-OVX. AG-OVX presented hypertensive levels of blood pressure (systolic: 155 ± 5, diastolic: 111 ± 3 mmHg). In contrast, AG-OVXt presented blood pressure values similar to Y rats (systolic: 129 ± 3, diastolic: 112 ± 3 mmHg). TR and BR were reduced by 70% and 46%, respectively, in AG-OVX vs. Y. Once more, AG-OVXt presented similar results to Y. ET decreased LPO in the heart and kidney. In the latter, renal CAT and SOD were corrected by ET, while cardiac redox balance was partially recovered. Improved BRS was correlated with improved oxidative stress markers.

CONCLUSIONS

Even when initiated after aging and ovariectomy deleterious effects, ET is able to normalize BRS and highly improve cardiac and renal oxidative stress.

Combined Aerobic and Resistance Exercise Training Improve Hypertension Associated With Menopause

The prevalence of hypertension sharply increases in menopausal women. Recent studies have demonstrated that aerobic or resistance training may help control hypertension. In this study, we report that combining aerobic and resistance training may provide an effective therapeutic approach for hypertension control, attenuating inflammation and oxidative stress in ovariectomized rats. Female Wistar and spontaneous hypertensive rats (SHR) were distributed into four groups: sedentary control (C), sedentary hypertensive (HR), sedentary hypertensive ovariectomized (HR-O), and combined trained hypertensive ovariectomized (T-HR-O). Combined exercise training was performed on a motor treadmill (aerobic training) and on a ladder adapted to rats (resistance training), in alternate days for 8 weeks. Direct arterial pressure was recorded and oxidative stress and inflammation were evaluated in cardiac and renal tissue. Ovariectomy increases increased mean arterial blood pressure, sympathetic modulation, and oxidative stress in SHR. Combining aerobic and resistance training reduced mean arterial blood pressure (12% vs. HR-O), heart rate (8% vs. HR-O), vascular sympathetic modulation (40% vs. HR-O), and improved baroreflex sensitivity. Combined training reduced cardiac inflammation (TNF and IL-6) and cardiac and renal lipoperoxidation (59% and 57%, respectively vs. HR-O). It also enhanced cardiac (71%) and renal (76%) total antioxidant capacity when compared to HR-O group. In conclusion, combining aerobic and resistance training improves mean arterial blood pressure, cardiovascular autonomic control, preventing cardiac and renal oxidative stress and inflammation in an experimental hypertension model with surgical menopause induced with ovariectomy.

Baroreflex Impairment Precedes Cardiometabolic Dysfunction in an Experimental Model of Metabolic Syndrome: Role of Inflammation and Oxidative Stress

This study analyzes whether autonomic dysfunction precedes cardiometabolic alterations in spontaneously hypertensive rats (SHR) with fructose overload. Animals were randomly distributed into three groups: control, hypertensive and hypertensive with fructose overload. Fructose overload (100 g/L) was initiated at 30 days old, and the animals (n = 6/group/time) were evaluated after 7, 15, 30 and 60 days of fructose consumption. Fructose consumption reduced baroreflex sensitivity by day 7, and still induced a progressive reduction in baroreflex sensitivity over the time. Fructose consumption also increased TNFα and IL-6 levels in the adipose tissue and IL-1β levels in the spleen at days 15 and 30. Fructose consumption also reduced plasmatic nitrites (day 15 and 30) and superoxide dismutase activity (day 15 and 60), but increased hydrogen peroxide (day 30 and 60), lipid peroxidation and protein oxidation (day 60). Fructose consumption increased arterial pressure at day 30 (8%) and 60 (11%). Fructose consumption also induced a late insulin resistance at day 60, but did not affect glucose levels. In conclusion, the results show that baroreflex sensitivity impairment precedes inflammatory and oxidative stress disorders, probably by inducing hemodynamic and metabolic dysfunctions observed in metabolic syndrome.

Hypertension induces additional cardiometabolic impairments and attenuates aerobic exercise training adaptations in fructose-fed ovariectomized rats

We tested whether hypertension favors the development of additional cardiometabolic changes in fructose-fed ovariectomized rats and how it affects aerobic exercise training (ET) effects. All rats received fructose in drinking water (10%) beginning at weaning, were ovariectomized at 10 weeks of age and divided into the normotensive sedentary (NFOS) and trained (NFOT) and hypertensive sedentary (HFOS) and trained (HFOT) groups. ET was performed on a treadmill. Arterial pressure (AP) was directly recorded; heart rate and AP variabilities were analyzed. Lipoperoxidation (LPO) and antioxidant enzyme levels were measured in the left ventricle. In addition to increased AP levels, when compared with the NFOS group, the hypertensive groups had resting tachycardia, a reduction of 29% in the pulse interval variance (VAR-PI), 19% in RMSSD (root mean square of successive differences, a cardiac parasympathetic index) and 53% in the α-index (spontaneous baroreflex), while the systolic AP variance (VAR-SAP) and its low-frequency band (LF-SAP) were sharply increased. ET did not alter AP levels. Even in the presence of hypertension, ET induced resting bradycardia, decreases of 33% in VAR-SAP and 49% in LF-SAP, and an increase of more than 60% in VAR-PI and the α-index. However, some of these parameters were still impaired relative to those of normotensive rats. LPO was reduced and catalase was increased in both trained groups, with no difference between the normotensive and hypertensive groups. Negative correlations were obtained between LPO and RMSSD (r=-0.60, P<0.05) and α-index (r=-0.63, P<0.05). In conclusion, hypertension augmented the dysfunctions in fructose-fed ovariectomized rats and attenuated metabolic aerobic ET benefits. These changes may be related to cardiovascular autonomic and oxidative stress alterations.

Effects of 6-months' Exercise on Cardiac Function, Structure and Metabolism in Female Hypertensive Rats-The Decisive Role of Lysyl Oxidase and Collagen III

Purpose: According to the current therapeutic guidelines of the WHO physical activity and exercise are recommended as first-line therapy of arterial hypertension. Previous results lead to the conclusion, however, that hearts of spontaneously hypertensive rats (SHR) with established hypertension cannot compensate for the haemodynamic stresses caused by long-term exercise. The current study was initiated to investigate the effects of aerobic exercise on the cardiac remodeling as the sole therapeutic measure before and during hypertension became established.

Methods: Beginning at their 6th week of life, six SHR were provided with a running wheel over a period of 6 months. Normotensive Wistar rats served as non-hypertensive controls.

Results: In Wistar rats and SHR, voluntary exercise led to cardioprotective adaptation reactions that were reflected in increased mitochondrial respiration, reduced heart rate and improved systolic function. Exercise also had antioxidant effects and reduced the expression of maladaptive genes (TGF-β1, CTGF, and FGF2). However, at the end of the 6-months' training, the echocardiograms revealed that SHR runners developed a restrictive cardiomyopathy. The induction of lysyl oxidase (LOX), which led to an increased network of matrix proteins and a massive elevation in collagen III expression, was identified as the underlying cause.

Conclusions: Running-induced adaptive mechanisms effectively counteract the classic remodeling of hearts subject to chronic pressure loads. However, with sustained running stress, signaling pathways are activated that have a negative effect on left ventricular relaxation. Our data suggest that the induction of LOX may play a causative role in the diagnosed filling disorder in trained SHR.

Exercise Training Prevents Cardiovascular Derangements Induced by Fructose Overload in Developing Rats

The risks of chronic diseases associated with the increasing consumption of fructose-laden foods are amplified by the lack of regular physical activity and have become a serious public health issue worldwide. Moreover, childhood eating habits are strongly related to metabolic syndrome in adults. Thus, we aimed to investigate the preventive role of exercise training undertaken concurrently with a high fructose diet on cardiac function, hemodynamics, cardiovascular autonomic modulation and oxidative stress in male rats after weaning. Male Wistar rats were divided into 4 groups (n = 8/group): Sedentary control (SC), Trained control (TC), Sedentary Fructose (SF) and Trained Fructose (TF). Training was performed on a treadmill (8 weeks, 40–60% of maximum exercise test). Evaluations of cardiac function, hemodynamics, cardiovascular autonomic modulation and oxidative stress in plasma and in left ventricle (LV) were performed. Chronic fructose overload induced glucose intolerance and an increase in white adipose tissue (WAT) weight, in myocardial performance index (MPI) (SF:0.42±0.04 vs. SC:0.24±0.05) and in arterial pressure (SF:122±3 vs. SC:113±1 mmHg) associated with increased cardiac and vascular sympathetic modulation. Fructose also induced unfavorable changes in oxidative stress profile (plasmatic protein oxidation- SF:3.30±0.09 vs. SC:1.45±0.08 nmol/mg prot; and LV total antioxidant capacity (TRAP)- SF: 2.5±0.5 vs. SC:12.7±1.7 uM trolox). The TF group showed reduced WAT, glucose intolerance, MPI (0.35±0.04), arterial pressure (118±2mmHg), sympathetic modulation, plasmatic protein oxidation and increased TRAP when compared to SF group. Therefore, our findings indicate that cardiometabolic dysfunctions induced by fructose overload early in life may be prevented by moderate aerobic exercise training.

Association of exercise training and angiotensin-converting enzyme 2 activator improves baroreflex sensitivity of spontaneously hypertensive rats

The present study sought to determine cardiovascular effects of aerobic training associated with diminazene aceturate (DIZE), an activator of the angiotensin converting enzyme 2, in spontaneously hypertensive rats (SHRs). Male SHRs (280–350 g) were either subjected to exercise training or not (sedentary group). The trained group was subjected to 8 weeks of aerobic training on a treadmill (five times a week, lasting 60 min at an intensity of 50–60% of maximum aerobic speed). In the last 15 days of the experimental protocol, these groups were redistributed into four groups: i) sedentary SHRs with daily treatment of 1 mg/kg DIZE (S+D1); ii) trained SHRs with daily treatment of 1 mg/kg DIZE (T+D1); iii) sedentary SHRs with daily treatment of vehicle (S+V); and iv) trained SHRs with daily treatment of vehicle (T+V). After treatment, SHRs were anesthetized and subjected to artery and femoral vein cannulation prior to the implantation of ECG electrode. After 24 h, mean arterial pressure (MAP) and heart rate (HR) were recorded; the baroreflex sensitivity and the effect of double autonomic blockade (DAB) were evaluated in non-anesthetized SHRs. DIZE treatment improved baroreflex sensitivity in the T+D1 group as compared with the T+V and S+D1 groups. The intrinsic heart rate (IHR) and MAP were reduced in T+D1 group as compared with T+V and S+D1 groups. Hence, we conclude that the association of exercise training with DIZE treatment improved baroreflex function and cardiovascular regulation.

Resistance or aerobic training decreases blood pressure and improves cardiovascular autonomic control and oxidative stress in hypertensive menopausal rats

We investigated whether resistance training (RT) vs. aerobic training (AT) differentially impacts on arterial pressure and related mechanisms in ovariectomized spontaneously hypertensive rats (SHRs). Female SHRs were ovariectomized and assigned to one of the following groups: sedentary, AT, or RT; sham sedentary SHR were used as control group. AT was performed on a treadmill, whereas RT was performed on a vertical ladder. Both exercise protocols were performed for 8 wk, 5 days/wk. Arterial pressure, baroreflex sensitivity, autonomic modulation, and cardiac oxidative stress parameters (lipid peroxidation, protein oxidation, redox balance, NADPH oxidase, and antioxidant enzymes activities) were analyzed. Ovariectomy increased mean arterial pressure (∼9 mmHg), sympathetic modulation (∼40%), and oxidative stress in sedentary rats. Both RT and AT reduced mean arterial pressure (∼20 and ∼8 mmHg, respectively) and improved baroreflex sensitivity compared with sedentary ovariectomized rats. However, RT-induced arterial pressure decrease was significantly less pronounced than AT. Lipid peroxidation and protein oxidation were decreased while antioxidant enzymes were increased in both trained groups vs. sedentaries. The reduced gluthatione was higher after AT vs. other groups, whereas oxidized gluthatione was lower after RT vs. AT. Moreover, sympathetic and parasympathetic modulations were highly correlated with cardiac oxidative stress parameters. In conclusion, both RT and AT can decrease arterial pressure in a model of hypertension and menopause; although, at different magnitudes this decrease was related to attenuated autonomic dysfunction in association with cardiac oxidative stress improvement in both exercise protocols.

Positive effect of combined exercise training in a model of metabolic syndrome and menopause: autonomic, inflammatory, and oxidative stress evaluations

It is now well established that after menopause cardiometabolic disorders become more common. Recently, resistance exercise has been recommended as a complement to aerobic (combined training, CT) for the treatment of cardiometabolic diseases. The aim of this study was to evaluate the effects of CT in hypertensive ovariectomized rats undergoing fructose overload in blood pressure variability (BPV), inflammation, and oxidative stress parameters. Female rats were divided into the following groups ( n = 8/group): sedentary normotensive Wistar rats (C), and sedentary (FHO) or trained (FHOT) ovariectomized spontaneously hypertensive rats undergoing and fructose overload. CT was performed on a treadmill and ladder adapted to rats in alternate days (8 wk; 40–60% maximal capacity). Arterial pressure (AP) was directly measured. Oxidative stress and inflammation were measured on cardiac and renal tissues. The association of risk factors (hypertension + ovariectomy + fructose) promoted increase in insulin resistance, mean AP (FHO: 174 ± 4 vs. C: 108 ± 1 mmHg), heart rate (FHO: 403 ± 12 vs. C: 352 ± 11 beats/min), BPV, cardiac inflammation (tumor necrosis factor-α-FHO: 65.8 ± 9.9 vs. C: 23.3 ± 4.3 pg/mg protein), and oxidative stress cardiac and renal tissues. However, CT was able to reduce mean AP (FHOT: 158 ± 4 mmHg), heart rate (FHOT: 303 ± 5 beats/min), insulin resistance, and sympathetic modulation. Moreover, the trained rats presented increased nitric oxide bioavailability, reduced tumor necrosis factor-α (FHOT: 33.1 ± 4.9 pg/mg protein), increased IL-10 in cardiac tissue and reduced lipoperoxidation, and increased antioxidant defenses in cardiac and renal tissues. In conclusion, the association of risk factors promoted an additional impairment in metabolic, cardiovascular, autonomic, inflammatory, and oxidative stress parameters and combined exercise training was able to attenuate these dysfunctions.

Dynamic exercise training prevents exercise pressor reflex overactivity in spontaneously hypertensive rats

Cardiovascular responses to exercise are exaggerated in hypertension. We previously demonstrated that this heightened cardiovascular response to exercise is mediated by an abnormal skeletal muscle exercise pressor reflex (EPR) with important contributions from its mechanically and chemically sensitive components. Exercise training attenuates exercise pressor reflex function in healthy subjects as well as in heart failure rats. However, whether exercise training has similar physiological benefits in hypertension remains to be elucidated. Thus we tested the hypothesis that the EPR overactivity manifest in hypertension is mitigated by exercise training. Changes in mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) in response to muscle contraction, passive muscle stretch, and hindlimb intra-arterial capsaicin administration were examined in untrained normotensive Wistar-Kyoto rats (WKYUT; n = 6), exercise-trained WKY (WKYET; n = 7), untrained spontaneously hypertensive rats (SHRUT; n = 8), and exercise-trained SHR (SHRET; n = 7). Baseline MAP after decerebration was significantly decreased by 3 mo of wheel running in SHRET (104 ± 9 mmHg) compared with SHRUT (125 ± 10 mmHg). As previously reported, the pressor and renal sympathetic responses to muscle contraction, stretch, and capsaicin administration were significantly higher in SHRUT than WKYUT. Exercise training significantly attenuated the enhanced contraction-induced elevations in MAP (SHRUT: 53 ± 11 mmHg; SHRET: 19 ± 3 mmHg) and RSNA (SHRUT: 145 ± 32%; SHRET: 57 ± 11%). Training produced similar attenuating effects in SHR during passive stretch and capsaicin administration. These data demonstrate that the abnormally exaggerated EPR function that develops in hypertensive rats is significantly diminished by exercise training.

Hemodynamic effect of laser therapy in spontaneously hypertensive rats

Systemic arterial hypertension (SAH) is considered to be the greatest risk factor for the development of neuro-cardiovascular pathologies, thus constituting a severe Public Health issue in the world.

The Low-Level Laser Therapy (LLLT), or laser therapy, activates components of the cellular structure, therefore converting luminous energy into photochemical energy and leading to biophysical and biochemical reactions in the mitochondrial respiratory chain. The LLLT promotes cellular and tissue photobiomodulation by means of changes in metabolism, leading to molecular, cellular and systemic changes.

The objective of this study was to analyze the action of low-level laser in the hemodynamic modulation of spontaneously hypertensive rats, in the long term. Animals (n = 16) were randomly divided into the Laser Group (n = 8), which received three weekly LLLT irradiations for seven weeks, and into the Sham Group (n = 8), which received three weekly simulations of laser for seven weeks, accounting for 21 applications in each group. After seven weeks, animals were cannulated by the implantation of a catheter in the left carotid artery. On the following day, the systemic arterial pressure was recorded. The Laser Group showed reduced levels of mean blood pressure, with statistically significant reduction (169 ± 4 mmHg* vs. 182 ± 4 mmHg from the Sham Group) and reduced levels of diastolic pressure (143 ± 4 mmHg* vs. 157 ± 3 mmHg from the Sham Group), revealing a 13 and 14 mmHg decrease, respectively. Besides, there was a concomitant important decline in heart rate (312 ± 14 bpm vs. 361 ± 13 bpm from the Sham Group). Therefore, laser therapy was able to produce hemodynamic changes, thus reducing pressure levels in spontaneously hypertensive rats.

Dynamic resistance training decreases sympathetic tone in hypertensive ovariectomized rats

The aim of this study was to investigate the effects of resistance exercise training on hemodynamics and cardiac autonomic control in ovariectomized spontaneously hypertensive rats. Female rats were divided into 4 groups: sedentary control (SC), sedentary hypertensive (SH), sedentary hypertensive ovariectomized (SHO), and resistance-trained hypertensive ovariectomized (RTHO). Resistance exercise training was performed on a vertical ladder (5 days/week, 8 weeks) at 40-60% maximal load. Direct arterial pressure was recorded. Vagal and sympathetic tones were measured by heart rate (HR) responses to methylatropine (3 mg/kg, iv) and propranolol (4 mg/kg, iv). Ovariectomy resulted in additional increases in blood pressure in hypertensive rats and was associated with decreased vagal tone. Resistance exercise trained rats had lower mean arterial pressure than untrained rats (RTHO: 159±2.2 vs SHO: 177±3.4 mmHg), as well as resting bradycardia (RTHO: 332±9.0 vs SHO: 356±5 bpm). Sympathetic tone was also lower in the trained group. Moreover, sympathetic tone was positively correlated with resting HR (r=0.7, P<0.05). The additional arterial pressure increase in hypertensive rats caused by ovarian hormone deprivation was attenuated by moderate-intensity dynamic resistance training. This benefit may be associated with resting bradycardia and reduced cardiac sympathetic tone after training, which suggests potential benefits of resistance exercise for the management of hypertension after ovarian hormone deprivation.

Cardiovascular responses induced by Catalase Inhibitior into the Fourth Cerebral Ventricle is changed in Wistar rats exposed to sidestream cigarette smoke

OBJECTIVES

This experimental study aimed to evaluate the effects of central catalase inhibition on cardiovascular responses in rats exposed to sidestream cigarette smoke (SSCS) for 3 weeks.

METHODOLOGY

A total of 20 males Wistar rats (320-370g) were implanted with a stainless steel guide cannula into the fourth cerebral ventricle (4(th)V). Femoral artery and vein were cannulated for mean arterial pressure (MAP) and heart rate (HR) measurement and drug infusion, respectively. Rats were exposed to SSCS for three weeks, 180 minutes per day, 5 days/week [carbon monoxide (CO): 100-300 ppm)]. Baroreflex was tested with one pressor dose of phenylephrine (PHE, 8 μg/kg, bolus) and one depressor dose of sodium nitroprusside (SNP, 50 μg/kg, bolus). Cardiovascular responses were evaluated before and 15 minutes after 3-amino-1, 2, 4-triazole (ATZ, catalase inhibitor, 0.001g/100μL) injection into the 4(th) V.

RESULTS

Vehicle treatment into the 4(th) V did not change cardiovascular responses. Central catalase inhibition increased tachycardic peak, attenuated bradycardic peak and reduced HR range at 15 minutes, increased MAP at 5, 15 and 30 min and increased HR at 5 and 15 min. In rats exposed to SSCS, central ATZ increased basal MAP after 5 min and increased HR at 5, 15 and 30 minutes, respectively, and attenuated bradycardic peak at 15 minutes.

CONCLUSION

This study suggests that brain oxidative stress caused by SSCS influences autonomic regulation of the cardiovascular system.

An orally active angiotensin-(1-7) inclusion compound and exercise training produce similar cardiovascular effects in spontaneously hypertensive rats

Low angiotensin-(1-7) (Ang-(1-7)) concentration is observed in some cardiovascular diseases and exercise training seems to restore its concentration in the heart. Recently, a novel formulation of an orally active Ang-(1-7) included in hydroxy-propyl-beta-cyclodextrin (HPB-CD) was developed and chronically administered in experimental models of cardiovascular diseases. The present study examined whether chronic administration of HPB-CD/Ang-(1-7) produces beneficial cardiovascular effects in spontaneously hypertensive rats (SHR), as well as to compare the results obtained with those produced by exercise training. Male SHR (15-week old) were divided in control (tap water) or treated with HPB-CD/Ang-(1-7) (corresponding to 30μgkg(-1)day(-1) of Ang-(1-7)) by gavage, concomitantly or not to exercise training (treadmill, 10 weeks). After chronic treatment, hemodynamic, morphometric and molecular analysis in the heart were performed. Chronic HPB-CD/Ang-(1-7) decreased arterial blood pressure (BP) and heart rate in SHR. The inclusion compound significantly improved left ventricular (LV) end-diastolic pressure, restored the maximum and minimum derivatives (dP/dT) and decreased cardiac hypertrophy index in SHR. Chronic treatment improved autonomic control by attenuating sympathetic modulation on heart and vessels and the SAP variability, as well as increasing parasympathetic modulation and HR variability. Overall results were similar to those obtained with exercise training. These results show that chronic treatment with the HPB-CD/Ang-(1-7) inclusion compound produced beneficial effects in SHR resembling the ones produced by exercise training. This observation reinforces the potential cardiovascular therapeutic effect of this novel peptide formulation.

Pleiotropic effects of simvastatin in physically trained ovariectomized rats

This study tested the hypothesis that simvastatin treatment can improve cardiovascular and autonomic functions and membrane lipoperoxidation, with an increased effect when applied to physically trained ovariectomized rats. Ovariectomized rats were divided into sedentary, sedentary+simvastatin and trained+simvastatin groups (n = 8 each). Exercise training was performed on a treadmill for 8 weeks and simvastatin (5 mg/kg) was administered in the last 2 weeks. Blood pressure (BP) was recorded in conscious animals. Baroreflex sensitivity was evaluated by the tachycardic and bradycardic responses to BP changes. Cardiac vagal and sympathetic effects were determined using methylatropine and propranolol. Oxidative stress was evaluated based on heart and liver lipoperoxidation using the chemiluminescence method. The simvastatin-treated groups presented reduced body weight and mean BP (trained+simvastatin = 99 ± 2 and sedentary+simvastatin = 107 ± 2 mmHg) compared to the sedentary group (122 ± 1 mmHg). Furthermore, the trained group showed lower BP and heart rate compared to the other groups. Tachycardic and bradycardic responses were enhanced in both simvastatin-treated groups. The vagal effect was increased in the trained+simvastatin group and the sympathetic effect was decreased in the sedentary+simvastatin group. Hepatic lipoperoxidation was reduced in sedentary+simvastatin (≈21%) and trained+simvastatin groups (≈57%) compared to the sedentary group. Correlation analysis involving all animals demonstrated that cardiac lipoperoxidation was negatively related to the vagal effect (r = -0.7) and positively correlated to the sympathetic effect (r = 0.7). In conclusion, improvement in cardiovascular and autonomic functions associated with a reduction of lipoperoxidation with simvastatin treatment was increased in trained ovariectomized rats.

Effects of the administration of a catalase inhibitor into the fourth cerebral ventricle on cardiovascular responses in spontaneously hypertensive rats exposed to sidestream cigarette smoke

OBJECTIVE

Previous studies have demonstrated a relationship between brain oxidative stress and cardiovascular regulation. We evaluated the effects of central catalase inhibition on cardiovascular responses in spontaneously hypertensive rats exposed to sidestream cigarette smoke.

METHODS

Male Wistar Kyoto (WKY) rats and spontaneously hypertensive rats (SH) (16 weeks old) were implanted with a stainless steel guide cannula leading into the fourth cerebral ventricle (4th V). The femoral artery and vein were cannulated for arterial pressure and heart rate measurement and drug infusion, respectively. The rats were exposed to sidestream cigarette smoke for 180 minutes/day, 5 days/week for 3 weeks (CO: 100-300 ppm). The baroreflex was tested using a pressor dose of phenylephrine (8 μg/kg, bolus) and a depressor dose of sodium nitroprusside (50 μg/kg, bolus). Cardiovascular responses were evaluated before and 5, 15, 30 and 60 minutes after injection of a catalase inhibitor (3-amino-1,2,4-triazole, 0.001 g/100 μL) into the 4th V.

RESULTS

Vehicle administration into the 4th V did not affect the cardiovascular response, whereas administration of the central catalase inhibitor increased the basal HR and attenuated the bradycardic peak (p<0.05) to a greater extent in WKY rats exposed to sidestream cigarette smoke than in WKY rats exposed to fresh air. However, in spontaneously hypertensive rats, the effect of the catalase inhibitor treatment was stronger in the fresh air condition (p<0.05).

CONCLUSION

Administration of a catalase inhibitor into the 4th V combined with exposure to sidestream cigarette smoke has a stronger effect in WKY rats than in SH rats.

Redox imbalances incite the hypertensive, baroreflex, and autonomic effects of cyclosporine in rats

Previous studies including ours showed that cyclosporine (CSA) causes baroreflex dysfunction and hypertension. Here we tested the hypothesis that oxidative damage in central and peripheral tissues underlies the hypertensive, baroreflex and autonomic actions elicited by CSA in rats. We investigated the effects of individual and combined 7-day treatments with CSA (25 mg/kg/day, n=7) and 4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl (tempol, superoxide dismutase mimetic, 100 mg/kg/day, n=7) on blood pressure, reflex heart rate responses to peripherally mediated pressor and depressor responses, and biomarkers of oxidative stress. CSA elevated blood pressure and reduced reflex bradycardic (phenylephrine) and tachycardic (sodium nitroptrusside) responses. The ability of muscarinic (atropine, 1 mg/kg i.v.) or β-adrenoceptor blockade (propranolol, 1 mg/kg i.v.) to reduce reflex heart rate responses was reduced in CSA-treated rats, suggesting the impairment by CSA of reflex cardiac autonomic control. Concurrent administration of tempol abolished CSA-induced hypertension and normalized the associated impairment in baroreflex gain and cardiac autonomic control. Tempol also reversed the CSA-induced increases in aortic and brainstem nitrite/nitrate and malondialdehyde (MDA) and decreases in aortic superoxide dismutase (SOD). These findings implicate oxidative stress in peripheral and central cardiovascular sites in the deleterious actions of CSA on blood pressure and baroreceptor control of heart rate.

The effects of catalase inhibition into the fourth cerebral ventricle on the Bezold-Jarisch reflex in spontaneously hypertensive rats

Many studies have investigated the role of oxidative stress on cardiovascular system in the brainstem of spontaneously hypertensive rats (SHR). However, we do not know yet if catalase inhibition influences cardiopulmonary reflex (Bezol-Jarisch reflex). Thus, we aimed to evaluate the effects of central catalase inhibition on cardiopulmonary reflex in SHR. Males Wistar Kyoto (WKY) rats and SHR were implanted with a stainless steel guide cannula into the fourth cerebral ventricle (4th V). The femoral artery and vein were cannulated for mean arterial pressure (MAP) and heart rate (HR) measurement and drug infusion, respectively. The cardiopulmonary reflex was tested with phenylbiguanide (PBG, 8 μg/kg, bolus, i.v.). Cardiopulmonary reflex was evaluated before and 15 minutes after 3-amino-1,2,4-triazole (ATZ, 0.01 g/100 μL) injection into the 4th V. Vehicle treatment did not change basal MAP and HR and cardiopulmonary reflex responses in SHR and WKY rats. Central ATZ increased hypotensive (p=0.038) responses without influencing the bradycardic reflex (p=0.287) in WKY rats. In SHR, ATZ increased hypotension (p=0.0004) and bradycardic (p=0.04) responses to i.v. PBG. No changes were observed regarding basal MAP and HR after ATZ injection in SHR and WKY rats. We suggest central catalase inhibition affects cardiopulmonary reflex with more intensity in SHR compared to WKY rats.

Sidestream cigarette smoke effects on cardiovascular responses in conscious rats: involvement of oxidative stress in the fourth cerebral ventricle

Background

Cigarette exposure increases brain oxidative stress. The literature showed that increased brain oxidative stress affects cardiovascular regulation. However, no previous study investigated the involvement of brain oxidative stress in animals exposed to cigarette and its relationship with cardiovascular regulation. We aimed to evaluate the effects of central catalase inhibition on baroreflex and cardiovascular responses in rats exposed to sidestream cigarette smoke (SSCS).

Methods

We evaluated males Wistar rats (320-370 g), which were implanted with a stainless steel guide cannula into the fourth cerebral ventricle (4th V). Femoral artery and vein were cannulated for mean arterial pressure (MAP) and heart rate (HR) measurement and drug infusion, respectively. Rats were exposed to SSCS during three weeks, 180 minutes, 5 days/week (CO: 100-300 ppm). Baroreflex was tested with a pressor dose of phenylephrine (PHE, 8 μg/kg, bolus) to induce bradycardic reflex and a depressor dose of sodium nitroprusside (SNP, 50 μg/kg, bolus) to induce tachycardic reflex. Cardiovascular responses were evaluated before, 5, 15, 30 and 60 minutes after 3-amino-1,2,4-triazole (ATZ, catalase inhibitor, 0.001 g/100 μL) injection into the 4th V.

Results

Central catalase inhibition increased basal HR in the control group during the first 5 minutes. SSCS exposure increased basal HR and attenuated bradycardic peak during the first 15 minutes.

Conclusion

We suggest that SSCS exposure affects cardiovascular regulation through its influence on catalase activity.

Catalase inhibition into the fourth cerebral ventricle affects bradycardic parasympathetic response to increase in arterial pressure without changing the baroreflex

Exogenous catalase influences neural control of cardiovascular system; however, we do not know yet if its inhibition into the fourth cerebral ventricle (4(th) V) influences baroreflex regulation. We evaluated the effects of central catalase inhibition on baroreflex in conscious Wistar rats. We used males Wistar rats (320-370 g), which were implanted with a stainless steel guide cannula into 4(th) V. The femoral artery and vein were cannulated for mean arterial pressure (MAP) and heart rate (HR) measurement and drug infusion, respectively. After basal MAP and HR recordings, the baroreflex was tested with a pressor dose of phenylephrine (PHE, 8 μg/kg, bolus) and a depressor dose of sodium nitroprusside (SNP, 50 μg/kg, bolus). Baroreflex was evaluated before 5, 15, 30 and 60 minutes after 3-amino-1, 2, 4-triazole (ATZ, 0.001 g/100 μL) injection into the 4(th) V. Vehicle treatment did not change baroreflex responses. ATZ attenuated bradycardic peak and reduced HR range at 30 minutes. ATZ into the 4(th) V reduced bradycardic and tachycardic reflex responses to increase and decrease MAP, respectively (p<0.05) 30 minutes after its microinjection without significantly changing the basal MAP and HR. In conclusion, central catalase inhibition influenced the highest parasympathetic response to MAP increase in conscious Wistar rats without change baroreflex gain.

Cardiac autonomic function in acutely nitric oxide deficient hypertensive rats: role of the sympathetic nervous system and oxidative stress

We evaluated the role of the sympathetic nervous system and oxidative stress in hemodynamic and autonomic control after acute inhibition of the synthesis of nitric oxide, using intravenous (i.v.) injection of 30 mg·kg(-1) N(G)-nitro-l-arginine methyl ester (L-NAME) in adult Wistar rats. Baroreflex sensitivity (BRS) and heart rate variability (HRV) were measured as indices of cardiac autonomic control, before and after L-NAME treatment in rats with intact autonomic innervation, and in rats with chemical sympathectomy by 6-hydroxydopamine. Serum malondialdehyde (MDA) was measured as a marker of oxidative stress. In control rats, L-NAME treatment resulted in a significant rise in blood pressure, augmentation of BRS, and enhanced serum MDA. HRV showed an attenuation of total spectral power and high frequency spectral power, along with a rise of the low to high frequency ratio (LF:HF). Administration of L-NAME produced a pressor response even in sympathectomised rats, but augmented BRS was not observed, and the high frequency spectral power showed an increase, in addition to a significant decline of LF:HF and serum MDA. We therefore conclude that even though pressor response was unaffected, reversal of cardiac autonomic responses and decline in oxidative stress following sympathectomy in L-NAME-treated rats reflects a significant role for sympathetic innervation in acute L-NAME-induced hypertension.

Influence of anabolic steroid treatment associated to physical exercise in the ultrasonic vocalization of rats

Unlike humans, who communicate in frequency bands between 250 Hz and 6 kHz, rats can communicate in frequencies above 18 kHz. Their vocalization types depend on the context and are normally associated to subjective or emotional states. It was reported significant vocal changes due to administration of replacement testosterone in a trained tenor singer with hypogonadism. Speech-Language Pathology clinical practices are being sought by singers who sporadically use anabolic steroids associated with physical exercise. They report difficulties in reaching and keeping high notes, "breakage" in the passage of musical notes and post singing vocal fatigue. Those abnormalities could be raised by the association of anabolic steroids and physical exercise. Thus, in order to verify if this association could promote vocal changes, maximum, minimum and fundamental frequencies and call duration in rats treated with anabolic steroids and physically trained (10 weeks duration) were evaluated. The vocalizations were obtained by handling the animals. At the end of that period, rats treated and trained showed significant decrease in call duration, but not in other parameters. The decrease in call duration could be associated to functional alterations in the vocal folds of treated and trained animals due to a synergism between anabolic steroids and physical training.

Interaction between exercise and hypertension in spontaneously hypertensive rats: a meta-analysis of experimental studies

The effect of exercise on the progression of hypertension and development of heart failure has been extensively studied in spontaneously hypertensive rats (SHRs), but results published thus far have not revealed a clear picture. Studies differ with respect to the age and sex of rats, duration of exercise and exercise protocols. This study was aimed to examine the influence of age at the start of exercise and the effect of the duration of exercise on blood pressure and hypertrophy, which has not been previously investigated. We identified 18 reports in the literature (with a total of about 410 rats) that investigated the effect of exercise on SHR. A reduction in blood pressure was observed in rats that started exercise protocols in the pre-hypertensive or very early hypertensive state, but not in older rats. Exercise lowered the heart weight-to-body weight ratio in rats starting exercise at a very early age, but not in rats at an advanced age. A reduction in blood pressure was observed in animals that had a short period of training, but the effect was lost when the duration of exercise was prolonged. Exercise reduced resting heart rates in all groups and increased the heart weight-to-body weight ratio in groups that were exposed to free running wheels, but not in rats that performed treadmill exercise. In conclusion, exercise per se does not reduce blood pressure in SHR with established hypertension and may increase the incidence of myocardial hypertrophy, depending on the form of exercise.

Change in central kinin B2 receptor density after exercise training in rats

Cardiovascular responses elicited by the stimulation of kinin B2 receptors in the IV cerebral ventricle, paratrigeminal nucleus or in the thoracic spinal cord are similar to those observed during an exercise bout. Considering that the kalikrein-kinin system (KKS) could act on the cardiovascular modulation during behavioral responses as physical exercise or stress, this study evaluated the central B2 receptor densities of Wistar (W) and spontaneously hypertensive rats (SHR) after chronic moderate exercise. Animals were exercise-trained for ten weeks on a treadmill. Afterwards, systolic blood pressure decreased in both trained strains. Animals were killed and the medulla and spinal cord extracted for B2 receptor autoradiography. Trained animals were compared to their sedentary controls. Sedentary groups showed specific binding sites for Hoe-140 (fmol/mg of tissue) in laminas 1 and 2 of the spinal cord, nucleus of the solitary tract (NTS), area postrema (AP), spinal trigeminal tract (sp5) and paratrigeminal nucleus (Pa5). In trained W a significant increase (p<0.05) in specific binding was observed in the Pa5 (31.3%) and NTS (28.2%). Trained SHR showed a significant decrease in receptor density in lamina 2 (21.9%) of the thoracic spinal cord and an increase in specific binding in Pa5 (36.1%). We suggest that in the medulla, chronic exercise could hyper stimulate the KKS enhancing their efficiency through the increase of B2 receptor density, involving this receptor in central cardiovascular control during exercise or stress. In the lamina 2, B2 receptor might be involved in the exercise-induced hypotension.

Cardiac baroreflex is already blunted in eight weeks old spontaneously hypertensive rats

Background

The literature did not evidence yet with which age spontaneously hypertensive rats (SHR) start to present baroreflex reduction. We endeavored to evaluate the baroreflex function in eight-week-old SHR.

Methods

Male Wistar Kyoto (WKY) normotensive rats and SHR aged eight weeks were studied. Baroreflex was calculated as the variation of heart rate (HR) divided by the mean arterial pressure (MAP) variation (ΔHR/ΔMAP) tested with a depressor dose of sodium nitroprusside (SNP, 50 μg/kg) and with a pressor dose of phenylephrine (PHE, 8 μg/kg) in the right femoral venous approach through an inserted cannula in the animals. Significant differences for p < 0.05.

Results

Baseline MAP (p < 0.0001) and HR (p = 0.0028) was higher in SHR. Bradycardic peak was attenuated in SHR (p < 0.0001), baroreflex gain tested with PHE was also reduced in the SHR group (p = 0.0012). PHE-induced increase in MAP was increased in WKY compared to SHR (p = 0.039). Bradycardic reflex responses to intravenous PHE was decreased in SHR (p < 0.0001).

Conclusion

Eight weeks old SHR already presents impairment of the parasympathetic component of baroreflex.

Baroreflex deficit blunts exercise training-induced cardiovascular and autonomic adaptations in hypertensive rats

1. Baroreceptors regulate moment-to-moment blood pressure (BP) variations, but their long-term effect on the cardiovascular system remains unclear. Baroreceptor deficit accompanying hypertension contributes to increased BP variability (BPV) and sympathetic activity, whereas exercise training has been associated with an improvement in these baroreflex-mediated changes. The aim of the present study was to evaluate the autonomic, haemodynamic and cardiac morphofunctional effects of long-term sinoaortic baroreceptor denervation (SAD) in trained and sedentary spontaneously hypertensive rats (SHR). 2. Rats were subjected to SAD or sham surgery and were then further divided into sedentary and trained groups. Exercise training was performed on a treadmill (five times per week, 50-70% maximal running speed). All groups were studied after 10 weeks. 3. Sinoaortic baroreceptor denervation in SHR had no effect on basal heart rate (HR) or BP, but did augment BPV, impairing the cardiac function associated with increased cardiac hypertrophy and collagen deposition. Exercise training reduced BP and HR, re-established baroreflex sensitivity and improved both HR variability and BPV. However, SAD in trained SHR blunted all these improvements. Moreover, the systolic and diastolic hypertensive dysfunction, reduced left ventricular chamber diameter and increased cardiac collagen deposition seen in SHR were improved after the training protocol. These benefits were attenuated in trained SAD SHR. 4. In conclusion, the present study has demonstrated that the arterial baroreflex mediates cardiac disturbances associated with hypertension and is crucial for the beneficial cardiovascular morphofunctional and autonomic adaptations induced by chronic exercise in hypertension.

Exercise improves cardiovascular control in a model of dislipidemia and menopause

The present study investigated the effects of exercise training on arterial pressure, baroreflex sensitivity, cardiovascular autonomic control and metabolic parameters on female LDL-receptor knockout ovariectomized mice. Mice were divided into two groups: sedentary and trained. Trained group was submitted to an exercise training protocol. Blood cholesterol was measured. Arterial pressure (AP) signals were directly recorded in conscious mice. Baroreflex sensitivity was evaluated by tachycardic and bradycardic responses to AP changes. Cardiovascular autonomic modulation was measured in frequency (FFT) and time domains. Maximal exercise capacity was increased in trained as compared to sedentary group. Blood cholesterol was diminished in trained mice (191+/-8mg/dL) when compared to sedentary mice (250+/-9mg/dL, p<0.05). Mean AP and HR were reduced in trained group (101+/-3mmHg and 535+/-14bpm, p<0.05) when compared with sedentary group (125+/-3mmHg and 600+/-12bpm). Exercise training induced improvement in bradycardic reflex response in trained animals (-4.24+/-0.62bpm/mmHg) in relation to sedentary animals (-1.49+/-0.15bpm/mmHg, p<0.01); tachycardic reflex responses were similar between studied groups. Exercise training increased the variance (34+/-8 vs. 6.6+/-1.5ms(2) in sedentary, p<0.005) and the high-frequency band (HF) of the pulse interval (IP) (53+/-7% vs. 26+/-6% in sedentary, p<0.01). It is tempting to speculate that results of this experimental study might represent a rationale for this non-pharmacological intervention in the management of cardiovascular risk factors in dyslipidemic post-menopause women.

Exercise training reduces sympathetic modulation on cardiovascular system and cardiac oxidative stress in spontaneously hypertensive rats

BACKGROUND

Spontaneously hypertensive rats (SHRs) show increased cardiac sympathetic activity, which could stimulate cardiomyocyte hypertrophy, cardiac damage, and apoptosis. Norepinephrine (NE)-induced cardiac oxidative stress seems to be involved in SHR cardiac hypertrophy development. Because exercise training (ET) decreases sympathetic activation and oxidative stress, it may alter cardiac hypertrophy in SHR. The aim of this study was to determine, in vivo, whether ET alters cardiac sympathetic modulation on cardiovascular system and whether a correlation exists between cardiac oxidative stress and hypertrophy.

METHODS

Male SHRs (15-weeks old) were divided into sedentary hypertensive (SHR, n = 7) and exercise-trained hypertensive rats (SHR-T, n = 7). Moderate ET was performed on a treadmill (5 days/week, 60 min, 10 weeks). After ET, cardiopulmonary reflex responses were assessed by bolus injections of 5-HT. Autoregressive spectral estimation was performed for systolic arterial pressure (SAP) with oscillatory components quantified as low (LF: 0.2-0.75 Hz) and high (HF: 0.75-4.0 Hz) frequency ranges. Cardiac NE concentration, lipid peroxidation, antioxidant enzymes activities, and total nitrates/nitrites were determined.

RESULTS

ET reduced mean arterial pressure, SAP variability (SAP var), LF of SAP, and cardiac hypertrophy and increased cardiopulmonary reflex responses. Cardiac lipid peroxidation was decreased in trained SHRs and positively correlated with NE concentrations (r = 0.89, P < 0.01) and heart weight/body weight ratio (r = 0.72, P < 0.01), and inversely correlated with total nitrates/nitrites (r = -0.79, P < 0.01). Moreover, in trained SHR, cardiac total nitrates/nitrites were inversely correlated with NE concentrations (r = -0.82, P < 0.01).

CONCLUSIONS

ET attenuates cardiac sympathetic modulation and cardiac hypertrophy, which were associated with reduced oxidative stress and increased nitric oxide (NO) bioavailability.

Baroreflex sensitivity and oxidative stress in the LDL receptor knockout mice

This study aims at observing the effect of low-density lipoprotein (LDL) receptor deficiency in cholesterol blood levels, baroreflex sensitivity (BRS), nitric oxide (NO) bioavailability, and oxidative stress. The lack of LDL receptors in mice significantly increased the cholesterol blood levels (179+/-35 vs. 109+/-13mg/dL) in the knockout (KO) mice compared to control. There was no difference in basal mean arterial pressure and heart rate between the groups. However, in KO mice the BRS was significantly attenuated and the antioxidant enzyme activities, measured in erythrocytes and heart, were significantly decreased. On the other hand, the oxidative damage measured by chemiluminescence and carbonyls was increased, while total plasma nitrate levels were lower in KO mice, indicating a decrease in NO availability. In conclusion, these results indicate that the lack of LDL receptor increased cholesterol blood levels, induced oxidative stress and decreased BRS.

Maximal exercise test is a useful method for physical capacity and oxygen consumption determination in streptozotocin-diabetic rats

Background

The aim of the present study was to investigate the relationship between speed during maximum exercise test (ET) and oxygen consumption (VO₂) in control and STZ-diabetic rats, in order to provide a useful method to determine exercise capacity and prescription in researches involving STZ-diabetic rats.

Methods

Male Wistar rats were divided into two groups: control (CG, n = 10) and diabetic (DG, n = 8). The animals were submitted to ET on treadmill with simultaneous gas analysis through open respirometry system. ET and VO₂ were assessed 60 days after diabetes induction (STZ, 50 mg/Kg).

Results

VO₂ maximum was reduced in STZ-diabetic rats (72.5 ± 1 mL/Kg/min^-1) compared to CG rats (81.1 ± 1 mL/Kg/min^-1). There were positive correlations between ET speed and VO₂ (r = 0.87 for CG and r = 0.8 for DG), as well as between ET speed and VO₂ reserve (r = 0.77 for CG and r = 0.7 for DG). Positive correlations were also obtained between measured VO₂ and VO₂ predicted values (r = 0.81 for CG and r = 0.75 for DG) by linear regression equations to CG (VO₂ = 1.54 * ET speed + 52.34) and DG (VO₂ = 1.16 * ET speed + 51.99). Moreover, we observed that 60% of ET speed corresponded to 72 and 75% of VO₂ reserve for CG and DG, respectively. The maximum ET speed was also correlated with VO₂ maximum for both groups (CG: r = 0.7 and DG: r = 0.7).

Conclusion

These results suggest that: a) VO₂ and VO₂ reserve can be estimated using linear regression equations obtained from correlations with ET speed for each studied group; b) exercise training can be prescribed based on ET in control and diabetic-STZ rats; c) physical capacity can be determined by ET. Therefore, ET, which involves a relatively simple methodology and low cost, can be used as an indicator of cardio-respiratory capacity in future studies that investigate the physiological effect of acute or chronic exercise in control and STZ-diabetic male rats.