P2Y1 receptors expressed by C1 neurons determine peripheral chemoreceptor modulation of breathing, sympathetic activity, and blood pressure

Catecholaminergic C1 cells of the rostral ventrolateral medulla (RVLM) are key determinants of the sympathoexcitatory response to peripheral chemoreceptor activation. Overactivation of this reflex is thought to contribute to increased sympathetic activity and hypertension; however, molecular mechanisms linking peripheral chemoreceptor drive to hypertension remain poorly understood. We have recently determined that activation of P2Y1 receptors in the RVLM mimicked effects of peripheral chemoreceptor activation. Therefore, we hypothesize that P2Y1 receptors regulate peripheral chemoreceptor drive in this region. Here, we determine whether P2Y1 receptors are expressed by C1 neurons in the RVLM and contribute to peripheral chemoreceptor control of breathing, sympathetic activity, and blood pressure. We found that injection of a specific P2Y1 receptor agonist (MRS2365) into the RVLM of anesthetized adult rats increased phrenic nerve activity (≈55%), sympathetic nerve activity (38±6%), and blood pressure (23±1 mm Hg), whereas application of a specific P2Y1 receptor antagonist (MRS2179) decreased peripheral chemoreceptor–mediated activation of phrenic nerve activity, sympathetic nerve activity, and blood pressure. To establish that P2Y1 receptors are expressed by C1 cells, we determine in the brain slice preparation using cell-attached recording techniques that cells responsive to MRS2365 are immunoreactive for tyrosine hydroxylase (a marker of C1 cells), and we determine in vivo that C1-lesioned animals do not respond to RVLM injection of MRS2365. These data identify P2Y1 receptors as key determinants of peripheral chemoreceptor regulation of breathing, sympathetic nerve activity, and blood pressure.

Effects of pediatric adiposity on heart rate variability

The relationship between obesity and heart rate variability (HRV) has been studied in adults and adolescents, but is not determined in young pediatrics. The purpose of this study was to assess autonomic activity using HRV in a pediatric population. We hypothesized that obese children would have reduced parasympathetic and increased sympathetic activity compared to age-matched subjects. 42 pediatric subjects (ages 3-5) were classified into 3 groups based on body mass index-for-age; normal, overweight and obese. HRV and respiratory rate were recorded during 3 minute baseline, 2 minute isometric handgrip and 3 minute recovery. HRV was analyzed in the time domain [heart rate (HR), RR interval (RRI) and RRI standard deviation (RRISD)] and frequency domain [low frequency (LF), high frequency (HF) and LF/HF ratio] using repeated measures ANOVA. Spearman’s correlations were used to examine the relations between BMI and HRV at rest. Significant condition effects were found between baseline, exercise and recovery, but these responses were not significantly different between the normal, overweight and obese children. BMI was negatively correlated with LF/HF, while BMI was positively correlated with RRISD, LF, HF and nHF. Our data demonstrate that higher BMI in the pediatric population is correlated with higher parasympathetic and lower sympathetic activity. These findings are contrary to HRV responses observed in adults and adolescents, suggesting complex relationships between age, obesity and autonomic control of the heart. The data supports the concept of an age reliance of HRV and a novel relationship between adiposity and body mass index in 3-5 year olds.

Influence of transrectal and transabdominal ultrasound examination on salivary cortisol, heart rate, and heart rate variability in mares

Pregnancy diagnostics in equine reproduction are routinely performed using transrectal ultrasonography, although it is also possible to visualize the fetus by transabdominal ultrasound examinations from the 90th day of gestation onward. We hypothesized that ultrasound examinations may stress the mare and that the gestational stage status and lactation may influence the mare's stress reaction. To investigate the stress reaction, 25 thoroughbred mares of different age, pregnancy and lactational status underwent a transrectal examination. In pregnant mares, an additional transabdominal examination was performed. Salivary cortisol concentration, mean heart rate, and heart rate variability of mares were assessed to evaluate the reactions of hypothalamic–pituitary–adrenal (HPA) axis and of the autonomic nervous system. Significant differences were observed between lactating and nonlactating mares; with a lower responsiveness to stress in lactating mares. The transrectal ultrasound examination in nonlactating mares induced a significant increase in salivary cortisol (P < 0.05), and in the heart rate variability parameter, ratio of low to high frequencies (P < 0.05). This reflects an activation of the HPA axis and a shift to more sympathetic dominance. In contrast, a transabdominally performed pregnancy check did not induce an activation of the HPA axis over basal level but increased the mean heart rate and low to high frequency ratio. The results of this study indicate that checks of advanced pregnancies can be easily performed by transabdominal ultrasonography. With regard to animal welfare, this technique should be preferred during midgestation in nonlactating mares.

Angiotensin receptor blockade improves the net balance of cardiac Ca(2+) handling-related proteins in sympathetic hyperactivity-induced heart failure

Aims: The clinical benefits of angiotensin II type 1 (AT1) receptor blockers (ARB) in heart failure (HF) include cardiac anti-remodeling and improved ventricular function. However, the cellular mechanisms underlying the benefits of ARB on ventricular function need to be better clarified. In the present manuscript, we evaluated the effects of AT1 receptor blockade on the net balance of Ca(2+) handling proteins in hearts of mice lacking alpha(2A) and alpha(2C) adrenoceptors (alpha(2A)/alpha(2C)ARKO), which develop sympathetic hyperactivity (SH) induced-HF. Main methods: A cohort of male wild-type (WT) and congenic alpha(2A)/alpha(2C)ARKO mice in a C57BL6/J genetic background (5-7 mo of age) was randomly assigned to receive either placebo or ARB (Losartan, 10 mg/kg for 8wks). Ventricular function (VF) was assessed by echocardiography, and cardiac myocyte width and ventricular fibrosis by a computer-assisted morphometric system. Sarcoplasmic reticulum Ca(2+) ATPase (SERCA2), phospholamban (PLN), phospho-Ser(16)-PLN, phospho-Thr(17)-PLN, phosphatase 1 (PP1), Na(+)-Ca(2+) exchanger (NCX), Ca(2+)/calmodulin-dependent protein kinase 11 (CaMKII) and phospho-Thr(286)-CaMKII were analyzed by Western blot. Key findings: alpha(2A)/alpha(2C)ARKO mice displayed ventricular dysfunction, cardiomyocyte hypertrophy and cardiac fibrosis paralleled by decreased SERCA2 and increased phospho-Thr(17)-PLN, CaMKII, phospho-Thr(286)-CaMKII and NCX levels. ARB induced anti-cardiac remodeling effect and improved VF in alpha(2A)/alpha(2C)ARKO associated with increased SERCA2 and phospho-Ser(16)-PLN levels, and SERCA2:NCX ratio. Additionally, ARB decreased phospho-Thr(17)-PLN levels as well as reestablished NCX, CaMKII and phospho-Thr(286)-CaMKII toward WT levels. Significance: Altogether, these data provide new insights on intracellular Ca(2+) regulatory mechanisms underlying improved ventricular function by ARB therapy in HF. (c) 2011 Elsevier Inc. All rights reserved.

Exercise training reduces cardiac angiotensin II levels and prevents cardiac dysfunction in a genetic model of sympathetic hyperactivity-induced heart failure in mice

The role of exercise training (ET) on cardiac renin-angiotensin system (RAS) was investigated in 3-5 month-old mice lacking alpha(2A-) and alpha(2C-)adrenoceptors (alpha(2A)/alpha(2C)ARKO) that present heart failure (HF) and wild type control (WT). ET consisted of 8-week running sessions of 60 min, 5 days/week. In addition, exercise tolerance, cardiac structural and function analysis were made. At 3 months, fractional shortening and exercise tolerance were similar between groups. At 5 months, alpha(2A)/alpha(2C)ARKO mice displayed ventricular dysfunction and fibrosis associated with increased cardiac angiotensin (Ang) II levels (2.9-fold) and increased local angiotensin-converting enzyme activity (ACE 18%). ET decreased alpha(2A)/alpha(2C)ARKO cardiac Ang II levels and ACE activity to age-matched untrained WT mice levels while increased ACE2 expression and prevented exercise intolerance and ventricular dysfunction with little impact on cardiac remodeling. Altogether, these data provide evidence that reduced cardiac RAS explains, at least in part, the beneficial effects of ET on cardiac function in a genetic model of HF.

Intracellular mechanisms of specific beta-adrenoceptor antagonists involved in improved cardiac function and survival in a genetic model of heart failure

beta-blockers, as class, improve cardiac function and survival in heart failure (HF). However, the molecular mechanisms underlying these beneficial effects remain elusive. In the present study, metoprolol and carvedilol were used in doses that display comparable heart rate reduction to assess their beneficial effects in a genetic model of sympathetic hyperactivity-induced HF (alpha(2A)/alpha(2C)-ARKO mice). Five month-old HF mice were randomly assigned to receive either saline, metoprolol or carvedilol for 8 weeks and age-matched wild-type mice (WT) were used as controls. HF mice displayed baseline tachycardia, systolic dysfunction evaluated by echocardiography, 50% mortality rate, increased cardiac myocyte width (50%) and ventricular fibrosis (3-fold) compared with WT. All these responses were significantly improved by both treatments. Cardiomyocytes from HF mice showed reduced peak [Ca(2+)](i) transient (13%) using confocal microscopy imaging. Interestingly, while metoprolol improved [Ca(2+)](i) transient, carvedilol had no effect on peak [Ca(2+)](i) transient but also increased [Ca(2+)] transient decay dynamics. We then examined the influence of carvedilol in cardiac oxidative stress as an alternative target to explain its beneficial effects. Indeed, HF mice showed 10-fold decrease in cardiac reduced/oxidized glutathione ratio compared with WT, which was significantly improved only by carvedilol treatment. Taken together, we provide direct evidence that the beneficial effects of metoprolol were mainly associated with improved cardiac Ca(2+) transients and the net balance of cardiac Ca(2+) handling proteins while carvedilol preferentially improved cardiac redox state. (C) 2008 Elsevier Inc. All rights reserved.

The role of local and systemic renin angiotensin system activation in a genetic model of sympathetic hyperactivity-induced heart failure in mice

Sympathetic hyperactivity (SH) and renin angiotensin system (RAS) activation are commonly associated with heart failure (HF), even though the relative contribution of these factors to the cardiac derangement is less understood. The role of SH on RAS components and its consequences for the HF were investigated in mice lacking alpha(2A) and alpha(2C) adrenoceptor knockout (alpha(2A)/alpha(2C) ARKO) that present SH with evidence of HF by 7 mo of age. Cardiac and systemic RAS components and plasma norepinephrine (PN) levels were evaluated in male adult mice at 3 and 7 mo of age. In addition, cardiac morphometric analysis, collagen content, exercise tolerance, and hemodynamic assessments were made. At 3 mo, alpha(2A)/alpha(2C)ARKO mice showed no signs of HF, while displaying elevated PN, activation of local and systemic RAS components, and increased cardiomyocyte width (16%) compared with wild-type mice (WT). In contrast, at 7 mo, alpha(2A)/alpha(2C)ARKO mice presented clear signs of HF accompanied only by cardiac activation of angiotensinogen and ANG II levels and increased collagen content (twofold). Consistent with this local activation of RAS, 8 wk of ANG II AT(1) receptor blocker treatment restored cardiac structure and function comparable to the WT. Collectively, these data provide direct evidence that cardiac RAS activation plays a major role underlying the structural and functional abnormalities associated with a genetic SH-induced HF in mice.

Heart rate, blood lactate and kinematic data of elite colts (under-19) rugby union players during competition

Physiological and kinematic data were collected from elite under-19 rugby union players to provide a greater understanding of the physical demands of rugby union. Heart rate, blood lactate and time-motion analysis data were collected from 24 players (mean +/- s((x) over bar): body mass 88.7 +/- 9.9 kg, height 185 +/- 7 cm, age 18.4 +/- 0.5 years) during six competitive premiership fixtures. Six players were chosen at random from each of four groups: props and locks, back row forwards, inside backs, outside backs. Heart rate records were classified based on percent time spent in four zones (>95%, 85-95%, 75-84%, <75% HRmax). Blood lactate concentration was measured periodically throughout each match, with movements being classified as standing, walking, jogging, cruising, sprinting, utility, rucking/mauling and scrummaging. The heart rate data indicated that props and locks (58.4%) and back row forwards (56.2%) spent significantly more time in high exertion (85-95% HRmax) than inside backs (40.5%) and outside backs (33.9%) (P < 0.001). Inside backs (36.5%) and outside backs (38.5%) spent significantly more time in moderate exertion (75-84% HRmax) than props and locks (22.6%) and back row forwards (19.8%) (P < 0.05). Outside backs (20.1%) spent significantly more time in low exertion (< 75% HRmax) than props and locks (5.8%) and back row forwards (5.6%) (P < 0.05). Mean blood lactate concentration did not differ significantly between groups (range: 4.67 mmol.l(-1) for outside backs to 7.22 mmol.l(-1) for back row forwards; P < 0.05). The motion analysis data indicated that outside backs (5750 m) covered a significantly greater total distance than either props and locks or back row forwards (4400 and 4080 m, respectively; P < 0.05). Inside backs and outside backs covered significantly greater distances walking (1740 and 1780 m, respectively; P < 0.001), in utility movements (417 and 475 m, respectively; P < 0.001) and sprinting (208 and 340 m, respectively; P < 0.001) than either props and locks or back row forwards (walking: 1000 and 991 m; utility movements: 106 and 154 m; sprinting: 72 and 94 m, respectively). Outside backs covered a significantly greater distance sprinting than inside backs (208 and 340 m, respectively; P < 0.001). Forwards maintained a higher level of exertion than backs, due to more constant motion and a large involvement in static high-intensity activities. A mean blood lactate concentration of 4.8-7.2 mmol.l(-1) indicated a need for 'lactate tolerance' training to improve hydrogen ion buffering and facilitate removal following high-intensity efforts. Furthermore, the large distances (4.2-5.6 km) covered during, and intermittent nature of, match-play indicated a need for sound aerobic conditioning in all groups (particularly backs) to minimize fatigue and facilitate recovery between high-intensity efforts.

Effects of maternal glycemia on fetal heart rate in pregnancies complicated by pregestational diabetes mellitus

Objective: To investigate the influence of maternal glycemia on fetal heart rate (FHR) parameters analyzed by computerized cardiotocography in fetuses of diabetic mothers in the third trimester. Study design: Thirty-nine pregnant women with pregestational diabetes mellitus were studied prospectively. The inclusion criteria were a diagnosis of pregestational diabetes, singleton pregnancy between 36 and 40 weeks, and absence of fetal abnormalities. Computerized cardiotocography (System 8002) was performed over a period of 60 min and capillary glycemia was measured immediately before and 30 and 60 min after the beginning of the exam. The evaluations were done 2 h after lunch. Results: Nineteen patients (48.7%) presented mean glycemia >= 120 mg/dL The mean basal FHR was 136.7 +/- 10.0 bpm in the group with glycemia <120 mg/dL and 144.8 +/- 9.4 bpm in the group with glycemia >= 120 mg/dL (p = 0.013, Student`s t test). There was a significant positive correlation (Pearson`s test, p = 0.0001, r = 0.57) between basal FHR and mean glycemia. A significant negative correlation was observed between short-term variation and mean glycemia (Pearson`s test, p = 0.003, r = -0.47). No significant differences were observed between the other indices evaluated by computerized cardiotocography and glycemia. Conclusions: Maternal hyperglycemia at the time of cardiotocography is associated with elevated FHR. It seems to be important to understand how FHR parameters are influenced by maternal glycemic status at the time of fetal assessment in pregnancies complicated by diabetes. (C) 2009 Published by Elsevier Ireland Ltd.

Abnormal chronotropic reserve and heart rate recovery in patients with SLE: a case-control study

Abnormal heart-rate (HR) response during or after a graded exercise test has been recognized as a strong and an independent predictor of all-cause mortality in healthy and diseased subjects. The purpose of the present study was to evaluate the HR response during exercise in women with systemic lupus erythematosus (SLE). In this case-control study, 22 women with SLE (age 29.5 perpendicular to 1.1 years) were compared with 20 gender-, BMI-, and age-matched healthy subjects (age 26.5 +/- 1.4 years). A treadmill cardiorespiratory test was performed and HR response during exercise was evaluated by the chronotropic reserve (CR). HR recovery (Delta HRR) was defined as the difference between HR at peak exercise and at both first (Delta HRR1) and second (Delta HRR2) minutes after exercising. SLE patients presented lower peak VO(2) when compared with healthy subjects (27.6 perpendicular to 0.9 vs. 36.7 perpendicular to 1.1 ml/kg/min, p = 0.001, respectively). Additionally, SLE patients demonstrated lower CR (71.8 +/- 2.4 vs. 98.2 +/- 2.6%, p = 0.001), Delta HRR1 (22.1 +/- 2.5 vs. 32.4 +/- 2.2%, p = 0.004) and Delta HRR2 (39.1 +/- 2.9 vs. 50.8 +/- 2.5%, p = 0.001) than their healthy peers. In conclusion, SLE patients presented abnormal HR response to exercise, characterized by chronotropic incompetence and delayed Delta HRR. Lupus (2011) 20, 717-720.

Physiological Responses to Brain Stimulation During Limbic Surgery: Further Evidence of Anterior Cingulate Modulation of Autonomic Arousal

Background: In view of conflicting neuroimaging results regarding autonomic-specific activity within the anterior cingulate cortex (ACC), we investigated autonomic responses to direct brain stimulation during sterecitactic limbic surgery. Methods: Skin conductance activity and accelerative heart rate responses to multi-voltage stimulation of the ACC (n = 7) and paralimbic subcauclate (n = 5) regions were recorded during bilateral anterior cingulotomy and bilateral subcauclate tractotomy (in patients that had previously received an adequate lesion in the ACC), respectively. Results: Stimulations in both groups were accompanied by increased autonomic arousal. Skin conductance activity was significantly increased during ACC stimulations compared with paralimbic targets at 2 V (2.34 +/- .68 [score in microSiemens +/- SE] vs. .34 +/- .09, p = .013) and 3 V (3.52 +/- .86 vs. 1.12 +/- .37, p = .036), exhibiting a strong ""voltage-response"" relationship between stimulus magnitude and response amplitude (difference from 1 to 3 V = 1.15 +/- .90 vs. 3.52 +/- .86, p = .041). Heart rate response was less indicative of between-group differences. Conclusions: This is the first study of its kind aiming at seeking novel insights into the mechanisms responsible for central autonomic modulation. It supports a concept that interregional interactions account for the coordination of autonomic arousal.

Elevation of Uterine Basal Tone and Fetal Heart Rate Abnormalities After Labor Analgesia A Randomized Controlled Trial

OBJECTIVE: To estimate the effects of combined spinal-epidural and traditional epidural analgesia on uterine basal tone and its association with the occurrence of fetal heart rate (FHR) abnormalities. METHODS: Seventy-seven laboring patients who requested pain relief during labor were randomly assigned to combined spinal-epidural (n=41) or epidural analgesia (n=36). Uterine contractions and FHR were recorded 15 minutes before and after analgesia. Uterine tone was evaluated with intrauterine pressure catheter. Primary outcomes were the elevation of baseline uterine tone and occurrence of FHR prolonged decelerations or bradycardia after analgesia. The influence of other variables such as oxytocin use, hypotension, and speed of pain relief were estimated using a logistic regression model. RESULTS: The incidence of all outcomes was significantly greater in the combined spinal-epidural group compared with epidural: uterine hypertonus (17 compared with 6; P=.018), FHR abnormalities (13 compared with 2; P<.01), and both events simultaneously (11 compared with 1; P<.01). Logistic regression analysis showed the type of analgesia as the only independent predictor of uterine hypertonus (odds ratio 3.526, 95% confidence interval 1.21-10.36; P=.022). For the occurrence of FHR abnormalities, elevation of uterine tone was the independent predictor (odds ratio 18.624, 95% confidence interval 4.46-77.72; P<.001). Regression analysis also found a correlation between decrease on pain scores immediately after analgesia and the estimated probability of occurrence of hypertonus and FHR abnormalities. CONCLUSION: Combined spinal-epidural analgesia is associated with a significantly greater incidence of FHR abnormalities related to uterine hypertonus compared with epidural analgesia. The faster the pain relief after analgesia, the higher the probability of uterine hypertonus and FHR changes. CLINICAL TRIAL REGISTRATION: Umin Clinical Trials Registry, http://www.umin.ac.jp/ctr/index.htm, UMIN000001186

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), LIF 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. Am J Hypertens 2008;21:1138-1193 (C) 2008 American Journal of Hypertension, Ltd.

Effects of changing blood viscosity and heart rate on vena contracta width as evaluated by color Doppler flow mapping. An in vitro study with a pulsatile flow model

Background: There is only limited knowledge on how the quantification of valvular regurgitation by color Doppler is affected by changing blood viscosity. This study was designed to evaluate the effect of changing blood viscosity on the vena contracta width using an in vitro model of valvular insufficiency capable of providing ample variation in the rate and stroke volume. Methods: We constructed a pulsatile flow model filled with human blood at varying hematocrit (15%, 35%, and 55%) and corresponding blood viscosity (blood/water viscosity: 2.6, 4.8, 9.1) levels in which jets were driven through a known orifice (7 mm(2)) into a 110 mL compliant receiving chamber (compliance: 2.2 mL/mmHg) by a pulsatile pump. In addition, we used variable pump stroke volumes (5, 7.5, and 10 mL) and rates (40, 60, and 80 ppm). Vena contracta region was imaged using a 3.5 MHz transducer. Pressure and volume in the flow model were kept constant during each experimental condition, as well as ultrasound settings. Results: Blood viscosity variation in the experimental range did not induce significant changes in vena contracta dimensions. Also, vena contracta width did not change from normal to low hematocrit and viscosity levels. A very modest increase only in vena contracta dimension was observed at very high level of blood viscosity when hematocrit was set to 55% . Pump rate, in the evaluated range, did not influence vena contracta width. These results in controlled experimental settings suggest that the vena contracta is an accurate quantitative method for quantifying valvular regurgitation even when this condition is associated with anemia, a frequent finding in patients with valvular heart disease.

The effect of aerobic physical training on cardiac autonomic control of rats submitted to ovariectomy

Objective: To investigate the effect of aerobic physical training on cardiovascular autonomic control in ovariectomized rats using different approaches. Design: Female Wistar rats were divided into four groups: sedentary sham rats (group SSR), trained sham rats (group TSR), sedentary ovariectomized rats (group SOR), and trained ovariectomized rats (group TOR). Animals from the trained groups were submitted to a physical training protocol (swimming) for 12 weeks. Results: Pharmacological evaluation showed that animals from group TSR had an increase in their cardiac vagal tonus compared with the animals from groups SSR and SOR. The analysis of heart rate variability (HRV) showed that groups TSR and SOR had fewer low-frequency oscillations (0.20-0.75 Hz) compared with groups SSR and TOR. When groups TSR and SOR were compared, the former was found to have fewer oscillations. With regard to high-frequency oscillations (0.75-2.5 Hz), group SSR had a reduction compared with the other groups, whereas group TSR had the greatest oscillation compared with groups SOR and TOR, with all values expressed in normalized units. Analysis of HRV was performed after pharmacological blockade, and low-frequency oscillations were found to be predominantly sympathetic in sedentary animals, whereas there was no predominance in trained animals. Conclusion: Ovariectomy did not change the tonic autonomic control of the heart and, in addition, reduced the participation of sympathetic component in cardiac modulation. Physical training, on the other hand, increased the participation of parasympathetic modulation on the HRV, including ovariectomized rats.