Hugo Celso Dutra de Souza

Attenuated pressor responses to amino acids in the rostral ventrolateral medulla after swimming training in conscious rats.

The cardiovascular effects of microinjection of the amino acids glutamate and glycine within the rostral ventrolateral medulla (RVLM) after swimming training (ST) in unrestrained awake rats were investigated. Unilateral microinjection of l-glutamate (5, 20 and 50 mM, in 100 nl) produced a dose dependent increase in mean arterial pressure (MAP) in control (C) (16+/-5 mm Hg; 29+/-6 mm Hg; 43+/-6 mm Hg) and swim (SW) (1+/-1 mm Hg; 16+/-2 mm Hg; 25+/-3 mm Hg) groups. However, the magnitude of this response was lower in the swim group. Prazosin injection produced hypotension and tachycardia in both groups (C=-43+/-3 mm Hg/98+/-16 bpm; SW=-61+/-5 mm Hg/115+/-32 bpm). In the SW group the hypotension caused by prazosin was greater compared to C group, but the tachycardia was not different between them. After prazosin, glutamate response in RVLM was blocked in both groups as well. When glycine (10 mM or 1 M, in 100 nl) were microinjected into the RVLM of C group we observed two different effects: decrease in MAP with the lower dose and an increase in MAP with the higher dose (10 mM=-13+/-2 mm Hg; 1 M=47+/-6 mm Hg). However, after ST the hypertensive response to glycine was blunted with no alterations in the hypotensive response (10 mM=-14+/-1 mm Hg; 1 M=18+/-4 mm Hg). These findings suggest that RVLM is involved in the modulation of the sympathetic outflow to the cardiovascular system during exercise training.

Heart rate and arterial pressure variability in the experimental renovascular hypertension model in rats

This study was conducted in one kidney, one clip (1K1C) Goldblatt hypertensive rats to evaluate vascular and cardiac autonomic control using different approaches: 1) evaluation of the autonomic modulation of heart rate (HR) and systolic arterial pressure (SAP) by means of autoregressive power spectral analysis 2) assessment of the cardiac baroreflex sensitivity; and 3) double blockade with methylatropine and propranolol. The 1K1C group developed hypertension and tachycardia. The 1K1C group also presented reduction in variance as well as in LF (0.23+/-0.1 vs. 1.32+/-0.2 ms2) and HF (6.6+/-0.49 vs. 15.1+/-0.61 ms2) oscillations of pulse interval. Autoregressive spectral analysis of SAP showed that 1K1C rats had an increase in variance and LF band (13.3+/-2.7 vs. 7.4+/-1.01 mmHg2) in comparison with the sham group. The baroreflex gain was attenuated in the hypertensive 1K1C (-1.83+/-0.05 bpm/mmHg) rats in comparison with normotensive sham (-3.23+/-0.06 bpm/mmHg) rats. The autonomic blockade caused an increase in the intrinsic HR and sympathetic predominance on the basal HR of 1K1C rats. Overall, these data indicate that the tachycardia observed in the 1K1C group may be attributed to intrinsic cardiac mechanisms (increased intrinsic heart rate) and to a shift in the sympathovagal balance towards cardiac sympathetic over-activity and vagal suppression associated to depressed baroreflex sensitivity. Finally, the increase in the LF components of SAP also suggests an increase in sympathetic activity to peripheral vessels.

Nitric oxide synthesis blockade reduced the baroreflex sensitivity in trained rats.

OBJECTIVE The present study has investigated the effect of blockade of nitric oxide synthesis on cardiovascular autonomic adaptations induced by aerobic physical training using different approaches: 1) double blockade with methylatropine and propranolol; 2) systolic arterial pressure (SAP) and heart rate variability (HRV) by means of spectral analysis; and 3) baroreflex sensitivity. METHODS Male Wistar rats were divided into four groups: sedentary rats (SR); sedentary rats treated with N(omega)-nitro-l-arginine methyl ester (L-NAME) for one week (SRL); rats trained for eight weeks (TR); and rats trained for eight weeks and treated with L-NAME in the last week (TRL). RESULTS Hypertension and tachycardia were observed in SRL group. Previous physical training attenuated the hypertension in L-NAME-treated rats. Bradycardia was seen in TR and TRL groups, although such a condition was more prominent in the latter. All trained rats had lower intrinsic heart rates. Pharmacological evaluation of cardiac autonomic tonus showed sympathetic predominance in SRL group, differently than other groups. Spectral analysis of HRV showed smaller low frequency oscillations (LF: 0.2-0.75 Hz) in SRL group compared to other groups. Rats treated with L-NAME presented greater LF oscillations in the SAP compared to non-treated rats, but oscillations were found to be smaller in TRL group. Nitric oxide synthesis inhibition with L-NAME reduced the baroreflex sensitivity in sedentary and trained animals. CONCLUSION Our results showed that nitric oxide synthesis blockade impaired the cardiovascular autonomic adaptations induced by previous aerobic physical training in rats that might be, at least in part, ascribed to a decreased baroreflex sensitivity.

Role of paraventricular nucleus in exercise training-induced autonomic modulation in conscious rats

The paraventricular nucleus (PVN) of the hypothalamus is an important site for autonomic regulation, where gamma-aminobutyric acid (GABA) system plays an important role. The central mechanisms underlying modulatory effects of exercise training have yet to be characterized. Our objective was to analyze the effects on the autonomic modulation and hemodynamic parameters after bicuculline or muscimol injections into the PVN of sedentary (control, C) and previously submitted to swimming training (ST) rats. After ST protocol, adult male Wistar rats, instrumented with guide cannulas to PVN and femoral artery and vein catheters were submitted to mean arterial pressure (MAP) recording. The exercise training reduced the LF oscillations in normalized units and increased the HF oscillations in absolute and normalized units. Compared with the C group, muscimol microinjections in the ST group promoted a higher decrease in MAP (C=-14+/-1 vs. ST=-28+/-4 mm Hg). Spectral analysis of HR (pulse interval) showed that the muscimol microinjections also reduced LF and HF oscillations in absolute units in both groups. Bicuculline microinjections increased the systolic arterial pressure (C=155+/-5, ST=164+/-5 mm Hg) in ST compared with the C group. Bicuculline injections also increased the LF oscillations of HR in absolute units in C and ST groups. Meanwhile, in normalized units only the ST group showed an increase in the LF oscillations. Our data showed that PVN has an important role in autonomic modulation after exercise training.

Effects of training periodization on cardiac autonomic modulation and endogenous stress markers in volleyball players

We investigated the effects of selective loads of periodization model (SLPM) on autonomic modulation of heart rate variability (HRV) and endogenous stress markers before and after a competition period in volleyball players (N=32). The experimental protocol for the evaluation of HRV consisted of using spectral analysis of time series composed of the R–R intervals derived from electrocardiogram obtained in the supine position and during the tilt test. Stress marker levels were determined by quantifying the plasma concentration of endogenous catecholamines, cortisol and free testosterone. The results showed no changes between the levels of HRV before and after a competition period. In contrast, the quantification of the plasma concentration of endogenous stress markers revealed reductions in the levels of total catecholamines, noradrenaline and cortisol. These changes were accompanied by increases in the concentration of free testosterone and in the testosterone/cortisol ratio. In conclusion, our results demonstrate that the SLPM did not change the cardiac autonomic modulation of HRV, but promoted beneficial adaptations in athletes, including positive changes in the plasma concentration of the endogenous stress markers. The absence of changes in HRV indicates that there is no direct relationship between cardiac autonomic modulation and endogenous stress markers in the present study.

Cardiac Autonomic Modulation Is Determined by Gender and Is Independent of Aerobic Physical Capacity in Healthy Subjects

Background Aerobic physical capacity plays an important role in reducing morbidity and mortality rates in subjects with cardiovascular diseases. This action is often related to an improvement in the autonomic modulation of heart rate variability (HRV). However, controversies remain regarding the effects of physical training on cardiac autonomic control in healthy subjects. Therefore, our objective was to investigate whether aerobic capacity interferes with the autonomic modulation of HRV and whether gender differences exist. Methods Healthy men and women (N=96) were divided into groups according to aerobic capacity: low (VO2: 22-38 ml/kg-1 min-1), moderate (VO2: 38-48 ml/kg-1 min-1) and high (VO2 >48 ml/kg-1 min-1.) We evaluated the hemodynamic parameters and body composition. The autonomic modulation of HRV was investigated using spectral analysis. This procedure decomposes the heart rate oscillatory signal into frequency bands: low frequency (LF=0.04-0.15Hz) is mainly related to sympathetic modulation, and high frequency (HF=0.15-0.5Hz) corresponds to vagal modulation. Results Aerobic capacity, regardless of gender, determined lower values of body fat percentage, blood pressure and heart rate. In turn, the spectral analysis of HRV showed that this parameter did not differ when aerobic capacity was considered. However, when the genders were compared, women had lower LF values and higher HF values than the respective groups of men. Conclusion The results suggest that aerobic physical capacity does not interfere with HRV modulation; however, the cardiac modulatory balance differs between genders and is characterized by a greater influence of the autonomic vagal component in women and by the sympathetic component in men.

Nitric oxide inhibition in paraventricular nucleus on cardiovascular and autonomic modulation after exercise training in unanesthetized rats

It is well known that regular physical exercise alter cardiac function and autonomic modulation of heart rate variability (HRV). The paraventricular nucleus of hypothalamus (PVN) is an important site of integration for autonomic and cardiovascular responses, where nitric oxide (NO) plays an important role. The aim of our study was to evaluate the cardiovascular parameters and autonomic modulation by means of spectral analysis after nitric oxide synthase (NOS) inhibition in the PVN in conscious sedentary (S) or swimming trained (ST) rats. After swimming training protocol, adult male Wistar rats, instrumented with guide cannulas to PVN and femoral artery and vein catheters were submitted to mean arterial pressure (MAP) and heart rate (HR) recording. At baseline, the physical training induced a resting bradycardia (S: 374±5, ST: 346±1bpm) and promoted adaptations in HRV characterized by an increase in high-frequency oscillations (HF; 26.43±6.91 to 88.96±2.44) and a decrease in low-frequency oscillations (LF; 73.57±6.91 to 11.04±2.44) in normalized units. The microinjection of N(ω)-nitro-l-arginine methyl ester (l-NAME) in the PVN of sedentary and trained rats promoted increase in MAP and HR. l-NAME in the PVN did not significantly alter the spectral parameters of HRV of sedentary animals, however in the trained rats increased LF oscillations (11.04±2.44 to 27.62±6.97) and decreased HF oscillations (88.96±2.44 to 72.38±6.97) in normalized units compared with baseline. Our results suggest that NO in the PVN may collaborate to cardiac autonomic modulation after exercise training.

Physical exercise improves cardiac autonomic modulation in hypertensive patients independently of angiotensin-converting enzyme inhibitor treatment

We investigated the influence of angiotensin-converting enzyme inhibitor (ACEi) treatment and physical exercise on arterial pressure (AP) and heart rate variability (HRV) in volunteer patients with hypertension. A total of 54 sedentary volunteers were divided into three groups: normotensive (NT Group), hypertensive (HT Group) and HT volunteers treated with ACEi (ACEi Group). All volunteers underwent an aerobic physical-training protocol for 15 weeks. HRV was investigated using a spectral analysis of a time series of R–R interval (RRi) that was obtained in a supine position and during a tilt test. Physical training promoted a significant reduction in the mean arterial pressure of the HT group (113±3 vs. 106±1 mm Hg) and the ACEi group (104±2 vs. 98±2 mm Hg). Spectral analysis of RRi in the supine position before physical training demonstrated that the NT and ACEi groups had similar values at low frequency (LF; 0.04–0.15 Hz) and high frequency (HF; 0.15–0.5 Hz) oscillations. The HT group had an increase in LF oscillations in absolute and normalized units and a decrease in HF oscillations in normalized units compared with the other groups. The HT group had the lowest responses to the tilt test during LF oscillations in normalized units. Physical training improved the autonomic modulation of the heart rate in the supine position only in the HT group. Physical training promoted a similar increase in autonomic modulation responses in the tilt test in all groups. Our findings show that aerobic physical training improves cardiac autonomic modulation in HT volunteers independently of ACEi treatment.

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.

Aerobic physical training has little effect on cardiovascular autonomic control in aging rats subjected to early menopause

We investigated and compared the effects of physiological menopause (PM) and early menopause (EM) and the adaptations promoted by physical training on the cardiovascular autonomic control of aged rats. Female Wistar rats (N=72) were assigned to 3 groups: control (22 weeks old rats, undergoing sham surgery in the 10th week of life), PM (82 weeks old rats, undergoing sham surgery in the 10th week of life) and EM (82 weeks old rats, undergoing ovariectomy in the 10th week of life). In each group, half of the rats were subjected to swimming training over a period of 10 weeks. Sedentary PM and EM groups had higher basal mean arterial pressure (MAP) and heart rate (HR) and lower intrinsic HR compared to the sedentary control group. Physical training reduced MAP in PM group. All trained groups had lower basal HR; however, only control and PM-trained groups showed decreased intrinsic HR. The assessment of cardiac autonomic balance showed that PM and EM sedentary groups exhibited sympathetic predominance compared to control group. After physical training, only EM group presented sympathetic predominance. HR variability (pulse interval) was similar among all sedentary groups. However, control and PM-trained groups showed lower power in low frequency band (LF; 0.2-0.75 Hz) and higher power in high frequency band (HF; 0.75-3.0 Hz). The analysis of systolic arterial pressure variability revealed that PM and EM sedentary groups had higher LF power. However, PM group showed lower LF power following physical training. Finally, PM and EM groups had a reduction in spontaneous baroreflex sensitivity, that was attenuated by physical training. The overall results suggest that PM or EM promotes similar negative effects on MAP, HR and cardiovascular autonomic control. However, unlike the PM group, physical training was not able to mitigate all negative effects of EM on cardiovascular autonomic control.