Effect of carotid and aortic baroreceptors on cardiopulmonary reflex: the role of autonomic function

We determined the sympathetic and parasympathetic control of heart rate (HR) and the sensitivity of the cardiopulmonary receptors after selective carotid and aortic denervation. We also investigated the participation of the autonomic nervous system in the Bezold-Jarish reflex after selective removal of aortic and carotid baroreceptors. Male Wistar rats (220-270 g) were divided into three groups: control (CG, N = 8), aortic denervation (AG, N = 5) and carotid denervation (CAG, N = 9). AG animals presented increased arterial pressure (12%) and HR (11%) compared with CG, while CAG animals presented a reduction in arterial pressure (16%) and unchanged HR compared with CG. The sequential blockade of autonomic effects by atropine and propranolol indicated a reduction in vagal function in CAG (a 50 and 62% reduction in vagal effect and tonus, respectively) while AG showed an increase of more than 100% in sympathetic control of HR. The Bezold-Jarish reflex was evaluated using serotonin, which induced increased bradycardia and hypotension in AG and CAG, suggesting that the sensitivity of the cardiopulmonary reflex is augmented after selective denervation. Atropine administration abolished the bradycardic responses induced by serotonin in all groups; however, the hypotensive response was still increased in AG. Although the responses after atropine were lower than the responses before the drug, indicating a reduction in vagal outflow after selective denervation, our data suggest that both denervation procedures are associated with an increase in sympathetic modulation of the vessels, indicating that the sensitivity of the cardiopulmonary receptors was modulated by baroreceptor fibers.

Evidence that blood pressure remains under the control of arterial baroreceptors in renal hypertensive rats

The purpose of the present study was to determine the range of the influence of the baroreflex on blood pressure in chronic renal hypertensive rats. Supramaximal electrical stimulation of the aortic depressor nerve and section of the baroreceptor nerves (sinoaortic denervation) were used to obtain a global analysis of the baroreceptor-sympathetic reflex in normotensive control and in chronic (2 months) 1-kidney, 1-clip hypertensive rats. The fall in blood pressure produced by electrical baroreceptor stimulation was greater in renal hypertensive rats than in normotensive controls (right nerve: -47 +/- 8 vs -23 +/- 4 mmHg; left nerve: -51 +/- 7 vs -30 +/- 4 mmHg; and both right and left nerves: -50 +/- 8 vs -30 +/- 4 mmHg; P < 0.05). Furthermore, the increase in blood pressure level produced by baroreceptor denervation in chronic renal hypertensive rats was similar to that observed in control animals 2-5 h (control: 163 +/- 5 vs 121 +/- 1 mmHg; 1K-1C: 203 +/- 7 vs 170 +/- 5 mmHg; P < 0.05) and 24 h (control: 149 +/- 3 vs 121 +/- 1 mmHg; 1K-1C: 198 +/- 8 vs 170 +/- 5 mmHg; P < 0.05) after sinoaortic denervation. Taken together, these data indicate that the central and peripheral components of the baroreflex are acting efficiently at higher arterial pressure in renal hypertensive rats when the aortic nerve is maximally stimulated or the activity is abolished.

Obstructive sleep apnea, masked hypertension, and arterial stiffness in men

BACKGROUND

Obstructive sleep apnea (OSA) is an established cause of hypertension. However, it is not clear whether the frequency of masked hypertension in patients with OSA and whether OSA have an independent role on arterial stiffness taking into account ambulatory blood pressure (BP) monitoring (ABPM).

METHODS

We evaluated 61 male normotensive participants as determined by casual clinic BP level <140/90 mm Hg without clinical evidence of cardiovascular disease and on no medications (43 patients with moderate-to-severe OSA (apnea-hypopnea index (AHI) > or = 15 events/hour by polysomnography) and 18 age- and body mass index-matched controls without OSA (AHI <5 events/hour)). Pulse wave velocity (PWV), an index of arterial stiffness, and 24-h ABPM were performed in a blinded fashion. Masked hypertension was defined when abnormal daytime ABPM was > or = 135 or > or = 85 mm Hg.

RESULTS

The AHI and lowest oxygen saturation were 2.6 +/- 1.6 and 90 +/- 2 vs. 52.8 +/- 21.0 events/hour and 75 +/- 10% for controls and OSA patients, respectively; P < 0.001. Compared with controls, patients with OSA had higher office systolic BP (113 +/- 9 vs. 118 +/- 10 mm Hg; P = 0.05) and a higher unadjusted proportion of masked hypertension (2 controls (11.1%) vs. 13 patients (30.2%); P < 0.05). PWV was 8.7 +/- 0.7, 9.4 +/- 1.0, and 10.6 +/- 1.1 m/s in the control, OSA without and with masked hypertension groups, respectively (P < 0.01 for each comparison). Multiple regression showed that systolic daytime ABPM and the lowest oxygen saturation were independently related to PWV (adjusted R2 = 0.34; P < 0.01).

CONCLUSIONS

Patients with OSA presented a higher unadjusted rate of masked hypertension than matched controls. Lowest oxygen saturation has an independent association with arterial stiffness.

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.

Plasma kinetics of chylomicron-like emulsion in renal transplant patients receiving cyclosporin-based immunosuppression

BACKGROUND

Atherosclerotic cardiovascular disease is prevalent among renal transplant patients. Increase in serum total cholesterol, low-density lipoprotein, and very low-density lipoprotein is common in those patients. Alterations in chylomicron metabolism, however, are also related to atherogenesis and were not studied in renal transplant.

HYPOTHESIS

The aim of this study was to evaluate chylomicron metabolism in renal transplant recipients receiving cyclosporin-based immunosuppression. We determined the plasma kinetics of triglyceride-rich emulsions labeled with [3H]triolein and [14C]cholesteryl oleate that are known to mimic the chylomicron metabolism when injected into the blood stream.

METHODS

Fourteen renal transplant recipients with normal renal function (10 men, 4 women, aged 40 +/- 6.1 years) and 17 age- and gender-matched healthy controls received bolus injections of the chylomicron-like emulsion. Plasma samples were then taken at regular intervals during 60 min. Disappearance curves of the labels and the respective fractional clearance rates (FCR) were calculated in order to measure lipolysis and chylomicron remnant removal from the plasma.

RESULTS

Fasting serum lipid levels did not differ in the two groups. The difference between Median FCR of [3H]triolein emulsion in renal transplant patients and that obtained in the controls (0.07 vs. 0.11 min-1, NS) was not statistically significant. Median FCR of [14C]cholesteryl oleate also did not differ between the groups (patients: 0.044; controls: 0.046, NS).

CONCLUSION

These results indicate that neither chylomicron lipolysis nor remnant removal are affected in stable renal transplant patients treated with cyclosporin-based immunosuppression.

The fate of circulating biologically active peptides in the lungs

The factors which regulate the disappearance of endogenous active substances during pulmonary transit are discussed. The presence of hydrolytic enzymes in the cytosol is not the only factor regulating pulmonary metabolism. An uptake-transport process is required to permit access to intracellular enzymes. No endothelial cell transport mechanism has yet been described for peptides. However, bradykinin and angiotensin I are metabolized by the pulmonary circulation because the enzyme is localized on the luminal surface of the endothelial cells. The pulmonary and extrapulmonary conversion of angiotensin in rat is still a matter of debate. Evidence is presented which supports the idea that when low doses of angiotensin I (greater than 10 ng) are given intravenously, most of the conversion is pulmonary. With higher doses, extrapulmonary conversion also contributes to the final pressor effect of angiotensin I.

Influence of cardiopulmonary reflex on the sympathetic activity during myocardial infarction

The time-course of changes in renal sympathetic nerve activity (RSNA), arterial and cardiopulmonary baroreflexes sensitivities was evaluated in conscious rats eight hours (8 h) and ten days (10 day) after myocardial infarction (MI), induced by coronary artery ligation. RSNA was recorded by a platinum electrode implanted in left renal nerve. Arterial and cardiopulmonary baroreflexes sensitivities were evaluated by changes in blood pressure and serotonin administration, respectively. Both 8 h and 10 day groups presented hypotension (103+/-4 vs. 102+/-2 vs. 115+/-4 mm Hg), but only 8 h showed tachycardia (422+/-22 vs. 378+/-11 vs. 384+/-9 bpm) when compared to Control rats. RSNA was depressed 8 h after MI and increased in 10 day group (12+/-2 vs. 39+/-8 vs. 22+/-2 mV/cycle). Although arterial baroreflex control of heart rate was similar in all groups, the arterial baroreflex control of RSNA in 8 h group was impaired during reductions (-0.35+/-0.10 vs. -1.66+/-0.23 vs. -0.09+/-0.14 mV/cycle/mm Hg) or increases (-0.77+/-0.17 vs. -1.63+/-0.58 vs. -1.66+/-0.17 mV/cycle/mm Hg) in blood pressure when compared to Control animals. Moreover, cardiopulmonary baroreflex bradycardic response was increased in 8 h rats and normalized in 10 day group. The results suggest that the increased cardiopulmonary baroreflex sensitivity in 8 h may contribute to the reduction in the tonic level of RSNA as well as in the impairment of the baroreflex control of RSNA in the presence of hypotension.

Acute water ingestion increases arterial blood pressure in hypertensive and normotensive subjects

In patients with severe autonomic dysfunction, water ingestion elicits an acute pressor response. Hypertension may be associated with changes in cardiovascular autonomic modulation, but there is no information on the acute effects of water ingestion in patients with hypertension. In this study, we compared the effect of acute water ingestion on haemodynamic and autonomic responses of hypertensive and normotensive individuals. Eight patients with mild hypertension were compared to 10 normotensive individuals. After 30 min resting in the supine position all subjects ingested 500 ml of water. At baseline and after water ingestion, venous blood samples for plasma volume determination were collected, and electrocardiographic tracings, finger blood pressure, forearm blood flow and muscle sympathetic nerve activity (MSNA) were obtained. Water ingestion resulted in similar and minor reduction in plasma volume. Systolic and diastolic blood pressure increased in both hypertensive (mean+/-s.d.: 19/14+/-6/3 mm Hg) and normotensive subjects (17/14+/-6/3 mm Hg). There was an increase in forearm vascular resistance and in MSNA. Heart rate was reduced (hypertensive: 5+/-1 beats/min, normotensive: 5+/-6 beats/min) and the high-frequency component of heart rate and systolic blood pressure variability was increased. In hypertensive and normotensive individuals, acute water ingestion elicits a pressor response, an effect that is most likely determined by an increased vasoconstrictor sympathetic activity, and is counterbalanced by an increase in blood pressure and heart rate vagal modulation.

Phenotypic characteristics associated with hypertension in patients with obstructive sleep apnea

Obstructive sleep apnea (OSA) causes secondary hypertension. However, the reasons why the prevalence of hypertension among OSA patients varies widely (35-70%) are not clear. We sought to investigate the phenotypic characteristics of patients with and without hypertension among OSA patients who were matched for disease severity. We studied 152 OSA patients (76 normotensive and 76 hypertensive) diagnosed by polysomnography. Detailed phenotypic characteristics, including laboratorial analysis, were determined in all patients. Univariate analysis followed by multiple logistic regression analysis was used to identify variables that were independently associated with hypertension. The apnea-hypopnea index in normotensive and hypertensive patients was similar (48+/-26 and 48+/-26 events/h, respectively) as well as minimum arterial oxygen saturation (76+/-10 and 75+/-10%, respectively) and total sleep time with oxyhaemoglobin saturation <90% (25+/-25 and 28+/-26%, respectively). Hypertensive patients were older (57+/-11 vs 47+/-12 years; P<0.001), had a higher body mass index (BMI; 34+/-7 vs 30+/-5 kg/m(2); P<0.001), had a higher frequency of women (37 vs 8%; P<0.001), had a higher incidence of diabetes (25 vs 6%; P=0.002) and a higher family history of hypertension (75 vs 42%; P=0.01) than did the normotensive patients. Multiple logistic regression analysis indicated that age (P=0.004), familial history of hypertension (P=0.004), BMI (P=0.04) and female sex (P=0.03) were the independent variables associated with hypertension. We concluded that increasing age and BMI, familial history of hypertension as well as female gender are phenotypic characteristics associated with hypertension among OSA patients with similar disease severity.

A semi-automatic computerized method to measure baroreflex-mediated heart rate responses that reduces interobserver variability

Arterial baroreflex sensitivity estimated by pharmacological impulse stimuli depends on intrinsic signal variability and usually a subjective choice of blood pressure (BP) and heart rate (HR) values. We propose a semi-automatic method to estimate cardiovascular reflex sensitivity to bolus infusions of phenylephrine and nitroprusside. Beat-to-beat BP and HR time series for male Wistar rats (N = 13) were obtained from the digitized signal (sample frequency = 2 kHz) and analyzed by the proposed method (PRM) developed in Matlab language. In the PRM, time series were low-pass filtered with zero-phase distortion (3rd order Butterworth used in the forward and reverse direction) and presented graphically, and parameters were selected interactively. Differences between basal mean values and peak BP (deltaBP) and HR (deltaHR) values after drug infusions were used to calculate baroreflex sensitivity indexes, defined as the deltaHR/deltaBP ratio. The PRM was compared to the method traditionally (TDM) employed by seven independent observers using files for reflex bradycardia (N = 43) and tachycardia (N = 61). Agreement was assessed by Bland and Altman plots. Dispersion among users, measured as the standard deviation, was higher for TDM for reflex bradycardia (0.60 +/- 0.46 vs 0.21 +/- 0.26 bpm/mmHg for PRM, P < 0.001) and tachycardia (0.83 +/- 0.62 vs 0.28 +/- 0.28 bpm/mmHg for PRM, P < 0.001). The advantage of the present method is related to its objectivity, since the routine automatically calculates the desired parameters according to previous software instructions. This is an objective, robust and easy-to-use tool for cardiovascular reflex studies.

Pressure and time dependence of the cardiopulmonary reflex response in patients with hypertensive cardiomyopathy

The first minutes of the time course of cardiopulmonary reflex control evoked by lower body negative pressure (LBNP) in patients with hypertensive cardiomyopathy have not been investigated in detail. We studied 15 hypertensive patients with left ventricular dysfunction (LVD) and 15 matched normal controls to observe the time course response of the forearm vascular resistance (FVR) during 3 min of LBNP at -10, -15, and -40 mmHg in unloading the cardiopulmonary receptors. Analysis of the average of 3-min intervals of FVR showed a blunted response of the LVD patients at -10 mmHg (P = 0.03), but a similar response in both groups at -15 and -40 mmHg. However, using a minute-to-minute analysis of the FVR at -15 and -40 mmHg, we observed a similar response in both groups at the 1st min, but a marked decrease of FVR in the LVD group at the 3rd min of LBNP at -15 mmHg (P = 0.017), and -40 mmHg (P = 0.004). Plasma norepinephrine levels were analyzed as another neurohumoral measurement of cardiopulmonary receptor response to LBNP, and showed a blunted response in the LVD group at -10 (P = 0.013), -15 (P = 0.032) and -40 mmHg (P = 0.004). We concluded that the cardiopulmonary reflex response in patients with hypertensive cardiomyopathy is blunted at lower levels of LBNP. However, at higher levels, the cardiopulmonary reflex has a normal initial response that decreases progressively with time. As a consequence of the time-dependent response, the cardiopulmonary reflex response should be measured over small intervals of time in clinical studies.

Exercise training changes autonomic cardiovascular balance in mice

Experiments were performed to investigate the influence of exercise training on cardiovascular function in mice. Heart rate, arterial pressure, baroreflex sensitivity, and autonomic control of heart rate were measured in conscious, unrestrained male C57/6J sedentary ( n = 8) and trained mice ( n = 8). The exercise training protocol used a treadmill (1 h/day; 5 days/wk for 4 wk). Baroreflex sensitivity was evaluated by the tachycardic and bradycardic responses induced by sodium nitroprusside and phenylephrine, respectively. Autonomic control of heart rate and intrinsic heart rate were determined by use of methylatropine and propranolol. Resting bradycardia was observed in trained mice compared with sedentary animals [485 ± 9 vs. 612 ± 5 beats/min (bpm)], whereas mean arterial pressure was not different between the groups (106 ± 2 vs. 108 ± 3 mmHg). Baroreflex-mediated tachycardia was significantly enhanced in the trained group (6.97 ± 0.97 vs. 1.6 ± 0.21 bpm/mmHg, trained vs. sedentary), whereas baroreflex-mediated bradycardia was not altered by training. The tachycardia induced by methylatropine was significantly increased in trained animals (139 ± 12 vs. 40 ± 9 bpm, trained vs. sedentary), whereas the propranolol effect was significantly reduced in the trained group (49 ± 11 vs. 97 ± 11 bpm, trained vs. sedentary). Intrinsic heart rate was similar between groups. In conclusion, dynamic exercise training in mice induced a resting bradycardia and an improvement in baroreflex-mediated tachycardia. These changes are likely related to an increased vagal and decreased sympathetic tone, similar to the exercise response observed in humans.

Dysregulation of peripheral and central chemoreflex responses in Chagas' heart disease patients without heart failure

BACKGROUND

The peripheral and central chemoreflexes are important autonomic mechanisms for regulating breathing and cardiovascular function. Although pathological inflammatory infiltration of the peripheral chemoreceptors and central nervous system has been reported in Chagas' disease, functional evaluation of chemoreflexes has not yet been performed.

METHODS AND RESULTS

The hypothesis that chemoreflex function is altered in patients with Chagas' heart disease (CH) but normal left ventricle function was tested in 12 CH patients and 13 matched control subjects. The ventilatory rate, minute ventilation, heart rate, mean arterial pressure, forearm blood flow, forearm vascular resistance, and venous norepi-nephrine responses to hypoxia and hypercapnia were determined. During hypoxia, the decrease in oxygen saturation was smaller in CH patients, despite a similar ventilatory response between groups. Both groups showed an increase in heart rate during hypoxia, but this response was blunted in CH patients. Although the mean arterial pressure response to hypoxia was similar in both groups, forearm vascular resistance significantly decreased in control subjects while remaining unchanged in CH patients. Moreover, a significant increase in plasma norepinephrine levels elicited by stimulation of peripheral chemoreceptors was observed only in the CH group. During hypercapnia, the increase in minute ventilation was smaller in CH patients, who did not exhibit the increase in norepinephrine observed in control subjects.

CONCLUSIONS

These data suggest that CH potentiates respiratory, cardiovascular, and autonomic responses to peripheral chemoreceptor activation by hypoxia in patients with normal left ventricular function. The ventilatory and sympathetic responses to central chemoreceptor activation by hypercapnia, however, are significantly blunted.

Chronic AT(1) receptor blockade alters autonomic balance and sympathetic responses in hypertension

In the coarctation hypertension model, we have shown that chronic treatment with losartan causes both normalization of impaired reflex control of heart rate and partial correction of the depressed aortic nerve activity/pressure relationship, even with the persistence of hypertension. In the present study, we analyzed the effects of angiotensin II blockade on the efferent pathways of coarcted and sham-operated groups treated chronically with vehicle or losartan (10 mg/kg per day PO). Hypertension was induced by subdiaphragmatic aortic coarctation, and the treatments lasted 9 days (4 control and 5 experimental days). On day 5, autoregressive power spectral analysis was performed on heart rate recordings made in conscious rats. Other groups were used for sympathetic splanchnic nerve activity recordings made simultaneously with pressure (anesthetized rats) at basal condition and during loading/unloading of baroreceptors. Losartan treatment induced a significant reduction in basal pressure but did not interfere with the development of hypertension (similar pressure increases of 24% and 28% over control values in losartan and vehicle groups, respectively). In vehicle-treated rats, establishment of hypertension was accompanied by a marked change in power spectral density from high- (1.19+/-0.06 Hz, 33+/-6%) to low-frequency components (0,42+/-0.03 Hz, 54+/-6%), with increased low-frequency-to-high-frequency ratio. When compared with sham-operated vehicle-treated rats, there was also increase in the gain of sympathetic activity/pressure relationship, with displacement of lower plateau toward high levels of sympathetic activity. No changes in the power spectral density and sympathetic activity/pressure relationship were observed when hypertension developed in the presence of chronic angiotensin type 1 (AT(1)) receptor blockade. The data suggest that angiotensin II, activated during the establishment of coarctation hypertension, acts via AT(1) receptors to alter sympathovagal balance, facilitating the sympathetic outflow to heart and peripheral circulation during baroreceptors unloading. Data also indicate that the observed effects are not conditioned by preexisting pressure levels.

Hemodynamic and metabolic profile in offspring of malignant hypertensive parents

Malignant hypertension is a serious form of arterial hypertension in which the physiopathological mechanisms include increased activity of the sympathetic nervous system, renin angiotensin system, and endothelium dysfunction. Family history of hypertension is an important predictive factor for hypertension and is associated with metabolic and hemodynamic abnormalities. Studies of these abnormalities in malignant hypertensive offspring have not yet been published. Therefore, we studied 42 offspring of malignant hypertensive parents (OMH group: age, 22+/-7 years; 23 male subjects; 27 white) and 35 offspring of normotensive parents (ONT group: age, 21+/-4 years; 23 male subjects; 25 white). All subjects had blood pressure <140/90 mm Hg. We evaluated body mass index; office blood pressure; 24-hour ambulatory and continuous beat-to-beat blood pressure monitoring (Finapres); biochemical analysis, including total cholesterol and fractions, triglycerides, glucose, and insulin; and hormonal analysis, including plasma renin activity, aldosterone, and catecholamines. The subjects were also submitted to cold pressure test and handgrip measurements. The body mass index was significantly higher in the OMH group (24+/-5 kg/m(2)) than in the ONT group (22+/-4 kg/m(2)). The OMH group showed significantly higher blood pressure and heart rate in office and Finapres measurements (P<0.05). In 24-hour ambulatory monitoring, the OMH group presented higher 24-hour blood pressure and heart rate, higher blood pressure during the night, and higher heart rate variability during the day compared with those of the ONT group. They also presented lower HDL cholesterol, higher levels of plasma insulin and norepinephrine, and higher insulin-to-glucose ratio (P<0.05) than the ONT group. There were no differences in the other biochemical parameters measured. In conclusion, OMH subjects show early hemodynamic, neurohumoral, and metabolic alterations that are typical of hypertensive metabolic syndrome.

Baroreflex depression persists in the early phase after hypertension reversal

The baroreflex control of heart rate (HR) was evaluated in conscious chronic renal hypertensive rats (RHR; 1K-1C, 2 mo) under control conditions and after reversal of hypertension by unclipping the renal artery or sodium nitroprusside infusion. Unclipping and nitroprusside infusion were both followed by significant decreases in the mean arterial pressure (unclipping: from 199 +/- 4 to 153 +/- 8 mmHg; nitroprusside infusion: from 197 +/- 9 to 166 +/- 6 mmHg) as well as slight and significant increases, respectively, in the baroreflex bradycardic response index (unclipping: from 0.2 +/- 0.04 to 0.6 +/- 0.1 beats x min(-1) x mmHg(-1); nitroprusside infusion: from 0.1 +/- 0.04 to 0.5 +/- 0.1 beats x min(-1) x mmHg(-1)). However, this index was still depressed compared with that for normotensive control rats (2.1 +/- 0.2 beats x min(-1) x mmHg(-1)). The index for the baroreflex tachycardic response was also depressed under control conditions and remained unchanged after hypertension reversal. RHR possessed markedly attenuated vagal tone as demonstrated by pharmacological blockade of parasympathetic and sympathetic control of HR with methylatropine and propranolol, respectively. A reduced bradycardic response was also observed in anesthetized RHR during electrical stimulation of the vagus nerve or methacholine chloride injection, indicating impairment of efferent vagal influence over the HR. Together, these data indicate that 2 h after hypertension reversal in RHR, the previously described normalization of baroreceptor gain occurs independent of the minimal or lack of recovery of baroreflex control over HR.

Effects of exercise training on baroreflex control of the cardiovascular system

Dynamic exercise training has been recommended as an antihypertensive therapy and as a way to modify the effects of many cardiovascular risk factors (Arakawa, 1993; Arroll and Beaglehole, 1992; Kelly and McClellan, 1994: see references 1-3 in the paper). However, the mechanisms underlying the blood-pressure lowering effect of chronic exercise are still poorly understood. It has been suggested that a decrease in sympathetic tone is one of the major effects elicited by chronic exercise on the cardiovascular system. The importance of the sympathetic component is confirmed in this review, since it was found that in spontaneously hypertensive rats (SHR) a marked decrease in sympathetic activity occurred after exercise training. Moreover, our findings suggest that this effect is mediated by improving the depressed baroreceptor function, which is, in part, responsible for the attenuation of the baroreflex sensitivity observed in the sedentary SHR (Krieger et al., 1998, 1999; see references 4 and 5 in the paper).

Baseline blood pressure and other variables influencing survival on haemodialysis of patients without overt cardiovascular disease

BACKGROUND

Age, diabetes and concomitant cardiovascular disease, recorded at the initiation of dialysis, allows the identification of patients with a high probability of early mortality. When all of these factors are taken into account the mortality rate of dialysis patients is still 3.5 times higher than for the general population. Information on the factors that increase the mortality of patients lacking the major cardiovascular risk factors is important because these are likely to be correctable, especially if detected early.

METHODS

We investigated prospectively the relevance of blood pressure and other variables recorded at the initiation of dialysis treatment on the survival of a group of 103 relatively young adult haemodialysis patients (mean age 44.3 years +/-13 SD), with a low prevalence of comorbidity and a median follow-up period of 79 months. Data were analysed by the Cox proportional regression model and survival curves were constructed by the Kaplan-Meier method.

RESULTS

Forty-four patients died, 20 (46%) of whom as a result of cardiovascular causes. Multivariate analysis showed that mortality was associated with age (P=0.0001), serum creatinine (P=0.005, negative association), left ventricular (LV) mass (P=0.003) and hypertension (P=0.03). Mortality was increased by 7% for each additional year of age, by 0.7% for each 1 g increase in LV mass, and was reduced by 23% for each additional mg/dl of serum creatinine. Hypertensive patients had a higher probability (x2.2) of dying compared with normotensive patients.

CONCLUSIONS

In addition to age and conditions of occult malnutrition, hypertension and LV hypertrophy, when present at the initiation of dialysis, play a major role in the mortality of low risk, relatively young dialysis patients. These potentially correctable factors should be actively sought and treated during the early stage of renal insufficiency to improve prognosis.

Abnormal neurovascular control during exercise is linked to heart failure severity

The purpose of this study was to determine if abnormalities of sympathetic neural and vascular control are present in mild and/or severe heart failure (HF) and to determine the underlying afferent mechanisms. Patients with severe HF, mild HF, and age-matched controls were studied. Muscle sympathetic nerve activity (MSNA) and forearm vascular resistance (FVR) in the nonexercising arm were measured during mild and moderate static handgrip. MSNA during moderate handgrip was higher at baseline and throughout exercise in severe HF vs. mild HF (peak MSNA 67 +/- 3 vs. 54 +/- 3 bursts/min, P < 0.0001) and higher in mild HF vs. controls (33 +/- 3 bursts/min, P < 0.0001), but the change in MSNA was not different between the groups. The change in FVR was not significantly different between the three groups during static exercise. During isolation of muscle metaboreceptors, MSNA and blood pressure remained elevated in normal controls and mild HF but not in severe HF. During mild handgrip, the increase in MSNA was exaggerated in severe HF vs. controls and mild HF, in whom MSNA did not increase. In summary, the increase in MSNA during static exercise in severe HF appears to be attributable to exaggerated central command or muscle mechanoreceptor control, not muscle metaboreceptor control.

Decreased cardiopulmonary baroreflex sensitivity in Chagas' heart disease

No study has been performed on reflexes originating from receptors in the heart that might be involved in the pathological lesions of Chagas' heart disease. Our study was undertaken to analyze the role of cardiopulmonary reflex on cardiovascular control in Chagas' disease. We studied 14 patients with Chagas' disease without heart failure and 12 healthy matched volunteers. Central venous pressure, arterial blood pressure, heart rate, forearm blood flow, and forearm vascular resistance were recorded during deactivation of cardiopulmonary receptors. By reducing central venous pressure by applying -10 and -15 mm Hg of negative pressure to the lower body, we observed (a) a similar decrease of central venous pressure in both groups; (b) a marked increase in forearm vascular resistance in the control group but a blunted increase in the Chagas' group; and (c) no significant changes in blood pressure and heart rate. To analyze cardiopulmonary and arterial receptors, we applied -40 mm Hg of lower-body negative pressure. As a consequence, (a) central venous pressure decreased similarly in both groups; (b) blood pressure was maintained in the control group, whereas in patients with Chagas' disease, a decrease in systolic and mean arterial pressure occurred; (c) heart rate increased in both groups; and (d) forearm vascular resistance increased significantly and similarly in both groups. Unloading of receptors with low levels of lower-body negative pressure did not increase forearm vascular resistance in patients with Chagas' disease, which suggests that the reflex mediated by cardiopulmonary receptors is impaired in patients with Chagas' disease without heart failure. Overall control of circulation appears to be compromised because patients did not maintain blood pressure under high levels of lower-body negative pressure.

Exercise training increases baroreceptor gain sensitivity in normal and hypertensive rats

Exercise training attenuates arterial hypertension and increases baroreflex sensitivity in spontaneous hypertension. However, no information exists regarding the portion of the baroreflex arch in which this attenuation takes place. We tested the hypothesis that exercise training increases the afferent pathway sensitivity of baroreflex control in both normotensive and spontaneously hypertensive rats (SHR). Arterial pressure and whole-nerve activity of the aortic baroreceptor (multifiber preparation) were evaluated in 30 male rats assigned to 4 groups: sedentary and exercise-trained normotensive rats and sedentary and exercise-trained SHR. Exercise training was performed on a motor treadmill, 5 d/wk for 60 minutes, gradually progressing toward a speed of 26.8 m/min. Exercise training reduced mean arterial pressure in conscious exercise-trained SHR (183+/-4 versus 165+/-7 mm Hg). The relation between changes in aortic baroreceptor discharge and changes in systolic arterial pressure increased significantly in exercise-trained normotensive rats (2.09+/-0.1 versus 1.44+/-0.1%/mm Hg) and exercise-trained SHR (0.92+/-0.1 versus 0.71+/-0.1%/mm Hg) compared with their respective sedentary rats. Likewise, the average aortic baroreceptor gain sensitivity (calculated by logistic equation) was significantly higher in exercise-trained normotensive rats (2.25+/-0.19 versus 1.77+/-0.03%/mm Hg) and exercise-trained SHR (1.07+/-0.04 versus 0.82+/-0.05%/mm Hg) compared with their respective sedentary control rats. In conclusion, exercise training increases aortic baroreceptor gain sensitivity in normotensive and SHR, thus improving baroreceptor sensitivity, which may result in a more efficient arterial pressure regulation by the baroreflexes.

Acute AT1 receptor blockade does not improve the depressed baroreflex in rats with chronic renal hypertension

To assess the role of angiotensin II in the sensitivity of the baroreflex control of heart rate (HR) in normotensive rats (N = 6) and chronically hypertensive rats (1K1C, 2 months, N = 7), reflex changes of HR were evaluated before and after (15 min) the administration of a selective angiotensin II receptor antagonist (losartan, 10 mg/kg, iv). Baseline values of mean arterial pressure (MAP) were higher in hypertensive rats (195 +/- 6 mmHg) than in normotensive rats (110 +/- 2 mmHg). Losartan administration promoted a decrease in MAP only in hypertensive rats (16%), with no changes in HR. During the control period, the sensitivity of the bradycardic and tachycardic responses to acute MAP changes were depressed in hypertensive rats (approximately 70% and approximately 65%, respectively) and remained unchanged after losartan administration. Plasma renin activity was similar in the two groups. The present study demonstrates that acute blockade of AT1 receptors with losartan lowers the MAP in chronic renal hypertensive rats without reversal of baroreflex hyposensitivity, suggesting that the impairment of baroreflex control of HR is not dependent on an increased angiotensin II level.

Aging and baroreflex control of RSNA and heart rate in rats

Aging is associated with altered autonomic control of cardiovascular function, but baroreflex function in animal models of aging remains controversial. In this study, pressor and depressor agent-induced reflex bradycardia and tachycardia were attenuated in conscious old (24 mo) rats [57 and 59% of responses in young (10 wk) Wistar rats, respectively]. The intrinsic heart rate (HR, 339 +/- 5 vs. 410 +/- 10 beats/min) was reduced in aged animals, but no intergroup differences in resting mean arterial blood pressure (MAP, 112 +/- 3 vs. 113 +/- 5 mmHg) or HR (344 +/- 9 vs. 347 +/- 9 beats/min) existed between old and young rats, respectively. The aged group also exhibited a depressed (49%) parasympathetic contribution to the resting HR value (vagal effect) but preserved sympathetic function after intravenous methylatropine and propranolol. An implantable electrode revealed tonic renal sympathetic nerve activity (RSNA) was similar between groups. However, old rats showed impaired baroreflex control of HR and RSNA after intravenous nitroprusside (-0.63 +/- 0. 18 vs. -1.84 +/- 0.4 bars x cycle(-1) x mmHg(-1) x s(-1)). Therefore, aging in rats is associated with 1) preserved baseline MAP, HR, and RSNA, 2) impaired baroreflex control of HR and RSNA, and 3) altered autonomic control of resting HR.

Cardiac effects of persistent hemodialysis arteriovenous access in recipients of renal allograft

In hemodialysis patients, large arteriovenous (AV) fistulas for vascular access may cause ventricular hypertrophy and high-output cardiac failure. The long-term cardiac consequences of functional AV fistulas in renal transplant patients are unclear. A precise knowledge of these consequences is important to decide if and when such fistulas should be closed in successfully transplanted patients. In this retrospective study including 61 stable renal transplant patients with adequate renal function (serum creatinine <2.0 mg/100 ml), echocardiography was performed in 39 patients with a functional AV fistula (group 1) and in 22 whose fistulas had been closed, for esthetic reasons, within 2 months postoperatively (group 2). The volume flow of the fistulas, measured in 22 randomly selected individuals of group 1, was 900 +/- 350 ml/min (range 500-1,600). Patients of group 1 were older (40 +/- 12 vs. 33 +/- 12 years, p < 0.05), had longer duration of the fistula (62 +/- 31 vs. 36 +/- 30 months, p < 0.05), higher body mass index (24 +/- 4 vs. 22 +/- 3 kg/m2, p < 0.05), systolic (154 +/- 24 vs. 138 +/- 18 mm Hg, p < 0.05) and diastolic (96 +/- 12 vs. 89 +/- 11 mm Hg, p < 0.05) blood pressure and increased left ventricular (LV) end-diastolic dimension (53 +/- 5 vs. 49 +/- 5 mm, p < 0.01). LV mass, cardiac index, ejection fraction and the proportion of patients with LV hypertrophy were comparable in the two groups. LV end-diastolic dimension was positively and independently influenced only by the presence of the AV fistula (p < 0.01) after adjusting for age, duration of the fistula, body mass index, systolic and diastolic blood pressure and the nature of the antihypertensive drugs used. In conclusion, the persistence of large, high-flow AV fistulas for prolonged periods of time had little impact on cardiac morphology and function of stable renal transplant patients with adequate renal function. The data do not support routine closure of these fistulas in all renal transplant patients.

Outcome of patients with malignant hypertension and end-stage renal failure treated by long-term hemodialysis

Malignant hypertension is associated with high mortality and morbidity usually caused by cardiovascular events. The course and prognosis of malignant hypertension patients treated with renal replacement therapy has not been thoroughly investigated. In the present work, we compared the clinical evolution and survival of 24 end-stage renal failure malignant hypertension patients with that of a group of individually matched renal failure patients admitted to the same dialysis center during a period of 21 years. Survival rates at 1, 5 and 8 years were 87, 82 and 50% for malignant hypertension patients and 87, 75 and 65% for controls, respectively (p = 0.766, NS). Nonfatal cardiovascular complications occurred in 2 individuals of each group. The most important cause of death in both groups was cardiovascular. The frequency of fatal cardiovascular events was similar in the two groups: 64% of deaths for malignant hypertension and 71% for controls (NS). In conclusion, previous malignant hypertension did not increase the risk of patients in long-term hemodialysis in our series.

Autonomic abnormalities demonstrable in young normotensive subjects who are children of hypertensive parents

Although a slightly elevated office blood pressure (BP) has been reported in several studies, little is known about the prolonged resting blood pressure, heart rate (HR) and baroreflex sensitivity (BRS) of prehypertensive subjects with a family history of hypertension. Office blood pressure, prolonged resting (1 h) BP and HR were measured in 25 young normotensives with a positive family history of hypertension (FH+) and 25 young normotensives with a negative family history of hypertension (FH-), matched for age, sex, and body mass index. After BP and HR measurements, blood samples were collected for the determination of norepinephrine, plasma renin activity and aldosterone levels, and baroreflex sensitivity was then tested. Casual BP, prolonged resting BP and heart rate were significantly higher in the FH+ group (119.9 +/- 11.7/78.5 +/- 8.6 mmHg, 137.3 +/- 12.3/74.4 +/- 7.9 mmHg, 68.5 +/- 8.4 bpm) compared to the FH- group (112.9 +/- 11.4/71.2 +/- 8.3 mmHg, 128.0 +/- 11. 8/66.5 +/- 7.4 mmHg, 62.1 +/- 6.0 bpm). Plasma norepinephrine level was significantly higher in the FH+ group (220.1 +/- 104.5 pg/ml) than in the FH- group (169.1 +/- 63.3 pg/ml). Baroreflex sensitivity to tachycardia (0.7 +/- 0.3 vs 1.0 +/- 0.5 bpm/mmHg) was depressed in the FH+ group (P<0.05). The FH+ group exhibited higher casual blood pressure, prolonged resting blood pressure, heart rate and plasma norepinephrine levels than the FH- group (P<0.05), suggesting an increased sympathetic tone in these subjects. The reflex tachycardia was depressed in the FH+ group.

Cardiopulmonary reflex impairment in experimental diabetes in rats

The aim of the present study was to evaluate the sensitivity of the cardiopulmonary receptors in experimental diabetes induced by streptozotocin by the use of 2 different methods: (1) administration of increasing doses of serotonin to analyze peak changes of arterial pressure and heart rate for each given dose in conscious intact normal and diabetic rats; (2) expanding blood volume with the use of dextran (6%) to produce similar increases in left ventricular end-diastolic pressure to quantify the arterial pressure, heart rate, and renal sympathetic nerve activity in sinoaortic, denervated, anesthetized normal and diabetic rats. Blood samples were collected to measure blood glucose. Diabetic rats showed hyperglycemia (22+/-0. 7 versus 7+/-0.2 mmol/L), reduced body weight (226+/-12 versus 260+/-4 g) and heart rate (294+/-14 versus 350+/-10 bpm), and similar arterial pressure (104+/-4 versus 113+/-4 mm Hg) when compared with control rats. Serotonin induced significant bradycardia and hypotension, which were similar and proportional to the dose injected in both groups. Mean arterial pressure and heart rate decreases in response to volume overload were significantly lower in diabetic than in control rats. The reflex reduction of the renal sympathetic nerve activity as expressed by percentage changes in nerve activity in response to increasing left end-diastolic pressure was abolished in diabetic animals (1.9+/-0.8% versus -14+/-4%/mm Hg in controls). These results showed an impairment of cardiopulmonary reflex control of circulation in diabetes during acute volume expansion. The normal responses to serotonin administration indicated that the cardiopulmonary reflex is still preserved in diabetic rats.

State-of-the-Art lecture: influence of exercise training on neurogenic control of blood pressure in spontaneously hypertensive rats

Exercise training plays an important role in the reduction of high blood pressure. In this review, we discuss the effect of distinct intensities of exercise training on the reduction of high blood pressure in spontaneously hypertensive rats (SHR). In addition, we present some hemodynamic mechanisms and associated neural controls by which exercise training attenuates hypertension in SHR. Low-intensity exercise training is more effective in reducing high blood pressure than is high-intensity exercise training in SHR. The decrease in blood pressure is due to resting bradycardia, and in consequence, lower cardiac output. Sympathetic attenuation to the heart is the major explanation for the resting bradycardia. Recovery of the sensitivity of baroreflex control of heart rate, which is usually impaired in SHR, is an important neurogenic component involved in the benefits elicited by exercise training.

Comparison of three methods for the determination of baroreflex sensitivity in conscious rats

Baroreflex sensitivity was studied in the same group of conscious rats using vasoactive drugs (phenylephrine and sodium nitroprusside) administered by three different approaches: 1) bolus injection, 2) steady-state (blood pressure (BP) changes produced in steps), 3) ramp infusion (30 s, brief infusion). The heart rate (HR) responses were evaluated by the mean index (mean ratio of all HR changes and mean arterial pressure (MAP) changes), by linear regression and by the logistic method (maximum gain of the sigmoid curve by a logistic function). The experiments were performed on three consecutive days. Basal MAP and resting HR were similar on all days of the study. Bradycardic responses evaluated by the mean index (-1.5 +/- 0.2, -2.1 +/- 0.2 and -1.6 +/- 0.2 bpm/mmHg) and linear regression (-1.8 +/- 0.3, -1.4 +/- 0.3 and -1.7 +/- 0.2 bpm/mmHg) were similar for all three approaches used to change blood pressure. The tachycardic responses to decreases of MAP were similar when evaluated by linear regression (-3.9 +/- 0.8, -2.1 +/- 0.7 and -3.8 +/- 0.4 bpm/mmHg). However, the tachycardic mean index (-3.1 +/- 0.4, -6.6 +/- 1 and -3.6 +/- 0.5 bpm/mmHg) was higher when assessed by the steady-state method. The average gain evaluated by logistic function (-3.5 +/- 0.6, -7.6 +/- 1.3 and -3.8 +/- 0.4 bpm/mmHg) was similar to the reflex tachycardic values, but different from the bradycardic values. Since different ways to change BP may alter the afferent baroreceptor function, the MAP changes obtained during short periods of time (up to 30 s: bolus and ramp infusion) are more appropriate to prevent the acute resetting. Assessment of the baroreflex sensitivity by mean index and linear regression permits a separate analysis of gain for reflex bradycardia and reflex tachycardia. Although two values of baroreflex sensitivity cannot be evaluated by a single symmetric logistic function, this method has the advantage of better comparing the baroreflex sensitivity of animals with different basal blood pressures.

Blood pressure and the risk of complex arrhythmia in renal insufficiency, hemodialysis, and renal transplant patients

Complex arrhythmia is frequent in hemodialysis patients but it is not clear if this is a consequence of dialysis or uremia or is secondary to the hemodynamic and cardiovascular alterations often associated with chronic renal failure. The incidence of complex ventricular arrhythmia (frequent multiform premature beats, couplets, and runs) in 31 subjects who had their uremic status recently corrected by renal transplant (Group 1) and in 23 predialysis (Group 2) and 73 hemodialysis (Group 3) chronic renal failure patients were studied with 24-h Holter monitoring. Patients were not receiving antiarrhythmic drugs or digitalis and significant coronary artery disease was excluded by clinical and noninvasive methods. Complex arrhythmia was two times more frequent in dialysis patients but the difference did not reach statistical significance (Group 1: 16%; Group 2: 17%; Group 3: 34%; chi2 4.9, P = .086). The stepwise model of logistic regression analysis identified systolic blood pressure (odds ratio 1.015, 95% confidence interval [CI] 1.001-1.027, P = .03) and left ventricular systolic dysfunction (odds ratio 7.04, 95% CI 1.3-36.7, P = .02) as the only factors that independently influenced the probability of complex arrhythmia. Age, gender, race, diabetes, smoking status, body mass index, diastolic blood pressure, serum creatinine, hematocrit, left ventricular mass index, and use of diuretics, beta-blockers, angiotensin converting enzyme (ACE) inhibitors, sympatolytics, and calcium channel blockers did not influence the occurrence of complex arrhythmia. The data indicate that blood pressure and myocardial dysfunction are more important determinants of complex arrhythmia than dialysis or uremia in chronic renal disease patients.

Role of arterial baroreceptor function on cardiovascular adjustments to acute and chronic dynamic exercise

Our series of experiments in rats, and other data of the literature, indicate that the arterial baroreceptors are actively involved in the reflex control of circulation during acute and chronic exercise. Although heart rate increases simultaneously with arterial blood pressure during an acute bout of dynamic exercise, the gain of the baroreflex bradycardia remains unchanged. Moreover, the more pronounced increase in mean arterial pressure during all exercise period observed in sino-aortic denervated rats, compared to sham-operated rats, suggests that the arterial baroreflex restrains the increase in blood pressure during dynamic exercise. However, the arterial baroreflex seems to have no influence on the development of exercise tachycardia. Exercise training can affect baroreflex bradycardia and tachycardia in the opposite direction, since decreased baroreflex bradycardia is observed despite increased baroreflex tachycardia. Since the increased baroreflex tachycardia may be attributed to an increased sensitivity of the afferent pathway of the baroreceptors, the attenuation of the baroreflex bradycardia is probably due to an impairment of the efferent pathway of the reflex. Finally, the decreased tonic sympathetic nerve activity produced by exercise training can be considered as one of the mechanisms involved in the attenuation of hypertension induced by exercise training.

Lack of effect of a single oral dose of cyclosporine on systemic blood pressure and on forearm blood flow and vascular resistance in humans

The acute hemodynamic effect of cyclosporine in man is controversial. A randomized, double blind, placebo-controlled, cross-over study was undertaken to evaluate the effect of a single oral dose of cyclosporine (20 mg/kg body weight) on mean blood pressure (MBP), heart rate (HR), forearm blood flow (FBF), and vascular resistance (FVR) in 16 healthy adult subjects. Subjects were studied twice, with an intervening period of 2 weeks, before and after the administration of either cyclosporine or the vehicle olive oil. Blood pressure was measured on brachial and digital arteries. After 30 min of rest, basal measurements were obtained and individuals were randomly assigned to receive either cyclosporine or the vehicle, and the same measurements were repeated 2 h later. Mean whole blood levels of cyclosporine were 1542+/-387 ng/mL (range 1000 to 2550) 2 h after the administration of a single oral dose of cyclosporine. Cyclosporine did not cause any significant change in the hemodynamic parameters when compared with vehicle. Pre- and post-cyclosporine data were as follows (means +/-/SD): MBP (determined by Finapres on the digital artery), 92+/-10 v 95+/-11 mm Hg; HR, 66+/-10 v 68+/-11 beats/min; FBF, 3.90+/-1.3 v 3.8+/-1.8 mL/ 100 mL/min; and FVR, 28+/-9 v 33 +/-18 units, respectively. For the vehicle the results were: MBP, 94+/-9 v 94+/-9; HR, 67+/-9v 67 /-11; FBF, 3.3+/-1.6 v 3.2+/-2.0; FVR, 35+/-14 v 37+/-15, respectively. These figures did not differ from those obtained with the auscultatory method applied to the brachial artery among 10 selected subjects studied with Finapres. In conclusion, we found no evidence that at supratherapeutic doses cyclosporine causes acute increase in blood pressure or peripheral vasoconstriction in humans.

Baroreflex control of sympathetic activity in experimental hypertension

The arterial baroreceptor reflex system is one of the most powerful and rapidly acting mechanisms for controlling arterial pressure. The purpose of the present review is to discuss data relating sympathetic activity to the baroreflex control of arterial pressure in two different experimental models: neurogenic hypertension by sinoaortic denervation (SAD) and high-renin hypertension by total aortic ligation between the renal arteries in the rat. SAD depresses baroreflex regulation of renal sympathetic activity in both the acute and chronic phases. However, increased sympathetic activity (100%) was found only in the acute phase of sinoaortic denervation. In the chronic phase of SAD average discharge normalized but the pattern of discharges was different from that found in controls. High-renin hypertensive rats showed overactivity of the renin angiotensin system and a great depression of the baroreflexes, comparable to the depression observed in chronic sinoaortic denervated rats. However, there were no differences in the average tonic sympathetic activity or changes in the pattern of discharges in high-renin rats. We suggest that the difference in the pattern of discharges may contribute to the increase in arterial pressure lability observed in chronic sinoaortic denervated rats.

Chronic AT1 receptor blockade alters aortic nerve activity in hypertension

In the chronic phase of coarctation hypertension (CH) we have shown both reduction in baroreceptor sensitivity (Hypertension. 1992;19[suppl II]:II-198-II-201.) and normalization of the depressed baroreceptor reflex control of heart rate, even with the persistence of hypertension in losartan-treated animals (Am J Physiol. 1995;269:H812-H818). In the present study we analyzed the effects of angiotensin II blockade on afferent aortic nerve activity of CH and sham-operated groups treated chronically with vehicle or losartan (10 mg/kg per day p.o.). CH was induced by subdiaphragmatic aortic coarctation, and the treatments lasted 8 days (4 control and 4 experimental days). Aortic pressure (conscious rats) and aortic nerve activity simultaneous to pressure (anesthetized rats) were recorded on the fourth day of the experimental period. Losartan-treated rats showed reduced tail pressure (104+/-3 versus 117+/-3 mm Hg in the vehicle group). In both groups, aortic coarctation caused a significant increase in pressure (25% and 28%, respectively) and a depression of the aortic nerve activity/pressure relationship when compared with sham-operated coarcted animals. In the physiological range of pressure changes, the depression was significantly smaller after losartan treatment (3.30+/-0.33 versus 2.18+/-0.37%/mm Hg in the losartan- and vehicle-treated CH groups, respectively, versus 5.05+/-0.33%/mm Hg in the sham-operated vehicle-treated group). Angiotensin type 1 (AT1) receptor blockade was also accompanied by reduced variability of the afferent discharge. The data suggested that apart from its pressure effect, angiotensin II acts at AT1 receptors to decrease the sensitivity of aortic afferents during physiological (+/-10 mm Hg) increases and decreases in pressure. Thus, angiotensin II may contribute to reductions of baroreceptor gain in chronic hypertension.

Effects and tolerability of irbesartan versus enalapril in patients with severe hypertension. Irbesartan Multicenter Investigators

In this double-blind, randomized study, an antihypertensive regimen based on irbesartan, an angiotensin II receptor antagonist, reduced systolic and diastolic blood pressure by 40/30 mm Hg at week 12 in patients with severe hypertension; this reduction was at least equivalent to that of a regimen using enalapril up to 40 mg. The irbesartan-based regimen had a better tolerability profile with fewer adverse events (55% vs 64%) and significantly less cough (2.5% vs 13.1%, p = 0.007).

Low-intensity exercise training decreases cardiac output and hypertension in spontaneously hypertensive rats

The decrease in cardiac sympathetic tone and heart rate after low-intensity exercise training may have hemodynamic consequences in spontaneously hypertensive rats (SHR). The effects of exercise training of low and high intensity on resting blood pressure, cardiac output, and total peripheral resistance were studied in sedentary (n = 17), low- (n = 17), and high-intensity exercise-trained (n = 17) SHR. Exercise training was performed on a treadmill for 60 min, 5 times per week for 18 weeks, at 55% or 85% maximum oxygen uptake. Blood pressure was evaluated by a cannula inserted into the carotid artery, and cardiac output was evaluated by a microprobe placed around the ascending aorta. Low-intensity exercise-trained rats had a significantly lower mean blood pressure than sedentary and high-intensity exercise-trained rats (160 +/- 4 vs. 175 +/- 3 and 173 +/- 2 mmHg, respectively). Cardiac index (20 +/- 1 vs. 24 +/- 1 and 24 +/- 1 ml.min-1 x 100 g-1, respectively) and heart rate (332 +/- 6 vs. 372 +/- 14 and 345 +/- 9 beats/min, respectively) were significantly lower in low-intensity exercise-trained rats than in sedentary and high-intensity exercise-trained rats. No significant difference was observed in stroke volume index and total peripheral resistance index in all groups studied. In conclusion, low-intensity, but not high-intensity, exercise training decreases heart rate and cardiac output and, consequently, attenuates hypertension in SHR.

Hemodynamics of chemoreflex activation in unanesthetized rats

Experiments were performed on unanesthetized rats (n=6) to determine the systemic hemodynamics during chemoreflex activation by intravenous KCN. Rats chronically instrumented with ultrasonic flow probes in the ascendant aorta were submitted to KCN injections (30 microg/kg) before and after sequential administration of the autonomic blockers atropine and propranolol. In the control period KCN injections produced a 60% reduction in heart rate (HR) and a 46% elevation in blood pressure (BP), while cardiac output (CO) decreased 76%, stroke volume (SV) decreased 40%, and calculated total peripheral resistance (TPR) increased 900%. Atropine administration increased resting HR, whereas no change was observed in CO or BP. Chemoreflex-induced bradycardia was markedly attenuated (26%), and the pressor response was potentiated (59%) after atropine administration. CO and TPR responses were both attenuated after atropine administration (68% and 718%, respectively). Sequential administration of propranolol decreased HR but did not change the cardiovascular responses to KCN injections compared with the responses observed after atropine administration. In conclusion, CO is greatly reduced during KCN-evoked chemoreflex. Besides the intense bradycardia, a decrease in SV contributed to this reduction. Bradycardic response was most dependent on the cardiac parasympathetic activation, and the reduction in SV was probably most dependent on the increased cardiac afterload due to the sudden increase in BP.

Lipid metabolism alterations in normotensive subjects with positive family history of hypertension

Metabolic abnormalities are usually reported in hypertensive patients. These metabolic alterations seem to begin in childhood. The young offspring of hypertensive parents have not been studied thoroughly for metabolic alterations. The aim of this study was to examine the level of total cholesterol, LDL cholesterol, VLDL cholesterol, HDL cholesterol, uric acid, glycemia, aldosterone, and plasma renin activity in a population of 42 young, slender normotensive subjects with positive family history of hypertension (FH+) or negative family history of hypertension (FH-). Measurements were made in 20 young normotensive subjects (age 21.1+/-2.2 years, 11 males, 15 white, 5 oriental, body mass index of 22.1+/-2.3 kg/m2) with FH+ and 22 young normotensive subjects (age 19.9+/-1.4 years, 17 males, 17 white, 5 oriental, body mass index of 22.1+/-2.3 kg/m2) with FH-. The total cholesterol (4.47+/-0.8 versus 3.95+/-0.6 mmol/L), LDL cholesterol (2.74+/-0.63 versus 2.36+/-0.61 mmol/L), VLDL cholesterol (0.5+/-0.25 versus 0.35+/-0.09 mmol/L), and triglycerides (2.52+/-1.26 versus 1.76+/-0.5 mmol/L) were significantly elevated (P<.05) in the FH+ group compared with the FH- group. The total cholesterol/HDL cholesterol ratio was significantly higher in the group with a positive family history of hypertension (3.75+/-0.02 versus 3.11+/-0.02, P<.05). Glycemia was slightly elevated in the FH+ group (2.16+/-0.29 mmol/L) but was not significantly different from that of the FH- group (2+/-0.2 mmol/L). Uric acid, plasma renin activity, and aldosterone were similar in both groups. We conclude that young, slender normotensive subjects with a positive history of hypertension show alterations in lipid metabolism, suggesting a positive correlation between lipid metabolism and hypertension heredity.

Acute and chronic effects of exercise on baroreflexes in spontaneously hypertensive rats

We studied the effects of acute and chronic exercise on the arterial baroreflex and chemosensitive cardiopulmonary baroreflex (CCB) in spontaneously hypertensive rats (SHR). Arterial baroreflex and CCB were evaluated in normotensive rats (NR, n=11) and SHR (n=5) at rest and after 30 minutes of an acute bout of exercise (45 minutes at 50% of VO2max). In addition, these baroreflexes were evaluated in sedentary (n=5) and exercise-trained (n=9) SHR. Exercise training was performed on a motor treadmill, 5 days/week, during 60 minutes, at 50% of VO2max. Baroreflex bradycardia and tachycardia, analyzed by baroreflex sensitivity index (delta heart rate/delta mean arterial pressure), were significantly lower in SHR than in NR (0.7+/-0.1 versus 2.0+/-0.1 and 1.8+/-0.2 versus 3.4+/-0.1 beats per minute [bpm]/mm Hg, respectively). During the recovery period from acute exercise, baroreflex bradycardia was significantly higher than at rest only in SHR (1.7+/-0.1 versus 0.7+/-0.1 bpm/mm Hg). Hypotension and bradycardia induced by CCB stimulation (5-hydroxytryptamine, I.V.) were similar between SHR and NR, and an acute exercise bout did not change these responses. Exercise training markedly improved baroreflex bradycardia and tachycardia in SHR (1.9+/-0.1 versus 0.7+/-0.1 and 2.9+/-0.1 versus 1.8+/-0.2 bpm/mm Hg, respectively). Exercise-trained rats had greater bradycardiac (118+/-26 versus 14+/-2 and 209+/-30 versus 19+/-5 bpm to 1 and 2 microg/kg 5-HT, respectively) and hypotensive (30+/-6 versus 15+/-3 and 45+/-7 versus 17+/-2 mm Hg to 1 and 2 microg/kg 5-hydroxytryptamine, respectively) responses to CCB stimulation. In conclusion, an acute bout of exercise increases baroreflex bradycardia in SHR, and exercise training attenuates hypertension concomitant with improved arterial baroreflex and CCB sensitivity in SHR.

In vivo adaptive responses of the aorta to hypertension and aging

To investigate the dynamic behavior of the aorta of freely moving rats during the maintenance of hypertension, a longitudinal study was performed in renal hypertensive (Goldblatt 1 kidney, 1 clip) rats aged 3, 6, and 9 mo in which hypertension was maintained for 1, 3, and 6 mo, respectively. The pulsatile caliber of the thoracic aorta was measured (electrolytic strain gauge chronically implanted) simultaneously with aortic pressure under basal conditions and during transient changes of blood pressure. Aortic thickness was determined postmortem by morphometry. Establishment of hypertension (179 +/- 5 mmHg) by increasing the stress developed by the aorta caused increases in the resting values of caliber (20%), thickness (21%), and strain (95%); the maintenance of hypertension for a 6-mo period caused a further increase in thickness (58% vs. age-matched normotensive aortas) but not in aortic caliber and strain, the subsequent alterations of which were due only to growth/aging. Although different calibers, thicknesses, and dynamic strains were presented, the stress-strain relationship during transient blood pressure changes was similar for all hypertensive and normotensive groups with the exception of renal hypertensive rats aged 6 mo, which presented a steeper relationship (a large transitory increase in aortic distensibility was observed at that age). Dynamic adaptive responses of the aorta to hypertension compensate for geometric changes in such a way as to maintain a near-constant distensibility. It was concluded that, in contrast to the extrathoracic vessels, the adaptive responses of the aorta to hypertension were directed to maintain its compliance without changing the distensibility and stress-strain relationship, contributing to partially counterbalance the increased pressure and the decreased compliance of the more peripheral components of the arterial tree.

Early elevation of lipoprotein(a) levels in chronic renal insufficiency

Serum lipoprotein(a) [Lp(a)] concentrations in chronic renal failure patients were investigated in relation to the degree of renal insufficiency, treatment by maintenance hemodialysis, and correction of uremia by renal transplantation with or without cyclosporin immunosuppression. Fast serum levels of Lp(a) (mg/100 mL) were determined in 34 chronic renal failure patients not in need of maintenance dialysis (16 with serum creatinine 2.0-4.0 mg/100 mL; 18 with serum creatinine higher than 4.0 mg/100 mL), 40 patients treated by hemodialysis, 55 successful renal transplant recipients (28 under cyclosporin treatment and 27 receiving no cyclosporin), and 34 healthy controls. Age and sex distributions were similar among groups. Pregnant women; non-White individuals; subjects with obesity, diabetes, nephrotic syndrome, and hepatic and thyroid diseases; and those treated with oral contraceptives or lipid-lowering drugs were excluded from the study. Compared to controls, median Lp(a) was increased in nondialyzed renal failure patients (11 vs. 47.5 p < 0.001) and this was the only lipid abnormally observed in the group. There was no significant difference in Lp(a) levels between nondialized renal failure patients with serum creatinine 2.0-4.0 and > 4.0 mg/100 mL (47 vs. 49, NS). Moreover, Pearson correlation coefficient (r = 0.01, NS) showed that Lp(a) values were not related to serum creatinine in nondialyzed patients, In hemodialysis subjects Lp(a) concentrations (median = 29) were intermediate between those observed in nondialyzed patients and controls but the differences were not significant. Lp(a) levels in renal transplant patients treated with cyclosporin (median = 6) and not receiving cyclosporin (median = 13) were similar and did not differ from controls. Serum Lp(a) increases and attains maximum levels with mild/moderate reduction in renal function, and does not seem to change through late renal failure stages or in relation to the introduction of maintenance hemodialysis treatment. Correction of uremia by successful renal transplant caused normalization of Lp(a) levels regardless of the use of cyclosporin. Increased Lp(a) levels may be the earliest and more consistent lipid alteration seen in predialysis renal failure.

Viscoelastic mechanisms of aortic baroreceptor resetting to hypotension and to hypertension

Viscoelastic and electrophysiological mechanisms have been implicated in the resetting of baroreceptors in hypertension, but resetting in response to hypotension has been less studied. To evaluate the temporal relationship between viscoelastic mechanisms and acute resetting, we examined the "in vivo" behavior of aortic caliber and aortic baroreceptor activity during step changes in pressure. Fifteen-minute hemorrhage in Wistar rats produced stable hypotension (30 mmHg) and viscoelastic contraction (111 +/- 14.2 microns systolic caliber; P < 0.01). Integrated aortic activity fell to 19.8 +/- 3.9% of control (P < 0.001) after 3 s of hypotension but recovered to 64 +/- 4.1% 15 min later (P < 0.01 from 3 s). Recovery of baroreceptor activity was linearly correlated to viscoelastic contraction (r = 0.963; P < 0.0001). Thirty-minute phenylephrine infusion (1.0-4.0 micrograms/min) produced stable hypertension (30 mmHg) and viscoelastic dilation (211 +/- 37.0 microns systolic caliber). Integrated aortic activity increased to 218.0 +/- 18% of control values (P < 0.001) 30 s after hypertension and was reduced to 164.0 +/- 12.0% (P < 0.001 from 3 s) within 30 min. Reduction of baroreceptor activity correlated linearly with viscoelastic relaxation (r = 0.963; P < 0.0001). The results indicate that in the in vivo rat aorta, viscoelastic mechanisms parallel and may contribute to the baroreceptor resetting during hypotension and hypertension.

Arterial blood pressure and left ventricular hypertrophy in haemodialysis patients

OBJECTIVE

To test the hypothesis that there is an association between arterial blood pressure and left ventricular hypertrophy and patterns of ventricular geometry, defined echocardiographically, in a group of stable haemodialysis patients with a low prevalence of extrarenal diseases.

DESIGN AND METHODS

Patients with end-stage renal failure treated by regular haemodialysis (aged 44.3 +/- 12.9 years, n = 103, among whom 52 men and 23 blacks, dialysis duration 49.8 +/- 35.3 months) were subjected to echocardiographic evaluation (M-mode, bidimensional and Doppler) on the day preceding dialysis. The average of all predialysis blood pressure determinations during the 3 months preceding the tests (34-38 determinations in each patient) were used as baseline data. Univariate and multivariate tests were used to assess the main variables associated with echocardiographically defined cardiac alterations and with patterns of ventricular geometry.

RESULTS

The systolic blood pressure was significantly associated with the left ventricular mass index and was significantly and independently correlated with left ventricular hypertrophy, posterior wall hypertrophy, left ventricle dilation and increased relative wall thickness. Other significant correlations were between the haematocrit level and left ventricular hypertrophy and between age and altered systolic and diastolic functions. Concentric ventricular hypertrophy was observed only in patients with a history of hypertension, whereas the prevalence of normal geometry was higher in patients without a history of hypertension.

CONCLUSION

The systolic blood pressure is an important factor influencing the occurrence of left ventricular hypertrophy in haemodialysis patients and also affects the left ventricle geometry in this population.

Alterations in the cardiovascular control by the chemoreflex and the baroreflex in old rats

The aging process is associated with alterations in the autonomic control of cardiovascular function. In the present study, we observed that reflex bradycardia and tachycardia produced by pressor and depressor agents were attenuated in old (24 mo) rats [70 and 56% of responses in young rats (4 mo), respectively]. In contrast, the bradycardia induced by chemoreflex activation with increasing doses of KCN (60, 100, 140, and 180 micrograms/kg) was greater in old [-30 +/- 19, -155 +/- 32, -198 +/- 15, and -204 +/- 24 beats/ min (bpm)] than in young rats [-13 +/- 6, -75 +/- 20 (P < 0.05), -99 +/- 26 (P < 0.05), and -103 +/- 20 (P < 0.05) bpm]. The chemoreflex-pressor responses tended to be greater in old (12 +/- 6, 47 +/- 6, 54 +/- 7, and 55 +/- 5 mmHg) than in young rats (4 +/- 2, 32 +/- 8, 42 +/- 6, and 44 +/- 4 mmHg), but the differences between both groups were not statistically significant. However, pressor responses were higher in old rats after the chemoreflex-activated bradycardia was attenuated by atropine (4 mg/kg iv) [old (17 +/- 9(1) P < 0.05; 57 +/- 4, P < 0.05; 61 +/- 4; and 64 +/- 5 mmHg) vs. young (3 +/- 2, 29 +/- 9(1) 50 +/- 5, and 58 +/- 7 mmHg)]. Administration of the alpha 1-blocker prazosin (1 mg/kg iv) blunted pressor responses but did not change the bradycardia induced by chemoreflex in both groups. In conclusion, our data indicate that the bradycardia and pressor responses to chemoreflex activation were exaggerated, whereas the heart rate responses (bradycardia and tachycardia) to baroreflex were depressed in old rats.

Malignant hypertension is accompanied by marked alterations in chylomicron metabolism

Malignant hypertension (MH) is a severe complication of untreated arterial hypertension that damages the vascular system. It is often accompanied by disturbances in lipid metabolism that could contribute to its pathophysiology. We examined chylomicron metabolism in MH patients using a triglyceride-rich emulsion known to mimic natural chylomicrons when injected into the bloodstream. The emulsion was labeled with [3H]triolein and [14C]cholesteryl oleate and injected intravenously into 15 normolipidemic MH patients aged 29 to 56 years (8 men) for comparison with 17 healthy control subjects. Consecutive plasma samples were taken at regular intervals during 1 hour for determination of the disappearance curves of the labels. The fractional clearance rate of the [3H]triolein emulsion in MH patients was twice as small as that of control subjects (0.061 +/- 0.012 and 0.141 +/- 0.074 min-1, respectively). On the other hand, [14C]cholesteryl oleate fractional clearance rate was not statistically different in MH patients and control subjects (0.032 +/- 0.004 and 0.056 +/- 0.014 min-1, respectively). These results indicate that in MH, lipolysis (measured by the fractional clearance rate of [3H]triolein) is pronounced diminished, whereas the removal of the remnant particles (measured by the fractional clearance rate of [14C]cholesteryl oleate) is not importantly affected. In conclusion, there is an alteration in the circulatory transport of dietary lipids that may be an important component in the vascular disease associated with MH.

Changes of renal sympathetic activity in acute and chronic conscious sinoaortic denervated rats

The arterial pressure level attained in sinoaortic denervated rats depends on the net effect of eliminating excitatory and inhibitory influences (chemoreceptor and baroreceptor elimination, respectively). After sinoaortic denervation is completed, the hypertension usually observed within the first few days is followed by normotension at the chronic stages. In this work renal sympathetic nerve activity was measured in conscious, unrestrained rats 6 hours (acute) and 20 days (chronic) after sinoaortic denervation. Increased arterial pressure (154 +/- 10 versus 114 +/- 3 mm Hg in controls) and renal sympathetic nerve activity (32 +/- 5 versus 13 +/- 2 bars per cycle in controls) with no changes in heart rate (404 +/- 17 vs 380 +/- 26 beats per minute) were observed in rats with acute sinoaortic denervation. In rats with chronic sinoaortic denervation, arterial pressure (119 +/- 8 mm Hg) and renal sympathetic nerve activity (13 +/- 6 bars per cycle) returned to control levels. Bradycardiac and tachycardiac responses to changes in blood pressure were reduced to 88% and 89%, respectively, in rats with acute sinoaortic denervation and 76% and 74%, respectively, in rats with chronic sinoaortic denervation. The reflex control of renal sympathetic nerve activity after acute and chronic sinoaortic denervation showed an impairment of sympathoinhibition (0.13 +/- 0.02 and 0.25 +/- 0.1 bars per cycle, respectively, versus 0.9 +/- 0.17 bars per cycle in controls). Sympathoexcitatory responses also were impaired in rats with acute and chronic sinoaortic denervation (0.08 +/- 0.03 and 0.37 +/- 0.1 bars per cycle, respectively, compared with 0.98 +/- 0.2 bars per cycle in controls).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood pressure influences the occurrence of complex ventricular arrhythmia in hemodialysis patients

We investigated the relationship between blood pressure and the occurrence of complex ventricular arrhythmias (multiform, couplets, or runs) as assessed by 48-hour Holter monitoring in 74 stable long-term hemodialysis patients (44.5 +/- 12 years old; 54% men; 74% whites; dialysis duration, 51.3 +/- 36.1 months; systolic pressure, 146.6 +/- 19.3 mm Hg; diastolic pressure, 89.2 +/- 12.1 mm Hg; prevalence of arterial hypertension, 33.8%). Systolic and diastolic pressures represented the average of all predialysis determinations during the 3 months preceding the tests. Hemodialysis was performed midway through the Holter monitoring period. M-mode and bidimensional echocardiograms and myocardial perfusion tests were also obtained from all patients. Complex arrhythmias were observed in 37 individuals (50%). Univariate analysis showed that systolic pressure (P < .001), diastolic pressure (P < .05), age (P < .001), left ventricular posterior wall thickness (P < .01), left ventricular mass index (P < .05), and ischemic alterations on myocardial perfusion tests (P < .005) were significantly associated with complex arrhythmias. With the use of a multivariate model (stepwise logistic regression analysis) only systolic pressure (P < .01) and age (P < .05) were independently associated with complex arrhythmias. Sex; angina; dialysis duration; New York Heart Association functional class; use of digitalis; plasma levels of creatinine, sodium, potassium, calcium, and phosphate; hematocrit; left ventricular fractional shortening; left ventricular diastolic diameter; and ST segment deviation were not correlated with complex arrhythmias. The severity and frequency of complex arrhythmias were not influenced by hemodialysis. At follow-up (5 to 80 months) 5 patients had died of sudden death, 4 of whom were hypertensive and older than 45 years.(ABSTRACT TRUNCATED AT 250 WORDS)

Low-intensity exercise training attenuates cardiac beta-adrenergic tone during exercise in spontaneously hypertensive rats

Acute and chronic exercise decrease peripheral sympathetic nerve activity, but the effect of exercise training of varying intensity on the sympathetic control of heart rate of spontaneously hypertensive rats has not yet been described. The effect of low and high intensities of exercise training on the vagal and sympathetic activities that control heart rate at rest and during dynamic exercise at 0.5, 0.8, and 1.0 mph for 4 minutes per stage was investigated in sedentary (SED, n = 11), high-intensity (HT, n = 12), and low-intensity exercise-trained (LT, n = 13) spontaneously hypertensive rats. Exercise training was performed on a treadmill for 60 minutes, 5 days per week for 18 weeks, at 55% maximum oxygen consumption for the LT group and 85% for the HT group. Vagal and sympathetic activities were studied after administration of methylatropine (3 mg/kg) and propranolol (4 mg/kg), respectively. The LT group had a significantly lower heart rate (at 0.5, 0.8, 1.0 mph versus rest: 410 +/- 7, 464 +/- 9, and 295 +/- 6 beats per minute [bpm], respectively) than the HT (440 +/- 6, 453 +/- 7, 474 +/- 5, and 315 +/- 4 bpm) and the SED (474 +/- 11, 500 +/- 11, 523 +/- 10, and 327 +/- 3 bpm) groups. Sympathetic effect (LT: 84 +/- 10, 88 +/- 12, 105 +/- 12, and 9 +/- 4; HT: 123 +/- 8, 125 +/- 7, 133 +/- 7, and 34 +/- 7; SED: 130 +/- 13, 143 +/- 12, 150 +/- 10, and 38 +/- 7 bpm) and sympathetic tonus (LT: 125 +/- 6, 121 +/- 5, 112 +/- 6, and 91 +/- 6; HT: 145 +/- 9, 136 +/- 6, 142 +/- 8, and 118 +/- 7; SED: 136 +/- 6, 129 +/- 6, 132 +/- 7, and 118 +/- 8 bpm) were significantly decreased by low-intensity exercise training. In conclusion, low- but not high-intensity exercise training causes resting bradycardia and attenuation of tachycardiac response during progressive dynamic exercise in spontaneously hypertensive rats. This effect can be attributed to a significantly decreased beta-adrenergic tone that controls heart rate.