ProANP31-67 ameliorates adverse cardiac remodeling and improves systolic and diastolic functions in a preclinical model of cardiorenal syndrome

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): South-Eastern Norway Regional Health Authority (HSØ-RHF, Project No. 25674)

Background

The cardiac hormone proANP31-67, a linear fragment of the N-terminal Atrial Natriuretic Peptide, has known enhancing renal effects. More recently, we described the cardio protective effects of this hormone in a model of chronic hypertension. More specifically, independently of the blood pressure level, proANP31-67 improved diastolic function, attenuated cardiac fibrosis, and reduced hypertrophy.

Purpose

The current study was designed to assess the cardiorenal effects of proANP31-67 in a rodent model of hampered renal function, followed by cardiac injury produced by ischemia/reperfusion (I/R).

Methods

Right uninephrectomy (UNX) was performed in Wistar rats (n=28). Sixteen weeks after UNX, rats underwent cardiac I/R injury and randomly assigned to proANP31-67 (50 ng/kg/day s.c., n=15) or Vehicle (n=13) for four weeks post I/R. Echocardiographic examinations were performed at baseline (before UNX), 16 weeks after UNX, and four weeks after I/R. At the end of the study, cardiomyocytes were isolated and tissue samples were collected.

Results

Chronic UNX resulted in diastolic impairment (E/A: 1.47±0.08 at baseline vs 0.98±0.14 at 16 wks post UNX, p=0.0010). I/R further accentuated the development of the cardiorenal syndrome, and induced a mild systolic dysfunction in the placebo treated animals. However, four weeks of treatment with proANP31-67 preserved systolic function (EF: 62±3% placebo vs 74±2% proANP31-67, p<0.0001), and reverted the diastolic dysfunction (E/A: 0.72±0.15 placebo vs 1.24±0.11 proANP31-67, p=0.0134). ProANP31-67 ameliorated the adverse cardiac remodeling (i.e., reduction in the cardiomyocyte cross-sectional area and interstitial fibrosis), enhanced Ca2+ handling, and improved cardiomyocyte t-tubules´ structural changes compared to vehicle. At the cellular level, in vitro experiments demonstrated the direct effect of proANP31-67 on cardiomyocyte hypertrophy (assessed by [3H]-leucine incorporation) induced by endothelin 1 and angiotensin II.

Conclusion

ProANP31-67 has a direct cardiomyocyte protective effect, leading to an improvement in Ca2+ homeostasis and t-tubules´ structures and, prevents the development of systolic and diastolic dysfunction in a pre-clinical model of cardiorenal syndrome.

Etiology-Dependent Impairment of Diastolic Cardiomyocyte Calcium Homeostasis in Heart Failure With Preserved Ejection Fraction

BACKGROUND

Whereas heart failure with reduced ejection fraction (HFrEF) is associated with ventricular dilation and markedly reduced systolic function, heart failure with preserved ejection fraction (HFpEF) patients exhibit concentric hypertrophy and diastolic dysfunction. Impaired cardiomyocyte Ca²⁺ homeostasis in HFrEF has been linked to disruption of membrane invaginations called t-tubules, but it is unknown if such changes occur in HFpEF.

OBJECTIVES

This study examined whether distinct cardiomyocyte phenotypes underlie the heart failure entities of HFrEF and HFpEF.

METHODS

T-tubule structure was investigated in left ventricular biopsies obtained from HFrEF and HFpEF patients, whereas cardiomyocyte Ca²⁺ homeostasis was studied in rat models of these conditions.

RESULTS

HFpEF patients exhibited increased t-tubule density in comparison with control subjects. Super-resolution imaging revealed that higher t-tubule density resulted from both tubule dilation and proliferation. In contrast, t-tubule density was reduced in patients with HFrEF. Augmented collagen deposition within t-tubules was observed in HFrEF but not HFpEF hearts. A causative link between mechanical stress and t-tubule disruption was supported by markedly elevated ventricular wall stress in HFrEF patients. In HFrEF rats, t-tubule loss was linked to impaired systolic Ca²⁺ homeostasis, although diastolic Ca²⁺ removal was also reduced. In contrast, Ca²⁺ transient magnitude and release kinetics were largely maintained in HFpEF rats. However, diastolic Ca²⁺ impairments, including reduced sarco/endoplasmic reticulum Ca²⁺-ATPase activity, were specifically observed in diabetic HFpEF but not in ischemic or hypertensive models.

CONCLUSIONS

Although t-tubule disruption and impaired cardiomyocyte Ca²⁺ release are hallmarks of HFrEF, such changes are not prominent in HFpEF. Impaired diastolic Ca²⁺ homeostasis occurs in both conditions, but in HFpEF, this mechanism for diastolic dysfunction is etiology-dependent.

Cardiac LXRα protects against pathological cardiac hypertrophy and dysfunction by enhancing glucose uptake and utilization

Pathological cardiac hypertrophy is characterized by a shift in metabolic substrate utilization from fatty acids to glucose, but the molecular events underlying the metabolic remodeling remain poorly understood. Here, we investigated the role of liver X receptors (LXRs), which are key regulators of glucose and lipid metabolism, in cardiac hypertrophic pathogenesis. Using a transgenic approach in mice, we show that overexpression of LXRα acts to protect the heart against hypertrophy, fibrosis, and dysfunction. Gene expression profiling studies revealed that genes regulating metabolic pathways were differentially expressed in hearts with elevated LXRα. Functionally, LXRα overexpression in isolated cardiomyocytes and murine hearts markedly enhanced the capacity for myocardial glucose uptake following hypertrophic stress. Conversely, this adaptive response was diminished in LXRα-deficient mice. Transcriptional changes induced by LXRα overexpression promoted energy-independent utilization of glucose via the hexosamine biosynthesis pathway, resulting in O-GlcNAc modification of GATA4 and Mef2c and the induction of cytoprotective natriuretic peptide expression. Our results identify LXRα as a key cardiac transcriptional regulator that helps orchestrate an adaptive metabolic response to chronic cardiac stress, and suggest that modulating LXRα may provide a unique opportunity for intervening in myocyte metabolism.

Preservation of cardiac function in left ventricle cardiac hypertrophy using an AAV vector which provides VEGF-A expression in response to p53

Here we present the application of our adeno-associated virus (AAV2) vector where transgene expression is driven by a synthetic, p53-responsive promoter, termed PG, used to supply human vascular endothelial growth factor-A165 (VEGF-A). Thus, p53 is harnessed to promote the beneficial expression of VEGF-A encoded by the AAVPG vector, bypassing the negative effect of p53 on HIF-1α which occurs during cardiac hypertrophy. Wistar rats were submitted to pressure overload induced by thoracic aorta coarctation (TAC) with or without concomitant gene therapy (intramuscular delivery in the left ventricle). After 12 weeks, rats receiving AAVPG-VEGF gene therapy were compared to those that did not, revealing significantly improved cardiac function under hemodynamic stress, lack of fibrosis and reversal of capillary rarefaction. With these functional assays, we have demonstrated that application of the AAVPG-VEGF vector under physiologic conditions known to stimulate p53 resulted in the preservation of cardiac performance.

Reversible pulmonary trunk banding: VII. Stress echocardiographic assessment of rapid ventricular hypertrophy in young goats

BACKGROUND

Ventricle retraining with abrupt systolic overload can cause myocardial edema and necrosis, followed by late ventricular failure. Intermittent systolic overload could minimize the inadequacy of conventional pulmonary artery banding. The present study compared ventricle function under dobutamine stress in 2 protocols of systolic overload in young goats.

METHODS

Nineteen young goats were divided into 3 groups: sham (n = 7; no systolic pressure overload), continuous (n = 6; systolic overload maintained for 96 hours), and intermittent (n = 6; 4 periods of 12-hour systolic overload, paired with a 12-hour resting period). Echocardiographic and hemodynamic evaluations were performed daily. The myocardial performance index and ejection fraction were evaluated at rest and during dobutamine stress. The goats were then killed for morphologic evaluation.

RESULTS

The intermittent group underwent less systolic overload than the continuous group (P < .05). Nevertheless, both groups had increased right ventricular and septal masses compared with the sham group (P < .0002). Echocardiography revealed a major increase in right ventricular wall thickness in the intermittent group (+64.8% ± 23.37%) compared with the continuous group (+43.9% ± 19.26%; P = .015). Only the continuous group remained with significant right ventricular dilation throughout the protocol (P < .001). The intermittent group had a significantly better myocardial performance index at the end of the protocol, under resting and dobutamine infusion, compared with the continuous group (P < .012).

CONCLUSIONS

Both systolic overload protocols have induced rapid right ventricular hypertrophy. However, only the intermittent group had better preservation of right ventricular function at the end of the protocol, both at rest and during dobutamine infusion.

Reversible pulmonary trunk banding. VI: Glucose-6-phosphate dehydrogenase activity in rapid ventricular hypertrophy in young goats

OBJECTIVE

Increased myocardial glucose-6-phosphate dehydrogenase (G6PD) activity occurs in heart failure. This study compared G6PD activity in 2 protocols of right ventricle (RV) systolic overload in young goats.

METHODS

Twenty-seven goats were separated into 3 groups: sham (no overload), continuous (continuous systolic overload), and intermittent (four 12-hour periods of systolic overload paired with a 12-hour resting period). During a 96-hour protocol, systolic overload was adjusted to achieve a 0.7 RV/aortic pressure ratio. Echocardiographic and hemodynamic evaluations were performed before and after systolic overload every day postoperatively. After the study period, the animals were humanely killed for morphologic and G6PD tissue activity assessment.

RESULTS

A 92.1% and 46.5% increase occurred in RV and septal mass, respectively, in the intermittent group compared with the sham group; continuous systolic overload resulted in a 37.2% increase in septal mass. A worsening RV myocardial performance index occurred in the continuous group at 72 hours and 96 hours, compared with the sham (P < .039) and intermittent groups at the end of the protocol (P < .001). Compared with the sham group, RV G6PD activity was elevated 130.1% in the continuous group (P = .012) and 39.8% in the intermittent group (P = .764).

CONCLUSIONS

Continuous systolic overload for ventricle retraining causes RV dysfunction and upregulation of myocardial G6PD activity, which can elevate levels of free radicals by NADPH oxidase, an important mechanism in the pathophysiology of heart failure. Intermittent systolic overload promotes a more efficient RV hypertrophy, with better preservation of myocardial performance and and less exposure to hypertrophic triggers.

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.

Cuff-induced vascular intima thickening is influenced by titration of the Ace gene in mice

We tested the hypothesis that small changes in angiotensin I-converting enzyme (ACE) expression can alter the vascular response to injury. Male mice containing one, two, three, and four copies of the Ace gene with no detectable vascular abnormality or changes in blood pressure were submitted to cuff-induced femoral artery injury. Femoral thickening was higher in 3- and 4-copy mice (42.4 ± 4.3% and 45.7 ± 6.5%, respectively) compared with 1- and 2-copy mice (8.3 ± 1.3% and 8.5 ± 0.9%, respectively). Femoral ACE levels from control and injured vessels were assessed in 1- and 3-copy Ace mice, which represent the extremes of the observed response. ACE vascular activity was higher in 3- vs. 1-copy Ace mice (2.4-fold, P < 0.05) in the control uninjured vessel. Upon injury, ACE activity significantly increased in both groups [2.41-fold and 2.14-fold ( P < 0.05) for 1- and 3-copy groups, respectively] but reached higher levels in 3- vs. 1-copy Ace mice ( P < 0.05). Pharmacological interventions were then used as a counterproof and to indirectly assess the role of angiotensin II (ANG II) on this response. Interestingly, ACE inhibition (enalapril) and ANG II AT1 receptor blocker (losartan) reduced intima thickening in 3-copy mice to 1-copy mouse values ( P < 0.05) while ANG II treatment significantly increased intima thickening in 1-copy mice to 3-copy mouse levels ( P < 0.05). Together, these data indicate that small physiologically relevant changes in ACE, not associated with basal vascular abnormalities or blood pressure levels, do influence the magnitude of cuff-induced neointima thickening in mice.

[IV Pulmonary trunk reversible banding: analysis of right ventricle acute hypertrophy in an intermittent loading experimental model]

OBJECTIVES

Adjustable pulmonary trunk (PT) banding device may induce a more physiologic ventricle retraining for the two-stage Jatene operation. This experimental study evaluates the acute hypertrophy (96 hours) of the right ventricle (RV) submitted to an intermittent pressure overload.

METHODS

Five groups of seven young goats were distributed according to RV intermittent systolic overload duration (0, 24, 48, 72 and 96 hours). The zero-hour group served as a control group. Echocardiographic and hemodynamic evaluations were performed daily. After completing the training program for each group, the animals were sacrificed for water content and cardiac masses evaluation.

RESULTS

There was a significant increase in RV free wall thickness starting with the 48-hour group (p<0.05). However, a decreased RV ejection fraction, associated with an important RV dilation and a significant increase in the RV volume to mass ratio was observed at 24-hour training period, when compared to 96-hour period (p=0.003), with subsequent recovery throughout the protocol. A 104.7% increase in RV mass was observed in the 96-hour group, as compared to the control group, with no differences in water content between these two groups. The daily mean increase in RV mass during the study period was 21.6% +/- 26.8%. The rate of RV mass acquisition for the overall study period of intermittent systolic overload was 0.084 g/h +/- 0.035 g/h.

CONCLUSION

Intermittent PT banding has allowed a significant RV mass acquisition in the 96-hour trained group. No myocardial water content changes were observed in this group, suggesting an increased myocardial protein synthesis.

Association between glutathione S-transferase polymorphisms and triglycerides and HDL-cholesterol

OBJECTIVE

Null genotypes of glutathione S-transferase (GSTs) exhibit absence of enzymatic activity and are hypothesized to modulate an increased risk of developing cardiovascular disease. The aim of this study was to identify the potential association between GSTM1 and GSTT1 deleted polymorphisms with cardiovascular risk factors and coronary atherosclerosis in two independent urban populations.

METHODS AND RESULTS

Genotype distribution of GSTM1 and GSTT1 deleted polymorphism were examined in a sample of 1577 individuals from the general population and a replication sample of 871 individuals submitted to coronary angiography. Triglycerides, HDL-cholesterol and the triglycerides/HDL ratio were significantly associated with a double-deleted genotype in individuals from the general population. These findings were replicated in a second, independent, population of individuals submitted to coronary angiography. In addition, coronary artery disease severity was also associated with GSTs genotypes and the risk conferred from GSTs genotype was mainly due to triglycerides/HDL ratio information.

CONCLUSIONS

The data suggest that the presence of a double deletion genotypes of the GSTM1 and GSTT1 genes is associated with hypertriglyceridemia and low HDL-cholesterol levels in humans. These novel findings may provide a new unexplored link between lipid metabolism and GST homeostasis.

Congenic strains provide evidence that four mapped loci in chromosomes 2, 4, and 16 influence hypertension in the SHR

To dissect the genetic architecture controlling blood pressure (BP) regulation in the spontaneously hypertensive rat (SHR) we derived congenic rat strains for four previously mapped BP quantitative trait loci (QTLs) in chromosomes 2, 4, and 16. Target chromosomal regions from the Brown Norway rat (BN) averaging 13-29 cM were introgressed by marker-assisted breeding onto the SHR genome in 12 or 13 generations. Under normal salt intake, QTLs on chromosomes 2a, 2c, and 4 were associated with significant changes in systolic BP (13, 20, and 15 mmHg, respectively), whereas the QTL on chromosome 16 had no measurable effect. On high salt intake (1% NaCl in drinking water for 2 wk), the chromosome 16 QTL had a marked impact on SBP, as did the QTLs on chromosome 2a and 2c (18, 17, and 19 mmHg, respectively), but not the QTL on chromosome 4. Thus these four QTLs affected BP phenotypes differently: 1) in the presence of high salt intake (chromosome 16), 2) only associated with normal salt intake (chromosome 4), and 3) regardless of salt intake (chromosome 2c and 2a). Moreover, salt sensitivity was abrogated in congenics SHR.BN2a and SHR.BN16. Finally, we provide evidence for the influence of genetic background on the expression of the mapped QTLs individually or as a group. Collectively, these data reveal previously unsuspected nuances of the physiological roles of each of the four mapped BP QTLs in the SHR under basal and/or salt loading conditions unforeseen by the analysis of the F2 cross.

Effects of sinoaortic denervation on hemodynamic parameters during natural sleep in rats

STUDY OBJECTIVES

To analyze the role of arterial baroreflex on hemodynamic changes during synchronized and desynchronized sleep phases of natural sleep in rats.

DESIGN

Experimental study.

SETTING

Laboratory.

PARTICIPANTS

Seventeen male Wistar rats.

INTERVENTIONS

No intervention (control, n = 8) or sinoaortic denervation (SAD, n = 9).

MEASUREMENTS AND RESULTS

Sleep phases were monitored by electrocorticogram, and blood pressure was measured directly by a catheter in the carotid artery. Cardiac output, as well as total and regional vascular resistances, were determined by measuring the subdiaphragmatic aorta and iliac artery flows with Doppler flow probes, respectively. In contrast to the control group, the SAD group had a strong reduction in blood pressure (-19.9% +/- 2.6% vs -0.7% +/- 2.1%) during desynchronized sleep, and cardiac output showed an exacerbated reduction (-10.4% +/- 3.5% vs 1.1% +/- 1.7%). In SAD rats, total vascular resistance decreased during desynchronized sleep (-10.1% +/- 3.5% vs -1.0% +/- 1.7%), and the increase in regional vascular resistance observed in the control group was abolished (27.5% +/- 8.3% vs -0.8% +/- 9.4%).

CONCLUSIONS

SAD caused profound changes in blood pressure, cardiac output, and total vascular resistance, with a significant increase in muscle vascular resistance during synchronized sleep. Our results suggest that baroreflex plays an important role in maintaining the normal balance of cardiac output and total vascular resistance during sleep.

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.

ACE gene dosage modulates pressure-induced cardiac hypertrophy in mice and men

The influence of genetic factors on complex phenotypes is context dependent, posing a challenge to quantify the role of single gene variants on this process. Moreover, redundancy and reserve capacity among control systems prevent most physiological stimuli to destabilize these processes. To test whether small gene perturbation can disrupt this equilibrium under pathological conditions, mice harboring one, two, or three copies of the angiotensin converting enzyme ( Ace) gene were submitted to 3 and 6 wk of pressure overload (PO). Direct systolic blood pressure (SBP), as an index of cardiac afterload, and left ventricle mass index (LVMI) were measured. LVMI under normotension was the same regardless of the Ace genotype, but the slopes of the LVMI/SBP curves increased in the three- vs. one-copy group by ∼50% upon 3- or 6-wk PO. Angiotensin II AT1 receptor blocker treatment produced a significant pressure independent decrease in the LVMI/SBP ratio. Unlike the one-copy group, PO resulted in a significant reduction in angiotensinogen and an increase in Ace mRNA expression accompanied by an increase in cardiac angiotensin II levels in the three-copy group. Similarly, the human ACE D gene variant influenced cardiac mass, estimated by Sokolov-Lyon index, in a sample of 1,507 individuals from an urban population only in individuals in the 4th quartile of the blood pressure distribution. Collectively, these data provide direct evidence that ACE gene dosage per se does not influence cardiac mass but upon a pathological stimulus, such as elevation in blood pressure, it modulates cardiac mass in both mice and humans.

Exercise training improves aortic depressor nerve sensitivity in rats with ischemia-induced heart failure

Exercise training improves arterial baroreflex control in heart failure (HF) rabbits. However, the mechanisms involved in the amelioration of baroreflex control are unknown. We tested the hypothesis that exercise training would increase the afferent aortic depressor nerve activity (AODN) sensitivity in ischemic-induced HF rats. Twenty ischemic-induced HF rats were divided into trained ( n = 11) and untrained ( n = 9) groups. Nine normal control rats were also studied. Power spectral analysis of pulse interval, systolic blood pressure, renal sympathetic nerve activity (RSNA), and AODN were analyzed by means of autoregressive parametric spectral and cross-spectral algorithms. Spontaneous baroreflex sensitivity of heart rate (HR) and RSNA were analyzed during spontaneous variation of systolic blood pressure. Left ventricular end-diastolic pressure was higher in HF rats compared with that in the normal control group ( P = 0.0001). Trained HF rats had a peak oxygen uptake higher than untrained rats and similar to normal controls ( P = 0.01). Trained HF rats had lower low-frequency [1.8 ± 0.2 vs. 14.6 ± 3 normalized units (nu), P = 0.0003] and higher high-frequency (97.9 ± 0.2 vs. 85.0 ± 3 nu, P = 0.0005) components of pulse interval than untrained rats. Trained HF rats had higher spontaneous baroreceptor sensitivity of HR (1.19 ± 0.2 vs. 0.51 ± 0.1 ms/mmHg, P = 0.003) and RSNA [2.69 ± 0.4 vs. 1.29 ± 0.3 arbitrary units (au)/mmHg, P = 0.04] than untrained rats. In HF rats, exercise training increased spontaneous AODN sensitivity toward normal levels (trained HF rats, 1,791 ± 215; untrained HF rats, 1,150 ± 158; and normal control rats, 2,064 ± 327 au/mmHg, P = 0.05). In conclusion, exercise training improves AODN sensitivity in HF rats.

Exercise Training Improves the Depressed Sensitivity of the Baroreceptors in Spontaneously Hypertensive Rats

P43

We have previously demonstrated that low-intensity exercise traning (ET) diminishes blood pressure and partially restores the sensitivity of the baroreflex bradycardia and tachycardia that are depressed in spontaneously hypertensive rats (SHR). Presently, the influence of the exercise trainig (ET) on the afferent part of the baroreflex (baroreceptor function curve) and its implication on the baroreflex was analysed in SHR and in normal control rats (NCR). NCR and SHR were subdivided in sedentary (S) and ET groups: SHR-S (n=8) and SHR-ET (n=6), and NCR-S (n=8) and NCR-ET (n=8). ET was performed on treadmill, during 60 min, 5 days/wk, at 50% of VO 2 max, for 12 wk. Arterial baroreflex sensitivity was evaluated by bradycardiac responses to phenylephrine (0.5;1;2;4;8 and 16 μg/ml, i.v.) and tachycardiac responses to sodium nitroprusside (0.5;1;2;4;8 and 16 μg/ml, i.v.). Aortic baroreceptor function curve was evaluated under pentobarbital anesthesia (40 mg/kg) during rapid variations of arterial pressure (AT/CODAS, 3kHz per channel). The relationship between changes in baroreceptor discharge (0-100%) and systolic arterial pressure was analysed using a sigmoidal regression. Mean arterial pressure was reduced in SHR-ET compared to SHR-S group (165±7 vs. 183±4 mmHg) but remained inaltared in NCR-ET compared to NCR-S (112±3 vs. 115±3 mmHg). In SHR, ET increased the sensitivity of baroreflex bradycardia (1.9±0.1 vs. 0.7±0.1 bpm.mmHg -1 ) and tachycardia (2.9±0.1 vs. 1.8±0.2 bpm.mmHg -1 ) which were depressed. In NCR-ET baroreflex bradycardia was decreased (1.4±0.1 vs. 1.7±0.1 bpm.mmHg -1 ) but baroreflex tachycardia was increased (4.6±0.5 vs. 3.0±0.2 bpm.mmHg -1 ). ET increased the aortic baroreceptor gaing-sensitivity in both groups: SHR (0.9±0.1 vs. 0.7±0.1 %.mmHg -1 ) and NCR (2.1±0.1 vs. 1.4±0.1 %.mm Hg -1 ). Conclusion:1. ET increases aortic baroreceptor gain-sensitivity in NCR as well in SHR; 2. The improvement of the baroreflex produced by ET in SHR is partially explainedd by the recovery of the baroreceptor sensitivity, which may also participate in the reduction of high blood pressure.