Exercise intolerance in rats with hypertensive heart disease is associated with impaired diastolic relaxation

Exercise intolerance in volume overload heart failure is associated with low carotid body mediated chemoreflex drive

Mounting an appropriate ventilatory response to exercise is crucial to meeting metabolic demands, and abnormal ventilatory responses may contribute to exercise-intolerance (EX-inT) in heart failure (HF) patients. We sought to determine if abnormal ventilatory chemoreflex control contributes to EX-inT in volume-overload HF rats. Cardiac function, hypercapnic (HCVR) and hypoxic (HVR) ventilatory responses, and exercise tolerance were assessed at the end of a 6 week exercise training program. At the conclusion of the training program, exercise tolerant HF rats (HF + EX-T) exhibited improvements in cardiac systolic function and reductions in HCVR, sympathetic tone, and arrhythmias. In contrast, HF rats that were exercise intolerant (HF + EX-inT) exhibited worse diastolic dysfunction, and showed no improvements in cardiac systolic function, HCVR, sympathetic tone, or arrhythmias at the conclusion of the training program. In addition, HF + EX-inT rats had impaired HVR which was associated with increased arrhythmia susceptibility and mortality during hypoxic challenges (~ 60% survival). Finally, we observed that exercise tolerance in HF rats was related to carotid body (CB) function as CB ablation resulted in impaired exercise capacity in HF + EX-T rats. Our results indicate that: (i) exercise may have detrimental effects on cardiac function in HF-EX-inT, and (ii) loss of CB chemoreflex sensitivity contributes to EX-inT in HF.

Calcium homeostasis behavior and cardiac function on left ventricular remodeling by pressure overload

Sarcoplasmic reticulum Ca²⁺-ATPase (SERCA2a) and sarcolemmal Na⁺/Ca²⁺ exchanger (NCX1) structures are involved in heart cell Ca²⁺ homeostasis. Previous studies have shown discrepancies in their function and expression in heart failure. The goal of this study was to evaluate heart function and hypertrophied muscle Ca²⁺-handling protein behavior under pressure overload. Twenty male Wistar rats were divided into two groups: Aortic stenosis (AoS), induced by a clip placed at the beginning of the aorta, and Control (Sham). After 18 weeks, heart function and structure were evaluated by echocardiogram. Myocardial function was analyzed by isolated papillary muscle (IPM) at basal condition and Ca²⁺ protein functions were evaluated after post-pause contraction and blockage with cyclopiazonic acid in IPM. Ca²⁺-handling protein expression was studied by western blot (WB). Echocardiogram showed that AoS caused concentric hypertrophy with enhanced ejection fraction and diastolic dysfunction inferred by dilated left atrium and increased relative wall thickness. IPM study showed developed tension was the same in both groups. AoS showed increased stiffness revealed by enhanced resting tension, and changes in Ca²⁺ homeostasis shown by calcium elevation and SERCA2a blockage maneuvers. WB revealed decreased NCX1, SERCA2a, and phosphorylated phospholambam (PLB) on serine-16 in AoS. AoS had left ventricular hypertrophy and diastolic dysfunction compared to Sham; this could be related to our findings regarding calcium homeostasis behavior: deficit in NCX1, SERCA2a, and phosphorylated PLB on serine-16.

Muscular changes in animal models of heart failure with preserved ejection fraction: what comes closest to the patient?

AIMS

Heart failure with preserved ejection fraction (HFpEF) is associated with reduced exercise capacity elicited by skeletal muscle (SM) alterations. Up to now, no clear medical treatment advice for HFpEF is available. Identification of the ideal animal model mimicking the human condition is a critical step in developing and testing treatment strategies. Several HFpEF animals have been described, but the most suitable in terms of comparability with SM alterations in HFpEF patients is unclear. The aim of the present study was to investigate molecular changes in SM of three different animal models and to compare them with alterations of muscle biopsies obtained from human HFpEF patients.

METHODS AND RESULTS

Skeletal muscle tissue was obtained from HFpEF and control patients and from three different animal models including the respective controls-ZSF1 rat, Dahl salt-sensitive rat, and transverse aortic constriction surgery/deoxycorticosterone mouse. The development of HFpEF was verified by echocardiography. Protein expression and enzyme activity of selected markers were assessed in SM tissue homogenates. Protein expression between SM tissue obtained from HFpEF patients and the ZSF1 rats revealed similarities for protein markers involved in muscle atrophy (MuRF1 expression, protein ubiquitinylation, and LC3) and mitochondrial metabolism (succinate dehydrogenase and malate dehydrogenase activity, porin expression). The other two animal models exhibited far less similarities to the human samples.

CONCLUSIONS

None of the three tested animal models mimics the condition in HFpEF patients completely, but among the animal models tested, the ZSF1 rat (ZSF1-lean vs. ZSF1-obese) shows the highest overlap to the human condition. Therefore, when studying therapeutic interventions to treat HFpEF and especially alterations in the SM, we suggest that the ZSF1 rat is a suitable model.

Distinct features of calcium handling and β-adrenergic sensitivity in heart failure with preserved versus reduced ejection fraction

Key points

Heart failure (HF), the leading cause of death in developed countries, occurs in the setting of reduced (HFrEF) or preserved (HFpEF) ejection fraction. Unlike HFrEF, there are no effective treatments for HFpEF, which accounts for ∼50% of heart failure.

Abnormal intracellular calcium dynamics in cardiomyocytes have major implications for contractility and rhythm, but compared to HFrEF, very little is known about calcium cycling in HFpEF.

We used rat models of HFpEF and HFrEF to reveal distinct differences in intracellular calcium regulation and excitation‐contraction (EC) coupling.

While HFrEF is characterized by defective EC coupling at baseline, HFpEF exhibits enhanced coupling fidelity, further aggravated by a reduction in β‐adrenergic sensitivity.

These differences in EC coupling and β‐adrenergic sensitivity may help explain why therapies that work in HFrEF are ineffective in HFpEF.

Abstract

Heart failure with reduced or preserved ejection fraction (respectively, HFrEF and HFpEF) is the leading cause of death in developed countries. Although numerous therapies improve outcomes in HFrEF, there are no effective treatments for HFpEF. We studied phenotypically verified rat models of HFrEF and HFpEF to compare excitation‐contraction (EC) coupling and protein expression in these two forms of heart failure. Dahl salt‐sensitive rats were fed a high‐salt diet (8% NaCl) from 7 weeks of age to induce HFpEF. Impaired diastolic relaxation and preserved ejection fraction were confirmed in each animal echocardiographically, and clinical signs of heart failure were documented. To generate HFrEF, Sprague‐Dawley (SD) rats underwent permanent left anterior descending coronary artery ligation which, 8–10 weeks later, led to systolic dysfunction (verified echocardiographically) and clinical signs of heart failure. Calcium (Ca²⁺) transients were measured in isolated cardiomyocytes under field stimulation or patch clamp. Ultra‐high‐speed laser scanning confocal imaging captured Ca²⁺ sparks evoked by voltage steps. Western blotting and PCR were used to assay changes in EC coupling protein and RNA expression. Cardiomyocytes from rats with HFrEF exhibited impaired EC coupling, including decreased Ca²⁺ transient (CaT) amplitude and defective couplon recruitment, associated with transverse (t)‐tubule disruption. In stark contrast, HFpEF cardiomyocytes showed saturated EC coupling (increased I_Ca, high probability of couplon recruitment with greater Ca²⁺ release synchrony, increased CaT) and preserved t‐tubule integrity. β‐Adrenergic stimulation of HFpEF myocytes with isoprenaline (isoproterenol) failed to elicit robust increases in I_Ca or CaT and relaxation kinetics. Fundamental differences in EC coupling distinguish HFrEF from HFpEF.

Heart failure (HF), the leading cause of death in developed countries, occurs in the setting of reduced (HFrEF) or preserved (HFpEF) ejection fraction. Unlike HFrEF, there are no effective treatments for HFpEF, which accounts for ∼50% of heart failure.

Abnormal intracellular calcium dynamics in cardiomyocytes have major implications for contractility and rhythm, but compared to HFrEF, very little is known about calcium cycling in HFpEF.

We used rat models of HFpEF and HFrEF to reveal distinct differences in intracellular calcium regulation and excitation‐contraction (EC) coupling.

While HFrEF is characterized by defective EC coupling at baseline, HFpEF exhibits enhanced coupling fidelity, further aggravated by a reduction in β‐adrenergic sensitivity.

These differences in EC coupling and β‐adrenergic sensitivity may help explain why therapies that work in HFrEF are ineffective in HFpEF.

Central losartan administration increases cardiac workload during aerobic exercise

To assess the effects of central administration of losartan, an antagonist of angiotensin II AT₁ receptors, on cardiovascular function during aerobic exercise, heart rate, systolic and diastolic arterial pressures and rate pressure product of Wistar rats were measured as cardiac workload indexes. The animals ran on a treadmill until fatigue after an intracerebroventricular injection of losartan or saline. Pulsatile arterial pressure was recorded by a catheter implanted into the ascending aorta, from which were derived cardiovascular parameters to estimate the cardiac workload. Total exercise time and exercise workload were determined as performance indexes. The rats showed a more intense increase in heart rate after 8 min of exercise and sustained until fatigue (P < .05). Furthermore, the rats injected with losartan had a higher increase of both systolic and diastolic arterial pressures as well as rate pressure product from approximately 6 min of exercise until fatigued (P < .05). In addition, a 22% reduction in exercise time was found in losartan-rats (P < .01). This ergolytic effect induced by losartan was strongly inversely correlated with rate-pressure product during aerobic exercise (r = 0.78, P ≤ .01). The data shows that central administration of losartan augments the cardiac workload during aerobic exercise, which courses in parallel with the reduced exercise performance.

Exercise improves cardiac function and attenuates insulin resistance in Dahl salt-sensitive rats

BACKGROUND

The development of heart failure (HF) secondary to hypertension is a complex process related to a series of physiological and molecular factors including glucose dysregulation. The overall objective of this study was to investigate whether exercise training could improve cardiac function and insulin resistance in a rat model of hypertensive HF.

METHODS

Seven week old Dahl salt-sensitive rats received either 8% NaCl (n = 30) or 0.3% NaCl (n = 18) diet. After a 5-week diet, animals were randomly assigned to exercise training (treadmill running at 18 m/min, 5% inclination for 60 min, 5 days/week) or kept sedentary for 6 additional weeks. 2D echocardiography was used to calculate left ventricular (LV) dimensions, volumes and global functional parameters. LV global deformation parameters were measured with speckle tracking echocardiography. Insulin resistance was assessed using 1h oral glucose tolerance testing.

RESULTS

High salt diet led to cardiac hypertrophy and HF, characterized by increased wall thicknesses and LV volumes as well as reduced deformation parameters. In addition, high salt diet was associated with the development of insulin resistance. Exercise training improved cardiac function, reduced the extent of interstitial fibrosis and reduced insulin levels 60 min post-glucose administration.

CONCLUSIONS

Even if not fully reversed, exercise training in HF animals improved cardiac function and insulin resistance. Adjusted modalities of exercise training might offer new insights not only as a preventive strategy, but also as a treatment for HF patients.

Attenuated muscle metaboreflex-induced increases in cardiac function in hypertension

Sympathoactivation may be excessive during exercise in subjects with hypertension, leading to increased susceptibility to adverse cardiovascular events, including arrhythmias, infarction, stroke, and sudden cardiac death. The muscle metaboreflex is a powerful cardiovascular reflex capable of eliciting marked increases in sympathetic activity during exercise. We used conscious, chronically instrumented dogs trained to run on a motor-driven treadmill to investigate the effects of hypertension on the mechanisms of the muscle metaboreflex. Experiments were performed before and 30.9 ± 4.2 days after induction of hypertension, which was induced via partial, unilateral renal artery occlusion. After induction of hypertension, resting mean arterial pressure was significantly elevated from 98.2 ± 2.6 to 141.9 ± 7.4 mmHg. The hypertension was caused by elevated total peripheral resistance. Although cardiac output was not significantly different at rest or during exercise after induction of hypertension, the rise in cardiac output with muscle metaboreflex activation was significantly reduced in hypertension. Metaboreflex-induced increases in left ventricular function were also depressed. These attenuated cardiac responses caused a smaller metaboreflex-induced rise in mean arterial pressure. We conclude that the ability of the muscle metaboreflex to elicit increases in cardiac function is impaired in hypertension, which may contribute to exercise intolerance.

Cardiac allograft hypertrophy is associated with impaired exercise tolerance after heart transplantation

BACKGROUND

Exercise performance, an important aspect of quality of life, remains limited after heart transplantation (HTx). This study examines the effect of cardiac allograft remodeling on functional capacity after HTx.

METHODS

The total cohort of 117 HTx recipients, based on echocardiographic determination of left ventricle mass and relative wall thickness at 1 year after HTx, was divided into 3 groups: (1) NG, normal geometry; (2) CR, concentric remodeling; and (3) CH, concentric hypertrophy. Cardiopulmonary exercise testing was performed 5.03 ± 3.08 years after HTx in all patients. Patients with acute rejection or significant graft vasculopathy were excluded.

RESULTS

At 1 year post-HTx, 30% of patients had CH, 55% had CR and 15% had NG. Exercise tolerance, measured by maximum achieved metabolic equivalents (4.62 ± 1.44 vs 5.52 ± 0.96 kcal/kg/h), normalized peak Vo(2) (52 ± 14% vs 63 ± 12%) and Ve/Vco(2) (41 ± 17 vs 34 ± 6), was impaired in the CH group compared with the NG group. A peak Vo(2) ≤14 ml/kg/min was found in 6%, 22% and 48% of patients in the NG, CR and CH groups, respectively (p = 0.01). The CH pattern was associated with a 7.4-fold increase in relative risk for a peak Vo(2) ≤14 ml/kg/min compared with NG patients (95% confidence interval 1.1 to 51.9, p = 0.001). After multivariate analysis, a 1-year CH pattern was independently associated with a reduced normalized peak Vo(2) (p = 0.018) and an elevated Ve/Vco(2) (p = 0.035).

CONCLUSIONS

The presence of CH at 1 year after HTx is independently associated with decreased normalized peak Vo(2) and increased ventilatory response in stable heart transplant recipients. The identification of CH, a potentially reversible mechanism of impairment in exercise capacity after HTx, may have major clinical implications.

Additional salutary effects of the combination of exercise training and an angiotensin-converting enzyme inhibitor on the left ventricular function of spontaneously hypertensive rats

OBJECTIVES

To investigate whether the combination of exercise training with the angiotensin-converting enzyme inhibitor lisinopril will have an additional beneficial effect on left ventricular function in spontaneously hypertensive rats.

DESIGN

Twelve-week-old male rats were assigned to treadmill running (Ht-Ex; 20 m/min at 5 degrees grade, 1 h/day, 5 days/week), or lisinopril treatment (Ht-Lis; 15 mg/kg per day by gavage), or treadmill running while treated with lisinopril (Ht-ExLis), and were compared with a sedentary group (Ht-Sed). Age-matched and sex-matched Wistar-Kyoto rats were controls.

METHODS

After 10 weeks of experimentation, left ventricular morphology and function were assessed from M-mode echocardiograms and transmitral Doppler spectra [early (E) and atrial peak velocities (A), their ratio (E/A), and E-wave deceleration time (Edec time) and slope (Edec slope)].

RESULTS

Ht-Sed exhibited prominent concentric left ventricular hypertrophy with systolic and diastolic dysfunctions evidenced by a significantly reduced fractional shortening (%FS) and 'pseudonormalization' of left ventricular filling, characterized by an apparently normal E/A ratio despite an underlying left ventricular relaxation abnormality. Exercise training did not significantly alter left ventricular morphology or function. Lisinopril alone attenuated left ventricular hypertrophy and enhanced diastolic function but had no significant effect on systolic function. Combining exercise training with lisinopril treatment increased %FS by 25%, decreased the E/A ratio and Edec slope by 35% and 37%, respectively, and increased Edec time by 82%.

CONCLUSION

Our results provide experimental evidence that lisinopril administration, when combined with moderate exercise training, is more promising in attenuating cardiac dysfunction than either agent alone in hypertension of a genetic origin.

Cardiac performance during exercise in hypertensive patients without ventricular hypertrophy

BACKGROUND

Reduced systolic reserve on effort may be present in subjects with hypertension but no evidence of hypertensive cardiomyopathy. We assessed the determinants of abnormal cardiac performance during exercise in hypertensive patients without left ventricular hypertrophy.

MATERIALS AND METHODS

Thirty-five newly diagnosed, never-treated-earlier hypertensive patients without definite indication for left ventricular hypertrophy at echocardiography underwent radionuclide ambulatory monitoring of left ventricular function at rest and during upright bicycle exercise testing.

RESULTS

The patients were classified into two groups according to their ejection fraction response to exercise. In 21 patients (group 1), the ejection fraction increased > or = 5% with exercise and in 14 patients (group 2), the ejection fraction either increased < 5% or decreased with exercise. Patients of group 1 had lower peak filling rate at rest and less augmentation in end-diastolic volume during exercise (both P < 0.01) when compared with patients of group 2. A significant relationship between the magnitude of change in ejection fraction with exercise and both peak filling rate at rest (r = 0.58, P < 0.01) and exercise-induced change in end-diastolic volume (r = 0.45, P < 0.01) was found.

CONCLUSIONS

In newly diagnosed, never-treated-earlier hypertensive subjects with no evidence of hypertensive cardiomyopathy, the cardiac response to exercise is dependent on adequate diastolic filling volume to maintain systolic performance.

Echocardiographic predictors of functional capacity in endomyocardial fibrosis patients

AIMS

Endomyocardial fibrosis (EMF) is a restrictive cardiomyopathy manifested mainly by diastolic heart failure. It is recognized that diastole is an important determinant of exercise capacity. The purpose of this study was to determine whether resting echocardiographic parameters might predict oxygen consumption (VO(2p)) by ergoespirometry and the prognostic role of functional capacity in EMF patients.

METHODS AND RESULTS

A total of 32 patients with biventricular EMF (29 women, 55.3 +/- 11.4 years) were studied by echocardiography and ergoespirometry. The relationship between the echocardiographic indexes and the percentage of predicted VO(2p) (%VO(2p)) was investigated by the 'stepwise' linear regression analysis. The median VO(2p) was 11 +/- 3 mL/kg/min and the %VO(2p) was 53 +/- 9%. There was a correlation of %VO(2p) with an average of A' at four sites of the mitral annulus (A' peak, r = 0.471, P = 0.023), E'/A' of the inferior mitral annulus (r = -0.433, P = 0.044), and myocardial performance index (r = -0.352, P = 0.048). On multiple regression analysis, only A' peak was an independent predictor of %VO(2p) (%VO(2p)= 26.34 + 332.44 x A' peak). EMF patients with %VO(2p)< 53% had an increased mortality rate with a relative risk of 8.47.

CONCLUSION

In EMF patients, diastolic function plays an important role in determining the limitations to exercise and %VO(2p) has a prognostic value.

Diastolic dysfunction in exercise and its role for exercise capacity

Diastolic dysfunction is frequent in elderly subjects and in patients with left ventricular hypertrophy, vascular disease and diabetes mellitus. Patients with diastolic dysfunction demonstrate a reduced exercise capacity and might suffer from congestive heart failure (CHF). Presence of symptoms of CHF in the setting of a normal systolic function is referred to as heart failure with normal ejection fraction (HFNEF) or, if evidence of an impaired diastolic function is observed, as diastolic heart failure (DHF). Reduced exercise capacity in diastolic dysfunction results from a number of pathophysiological alterations such as slowed myocardial relaxation, reduced myocardial distensibility, elevated filling pressures, and reduced ventricular suction forces. These alterations limit the increase of ventricular diastolic filling and cardiac output during exercise and lead to pulmonary congestion. In healthy subjects, exercise training can enhance diastolic function and exercise capacity and prevent deterioration of diastolic function in the course of aging. In patients with diastolic dysfunction, exercise capacity can be enhanced by exercise training and pharmacological treatment, whereas improvement of diastolic function can only be observed in few patients.

Low-Intensity Exercise Training Improves Survival in Dahl Salt Hypertension

PURPOSE

The present study examined whether exercise training could increase survival in a rodent model of salt-sensitive hypertension.

METHODS

Male, inbred Dahl salt-sensitive rats arriving at 8 wk of age were randomly divided into a sedentary control group (N = 5) or an exercise-trained group (N = 8). Exercise training consisted of running 20 m.min(-1), 0% incline, 60 min.d(-1), 5 d.wk(-1) on a motorized driven treadmill. On arrival, animals were fed a low-salt diet (0.12% NaCl) during a 1-wk acclimatization period. At the end of this period, all rats were then fed a high-salt diet (7.8% NaCl) for the remainder of the study. Arterial systolic blood pressure (SBP) was measured via the tail-cuff method.

RESULTS

Systolic blood pressure (SBP) measured on the low salt diet was similar between groups. After 2 wk of a high-salt diet, SBP was similarly significantly elevated in both control and exercise groups relative to the low salt diet. Kaplan-Meier analysis showed that exercise training increased survival (P < 0.02) with an approximate 30% increase in the mean days survived with exercise training (P < 0.02).

CONCLUSION

These data suggest that exercise training is an important intervention for salt-sensitive hypertension and that the enhanced survival observed with exercise training appears to be independent of training-induced SBP lowering effects.

Growth hormone replacement attenuates diastolic dysfunction and cardiac angiotensin II expression in senescent rats

We tested the hypothesis that long-term growth hormone (GH) replacement in aged rats would preserve diastolic function and attenuate left ventricular remodeling associated with normal aging. Male Brown Norway x F344 rats were randomized to receive twice daily injections of porcine GH (200 microg/injection, subcutaneous) or saline from 24 to 30 months of age. Adult rats (6- to 9-months old) received saline injections throughout the study. Thirty-month-old, saline-treated rats exhibited low levels of insulin-like growth factor 1 (IGF-1), impaired diastolic left ventricular filling (Doppler), increased cardiac angiotensin II (Ang II), reduced plasma Ang II, and increased cardiac collagen. GH administration in old rats restored IGF-1 and diastolic indices to values comparable to those of adults. These effects were associated with reduced cardiac Ang II and attenuations in cardiac collagen. Age-related decreases in GH and IGF-1 may contribute to the decline in diastolic function of aging, in part through alterations in renin-angiotensin system-mediated ventricular remodeling.

Validation of echocardiographic and Doppler indexes of left ventricular relaxation in adult hypertensive and normotensive rats

This study was performed to validate echocardiographic and Doppler techniques for the assessment of left ventricular (LV) diastolic function in spontaneously hypertensive rats (SHR) and normotensive Wistar rats. In 11 Wistar rats and 20 SHR, we compared 51 sets of invasive and Doppler LV diastolic indexes. Noninvasive indexes of LV relaxation were related to the minimal rate of pressure decline (−dP/d tmin), particularly isovolumic relaxation time (IVRT), the Tei index, the early velocity of the mitral annulus ( Em) using Doppler tissue imaging, and early mitral flow propagation velocity using M-mode color ( r = 0.28–0.56 and P < 0.05–0.0001). When the role of systolic load was considered, the correlation between Doppler indexes of LV diastolic function and relaxation rate [(−dP/d tmin)/LV systolic pressure] improved ( r = 0.48–0.86 and P = 0.004–0.0001, respectively). Similarly, Doppler indexes of LV diastolic function and the time constant of isovolumic LV relaxation (τ) correlated well ( r = 0.50–0.84 and P = 0.0002–0.0001, respectively). In addition, eight SHR and eight Wistar rats were compared; their LV end-diastolic diameters were similar, whereas the SHR LV mass was greater. Furthermore, IVRT and Tei index were significantly higher and Em was lower in SHR. Moreover, τ was higher in SHR, demonstrating impaired LV relaxation. In conclusion, LV relaxation can be assessed reliably using echocardiographic and Doppler techniques, and, using these indexes, impaired relaxation was demonstrated in SHR.

Determinants of exercise capacity in patients with type 2 diabetes

OBJECTIVE

Type 2 diabetes is associated with reduced exercise capacity, but the cause of this association is unclear. We sought the associations of impaired exercise capacity in type 2 diabetes.

RESEARCH DESIGN AND METHODS

Subclinical left ventricular (LV) dysfunction was sought from myocardial strain rate and the basal segmental diastolic velocity (Em) of each wall in 170 patients with type 2 diabetes (aged 56 +/- 10 years, 91 men), good quality echocardiographic images, and negative exercise echocardiograms. The same measurements were made in 56 control subjects (aged 53 +/- 10 years, 29 men). Exercise capacity was calculated in metabolic equivalents, and heart rate recovery (HRR) was measured as the heart rate difference between peak and 1 min after exercise. In subjects with type 2 diabetes, exercise capacity was correlated with clinical, therapeutic, biochemical, and echocardiographic variables, and significant independent associations were sought using a multiple linear regression model.

RESULTS

Exercise capacity, strain rate, Em, and HRR were significantly reduced in type 2 diabetes. Exercise capacity was associated with age (r = -0.37, P < 0.001), male sex (r = 0.26, P = 0.001), BMI (r = -0.19, P = 0.012), HbA(1c) (A1C; r = -0.22, P = 0.009), Em (r = 0.43, P < 0.001), HRR (r = 0.42, P < 0.001), diabetes duration (r = -0.18, P = 0.021), and hypertension history (r = -0.28, P < 0.001). Age (P < 0.001), male sex (P = 0.007), BMI (P = 0.001), Em (P = 0.032), HRR (P = 0.013), and A1C (P = 0.0007) were independent predictors of exercise capacity.

CONCLUSIONS

Reduced exercise capacity in patients with type 2 diabetes is associated with diabetes control, subclinical LV dysfunction, and impaired HRR.

Effect of high-salt diet or chronic captopril treatment on exercise capacity in normotensive rats

1. We investigated whether chronic suppression of the renin-angiotensin system, which is known to be associated with reductions in microvascular density and vasodilator responsiveness of skeletal muscle, could affect exercise capacity in normotensive rats. 2. Rats were placed on normal rat chow, normal rat chow with captopril (100 mg/kg per day) or a high-salt diet (HS; 4%) for 4 weeks. Following these interventions, rats with indwelling carotid artery catheters were submitted to stepwise increasing exercise on a motor treadmill at a speed of 10, 20 and 30 m/min for 4 min while blood lactate was measured. 3. Blood lactate after exercise at a speed of 20 m/min was significantly higher and the duration during which rats were able to run at a speed of 30 m/min was significantly shorter in captopril-treated rats and rats fed an HS diet compared with control rats. 4. We conclude that chronic treatment with captopril or HS diet could reduce the exercise capacity in inactive normotensive rats, probably through chronic inhibition of the renin-angiotensin system.

Long-term left ventricular echocardiographic follow-up of SHR and WKY rats: effects of hypertension and age

Long-term follow-up of left ventricular (LV) function using echocardiography has not been reported and, in this study, was carried out in normotensive (WKY) rats and spontaneously hypertensive rats (SHR). In 10 WKY rats and SHR, LV diastolic and systolic diameter (LVEDD and LVSD), shortening fraction (SF), and weight (LVW) were determined at 8, 15, 20, 35, and 80 wk of age. The ratio of early to late mitral flow and mitral annulus velocity (VE/VA and Em/Am), isovolumic relaxation time (IVRT), deceleration time of the E wave (DTE), Tei index, and mitral flow propagation velocity (Vp) were measured. No difference in LVEDD was found between SHR and WKY rats; however, LVEDD was increased at 80 wk in both strains. SF decreased slightly in old WKY rats. LVW progressively increased from 20 to 80 wk in both strains and was greater in SHR. VE/VA and Em/Am decreased at 80 wk in WKY rats. LV relaxation (IVRT, Tei index, and Vp) was progressively impaired in SHR compared with WKY rats. LV compliance (DTE) was altered in old SHR. Echocardiography permitted a long follow-up of LV function in SHR and WKY rats. Ventricular relaxation was impaired early in the life of SHR and progressed with aging. Furthermore, LV compliance was altered, but systolic function remained unchanged, in old SHR. In contrast, relaxation and SF were only slightly altered in old WKY rats, suggesting that pressure-related changes in LV function were the dominant features in the SHR.

Cardiac adaptation to endurance exercise in rats

Endurance exercise is widely assumed to improve cardiac function in humans. This project has determined cardiac function following endurance exercise for 6 (n = 30) or 12 (n = 25) weeks in male Wistar rats (8 weeks old). The exercise protocol was 30 min/day at 0.8 km/h for 5 days/week with an endurance test on the 6th day by running at 1.2 km/h until exhaustion. Exercise endurance increased by 318% after 6 weeks and 609% after 12 weeks. Heart weight/kg body weight increased by 10.2% after 6 weeks and 24.1% after 12 weeks. Echocardiography after 12 weeks showed increases in left ventricular internal diameter in diastole (6.39 +/- 0.32 to 7.90 +/- 0.17 mm), systolic volume (49 +/- 7 to 83 +/- 11 miccrol) and cardiac output (75 +/- 3 to 107 +/- 8 ml/min) but not left wall thickness in diastole (1.74 +/- 0.07 to 1.80 +/- 0.06 mm). Isolated Langendorff hearts from trained rats displayed decreased left ventricular myocardial stiffness (22 +/- 1.1 to 19.1 +/- 0.3) and reduced purine efflux during pacing-induced workload increases. 31P-NMR spectroscopy in isolated hearts from trained rats showed decreased PCr and PCr/ATP ratios with increased creatine, AMP and ADP concentrations. Thus, this endurance exercise protocol resulted in physiological hypertrophy while maintaining or improving cardiac function.

Hyperhomocysteinemia leads to pathological ventricular hypertrophy in normotensive rats

A recent report indicated that hyperhomocysteinemia (Hhe), in addition to its atherothrombotic effects, exacerbates the adverse cardiac remodeling seen in response to hypertension, a powerful stimulus for pathological ventricular hypertrophy. The present study was undertaken to determine whether Hhe has a direct effect on ventricular remodeling and function in the absence of other hypertrophic stimuli. Male Wistar-Kyoto rats were fed either an amino acid-defined control diet or an intermediate Hhe-inducing diet. After 10 wk of dietary treatment, rats were subjected to echocardiographic assessment of left ventricular (LV) dimensions and systolic function. Subsequently, blood was collected for plasma homocysteine measurements, and the rats were killed for histomorphometric and biochemical assessment of cardiac remodeling and for in vitro cardiac function studies. Significant LV hypertrophy was detected by echocardiographic measurements, and in vitro results showed hypertrophy with significantly increased myocyte size in the LV and right ventricle (RV). LV and RV remodeling was characterized by a disproportionate increase in perivascular and interstitial collagen, coronary arteriolar wall thickening, and myocardial mast cell infiltration. In vitro study of LV function demonstrated abnormal diastolic function secondary to decreased compliance because the rate of relaxation did not differ between groups. LV systolic function did not vary between groups in vitro. In summary, in the absence of other hypertrophic stimuli short-term intermediate Hhe caused pathological hypertrophy and remodeling of both ventricles with diastolic dysfunction of the LV. These results demonstrate that Hhe has direct adverse effects on cardiac structure and function, which may represent a novel direct link between Hhe and cardiovascular morbidity and mortality, independent of other risk factors.