Physiological cardiac hypertrophy: critical role of AKT in the prevention of NHE-1 hyperactivity

BACKGROUND

The involvement of NHE-1 hyperactivity, critical for pathological cardiac hypertrophy (CH), in physiological CH has not been elucidated yet. Stimulation of NHE-1 increases intracellular Na(+) and Ca(2+) favouring calcineurin activation. Since myocardial stretch, an activator of NHE-1, is common to both types of CH, we speculate that NHE-1 hyperactivity may also happen in physiological CH. However, calcineurin activation is characteristic only for pathological hypertrophy. We hypothesize that an inhibitory AKT-dependent mechanism prevents NHE-1 hyperactivity in the setup of physiological CH.

METHODS

Physiological CH was induced in rats by swimming (90 min/day, 12 weeks) or in cultured isolated cardiomyocytes with IGF-1 (10 nmol/L).

RESULTS

Training induced eccentric CH development (left ventricular weight/tibial length: 22.0±0.3 vs. 24.3±0.7 mg/mm; myocyte cross sectional area: 100±3.2 vs. 117±4.1 %; sedentary (Sed) and swim-trained (Swim) respectively; p<0.05] with decreased myocardial stiffness and collagen deposition [1.7±0.05 % (Sed) vs. 1.4±0.09 % (Swim); p<0.05]. Increased phosphorylation of AKT, ERK1/2, p90(RSK) and NHE-1 at the consensus site for ERK1/2-p90(RSK) were detected in the hypertrophied hearts (P-AKT: 134±10 vs. 100±5; P-ERK1/2: 164±17 vs. 100±18; P-p90(RSK): 160±18 vs. 100±9; P-NHE-1 134±10 vs. 100±10; % in Swim vs. Sed respectively; p<0.05). No significant changes were detected neither in calcineurin activation [calcineurin Aβ 100±10 (Sed) vs. 96±12 (Swim)], nor NFAT nuclear translocation [100±3.11 (Sed) vs. 95±9.81 % (Swim)] nor NHE-1 expression [100±8.5 (Sed) vs. 95±6.7 % (Swim)]. Interestingly, the inhibitory phosphorylation of the NHE-1 consensus site for AKT was increased in the hypertrophied myocardium (151.6±19.4 (Swim) vs. 100±9.5 % (Sed); p<0.05). In isolated cardiomyocytes 24 hours IGF-1 increased cell area (114±1.3 %; p<0.05) and protein/DNA content (115±3.9 %, p<0.05), effects not abolished by NHE-1 inhibition with cariporide (114±3 and 117±4.4 %, respectively). IGF-1 significantly decreased NHE-1 activity during pHi recovery from sustained intracellular acidosis (JH+ at pHi 6.8: 4.08±0.74 and 9.09±1.21 mmol/L/min, IGF-1 vs. control; p<0.05), and abolished myocardial slow force response, the mechanical counterpart of stretch-induced NHE-1 activation.

CONCLUSIONS

NHE-1 hyperactivity seems not to be involved in physiological CH development, contrary to what characterizes pathological CH. We propose that AKT, through an inhibitory phosphorylation of the NHE-1, prevents its stretch-induced activation. This posttranslational modification emerges as an adaptive mechanism that avoids NHE-1 hyperactivity preserving its housekeeping functioning.

Sex-related difference in left ventricular mass in nonhypertensive young adults: role of arterial pressure

BACKGROUND

Blood pressure (BP) is higher in men than in women at similar ages through adult life. Interestingly, a similar pattern is detected in left ventricular mass (LVM), classically attributed to differences in body size. However, the existing difference in BP between sexes might be relevant in determining LVM and it has been not fully investigated. Therefore, we set out to determine the impact of nonhypertensive levels of BP on the sex-associated LVM difference.

METHODS

We conducted population-based study including 283 young students (52% male; age 20.62 ± 1.31 years). BP was determined twice using standard mercury sphygmomanometers in 2 occasions. LVM was determined with M-mode echocardiography. To dissect the relative contribution of BP, volume load, and body size to the sex-related difference in LVM, an analysis of covariance was performed.

RESULTS

Mean systolic and diastolic BP were 10.00 ± 0.96 and 4.59 ± 0.78 mm Hg higher and LVM was 34.87 ± 3.12 g larger in men than in women, respectively (P < 0.01, t test). When LVM was adjusted to mean BP, the sex difference was reduced by 16%. When LVM was adjusted to body size and hemodynamic load, this difference was reduced by 68.5%.

CONCLUSIONS

We report in a sample of young nonhypertensive students a difference in LVM between women and men that is partially explained (16%) by sex differences in BP, supporting an early effect of BP on cardiac mass even in the absence of hypertension. A more relevant effect could be expected as the population ages.

In vivo key role of reactive oxygen species and NHE-1 activation in determining excessive cardiac hypertrophy

Growing in vitro evidence suggests NHE-1, a known target for reactive oxygen species (ROS), as a key mediator in cardiac hypertrophy (CH). Moreover, NHE-1 inhibition was shown effective in preventing CH and failure; so has been the case for AT1 receptor (AT1R) blockers. Previous experiments indicate that myocardial stretch promotes angiotensin II release and post-translational NHE-1 activation; however, in vivo data supporting this mechanism and its long-term consequences are scanty. In this work, we thought of providing in vivo evidence linking AT1R with ROS and NHE-1 activation in mediating CH. CH was induced in mice by TAC. A group of animals was treated with the AT1R blocker losartan. Cardiac contractility was assessed by echocardiography and pressure-volume loop hemodynamics. After 7 weeks, TAC increased left ventricular (LV) mass by ~45% vs. sham and deteriorated LV systolic function. CH was accompanied by activation of the redox-sensitive kinase p90(RSK) with the consequent increase in NHE-1 phosphorylation. Losartan prevented p90(RSK) and NHE-1 phosphorylation, ameliorated CH and restored cardiac function despite decreased LV wall thickness and similar LV systolic pressures and diastolic dimensions (increased LV wall stress). In conclusion, AT1R blockade prevented excessive oxidative stress, p90(RSK) and NHE-1 phosphorylation, and decreased CH independently of hemodynamic changes. In addition, cardiac performance improved despite a higher work load.

Endurance Training in the Spontaneously Hypertensive Rat

The effect of endurance training (swimming 90 min/d for 5 days a week for 60 days) on cardiac hypertrophy was investigated in the spontaneously hypertensive rat (SHR). Sedentary SHRs (SHR-Cs) and normotensive Wistar rats were used as controls. Exercise training enhanced myocardial hypertrophy assessed by left ventricular weight/tibial length (228±7 versus 251±5 mg/cm in SHR-Cs and exercised SHRs [SHR-Es], respectively). Myocyte cross-sectional area increased ≈40%, collagen volume fraction decreased ≈50%, and capillary density increased ≈45% in SHR-Es compared with SHR-Cs. The mRNA abundance of atrial natriuretic factor and myosin light chain 2 was decreased by the swimming routine (100±19% versus 41±10% and 100±8% versus 61±9% for atrial natriuretic factor and myosin light chain 2 in SHR-Cs and SHR-Es, respectively). The expression of sarcoplasmic reticulum Ca 2+ pump was significantly augmented, whereas that of Na + /Ca 2+ exchanger was unchanged (93±7% versus 167±8% and 158±13% versus 157±7%, sarcoplasmic reticulum Ca 2+ pump and Na + /Ca 2+ exchanger in SHR-Cs and SHR-Es, respectively; P <0.05). Endurance training inhibited apoptosis, as reflected by a decrease in caspase 3 activation and poly(ADP-ribose) polymerase-1 cleavage, and normalized calcineurin activity without inducing significant changes in the phosphatidylinositol 3-kinase/Akt pathway. The swimming routine improved midventricular shortening determined by echocardiography (32.4±0.9% versus 36.9±1.1% in SHR-Cs and SHR-Es, respectively; P <0.05) and decreased the left ventricular free wall thickness/left ventricular cavity radius toward an eccentric model of cardiac hypertrophy (0.59±0.02 versus 0.53±0.01 in SHR-Cs and SHR-Es, respectively; P <0.05). In conclusion, we present data demonstrating the effectiveness of endurance training to convert pathological into physiological hypertrophy improving cardiac performance. The reduction of myocardial fibrosis and calcineurin activity plus the increase in capillary density represent factors to be considered in determining this beneficial effect.

[Echocardiographic study of left ventricular geometry in spontaneously hypertensive rats]

The purpose of this study was to analyze by echocardiogram left ventricular (LV) geometry in spontaneously hypertensive rats (SHR). Echocardiographic study, systolic blood pressure and heart rate were obtained in 114 male, 4-month old rats, 73 SHR and 41 Wistar (W). Left ventricular mass index (LVMI), relative wall thickness (RWT), stroke volume, and mid ventricular shortening were calculated with echocardiographic parameters. Normal LV was defined considering the mean plus 2 SD of LVMI and RWT in W. Patterns of abnormal LV geometry were: LV concentric remodeling, LVMI < 2.06 mg/g - RWT > 0.71; eccentric, left ventricular hypertrophy (LVH), LVMI > 2.06 mg/g - RWT < 0.71; and concentric LVH, LVMI > 2.06 mg/g - RWT > 0.71. Systolic blood pressure (SBP) and cardiac output (CO) were used to obtain total peripheral resistance (TPR). twelve % of SHR had normal LV geometry; 18% LV concentric remodeling; 33% concentric LVH and 37% eccentric LVH. LV concentric remodeling showed the smallest CO and highest TPR of any group. Eccentric LVH presented similar SBP as the other SHR groups and high CO with lower TPR. Our findings in SHR exhibit different patterns of LV geometry like in humans. These results strengthen the similarities between SHR and human essential hypertension.

Phosphodiesterase 5A Inhibition Induces Na + /H + Exchanger Blockade and Protection Against Myocardial Infarction

Acute phosphodiesterase 5A inhibition by sildenafil or EMD360527/5 promoted profound inhibition of the cardiac Na(+)/H(+) exchanger (NHE-1), detected by the almost null intracellular pH recovery from an acute acid load (ammonium prepulse) in isolated papillary muscles from Wistar rats. Inhibition of phosphoglycerate kinase-1 (KT5823) restored normal NHE-1 activity, suggesting a causal link between phosphoglycerate kinase-1 increase and NHE-1 inhibition. We then tested whether the beneficial effects of NHE-1 inhibitors against the deleterious postmyocardial infarction (MI) remodeling can be detected after sildenafil-mediated NHE-1 inhibition. MI was induced by left anterior descending coronary artery ligation in Wistar rats, which were randomized to placebo or sildenafil (100 mg kg(-1) day(-1)) for 6 weeks. Sildenafil significantly increased left ventricular phosphoglycerate kinase-1 activity in the post-MI group without affecting its expression. MI increased heart weight/body weight ratio, left ventricular myocyte cross-sectional area, interstitial fibrosis, and brain natriuretic peptide and NHE-1 expression. Sildenafil blunted these effects. Neither a significant change in infarct size nor a change in arterial or left ventricular systolic pressure was detected after sildenafil. MI decreased fractional shortening and the ratio of the maximum rate of rise of LVP divided by the pressure at the moment such maximum occurs, effects that were prevented by sildenafil. Intracellular pH recovery after an acid load was faster in papillary muscles from post-MI hearts (versus sham), whereas sildenafil significantly inhibited NHE-1 activity in both post-MI and sildenafil-treated sham groups. We conclude that increased phosphoglycerate kinase-1 activity after acute phosphodiesterase 5A inhibition blunts NHE-1 activity and protects the heart against post-MI remodeling and dysfunction.

Normalization of the calcineurin pathway underlies the regression of hypertensive hypertrophy induced by Na+/H+exchanger-1 (NHE-1) inhibitionThis paper is one of a selection of papers published in this Special Issue, entitled The Cellular and Molecular Basis of Cardiovascular Dysfunction, Dhalla 70th Birthday Tribute

Na+/H+exchanger-1 (NHE-1) inhibition induces cardiac hypertrophy regression and (or) prevention in several experimental models, although the intracellular events involved remain unclarified. We aimed to determine whether the calcineurin/NFAT pathway mediates this effect of NHE-1 inhibitors. Spontaneously hypertensive rats (SHR) with cardiac hypertrophy were treated with the NHE-1 inhibitors cariporide and BIIB723 for 30 days. Wistar rats served as normotensive controls. Their hearts were studied by echocardiography, immunoblotting, and real-time RT-PCR. Cytoplasmic Ca2+and calcineurin Aβ expression were measured in cultured neonatal rat ventricular myocytes (NRVM) stimulated with endothelin-1 for 24 h. NHE-1 blockade induced cardiac hypertrophy regression (heart mass/body mass = 3.63 ± 0.07 vs. 3.06 ± 0.05 and 3.02 ± 0.13 for untreated vs. cariporide- and BIIB723-treated SHR, respectively; p < 0.05) and decreased myocardial brain natriuretic peptide, calcineurin Aβ, and nuclear NFAT expressions. Echocardiographic evaluation demonstrated a reduction in left ventricular wall thickness without changes in cavity dimensions or a significant decrease in blood pressure. NHE-1-inhibitor treatment did not affect myocardial stiffness or endocardial shortening, but increased mid-wall shortening, suggesting that a positive inotropic effect develops after hypertrophy regression. Cariporide normalized the increased diastolic Ca2+and calcineurin Aβ expression observed in ET-1-stimulated NRVM. In conclusion, our data suggest that inactivation of calcineurin/NFAT pathway may underlie the regression of cardiac hyper-trophy induced by NHE-1 inhibition.

[Embolism predictors of infective endocarditis]

The embolic event (EE) increases the morbidity and mortality of infective endocarditis (IE). Prevalence of EE ranges between 22% and 50%, death rates being up to 25% of patients. EE may occur prior to diagnosis, during treatment or afterwards. The objective of this study was to evaluate the demographic, clinical, microbiological, echocardiographic and therapeutic characteristics in patients suffering from IE (with or without emboli) in order to determine predictors for EE. A descriptive study based on observations of patient population diagnosed with IE was conducted at the Hospital Italiano of La Plata during the period March 1996 - December 2004. Fifty-three patients with IE were analyzed (35 without EE and 18 with EE) in retrospect. We found that the presence of vegetations in the transthoracic (TTE) and/or transesophagic (TEE) echocardiographies at the time of diagnosis, the size > or = 10 mm and the compromise of the native mitral valve were the variables that showed significant statistical association with EE to be considered as predictors. The size _ 10 mm was the only variable associated with EE in the logistic regression analysis. During the elective antibiotic treatment, there was a reduction in EE, without their being present from the second week onwards.

Correlation between myocardial perfusion abnormalities detected with intermittent imaging using intravenous perfluorocarbon microbubbles and radioisotope imaging during high-dose dipyridamole stress echo

BACKGROUND

The clinical accuracy of myocardial contrast echocardiography (MCE) using intermittent harmonic imaging and intravenous perfluorocarbon containing microbubbles during dipyridamole stress has not been evaluated in a multicenter setting.

HYPOTHESIS

The accuracy of dipyridamole stress contrast echo in the detection of coronary artery disease (CAD) using myocardial perfusion images is high in comparison with technetium-99 (99Tc) sestamibi single-photon emission computed tomography (MIBI SPECT) and increases the accuracy of wall motion data.

METHODS

In 68 consecutive nonselected patients (46 men; mean age 66 years) from three different institutions in two countries. dipyridamole stress echo and SPECT with 99mTc MIBI were compared. Continuous intravenous (IV) infusion of perfluorocarbon exposed sonicated dextrose albumin (PESDA) (2-5 cc/min) was administered for baseline myocardial perfusion using triggered harmonic end systolic frames. Real-time digitized images were used for wall motion analysis. Dipyridamole was then injected in two steps: (1) 0.56 mg/kg for 3 min, (2) 0.28 mg/kg for 1 min, if the first step was negative for an inducible wall motion abnormality. After dipyridamole injection, myocardial contrast enhancement and wall motion were analyzed again by the same methodology.

RESULTS

There were 35 patients with perfusion defects by SPECT. Wall motion was abnormal in 22, while MCE was abnormal in 32. Wall motion and MCE each had one false positive. The proportion of correctly assigned patients was significantly better with MCE than with wall motion (p = 0.03; chi square test).

CONCLUSIONS

Myocardial contrast echocardiography, using intermittent harmonic imaging and intravenous perfluorocarbon containing microbubbles, is a very effective method for detecting coronary artery disease during dipyridamole stress echo.

The effect of xanthine oxidase inhibition upon ejection fraction in heart failure patients: La Plata Study

BACKGROUND

Reactive oxygen species (ROS) have been linked to hypertrophy, remodeling and abnormal excitation-contraction coupling. Previous data demonstrated that an increase in oxidative stress is associated to the pathogenesis of congestive heart failure (CHF). We examined whether inhibition of the superoxide anion (*O2(-))-generating enzyme xanthine oxidase (XO) with oxypurinol may improve cardiac function in patients with CHF.

METHODS AND RESULTS

A randomized, placebo-controlled, double-blind study on 60 patients (30/group) with New York Heart Association class II-III CHF, comparing 600-mg/day oxypurinol during 1 month with placebo, added to standard therapy. Effects on left ventricular ejection fraction (LVEF), serum uric acid (SUA) level, and 6-minute walking test were analyzed. SUA decreased by 16.0 +/- 2.8 mg/L from baseline to Week 4 in the oxypurinol group relative to placebo (P < .01, n = 30 per group). LVEF showed an increase of 4.7 +/- 2.6% from baseline to Week 4 in the oxypurinol group relative to placebo that did not reach statistical significance (P < .08). When patients with LVEF > 40% at baseline were excluded, a statistically significant increase of 6.8 +/- 2.8% from baseline to Week 4 was seen in the oxypurinol group relative to placebo (P < .02, n = 26 placebo, n = 21 oxypurinol). No treatment-related adverse effects or increase in walking capacity were detected.

CONCLUSION

Inhibition of XO by oxypurinol in patients with CHF decreases SUA and improves LVEF in patients with LVEF < or = 40% after 1 month of treatment.

Diagnostic role of new Doppler index in assessment of renal artery stenosis

Background

Renal artery stenosis (RAS) is one of the main causes of secondary systemic arterial hypertension. Several non-invasive diagnostic methods for RAS have been used in hypertensive patients, such as color Doppler ultrasound (US). The aim of this study was to assess the sensitivity and specificity of a new renal Doppler US direct-method parameter: the renal-renal ratio (RRR), and compare with the sensitivity and specificity of direct-method conventional parameters: renal peak systolic velocity (RPSV) and renal aortic ratio (RAR), for the diagnosis of severe RAS.

Methods

Our study group included 34 patients with severe arterial hypertension (21 males and 13 females), mean age 54 (± 8.92) years old consecutively evaluated by renal color Doppler ultrasound (US) for significant RAS diagnosis. All of them underwent digital subtraction arteriography (DSA). RAS was significant if a diameter reduction > 50% was found. The parameters measured were: RPSV, RAR and RRR. The RRR was defined as the ratio between RPSV at the proximal or mid segment of the renal artery and RPSV measured at the distal segment of the renal artery. The sensitivity and specificity cutoff for the new RRR was calculated and compared with the sensitivity and specificity of RPSV and RAR.

Results

The accuracy of the direct method parameters for significant RAS were: RPSV >200 cm/s with 97% sensitivity, 72% specificity, 81% positive predictive value and 95% negative predictive value; RAR >3 with 77% sensitivity, 90% specificity, 90% positive predictive value and 76% negative predictive value. The optimal sensitivity and specificity cutoff for the new RRR was >2.7 with 97% sensitivity (p < 0.004) and 96% specificity (p < 0.02), with 97% positive predictive value and 97% negative predictive value.

Conclusion

The new RRR has improved specificity compared with the direct method conventional parameters (RPSV >200cm/s and RAR >3). Both RRR and RPSV show better sensitivity than RAR for the RAS diagnosis.

[Echocardiographic analysis of the effect of different Na+/H+ exchanger inhibitors on left ventricular structure and function in spontaneously hypertensive rats]

The aim of this study was to analyze by echocardiogram, the action of two Na+/H+ exchange, inhibitors, HOE 642 (HOE) and BIIB 723 (BIIB) on left ventricular (LV) mass and LV systolic function. We studied 16 spontaneously hypertensive rats (SHR), 8 treated with HOE 30 mg/kg/day, 8 with 30 mg/kg/day of BIIB during 30 days and 4 SHR as controls during those 30 days. Results are expressed as mean values +/- SEM. The systolic blood pressure and the echocardiograpic parameters examined did not evidence changes during that period in the controls rats. Even though HOE determined a slight decrease in blood pressure (HOE C: 184 +/- 1.75 mm Hg; HOE 30d: 176.20 +/- 2.60 mm Hg - p < 0.01) which was not detected with BIIB, both drugs provoked an increase of peak systolic stress (HOE C: 166 +/- 29 kdynes/cm2; HOE 30d: 204 +/- 34 kdynes/cm2, p < 0.04; BIIB C: 164 +/- 25.90 kdynes/ cm2; BIIB 30d: 234 +/- 29.30 kdynes/cm2, p < 0.02). HOE and BIIB reduced LV mass after 30 days of administration (HOE C: 612.50 +/- 50 mg; 30d: 452 +/- 37 mg, p < 0.01. BIIB C: 544 +/- 16mg; 30d: 374 +/- 25 mg, p < 0.01). LV endocardial shortening was similar independently of the NHE inhibitors used (HOE C: 62.30 +/- 2.75%; 30d: 65.50 +/- 2.40%, ns. BIIB C: 63.20 +/- 2,39%; 30d 67,20 +/- 1.62%, ns). These data demonstrate that long-treatment with HOE or BIIB produced similar LV mass regression without changes in endocardial fractional shortening in spite of the increase of peak systolic stress. This finding could represent an increased inotropism previously depressed by the development of hypertrophy.

Serum carboxyl-terminal propeptide of procollagen type I in exercise-induced left ventricular hypertrophy

BACKGROUND

Left ventricular hypertrophy (LVH) induced by exercise is considered to be a physiologic adaptive mechanism without fibrogenic hyperactivity, as occurs in pathologic hypertrophy.

HYPOTHESIS

This study investigated serum markers of collagen synthesis and echo parameters of left ventricular diastolic function (LVdf) in 22 male athletes.

METHODS

Twenty-two highly competitive male athletes (10 cyclists, 12 soccer players) were studied with full history, clinical examination, Doppler echocardiogram, and serum concentration of the carboxyl-terminal propeptide of collagen type I (PIP). They were divided into two groups: normal left ventricular mass (N) with left ventricular mass index (LVMI) < 125 g/m2 (14 athletes) and LVH with LVMI > 125 g/m2 (8 athletes).

RESULTS

Age, body surface area, blood pressure, heart rate, and systolic function were not different between the groups. Serum concentration of PIP (N: 163 +/- 44.1 microg/l, LVH: 172.7 +/- 61.2 microg/l--NS) and LVdf (early to atrial peak mitral flow velocity ratio: [E/A] N: 1.77 +/- 0.47, LVH: 1.98 +/- 0.70--NS, and early to atrial peak mitral annulus velocity ratio: [Ea/Aa] N: 2.63 +/- 0.70, LVMI: 2.55 +/- 0.90 LV 1.61--NS) were similar in both groups.

CONCLUSIONS

Normal serum concentration of PIP in athletes with LVH in association with normal LVdf indicates the possibility that in this type of physiologic hypertrophy there is mainly an increase of myocyte size without interstitial fibrosis.

Myocardial hypertrophy of normotensive Wistar-Kyoto rats

In our studies with spontaneously hypertensive (SHR), Wistar-Kyoto (WKY), and Wistar rats, we observed normotensive WKY rats with cardiac hypertrophy determined by a greater left ventricular (LV) mass (LVM)-to-body weight (BW) ratio (LVM/BW) than that of normotensive Wistar rats. Thus we compared the following parameters in SHR, WKY, and Wistar rats: LVM/BW, cell capacitance as index of total surface area of the myocytes, length, width, and cross-sectional area of cardiac myocytes, LV collagen volume fraction, and myocardial stiffness. The LVM/BW of WKY (2.41 ± 0.03 mg/g, n = 41) was intermediate between SHR (2.82 ± 0.04 mg/g, n = 47) and Wistar rats (1.98 ± 0.04 mg/g, n = 28). A positive correlation between blood pressure and LVM was found in SHR, whereas no such relationship was observed in WKY or Wistar rats. Cell capacitance and cross-sectional area were not significantly different in SHR and WKY rats; these values were significantly higher than those of Wistar rats. The cell length was smaller but the width was similar in WKY compared with SHR. Papillary muscles isolated from the LV of WKY and SHR were stiffer than those from Wistar rats. Consistently, a greater level of myocardial fibrosis was detected in WKY and SHR compared with Wistar rats. These findings demonstrate blood pressure-independent cardiac hypertrophy in normotensive WKY rats.

Regression of isoproterenol-induced cardiac hypertrophy by Na+/H+ exchanger inhibition

Cardiac hypertrophy is often associated with an increased sympathetic drive, and both in vitro and in vivo studies have demonstrated the development of cardiomyocyte hypertrophy in response to either alpha- or beta-adrenergic stimulation. Because an association between the Na+/H+ exchanger and cellular growth has been proposed, this study aimed to analyze the possible role of the antiporter in isoproterenol-induced cardiac hypertrophy. Isoproterenol alone (5 mg/kg IP once daily) or combined with a selective inhibitor of the Na+/H+ exchanger activity (3 mg x kg(-1) x d(-1) BIIB723) was given to male Wistar rats for 30 days. Sex- and age-matched rats that received 0.9% saline IP daily served as controls. Echocardiographic follow-up showed a 33% increase in left ventricular mass in the isoproterenol-treated group, whereas it did not increase in the isoproterenol+BIIB723-treated group. Heart weight-to-body weight ratio at necropsy was 2.44+/-0.11 in controls and increased to 3.35+/-0.10 (P<0.05) with isoproterenol, an effect that was markedly attenuated by BIIB723 (2.82+/-0.07). Intense cardiomyocyte enlargement and severe subendocardial fibrosis were found in isoproterenol-treated rats, and both effects were attenuated by BIIB723. Myocardial Na+/H+ exchanger activity and protein expression significantly increased in isoproterenol-treated rats compared with the control group (1.45+/-0.11 vs 0.91+/-0.05 arbitrary units, P<0.05). This effect was significantly reduced by BIIB723 (1.17+/-0.02, P<0.05). In conclusion, our results show that Na+/H+ exchanger inhibition prevented the development of isoproterenol-induced hypertrophy and fibrosis, providing strong evidence in favor of a key role played by the antiporter in this model of cardiac hypertrophy.

[Left ventricular structure and function in young male students of La Plata University with stage I hypertension]

From an homogeneous population of 219 male medical students of La Plata University (20.9 +/- 1.6 years) who underwent a blood pressure screening, 34 were selected for measurements of left ventricular structure and function. Considering the JNC-V classification, samples from two groups were selected for comparisons: Optimal blood pressure (OBP) (21 males, 20.33 +/- 1.8 years) and Hypertensives stage I (H) (13 males, 20.85 +/- .66 years). The H showed values of body mass index (BMI) and heart rate (HR) higher than OBP (BMI OBP: 22.5 +/- 0.38 kg/m2, H: 24.26 +/- 0.84 kg/m2 -p < 0.04; HR OBP: 69.9 +/- 1.53 lat/min-H 80.5 +/- 3.58 lat/min -p < 0.03). Although the H were not reaching values of left ventricular mass index (LVMI) or septal (S) and posterior wall thickness to be considered hypertrophics, they were exceeding the OBP group (LVMI OBP: 89.6 +/- 3.33 g/m2, H: 124.5 +/- 6 g/m2 -p < 0.01; S OBP: 8.7 +/- 0.17 mm, H: 11.5 +/- 0.04 mm; P OBP: 7.9 +/- 0.18 mm, H: 10 +/- 0.13 mm -p < 0.01). Cardiac index (CI) was increased in H (OBP: 3.3 +/- 0.14 l/min/m2, H: 4.8 +/- 0.36 l/min/m2 -p < 0.01) supporting the existence of a hyperkinetic circulatory phase. OBP showed total peripheral resistance (TPR) higher than H group (OBP: 17 +/- 0.8 mmHg/l.min.m2, H: 13 +/- 1 mmHg/l.min.m2 -p < 0.008). Left ventricular (LV) systolic function indexes were not different in the two groups analyzed. The pattern of left ventricular late filling was however different between the two groups. The area of late diastolic flow (Area A) was lower in OBP (OBP: 2.64 +/- 0.09 cm2, H: 3.78 +/- 0.95 cm2 -p < 0.01) independently of HR value (adjusted mean OBP: 2.9 +/- 0.09 cm2, H: 3.52 +/- 0.95 cm2 -p < 0.01). The early filling fraction (EFF) was also detecting a significant shift to more prominent late diastolic filling in H (OBP 0.72 +/- 0.06%, H: 0.64 +/- 0.01% -p < 0.01) independently of HR values (adjusted mean PAO: 0.71 +/- 0.96%, H: 0.65 +/- 0.01% -p < 0.01). Healthy young males with hypertension stage I have similar LV systolic function, increased CI, LVMI, LV wall thickness, decreased TPR and evidence of impaired LV filling with shift of the pattern of filling to a late flow.

Bilateral atrial function after chemical cardioversion of atrial fibrillation with amiodarone: an echo-Doppler study

Cardioversion of atrial fibrillation transiently increases the risk of embolism presumably by decreased atrial mechanical function. It has been suggested that a component of early dysfunction relates to the mode of cardioversion. Amiodarone is one of the drugs used to restore sinus rhythm in patients with atrial fibrillation. However, the effect of this drug on left and right atrial mechanical function after conversion to sinus rhythm is not well known. Thirty-one patients (group AF) cardioverted from atrial fibrillation with intravenous amiodarone (average dose 1 gm/day) were prospectively studied to examine the effect of this drug on recovery of left and right atrial mechanical function. These patients were compared with 17 consecutive individuals without evidence of cardiac disease who became our control group (group C). Transmitral flow velocities and echocardiographic parameters were recorded within 24 hours after cardioversion and on the seventh day in group AF and one time in group C. Left and right atrial ejection force to evaluate atrial mechanical function was defined as 0.5 x 1.06 x mitral (m) or tricuspid (t) orifice area x (m or t peak A velocity)2. If this value in group AF was more than the mean minus 1 standard deviation of control group data, atrial ejection function after cardioversion was considered normal. The two groups were similar with respect to age, sex, arterial blood pressure, heart rate, left ventricular diameters, and left ventricular ejection fraction. Left and right atrial size was higher in group AF (left: group AF, 18.1 +/- 3.9 cm2; group C, 11.3 +/- 2.5 cm2, p < 0.01; right: group AF, 14.9 +/- 3.2 cm2; group C, 11.6 +/- 2.3, p < 0.01). Measurements of right and left atrial ejection force measured within 24 hours and on day 7 in group AF were similar to that in group C (left: group C, 11.9 +/- 5.3 kdyne; AF group, 24 hours, 19.4 +/- 15.5 kdyne [NS]; AF group, day 7, 14.7 +/- 13.6 kdyne [NS]; right: group C, 3.6 +/- 1.99 kdyne; AF group, 24 hours, 4.3 +/- 3.3 kdyne [NS]; AF group, day 7, 3.5 +/- 2.9 kdyne [NS]). Therefore almost all patients undergoing cardioversion for atrial fibrillation with amiodarone recovered bilateral atrial mechanical function within 24 hours after cardioversion (26 of 31-84%-left atrial ejection force; 28 of 31-93.5%-right atrial ejection force), with normal left atrial function in 97% of patients and normal right atrial function in 100% of patients on day 7 after conversion to sinus rhythm. These findings may have significant implications on postcardioversion anticoagulation strategies.

Study of the left ventricular function in pregnancy-induced hypertension

Left ventricular (LV) morphological and functional characteristics in 9 women suffering from pregnancy-induced hypertension (PIH) were studied by means of echocardiograms. In order to distinguish which changes depended on the pressure values and which were the result of pregnancy, 10 nonpregnant control women with no heart disease and 10 normal pregnant women (NP) were studied and the results of each of the groups compared. To evaluate the structure, left ventricular systodiastolic diameters and wall thickness were measured. The only statistically significant difference was in the diastolic diameters between the PIH (4.7 +/- 0.3 cm) and the control group (4.4 +/- 0.2 cm) p less than 0.01. Left ventricular mass was significantly increased (p less than 0.01) in the PIH patients (185 +/- 53.1 g) compared to the NP patients (161 +/- 29.6 g) and the control group (125 +/- 17.4 g). No statistically significant differences were found in the radius thickness ratio in the three groups. The systolic function assessed by the shortening percentage was significantly lower (p less than 0.05) in the control group (32.8 +/- 4.4%) and in the NP patients (37.8 +/- 5.2%) than in the PIH group (39 +/- 6.5%). Afterload assessed by isovolumic period stress was significantly greater (p less than 0.01) in the PIH patients (157 +/- 10.6 dyne/cm2) compared with the NP group (118.9 +/- 7.01 dyne/cm2). There were no significant differences between the first group and the control group (134.09 +/- 8.7 dyne/cm2). As evidence of the diastolic function, analysis was made, on the one hand, of diastolic isovolumic period length (DIP).(ABSTRACT TRUNCATED AT 250 WORDS)

[Use of ergometry for evaluating left ventricular function in chronic aortic insufficiency]

Fourteen patients with chronic aortic regurgitation (AR) underwent radionuclide angiography at rest and during supine exercise with ergometric controls. Ten subjects without evidence of heart disease were taken as controls. The behavior of heart rate, ST segment and R wave amplitude were analyzed at peak exercise in relationship with ejection fraction (EF) changes. Abnormal EF, (defined by an increase less than 10%, no change or decrease respect EF control), was present in 9 of 14 patients. Five of 14 patients had normal EF response to exercise defined by an increase of 10% or more than control value. Sensitivity and specificity of heart rate changes at exercise (abnormal: less than 10 beats to MET) to identify abnormal EF were 10% and 100%, respectively. The analysis of ST segment alterations at peak exercise (abnormal more than 2 mm ST depression) to the same objective showed 33% of sensitivity and 80% of specificity. Changes in R wave amplitude (abnormal: increase, no change or decrease less than 22% R wave amplitude at control) at peak exercise had 100% sensitivity and 80% of specificity to identify abnormal EF. Our results suggest that exercise test could be useful to analyze the response to left ventricular function during stress in patients with AR. Changes in R. wave amplitude at peak exercise appeared the best parameter.

The pulse in patients with atrial fibrillation: its irregularity and inequality

In 32 patients with atrial fibrillation the distributions of the R-R intervals and the carotid pulse records were analyzed in an attempt to define and quantify 'irregularity' and 'inequality' of the pulse and its relationship to the mean ventricular rate. Using our definition or irregularity and inequality of the pulse (the percentage scatter around the mean) we arrived at the conclusion that: (1) the same degree of irregularity is maintained with different mean ventricular rates in the range studied by us (digitalis administration had no significant effect on this irregularity (2) the 'inequality' between beats decreases at slower ventricular rates: (3) a relationship with the postextrasystolic potentiation is suggested.