Transgenic expression of sarcoplasmic reticulum Ca(2+) atpase modifies the transition from hypertrophy to early heart failure

To examine the contribution of sarcoplasmic reticulum Ca(2+) ATPase (SERCA2a) to early heart failure, we subjected transgenic (TG) mice expressing SERCA2a gene and wild-type (WT) mice to aortic stenosis (AS) for 7 weeks. At an early stage of hypertrophy (4-week AS), in vivo hemodynamic and echocardiographic indices were similar in TG and WT mice. By 7 weeks of AS, which is the stage of early failure in this model, TG mice with AS had lower mortality than WT mice with AS (6.7% versus 29%). The magnitude of left ventricular (LV) hypertrophy was similar in WT and TG 7-week AS mice. In vivo LV systolic function was higher in TG than in WT 7-week AS mice. In LV myocytes loaded with fluo-3, fractional cell shortening and the amplitude of the [Ca(2+)](i) transients were higher in TG than in WT 7-week AS mice under baseline conditions (0.5 Hz, 1.5 mmol/L [Ca(2+)](o), 25 degrees C). The rates of relengthening and decay in [Ca(2+)](i) were faster in TG than in WT 7-week AS myocytes. In myocytes from WT 7-week AS compared with sham-operated WT mice, contractile reserve in response to rapid pacing was depressed with impaired augmentation of both peak-systolic [Ca(2+)](i) and the SR Ca(2+) load. In contrast, contractile reserve and the capacity to augment SR Ca(2+) load were maintained in TG 7-week AS mice. SERCA2a protein levels were depressed in WT 7-week AS mice, but were preserved in TG 7-week AS mice. These data suggest that defective SR Ca(2+) loading contributes to the onset of contractile failure in animals with chronic pressure overload.

Cardiac-specific overexpression of cyclin-dependent kinase 2 increases smaller mononuclear cardiomyocytes

Cyclin-dependent kinase 2 (cdk2) plays a critical role in the G1- to S-phase checkpoint of the cell cycle. Adult cardiomyocytes are believed to withdraw from the cell cycle. To determine whether forced overexpression of cdk2 results in altered cell-cycle regulation in the adult heart, we generated transgenic mice specifically overexpressing cdk2 in hearts. Transgenic hearts expressed high levels of both cdk2 mRNA and catalytically active cdk2 proteins. Cdk2 overexpression significantly increased the levels of cdk4 and cyclins A, D3, and E. There was an increase in both DNA synthesis and proliferating cell nuclear antigen levels in the adult transgenic hearts. The ratio of heart weight to body weight in cdk2 transgenic mice was significantly increased in neonatal day 2 but not in adults compared with that of wild-type mice. Analysis of dispersed individual adult cardiomyocytes showed a 5.6-fold increase in the proportion of smaller mononuclear cardiomyocytes in the transgenic mice. Echocardiography revealed that transgenic heart was functionally normal. However, adult transgenic ventricles expressed beta-myosin heavy chain and atrial natriuretic factor. Surgically induced pressure overload caused an exaggerated maladaptive hypertrophic response in transgenic mice but did not change the proportion of mononuclear cardiomyocytes. The data suggest that overexpression of cdk2 promotes smaller, less-differentiated mononuclear cardiomyocytes in adult hearts that respond in an exaggerated manner to pressure overload.

Contractile reserve and intracellular calcium regulation in mouse myocytes from normal and hypertrophied failing hearts

Mouse myocyte contractility and the changes induced by pressure overload are not fully understood. We studied contractile reserve in isolated left ventricular myocytes from mice with ascending aortic stenosis (AS) during compensatory hypertrophy (4-week AS) and the later stage of early failure (7-week AS) and from control mice. Myocyte contraction and [Ca(2+)](i) transients with fluo-3 were measured simultaneously. At baseline (0.5 Hz, 1.5 mmol/L [Ca(2+)](o), 25 degrees C), the amplitude of myocyte shortening and peak-systolic [Ca(2+)](i) in 7-week AS were not different from those of controls, whereas contraction, relaxation, and the decline of [Ca(2+)](i) transients were slower. In response to the challenge of high [Ca(2+)](o), fractional cell shortening was severely depressed with reduced peak-systolic [Ca(2+)](i) in 7-week AS compared with controls. In response to rapid pacing stimulation, cell shortening and peak-systolic [Ca(2+)](i) increased in controls, but this response was depressed in 7-week AS. In contrast, the responses to both challenge with high [Ca(2+)](o) and rapid pacing in 4-week AS were similar to those of controls. Although protein levels of Na(+)-Ca(2+) exchanger were increased in both 4-week and 7-week AS, the ratio of SR Ca(2+)-ATPase to phospholamban protein levels was depressed in 7-week AS compared with controls but not in 4-week AS. This was associated with an impaired capacity to increase sarcoplasmic reticulum Ca(2+) load during high work states in 7-week AS myocytes. In hypertrophied failing mouse myocytes, depressed contractile reserve is related to an impaired augmentation of systolic [Ca(2+)](i) and SR Ca(2+) load and simulates findings in human failing myocytes.

Trastuzumab in the treatment of metastatic breast cancer : anticancer therapy versus cardiotoxicity

Trastuzumab, a monoclonal antibody against the HER2 receptor, was recently approved for the treatment of metastatic breast cancer. However, 28% of patients receiving both an anthracycline and trastuzumab developed heart failure. Although HER2 overexpression has been associated with the development of cancer, HER2 receptors seem to be cardioprotective because they mediate the activation of important cardiac survival pathways. Because the morbidity and mortality of heart failure surpasses that of many cancers, prudent medical practice mandates that physicians learn more about the mechanisms of trastuzumab-induced cardiotoxicity and develop algorithms for assessing risk/benefit ratios before extending the use of this agent to patients with less invasive forms of breast cancer.

Left ventricular hypertrophy in ascending aortic stenosis mice: anoikis and the progression to early failure

BACKGROUND

To determine potential mechanisms of the transition from hypertrophy to very early failure, we examined apoptosis in a model of ascending aortic stenosis (AS) in male FVB/n mice.

METHODS AND RESULTS

Compared with age-matched controls, 4-week and 7-week AS animals (n=12 to 16 per group) had increased ratios of left ventricular weight to body weight (4.7+/-0.7 versus 3.1+/-0.2 and 5. 7+/-0.4 versus 2.7+/-0.1 mg/g, respectively, P<0.05) with similar body weights. Myocyte width was also increased in 4-week and 7-week AS mice compared with controls (19.0+/-0.8 and 25.2+/-1.8 versus 14. 1+/-0.5 microm, respectively, P<0.01). By 7 weeks, AS myocytes displayed branching with distinct differences in intercalated disk size and staining for beta(1)-integrin on both cell surface and adjacent extracellular matrix. In vivo left ventricular systolic developed pressure per gram as well as endocardial fractional shortening were similar in 4-week AS and controls but depressed in 7-week AS mice. Myocyte apoptosis estimated by in situ nick end-labeling (TUNEL) was extremely rare in 4-week AS and control mice; however, a low prevalence of TUNEL-positive myocytes and DNA laddering were detected in 7-week AS mice. The specificity of TUNEL labeling was confirmed by in situ ligation of hairpin oligonucleotides.

CONCLUSIONS

Our findings indicate that myocyte apoptosis develops during the transition from hypertrophy to early failure in mice with chronic biomechanical stress and support the hypothesis that the disruption of normal myocyte anchorage to adjacent extracellular matrix and cells, a process called anoikis, may signal apoptosis.

Chronic N(G)-nitro-L-arginine methyl ester-induced hypertension : novel molecular adaptation to systolic load in absence of hypertrophy

BACKGROUND

Chronic N(G)-nitro-L-arginine methyl ester (L-NAME), which inhibits nitric oxide synthesis, causes hypertension and would therefore be expected to induce robust cardiac hypertrophy. However, L-NAME has negative metabolic effects on protein synthesis that suppress the increase in left ventricular (LV) mass in response to sustained pressure overload. In the present study, we used L-NAME-induced hypertension to test the hypothesis that adaptation to pressure overload occurs even when hypertrophy is suppressed.

METHODS AND RESULTS

Male rats received L-NAME (50 mg. kg(-1). d(-1)) or no drug for 6 weeks. Rats with L-NAME-induced hypertension had levels of systolic wall stress similar to those of rats with aortic stenosis (85+/-19 versus 92+/-16 kdyne/cm). Rats with aortic stenosis developed a nearly 2-fold increase in LV mass compared with controls. In contrast, in the L-NAME rats, no increase in LV mass (1. 00+/-0.03 versus 1.04+/-0.04 g) or hypertrophy of isolated myocytes occurred (3586+/-129 versus 3756+/-135 microm(2)) compared with controls. Nevertheless, chronic pressure overload was not accompanied by the development of heart failure. LV systolic performance was maintained by mechanisms of concentric remodeling (decrease of in vivo LV chamber dimension relative to wall thickness) and augmented myocardial calcium-dependent contractile reserve associated with preserved expression of alpha- and beta-myosin heavy chain isoforms and sarcoplasmic reticulum Ca(2+) ATPase (SERCA-2).

CONCLUSIONS

When the expected compensatory hypertrophic response is suppressed during L-NAME-induced hypertension, severe chronic pressure overload is associated with a successful adaptation to maintain systolic performance; this adaptation depends on both LV remodeling and enhanced contractility in response to calcium.

Dynamic changes in sarcoplasmic reticulum function in cardiac hypertrophy and failure

Previous studies have demonstrated that cardiac function changes with development of pressure overload-induced hypertrophy. The present study was undertaken to discover the basis for the changes in sarcoplasmic reticulum (SR) functions: uptake, (as related to the SR Ca2+ pump properties) and release in isolated, perfused hypertrophied rat hearts. Our results demonstrated significant prolongation of the time-to-90%-relaxation, both during the period of compensation (8 weeks after banding the ascending aorta, group HR1), when systolic function was preserved, and later with progressive hypertrophy (20 weeks after banding, group HR2) and contractile failure (20-22 weeks after banding, group F). The initial rates of the oxalate-supported SR Ca2+ uptake and the maximum transport rate (Vmax) of the SR Ca2+ pump, measured in the left ventricular homogenates, during blockade of the SR Ca2+ release channels with ruthenium red, were preserved in group HR1. To correlate early relaxation abnormalities with SR function, the [Ca2+] required for half-maximal pump activation (EC50) was examined and increased significantly in HRI vs. Sham1 (0.95+/-0.06 vs. 0.81+/-0.04 microM, P<0.05) indicating that the affinity of the SR Ca2+ pump for Ca2+ was reduced. The same tendency was demonstrated in groups HR2 (0.94+/-0.06 vs. 0.79+/-0.05) and F (0.89+/-0.05 vs. 0.78+/-0.05). In addition, with progression of hypertrophy we observed a significant decline in the amount of SR Ca2+ pump, as assessed by the Vmax, from 31.22+/-1.20 (Sham2) to 26.47+/-1.58 HR2) nmol/mg protein per min (P<0.05), and from 33.81+/-1.23 (Sham3) to 25.15+/-1.57 (F) nmol/mg protein per min, (P<0.01). This decrease was accompanied by a parallel reduction in the number of SR Ca2+ release channels by 14% (HR2) and 23% (F), as determined by maximum [3H] ryanodine binding (Bmax). These results suggest that pressure overload-induced changes in SR Ca2+ uptake (as reflected by Vmax and EC50) and SR Ca2+ release (as reflected by Bmax), both leading to diminished Ca2+ sequestration, may contribute to impaired cardiac relaxation with compensatory hypertrophy and failure.

Neuregulin in cardiac hypertrophy in rats with aortic stenosis. Differential expression of erbB2 and erbB4 receptors

BACKGROUND

Neuregulins are a family of peptide growth factors that promote cell growth and viability. The potential role of neuregulin-erbB signaling in hypertrophic growth and later failure in the adult heart in vivo is not known.

METHODS AND RESULTS

We used ribonuclease protection assays to quantify mRNA levels of neuregulin, erbB2, and erbB4 in left ventricular (LV) tissue and myocytes of normal rats and rats with aortic stenosis with pressure-overload hypertrophy 6 and 22 weeks after banding. At both stages of hypertrophy, Northern blot analyses of mRNA from LV myocytes showed upregulation of atrial natriuretic peptide, a molecular marker of hypertrophy (P<0.05). LV tissue neuregulin message levels were similar in animals with aortic stenosis compared with controls (P=NS) and were not detectable in myocytes. LV erbB2 and erbB4 message levels in LV tissue and myocytes were maintained during early compensatory hypertrophy in 6-week aortic stenosis animals compared with age-matched controls; in contrast, erbB2 and erbB4 message levels were depressed in 22-week aortic stenosis animals at the stage of early failure (both P<0.01 vs age-matched controls). Immunoblotting of erbB2 and erbB4 also showed normal protein levels in 6-week aortic stenosis animals compared with controls; however, erbB2 and erbB4 protein levels were depressed in 22-week aortic stenosis animals (48% decrease in erbB2, P<0.05, and 43% decrease in erbB4, P<0.01) relative to age-matched controls.

CONCLUSIONS

The neuregulin receptors erbB2 and erbB4 are downregulated at both the message and protein levels at the stage of early failure in animals with chronic hypertrophy secondary to aortic stenosis. These data suggest a role for disabled erbB receptor signaling in the transition from compensatory hypertrophy to failure.

Gender differences in molecular remodeling in pressure overload hypertrophy

OBJECTIVES

The objective of this study was to examine gender differences in left ventricular (LV) function and expression of cardiac genes in response to LV pressure overload due to ascending aortic stenosis in rats.

BACKGROUND

Clinical studies have documented gender differences in the pattern of adaptive LV hypertrophy. Whether these differences result from intrinsic differences in molecular adaptation to pressure overload between men and women, or are related to other factors is not known.

METHODS

Male (n = 8) and female (n = 8) Wistar rats underwent ascending aortic stenosis and were studied 6 weeks after banding with gender-matched control rats (male n = 7; female n = 7). The LV contractile reserve was examined in isolated hearts from each group. We compared LV messenger ribonucleic acid (mRNA) levels of atrial natriuretic factor (ANF), beta-myosin heavy chain, sarcoplasmic reticulum Ca2+-adenosine triphosphatase (ATPase) and Na+-Ca2+ exchanger. Reverse transcriptase polymerase chain reaction was used to identify estrogen receptor transcript in cardiac myocytes and LV tissue.

RESULTS

The magnitude of LV hypertrophy (LVH) and systolic wall stress were similar in male and female animals with LVH. Male LVH hearts demonstrated a depressed contractile reserve; in contrast, contractile reserve was preserved in female LVH hearts. The expression of beta-myosin heavy chain and ANF mRNA was greater in male versus female LVH hearts. Sarcoplasmic reticulum Ca2+-ATPase mRNA levels were depressed in male LVH but not in female LVH compared with control rats, and Na+-Ca2+ exchanger mRNA levels were increased similarly in both male and female LVH hearts. Estrogen receptor transcript was detected in both adult male and female cardiac myocytes and LV tissue.

CONCLUSIONS

There are significant gender differences in the LV adaptation to pressure overload despite a similar degree of LVH and systolic wall stress in male and female rats. There is the potential for estrogen signaling through the adult myocyte estrogen receptor in both male and female rats to contribute to gender differences in gene expression in pathologic hypertrophy.

Role of angiotensin AT1, and AT2 receptors in cardiac hypertrophy and disease

Angiotensin II modulates beat-to-beat cardiac performance as a potent vasocontrictor, inotrope, and regulator of water and electrolyte balance. It is also a growth factor that can stimulate the early molecular growth responses of proto-oncogene activation and new protein synthesis, and the later event of cardiocyte hypertrophy independent from load. Its effects are mediated through the angiotensin II type 1 (AT1) receptor, which exists as the AT1a and AT1b isoforms, and the angiotensin II type 2 (AT2) receptor. There is still controversy regarding the role of activation of the AT1 receptor subtype(s) as a mandatory signal versus modulatory regulator of the transduction of mechanical load in pressure-overload hypertrophy due to hypertension or aortic stenosis. The role of the AT2 receptor subtype in the heart is even less well understood, although this receptor appears to serve as an antigrowth signal in proliferating cells. Here we review current data on these controversies, including new data that support the notion that angiotensin II activation of the cardiac AT2 receptor subtype inhibits the effects of angiotensin II on the immediate growth response in the adult heart.

Pressure overload induces severe hypertrophy in mice treated with cyclosporine, an inhibitor of calcineurin

Cardiac hypertrophy is the fundamental adaptation of the adult heart to mechanical load. Recent work has shown that inhibition of calcineurin activity with cyclosporine suppresses the development of hypertrophy in calcineurin transgenic mice and in in vitro systems of neonatal rat cardiocytes stimulated with peptide growth factors. To test the hypothesis that the calcineurin signaling pathway is critical for load-induced hypertrophy in vivo, we examined the effects of cyclosporine treatment on left ventricular hypertrophy induced by experimental ascending aortic stenosis for 4 weeks in mice. Left ventricular systolic pressure was elevated to a similar level in aortic stenosis mice that were treated with cyclosporine versus no drug. Left ventricular mass and myocyte size were similar in treated and untreated aortic stenosis animals and significantly greater than control animals, showing that cyclosporine treatment does not suppress hypertrophic growth. Both treated and untreated animals showed increased left ventricular expression of the load-sensitive gene atrial natriuretic factor. Calcineurin activity was measured in the left ventricle and the spleen from control mice and aortic stenosis mice treated with cyclosporine versus no drug. Levels of calcineurin activity were similar in the spleens of control and untreated aortic stenosis mice. However, calcineurin activity was severely depressed in left ventricular tissue of untreated aortic stenosis mice compared with control mice and was further reduced by cyclosporine treatment. Thus, pathological hypertrophy and cardiac-restricted gene expression induced by pressure overload in vivo are not suppressed by treatment with cyclosporine and do not appear to depend on the elevation of left ventricular calcineurin activity.

Treatment with growth hormone enhances contractile reserve and intracellular calcium transients in myocytes from rats with postinfarction heart failure

BACKGROUND

Recombinant human growth hormone (GH) improves in vivo cardiac function in rats with postinfarction heart failure (MI). We examined the effects of growth hormone (14 days of 3.5 mg. kg-1. d-1 begun 4 weeks after MI) on contractile reserve in left ventricular myocytes from rats with chronic postinfarction heart failure.

METHODS AND RESULTS

Cell shortening and [Ca2+]i were measured with the indicator fluo 3 in myocytes from MI, MI+GH, control, and normal animals treated with GH (C+GH) under stimulation at 0.5 Hz at 37 degrees C. Cell length was similar in MI and MI+GH rats (150+/-5 and 157+/-5 microm) and was greater in these groups than in the control and C+GH groups (140+/-4 and 139+/-4 microm, P<0.05). At baseline perfusate calcium of 1.2 mmol/L, myocyte fractional shortening and [Ca2+]i transients were similar among the 4 groups. We then assessed contractile reserve by measuring the increase in myocyte fractional shortening in the presence of high-perfusate calcium of 3.5 mmol/L. In the control and C+GH groups, myocyte fractional shortening and peak systolic [Ca2+]i were similarly increased in the presence of high-perfusate calcium. In the presence of high-perfusate calcium, both myocyte fractional shortening and peak systolic [Ca2+]i were depressed in the MI compared with the control groups. In contrast, myocyte fractional shortening (14.1+/-.9% versus 11.1+/-.9%, P<0.05) and peak systolic [Ca2+]i (647+/-43 versus 509+/-37 nmol/L, P<0.05) were significantly higher in MI+GH than in MI rats and were comparable to controls. Left ventricular myocyte expression of sarcoplasmic reticulum Ca2+ ATPase 2 (SERCA-2) and left ventricular SERCA-2 protein levels were increased in MI+GH compared with MI rats.

CONCLUSIONS

Calcium-dependent contractile reserve is depressed in myocytes from rats with postinfarction heart failure. Long-term growth hormone therapy increases contractile reserve by restoring normal augmentation of systolic [Ca2+]i in myocytes from rats with postinfarction heart failure.

Angiotensin II type 2 receptor blockade amplifies the early signals of cardiac growth response to angiotensin II in hypertrophied hearts

BACKGROUND

We have previously shown that the acute molecular growth response of new protein synthesis and protein kinase C activation in response to angiotensin II (Ang II) is altered in left ventricular (LV) hypertrophy compared with normal hearts. We have also shown an upregulation of Ang II type 2 (AT2) receptors in hypertrophied hearts relative to controls. Activation of AT2 receptors is proposed to counteract growth effects of AT1 receptor in response to Ang II. Thus, we tested the hypothesis that in hypertrophied hearts, the AT2 receptor mediates inhibitory effects on the new cardiac protein synthesis in response to acute Ang II stimulation.

METHODS AND RESULTS

Flaccid buffer-perfused adult normal and hypertrophied rat hearts were perfused with Ang II 10(-8) mol/L plus prazosin 10(-7) mol/L or Ang II plus the AT2 blocker PD 123319 5x10(-7) mol/L. New protein synthesis was measured by the rate of [3H]phenylalanine incorporation into the LV proteins. In normal hearts, Ang II (n=8) increased the rate of [3H]phenylalanine incorporation by 74+/-27% (P<0.05 versus no drug). Treatment with PD123319 (n=8) did not increase protein synthesis compared with Ang II alone (32+/-11% versus Ang II alone, P=NS). In hypertrophied hearts, Ang II alone (n=6) increased the rate of [3H]phenylalanine incorporation only by 23+/-13% (P=NS versus no drug). In contrast, treatment with PD123319 (n=7) induced a 76+/-21% increase in new LV protein synthesis compared with Ang II alone (P<0.05). AT2 receptor blockade in Ang II-stimulated hypertrophied hearts was associated with enhanced membrane protein kinase C translocation and reduced LV cGMP content.

CONCLUSIONS

These data support the hypothesis that in adult hypertrophied rat hearts, inhibition of cardiac AT2 receptors, which are upregulated in chronic LV hypertrophy, amplifies the immediate LV growth response to Ang II. This appears to be related to augmented Ang II-stimulated PKC activation and suppression of cGMP signaling.

A dose-dependent increase in mortality with vesnarinone among patients with severe heart failure. Vesnarinone Trial Investigators

BACKGROUND

Vesnarinone, an inotropic drug, was shown in a short-term placebo-controlled trial to improve survival markedly in patients with severe heart failure when given at a dose of 60 mg per day, but there was a trend toward an adverse effect on survival when the dose was 120 mg per day. In a longer-term study, we evaluated the effects of daily doses of 60 mg or 30 mg of vesnarinone, as compared with placebo, on mortality and morbidity.

METHODS

We enrolled 3833 patients who had symptoms of New York Heart Association class III or IV heart failure and a left ventricular ejection fraction of 30 percent or less despite optimal treatment. The mean follow-up was 286 days.

RESULTS

There were significantly fewer deaths in the placebo group (242 deaths, or 18.9 percent) than in the 60-mg vesnarinone group (292 deaths, or 22.9 percent) and longer survival (P=0.02). The increase in mortality with vesnarinone was attributed to an increase in sudden death, presumed to be due to arrhythmia. The quality of life had improved significantly more in the 60-mg vesnarinone group than in the placebo group at 8 weeks (P<0.001) and 16 weeks (P=0.003) after randomization. Trends in mortality and in measures of the quality of life in the 30-mg vesnarinone group were similar to those in the 60-mg group but not significantly different from those in the placebo group. Agranulocytosis occurred in 1.2 percent of the patients given 60 mg of vesnarinone per day and 0.2 percent of those given 30 mg of vesnarinone.

CONCLUSIONS

Vesnarinone is associated with a dose-dependent increase in mortality among patients with severe heart failure, an increase that is probably related to an increase in deaths due to arrhythmia. A short-term benefit in terms of the quality of life raises issues about the appropriate therapeutic goal in treating heart failure.

Atrial natriuretic peptide has different effects on contractility and intracellular pH in normal and hypertrophied myocytes from pressure-overloaded hearts

BACKGROUND

Atrial natriuretic peptide (ANP) depresses contractility in left ventricular myocytes. Its expression is upregulated in pressure-overloaded hypertrophied hearts; however, the effects of ANP on contractility in hypertrophied myocytes are not known. Our aims were (1) to examine the cellular mechanisms of this depression in contractility in normal myocytes and (2) to test the hypothesis that the effects of ANP on contractility differ in hypertrophied myocytes from rats with ascending aortic stenosis.

METHODS AND RESULTS

We measured the myocyte shortening as an index of contractility, [Ca2+]i with fluo 3, and pHi with seminaphthorhodafluor-1 (SNARF-1). In normal control myocytes (n=26), ANP caused a concentration-dependent depression of contractility and reduction in pHi. In the presence of 10(-6) mol/L ANP, fractional cell shortening was 78+/-5% of baseline (P<0.05) and pHi was reduced by 0.16+/-0.04 U from baseline (P<0.01) without changes in [Ca2+]i. The magnitude of the depression of contraction caused by ANP was similar to that caused by intracellular acidification induced by an NH4Cl pulse. The effects of ANP on contractility and pHi were prevented in the presence of 5-(N-ethyl-N-isopropyl)-amiloride (EIPA), which inhibits the Na+/H+ exchanger. In hypertrophied myocytes (n=23), ANP did not depress either myocyte contractility or pHi at concentrations of either 10(-8), 10(-7), or 10(-6) mol/L. ANP caused no change in pHi or the [Ca2+]i transient in hypertrophied myocytes. The cGMP level was increased and Na+/H+ exchanger mRNA levels were normal in left ventricles from aortic stenosis rats compared with controls.

CONCLUSIONS

ANP directly depresses contractility in normal myocytes via intracellular acidification, which decreases myofilament [Ca2+]i sensitivity. In contrast, ANP causes no effects on contractility and pHi in hypertrophied myocytes, suggesting a suppression in the coupling of the ANP-cGMP intracellular signaling pathway to the Na+/H+ exchanger.

Hypertrophic remodeling: gender differences in the early response to left ventricular pressure overload

OBJECTIVES

To identify gender differences in left ventricular remodeling, hypertrophy, and function in response to pressure overload due to ascending aortic banding in rats.

BACKGROUND

Gender may influence the adaptation to pressure overload, as women with aortic stenosis have greater degrees of left ventricular hypertrophy and better left ventricular function than men.

METHODS

Fifty-two weanling rats underwent ascending aortic banding (16 males, 18 females), or sham surgery (9 males, 9 females). At 6 and 20 weeks, rats underwent transthoracic echo Doppler studies, and closed-chest left ventricular pressures with direct left ventricular puncture. Perfusion-fixed tissues from eight rats were examined morphometrically for myocyte cross-sectional area and percent collagen volume.

RESULTS

At 6 weeks after aortic banding, left ventricular remodeling, extent of hypertrophy, and function appeared similar in male and female rats. At 20 weeks, male but not female rats showed an early transition to heart failure, with onset of cavity dilatation (left ventricular diameter=155% vs. 121% of same-sex sham), loss of concentric remodeling (relative wall thickness=102% vs. 139% of sham), elevated wall stress (systolic stress=266% vs. 154% of sham), and diastolic dysfunction (deceleration of rapid filling=251% vs. 190% of sham). Left ventricular systolic pressures were higher in female compared with male rats (186+/-20 vs. 139+/-13 mm Hg), while diastolic pressures tended to be lower (14+/-4 vs. 17+/-4 mm Hg).

CONCLUSIONS

Gender significantly influences the evolution of the early response to pressure overload, including the transition to heart failure in rats with aortic stenosis.

Chronic L-arginine treatment increases cardiac cyclic guanosine 5'-monophosphate in rats with aortic stenosis: effects on left ventricular mass and beta-adrenergic contractile reserve

OBJECTIVES

We tested the hypothesis that nitric oxide (NO) cyclic guanosine 5'-monophosphate (GMP) signaling is deficient in pressure overload hypertrophy due to ascending aortic stenosis, and that long-term L-arginine treatment will increase cardiac cyclic GMP production and modify left ventricular (LV) pressure overload hypertrophy and beta-adrenergic contractile response.

BACKGROUND

Nitric oxide cyclic GMP signaling is postulated to depress vascular growth, but its effects on cardiac hypertrophic growth are controversial.

METHODS

Forty control rats and 40 rats with aortic stenosis left ventricular hypertrophy ([LVH] group) were randomized to receive either L-arginine (0.40 g/kg/day) or no drug for 6 weeks.

RESULTS

The dose of L-arginine did not alter systemic blood pressure. Animals with LVH had similar LV constitutive nitric oxide synthase (cNOS) mRNA and protein levels, and LV cyclic GMP levels as compared with age-matched controls. In rats with LVH L-arginine treatment led to a 35% increase in cNOS protein levels (p = 0.09 vs untreated animals with LVH) and a 1.7-fold increase in LV cyclic GMP levels (p < 0.05 vs untreated animals with LVH). However, L-arginine treatment did not suppress LVH in the animals with aortic stenosis. In contrast, in vivo LV systolic pressure was depressed in L-arginine treated versus untreated rats with LVH (163 +/- 16 vs 198 +/- 10 mm Hg, p < 0.05). In addition, the contractile response to isoproterenol was blunted in both isolated intact hearts and isolated myocytes from L-arginine treated rats with LVH compared with untreated rats with LVH. This effect was mediated by a blunted increase in peak systolic intracellular calcium in response to beta-adrenergic stimulation.

CONCLUSIONS

Left ventricular hypertrophy due to chronic mechanical systolic pressure overload is not characterized by a deficiency of LV cNOS and cyclic GMP levels. In rats with aortic stenosis, L-arginine treatment increased cardiac levels of cyclic GMP, but it did not modify cardiac mass in rats with aortic stenosis. However, long-term stimulation of NO-cyclic GMP signaling depressed in vivo LV systolic function in LVH rats and markedly blunted the contractile response to beta-adrenergic stimulation.

The restriction of diffusion of cations at the external surface of cardiac myocytes varies between species

In cardiac muscle sarcolemmal structures such as T-tubules, caveolae and negatively charged protein-polysaccharides may affect the rate of cation exchange on the external surface of the cells. To test this hypothesis, we examined the rate of external cation exchange in adult rabbit and rat ventricular myocytes using a rapid solution switcher to change the bulk external solution within 4 ms. To assess the rate of diffusion of monovalent cations, we increased [K+]o from 4.4 to 6.6 or 8.8 mM and measured the time required to achieve a stable membrane depolarization. In rat myocytes, the mean time to 90% depolarization (t90) was significantly longer than that in rabbit myocytes (137 and 64 ms, respectively) and the difference in t90 was not associated with the cell size. To assess the time course of exchange of external Ca2+, we rapidly exposed the myocytes to 0 Ca2+-2 mM EGTA solution at specific time points before action potentials or voltage clamp steps, and measured the rate of alteration of the normalized peak [Ca2+]i transient (Fluo-3) or Ca2+ current. Exposure to 0 Ca2+-2 mM EGTA solution caused a decline in the intracellular calcium transient. In rat myocytes, the rate of decline in the [Ca2+]i transient was much slower (t90 > 1500 ms, the time required for 90% decline) than for the rabbit (t90 = 295 ms). Also, the rate of decline in the Ca2+ current was prolonged in rat myocytes (t90 = 910 ms) compared with rabbit myocytes (t90 = 241 ms). These data indicate that there is a restricted space on the external surface of sarcolemma which limits diffusion of divalent cations more markedly than monovalent cations. The extent of this limitation of cation diffusion varies between species, and may have functional significance.

Failure to maintain a low ADP concentration impairs diastolic function in hypertrophied rat hearts

BACKGROUND

Mechanisms in addition to diastolic calcium overload may contribute to diastolic dysfunction in hypertrophied hearts. In this study, we tested the hypothesis that failure to maintain a low ADP concentration in hypertrophied hearts contributes to diastolic dysfunction by inhibiting the rate of cross-bridge cycling.

METHODS AND RESULTS

By perfusing isolated rat hearts with pyruvate and 2-deoxyglucose (2DG), we were able to perturb [ADP] with minimal changes in [ATP] and [inorganic phosphate] or the contribution of glycolytic ATP to ATP synthesis. The effects of 2DG were compared in aortic-banded (LVH, n=5) and sham-operated (control, n=5) rat hearts. 31P NMR spectroscopy was used to measure the concentrations of phosphorus-containing compounds. We found a threefold increase of left ventricular end-diastolic pressure (LVEDP) in LVH during 2DG perfusion, and this increase was concomitant with a threefold increase in intracellular free [ADP]. The [ADP] in the control hearts was maintained <40 micromol/L, and no change in LVEDP was observed. A linear relationship between increases in [ADP] and LVEDP was found (r2=.66, P=.001). Furthermore, the capacity of the creatine kinase reaction, a major mechanism for maintaining a low [ADP], was decreased in LVH (P=.0001).

CONCLUSIONS

Increased [ADP] contributes to diastolic dysfunction in LVH, possibly due to slowed cross-bridge cycling. Decreased capacity of the creatine kinase reaction to rephosphorylate ADP is a likely contributing mechanism to the failure to maintain a low [ADP] in LVH.

Load-induced growth responses in isolated adult rat hearts. Role of the AT1 receptor

BACKGROUND

Stimulation of the angiotensin II type 1 (AT1) receptor by angiotensin II appears to be mandatory for the acute load-induced hypertrophic response of cultured neonatal rat cardiocytes, but its role in the adult heart is controversial. We tested the hypothesis that AT1 receptor blockade will inhibit the acute induction of proto-oncogenes and protein synthesis by the elevation of systolic wall stress in isolated beating adult rat hearts.

METHODS AND RESULTS

Using the established isovolumic perfused heart preparation under constant coronary flow, we found that an increment in left ventricular balloon volume generated an increase in systolic wall stress. The induction of left ventricular c-fos and c-myc mRNA (Northern blotting) was assessed in hearts subjected to increased systolic load without AT1 blockade (No AT1, n = 11) and with AT1 blockade (AT1, n = 11, losartan 40 mg.kg-1.d-1 x 5 days followed by 10(-5) mol/L infusion during perfusion). Flaccid hearts (no left ventricular balloon) served as controls (C, n = 9). The stimulation of new protein synthesis in response to increased systolic load was measured by incorporation of [3H]phenylalanine into cardiac proteins. Elevation of systolic load was associated with a twofold (P < .05) increase in c-fos and c-myc mRNA levels that was not blocked by losartan. The rate of [3H]phenylalanine incorporation into cardiac proteins was increased 2.7-fold (P < .01) in hearts subjected to increased systolic load compared with control hearts. However, AT1 receptor blockade with losartan did not prevent the stimulation of [3H]phenylalanine incorporation (881 +/- 97 versus 923 +/- 82 nmol.g protein-1.h-1, P = NS).

CONCLUSIONS

In contrast with immature myocytes subjected to stretch, the acute growth responses induced by systolic pressure overload in adult rat hearts do not depend on AT1 receptor activation.

Effects of the nitric oxide donor sodium nitroprusside on intracellular pH and contraction in hypertrophied myocytes

BACKGROUND

We compared the effects of the nitric oxide donor sodium nitroprusside (SNP) on intracellular pH (pHi), intracellular calcium concentration ([Ca2+]i) transients, and cell contraction in hypertrophied adult ventricular myocytes from aortic-banded rats and age-matched controls.

METHODS AND RESULTS

pHi was measured in individual myocytes with SNARF-1, and [Ca2+]i transients were measured with indo 1 simultaneously with cell motion. Experiments were performed at 37 degrees C in myocytes paced at 0.5 Hz in HEPES-buffered solution (extracellular pH = 7.40). At baseline, calibrated pHi, diastolic and systolic [Ca2+]i values, and the amplitude of cell contraction were similar in hypertrophied and control myocytes. Exposure of the control myocytes to 10(-6) mol/L SNP caused a decrease in the amplitude of cell contraction (72 +/- 7% of baseline, P < .05) that was associated with a decrease in pHi (-0.10 +/- 0.03 U, P < .05) with no change in peak systolic [Ca2+]i. In contrast, in the hypertrophied myocytes exposure to SNP did not decrease the amplitude of cell contraction or cause intracellular acidification (-0.01 +/- 0.01 U, NS). The cGMP analogue 8-bromo-cGMP depressed cell shortening and pHi in the control myocytes but failed to modify cell contraction or pHi in the hypertrophied cells. To examine the effects of SNP on Na(+)-H+ exchange during recovery from intracellular acidosis, cells were exposed to a pulse and washout of NH4Cl. SNP significantly depressed the rate of recovery from intracellular acidosis in the control cells compared with the rate in hypertrophied cells.

CONCLUSIONS

SNP and 8-bromo-cGMP cause a negative inotropic effect and depress the rate of recovery from intracellular acidification that is mediated by Na(+)-H+ exchange in normal adult rat myocytes. In contrast, SNP and 8-bromo-cGMP do not modify cell contraction or pHi in hypertrophied myocytes.

Angiotensin AT1 receptor inhibition. Effects on hypertrophic remodeling and ACE expression in rats with pressure-overload hypertrophy due to ascending aortic stenosis

BACKGROUND

We tested the hypothesis that long-term administration of the specific angiotensin II subtype 1 (AT1)-receptor blocker BMS-186295 will regress hypertrophy and modify left ventricular angiotensin converting enzyme (ACE) expression in rats with ascending aortic stenosis.

METHODS AND RESULTS

Six weeks after surgery, rats with ascending aortic stenosis were randomized to receive either the AT1-receptor blocker BMS-186295 50 mg.kg-1.d-1 (n = 49), amlodipine 2.5 mg.kg-1.d-1 (n = 48) as a positive control for systemic vasodilation, or no drug (n = 48) and compared with sham-operated rats (n = 39). Drug treatment was continued for 15 weeks. Left ventricular ACE mRNA levels were measured by ribonuclease protection assay. The left ventricular/body weight ratio was increased 43% in hearts from rats with untreated left ventricular hypertrophy (LVH) versus control hearts (P < .05). However, there was no difference in either the left ventricular/body weight ratio (2.78 +/- 0.08 versus 2.81 +/- 0.20 mg/g; P = NS) or myocyte cross-sectional area in the AT1-blocker-treated versus untreated LVH hearts. Amlodipine also showed no effect on regression of hypertrophy. In vivo left ventricular systolic pressure was significantly higher in untreated LVH versus sham-operated rats (193 +/- 8 versus 118 +/- 4 mm Hg; P < .05), and there was a similar severe elevation of left ventricular systolic pressure in the AT1-blocker- and amlodipine-treated LVH groups (189 +/- 9 and 188 +/- 16 mm Hg; P = NS versus untreated LVH). In vivo left ventricular end-diastolic pressure was higher in the untreated LVH than in the sham-operated rats (14.8 +/- 2.3 versus 7.0 +/- 0.5 mm Hg; P < .05). Left ventricular end-diastolic pressure was lower in the AT1-blocker-treated (11.0 +/- 1.7 mm Hg) and amlodipine-treated rats (11.5 +/- 1.8 mm Hg) and was similar to left ventricular end-diastolic pressure in the sham-operated rats (P = NS). Left ventricular ACE mRNA levels were elevated in untreated LVH rats but were normalized in both the AT1-blocker-treated rats and amlodipine-treated rats.

CONCLUSIONS

Long-term AT1-receptor blockade did not regress LVH in rats with persistent systolic pressure overload due to ascending aortic stenosis. However, both AT1-receptor blockade and amlodipine improved in vivo left ventricular end-diastolic pressure in association with the normalization of left ventricular ACE mRNA levels.

Report of the National Heart, Lung, and Blood Institute Special Emphasis Panel on Heart Failure Research

The SEP identified priorities to support in future basic and clinical research and pointed out directions likely to result in advances against heart failure. The list is not intended to be all-encompassing and does not address, for example, exciting lines of work already under way. Rather, the recommendations are designed to point out gaps in current knowledge not being adequately addressed and highly promising new directions. Although the incidence of heart failure continues to grow, emerging lines of research provide hope that research advances will eventually lead to more effective treatment and ultimately to prevention. This research will be well served by bringing the latest multidisciplinary approaches and the best investigators to focus on the problems of heart failure. It is hoped the efforts of distinguished expert entities such as the task force and SEP will be a useful guide in addressing the needs of the biomedical community and assisting in its success.

Endothelin and angiotensin II stimulation of Na+-H+ exchange is impaired in cardiac hypertrophy

We compared the effects of endothelin-1 (ET-1) on intracellular pH, intracellular [Ca2+]i, and cell contraction in hypertrophied adult ventricular myocytes from ascending aortic banded rats and age-matched controls. Intracellular pH (pH(i)) was measured in individual myocytes with SNARF-1, and [Ca2+]i was measured with indo-1, simultaneous with cell motion. Experiments were performed at 36 degrees C in myocytes paced at 0.5 Hz in Hepes-buffered solution (pH(o) 7.40) containing 1.2 mM CaCl2. At baseline, calibrated pH(i), diastolic and systolic [Ca2+]i values, and the amplitude of cell contraction were similar in hypertrophied and control myocytes. Exposure of the control myocytes to 10 nM ET-1 caused an increase in the amplitude of cell contraction to 163+/-22% of baseline (P < 0.05), associated with intracellular alkalinization (pH(i) + 0.08+/-0.02 U, P < 0.05) and a slight increase in peak systolic [Ca2+]i (104+/-11% of baseline, P < 0.05). In contrast, in the hypertrophied myocytes, exposure to ET-1 did not increase the amplitude of cell contraction or cause intracellular alkalinization (-0.01+/-0.02 U, NS). Similar effects were observed in the hypertrophied and control myocytes in response to exposure to 10 nM angiotensin II. ET-1 also increased the rate of recovery from intracellular acidosis induced by the washout of NH4Cl in the control cells, but did not do so in the hypertrophied cells. In the presence of 10 microM 5-(N-ethyl-N-isopropyl)-amiloride, which inhibits Na+-H+ exchange, ET-1 did not cause a positive inotropic effect or intracellular alkalinization in control cells. The activation of protein kinase C by exposure to phorbol ester caused intracellular alkalinization and it increased the rate of recovery from intracellular acidification induced by an NH4Cl pulse in control cells but not in hypertrophied cells. ET-1, as well as angiotensin II, and phorbol ester, fail to stimulate forward Na+-H+ exchange in adult hypertrophied myocytes. These data suggest a defect in the coupling of protein kinase C signaling with Na+-H+ exchange in adult hypertrophied myocytes.

Long-term angiotensin-converting enzyme inhibition with fosinopril improves depressed responsiveness to Ca2+ in myocytes from aortic-banded rats

BACKGROUND

We have previously shown that long-term ACE inhibition with fosinopril prolongs survival and improves ventricular function despite persistent severe left ventricular pressure overload in ascending aortic-banded rats with left ventricular hypertrophy during the transition from compensation to failure.

METHODS AND RESULTS

To study the cellular mechanism of the effects of long-term ACE inhibition on the modification of the transition to failure in pressure-overload hypertrophy, we measured simultaneous intracellular Ca2+ transients and myocyte shortening in isolated left ventricular myocytes from fosinopril-treated aortic-banded rats (n = 9), untreated aortic-banded rats (n = 9), and normal age-matched control rats (n = 10). Fosinopril therapy was begun 6 weeks after banding and was continued until week 21 after banding, when the animals were killed. Collagenase-dissociated myocytes loaded with indo 1-AM were paced at 3 Hz at 36 degrees C and superfused at [Ca2+]o of 0.6, 1.2, and 3.0 mmol/L. In myocytes from untreated aortic-banded rats, peak systolic [Ca2+]i was higher than in control myocytes, and the relationship between myocyte shortening and [Ca2+]i was depressed relative to control myocytes, implicating impaired responsiveness to Ca2+. Long-term fosinopril treatment improved both myocyte shortening and the relationship of shortening to [Ca2+]i (P < .05 versus myocytes from untreated aortic-banded rats). Maximal Ca(2+)-activated force was depressed in chemically skinned left ventricular fibers from untreated aortic-banded hypertrophied rats relative to age-matched controls but not in the fosinopril-treated aortic-banded rats.

CONCLUSIONS

Long-term ACE inhibition improves responsiveness to Ca2+ in the presence of normalization of maximal Ca(2+)-activated force in aortic-banded rats subjected to persistent pressure overload. This may contribute to the favorable effects whereby ACE inhibition modifies the transition from compensated hypertrophy to failure.

Pericardial effusion in patients with cancer: outcome with contemporary management strategies

OBJECTIVE

To investigate the clinical presentation and current management strategies of pericardial effusion in patients with malignancy.

DESIGN

Retrospective single centre, consecutive observational study.

SETTING

University hospital.

PATIENTS

93 consecutive patients with a past or present diagnosis of cancer and a pericardial effusion, including 50 with a pericardial effusion > 1 cm.

RESULTS

Of the 50 patients with pericardial effusions > 1 cm, most had stage 4 cancer (64%), were symptomatic at the time of presentation (74%), and had right atrial collapse (74%). Twenty patients were treated conservatively (without pericardiocentesis) and were less symptomatic (55% v 87%, P = 0.012), had smaller pericardial effusions (1.5 (0.4) v 1.8 (0.5), P = 0.02), and less frequent clinical (10% v 40%, P = 0.02) and echocardiographic evidence of tamponade (40% v 97%, P < 0.001) than the 30 patients treated invasively with initial pericardiocentesis (n = 29) or pericardial window placement (n = 1). Pericardial tamponade requiring repeat pericardiocentesis occurred in 18 (62%) of 29 patients after a median of 7 days. In contrast, only four (20%) of 20 patients in the conservative group progressed to frank clinical tamponade and required pericardiocentesis (P = 0.005 v invasive group). The overall median survival was 2 months with a survival rate at 48 months of 26%. Survival, duration of hospital stay, and hospital charges were similar with both strategies. By multivariable analysis, the absence of symptoms was the only independent predictor of long-term survival (relative hazards ratio = 3.2, P = 0.05). Survival was similar in the 43 patients with cancer and pericardial effusions of < or = 1 cm.

CONCLUSION

Asymptomatic patients with cancer and pericardial effusion can be managed conservatively with close follow up. In patients with symptoms or clinical cardiac tamponade, pericardiocentesis provides relief of symptoms but does not improve survival and has a high recurrence rate. Surgical pericardial windows or possibly percutaneous balloon pericardiotomy should be used for recurrences and should be considered for initial treatment.

Alteration of growth responses in established cardiac pressure overload hypertrophy in rats with aortic banding

We examined the acute effects of elevated wall stress, norepinephrine, and angiotensin II on cardiac protein synthesis as well as protooncogene expression in hearts with established pressure overload left ventricular hypertrophy. Isolated rat hearts with chronic hypertrophy (LVH) were studied 12 wk after ascending aortic banding when systolic function was fully maintained. New protein synthesis (incorporation of [3H]phenylalanine [Phe]) was analyzed in isolated perfused rat hearts after a 3-h protocol; c-fos, c-jun, c-myc, and early growth response gene-1 (EGR-1) mRNA levels (Northern blot) were studied over a time course from 15 to 240 min of perfusion. Under baseline conditions (i.e., before mechanical or neurohormonal stimulation), [3H]-Phe-incorporation (280 nmoles/gram protein/h) and protooncogene mRNA levels were similar in age-matched control and LVH hearts. However, hearts with chronic LVH were characterized by a markedly blunted or absent [3H]-Phe-incorporation after acute imposition of isovolumic systolic load (90 mmHg/gram left ventricle), as well as norepinephrine (10(-6)M), or angiotensin II infusion (10(-8)M plus prazosin 10(-7)M) compared with nonhypertrophied control hearts. Similarly, stimulation of LVH hearts with acute systolic load or norepinephrine was associated with a significantly blunted increase of protooncogene mRNA levels relative to control hearts. The blunted induction of c-fos mRNA in LVH hearts was not due to feedback inhibition, since cycloheximide perfusion of hearts exposed to elevated wall stress further increased the differences between age-matched control and LVH hearts. The data suggest that acute molecular growth responses to mechanical or neurohormonal stimulation are altered in rat hearts with established LVH relative to nonhypertrophied control hearts. This alteration of molecular adaptations in hearts with compensatory hypertrophy may prevent inappropriate excess cardiac growth in response to mechanical and neurohormonal stimuli.

Cardiac renin-angiotensin system: role in development of pressure-overload hypertrophy

Recent studies are reviewed dealing with the putative roles of the cardiac renin-angiotensin system in the development of pressure-overload hypertrophy and the subsequent transition from adaptive hypertrophy to diastolic dysfunction, impaired systolic function and cardiac failure. The results of these studies, which employed the aortic banded rat model of cardiac hypertrophy, indicate that the intracardiac conversion of angiotensin I (Ang I) to angiotensin II (Ang II) is significantly increase in hypertrophied hearts compared with hearts from age-matched, sham-operated controls, and that Ang II may have a direct effect of slowing relaxation and altering diastolic tone in the hypertrophied heart. Furthermore, in patients with aortic stenosis and severe baseline abnormalities of diastolic relaxation and filling, acute intracardiac angiotensin-converting enzyme (ACE) inhibition, totally in the absence of any systemic effect on neurohormones, improved diastolic function. ACE inhibition was found to reduce net ACE activity and to increase plasma renin activity in aortic banded animals compared with untreated banded controls. There was also a trend for circulating noradrenaline levels to be increased at this stage of transition to failure in the untreated banded animals but ACE inhibition tended to restore the levels back to normal. In ACE inhibitor-treated animals, left ventricular (LV) diastolic pressure was significantly reduced, despite the persistent elevation of systolic pressure, but not yet restored completely to normal. In untreated, banded animals the transition to cardiac failure was evidenced as an increase in both systolic and diastolic dimensions with a reduction in fractional shortening.(ABSTRACT TRUNCATED AT 250 WORDS)

Glycolytic inhibition: effects on diastolic relaxation and intracellular calcium handling in hypertrophied rat ventricular myocytes

We tested the hypothesis that glycolytic inhibition by 2-deoxyglucose causes greater impairment of diastolic relaxation and intracellular calcium handling in well-oxygenated hypertrophied adult rat myocytes compared with control myocytes. We simultaneously measured cell motion and intracellular free calcium concentration ([Ca2+]i) with indo-1 in isolated paced myocytes from aortic-banded rats and sham-operated rats. There was no difference in either the end-diastolic or peak-systolic [Ca2+]i between control and hypertrophied myocytes (97 +/- 18 vs. 105 +/- 15 nM, 467 +/- 92 vs. 556 +/- 67 nM, respectively). Myocytes were first superfused with oxygenated Hepes-buffered solution containing 1.2 mM CaCl2, 5.6 mM glucose, and 5 mM acetate, and paced at 3 Hz at 36 degrees C. Exposure to 20 mM 2-deoxyglucose as substitution of glucose for 15 min caused an upward shift of end-diastolic cell position in both control (n = 5) and hypertrophied myocytes (n = 10) (P < 0.001 vs. baseline), indicating an impaired extent of relaxation. Hypertrophied myocytes, however, showed a greater upward shift in end-diastolic cell position and slowing of relaxation compared with control myocytes (delta 144 +/- 28 vs. 55 +/- 15% of baseline diastolic position, P < 0.02). Exposure to 2-deoxyglucose increased end-diastolic [Ca2+]i in both groups (P < 0.001 vs. baseline), but there was no difference between hypertrophied and control myocytes (218 +/- 38 vs. 183 +/- 29 nM, respectively). The effects of 2-deoxyglucose were corroborated in isolated oxygenated perfused hearts in which glycolytic inhibition which caused severe elevation of isovolumic diastolic pressure and prolongation of relaxation in the hypertrophied hearts compared with controls. In summary, the inhibition of the glycolytic pathway impairs diastolic relaxation to a greater extent in hypertrophied myocytes than in control myocytes even in well-oxygenated conditions. The severe impairment of diastolic relaxation induced by 2-deoxyglucose in hypertrophied myocytes compared with control myocytes cannot be explained by greater diastolic Ca2+ overload, which implicates an increase in myofilament Ca(2+)-responsiveness as a possible mechanism.

Serial echocardiographic-Doppler assessment of left ventricular geometry and function in rats with pressure-overload hypertrophy. Chronic angiotensin-converting enzyme inhibition attenuates the transition to heart failure

BACKGROUND

Although chronic pressure overload may progress to left ventricular (LV) failure, the pathophysiology of this transition is not well understood. In addition, the effects of chronic angiotensin-converting enzyme (ACE) inhibition on this transition are largely undefined.

METHODS AND RESULTS

To examine changes in LV structure and function during the transition to heart failure, rats with LV hypertrophy due to banding of the ascending aorta (LVH, n = 22) and age-matched sham-operated rats (n = 6) were studied 6, 12, and 18 weeks after aortic banding. Two-dimensionally guided transthoracic M-mode echocardiograms and transmitral Doppler spectra were recorded for assessment of LV geometry and systolic and diastolic functions. LVH rats were randomized to no treatment (n = 10) or treatment with the ACE inhibitor fosinopril (50 mg/kg per day, n = 12) after the baseline echocardiogram. Six weeks after banding, LVH rats had increased LV wall thickness with normal cavity dimensions and supranormal endocardial systolic shortening. However, midwall shortening was mildly depressed, and a restrictive diastolic filling pattern was present. After 18 weeks of untreated pressure overload, LV wall thickness was unchanged, but cavity dilation, a fall in endocardial shortening, and further deterioration of diastolic filling were evident. In contrast to untreated LVH rats, the fosinopril-treated rats showed no change in LV diastolic cavity dimension, and systolic and diastolic functions did not deteriorate or improved. Closed chest LV systolic pressures at 18 weeks were not different in LVH or LVH-fosinopril rats (197 versus 198 mm Hg), although end-diastolic pressure was higher in the untreated rats (18 versus 11 mm Hg). Calculated LV systolic wall stress was lower in fosinopril-treated than untreated LVH rats. The severity of LV diastolic filling abnormalities correlated strongly with operating LV chamber stiffness (r = .88, P < .0001).

CONCLUSIONS

This model of pressure overload is characterized initially by concentric LV hypertrophy with compensated LV chamber performance; however, markedly abnormal diastolic filling is present. The transition from compensated hypertrophy to early failure is heralded by LV dilation, impairment of systolic function, and progression of the abnormalities in LV filling. Chronic ACE inhibition in rats with supravalvular aortic banding (1) does not change in vivo LV systolic pressure but prevents increased LV cavity size and increased LV wall stress and (2) attenuates impairment of (or improves) both systolic and diastolic functions. The effects of fosinopril could be explained in part by inhibition of an intracardiac renin-angiotensin system.

Angiotensin II-induced growth responses in isolated adult rat hearts. Evidence for load-independent induction of cardiac protein synthesis by angiotensin II

Cardiac myocyte hypertrophy often occurs in response to both hemodynamic and neurohumoral factors. To study whether activation of the renin-angiotensin system by itself may induce a cardiac growth response, the acute effects of angiotensin II on cardiac protein synthesis were studied in isolated rat hearts. New protein synthesis in isolated buffer-perfused adult rat hearts was measured by incorporation of [3H]phenylalanine into cardiac proteins during a 3-hour perfusion protocol. Angiotensin II (1 x 10(-8) mol/L), administered alone or in combination with the alpha 1-blocker prazosin (1 x 10(-7) mol/L), stimulated protein synthesis in both ventricles. The rate of [3H]phenylalanine incorporation into cardiac proteins was 3.9-fold (P < .005) and 2.6-fold (P < .01) higher in angiotensin II-perfused (n = 6) than in vehicle-perfused (n = 6) left and right ventricles, respectively. The induction of new protein synthesis by angiotensin II was blocked by the angiotensin II type 1 (AT1) receptor antagonist losartan (1 x 10(-7) mol/L, n = 5). To study the pathways of angiotensin signal transduction, protein kinase C (PKC)-epsilon as well as cardiac c-fos and c-jun mRNA levels were analyzed. Angiotensin II (1 x 10(-8) mol/L, n = 20) resulted in a transient translocation of PKC-epsilon from the cytosol to the cellular membrane. However, compared with phorbol ester stimulation (phorbol 12-myristate 13-acetate [PMA], 1 x 10(-7) mol/L; n = 20), angiotensin II effects on PKC translocation were significantly less pronounced and required a more prolonged stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracardiac angiotensin-converting enzyme inhibition improves diastolic function in patients with left ventricular hypertrophy due to aortic stenosis

BACKGROUND

Cardiac hypertrophy is associated with elevated intracardiac angiotensin-converting enzyme activity, which may contribute to diastolic dysfunction.

METHODS AND RESULTS

We infused enalaprilat (0.05 mg/min) for 15 minutes into the left coronary arteries of 20 adult patients with left ventricular (LV) hypertrophy due to aortic stenosis (mean aortic valve area, 0.7 +/- 0.2 cm2) and 10 patients with dilated cardiomyopathy (mean ejection fraction, 35 +/- 4%) and assessed (1) simultaneous changes in LV micromanometer pressure and dimensions, (2) LV regional wall motion analyzed by the area method, and (3) Doppler flow-velocity profiles. Systemic neurohormonal activation did not occur with the selective left coronary artery infusion; there were no changes in plasma renin activity, angiotensin-converting enzyme activity, or atrial natriuretic peptide. In patients with aortic stenosis, LV end-diastolic pressure declined from 25 +/- 2 to 20 +/- 2 mm Hg (P < .05). LV pressure-volume and LV pressure-dimension relations showed downward shifts by ventriculography and echocardiography, respectively, indicating improved diastolic distensibility. Regional area change during isovolumic relaxation increased in the anterior segments perfused with enalaprilat but decreased in the inferior segments, indicating acceleration of isovolumic relaxation in the anterior segments and reciprocal shortening in the inferior segments. Regional peak filling rate increased in the anterior segments but not in the inferior segments, and the regional area stiffness constant decreased in the anterior segments but not in the inferior segments. There were no changes in heart rate, cardiac output, or right atrial pressure, excluding alterations in right ventricular/pericardial constraint. In contrast, in the patients with dilated cardiomyopathy the decrease in LV end-diastolic pressure from 22 +/- 2 to 18 +/- 2 mm Hg (P < .05) was accompanied by a significant fall in right atrial pressure (9 +/- 1 to 6 +/- 1 mm Hg), implicating alterations in pericardial constraint. The patients with dilated cardiomyopathy showed no improvement in regional diastolic relaxation, filling, or distensibility.

CONCLUSIONS

Intracoronary enalaprilat at a dosage that did not cause systemic neurohormonal activation improved LV diastolic chamber distensibility and regional relaxation and filling in patients with LV hypertrophy due to aortic stenosis. In contrast, these effects of intracoronary enalaprilat on diastolic function were not observed in patients with dilated cardiomyopathy who did not have concentric hypertrophy. These observations support the hypothesis that the cardiac renin-angiotensin system is activated in patients with concentric pressure-overload hypertrophy and that this activation may contribute to impaired diastolic function.

Effects of angiotensin II on intracellular Ca2+ and pH in isolated beating rabbit hearts and myocytes loaded with the indicator indo-1

1. Angiotensin II increases myocardial contractility in several species, including the rabbit and man. However, it is controversial whether the predominant mechanism is an increase in free cytosolic [Ca2+]i or a change in myofilament Ca2+ sensitivity. To address this question, we infused angiotensin II in isolated perfused rabbit hearts loaded with the Ca2+ indicator indo-1 AM and measured changes in beat-to-beat surface transients of the Ca2+i-sensitive 400:500 nm ratio and left ventricular contractility. The effects of angiotensin II were compared with the response to a Ca(2+)-dependent increase in the inotropic state produced by a change in the perfusate [Ca2+] from 0.9 to 3.6 nM. 2. In the isolated beating heart, an increase in perfusate [Ca2+] caused an increase in left ventricular pressure +dP/dt in association with an increase in peak systolic [Ca2+]i. Angiotensin II perfusion caused a similar increase in left ventricular +dP/dt in the absence of any increase in peak systolic [Ca2+]i. 3. To exclude any contribution of non-myocyte sources of Ca(2+)-sensitive fluorescence which may be present in the intact heart, we also compared the effects of angiotensin II and a change in superfusate [Ca2+] in collagenase-dissociated paced adult rabbit ventricular myocytes loaded with indo-1 AM. In the isolated rabbit myocytes a change in perfusate [Ca2+] from 0.9 to 3.6 mM caused an increase in peak systolic cell shortening coincident with an increase in peak systolic [Ca2+]i. In contrast, angiotensin II caused a similar increase in peak systolic cell shortening whereas there was no increase in peak systolic [Ca2+]i. There was also no change in inward Ca2+ current (ICa) in response to angiotensin II. 4. To investigate further the mechanism of the positive inotropic action of angiotensin II, its effects on intracellular pH were studied in isolated rabbit myocytes loaded with the fluorescent H+ probe SNARF 1. These experiments demonstrated that angiotensin II induced a 0.2 pH unit increase coincident with the development of a positive inotropic effect in isolated rabbit myocytes. 5. In summary, angiotensin II has a direct positive inotropic effect in beating rabbit hearts and in isolated paced rabbit myocytes. These experiments provide support for the hypothesis that the predominant mechanism is not an increase in free cytosolic Ca2+ but is due in part to an increase in myofilament Ca2+ sensitivity due to intracellular alkalosis.

Angiotensin-converting enzyme inhibition prolongs survival and modifies the transition to heart failure in rats with pressure overload hypertrophy due to ascending aortic stenosis

BACKGROUND

We tested the hypotheses that long-term administration of the angiotensin-converting enzyme (ACE) inhibitor fosinopril will regress hypertrophy, modify the transition to heart failure, and prolong survival in rats with chronic left ventricular (LV) pressure overload due to ascending aortic stenosis.

METHODS AND RESULTS

Aortic stenosis was created in weanling male Wistar rats by a stainless steel clip placed on the ascending aorta. Age-matched control animals underwent a sham operation (Sham group, n = 57). Six weeks after surgery, rats with aortic stenosis were randomized to receive either oral fosinopril 50 mg.kg-1.d-1 (Fos/LVH group, n = 38) or no drug (LVH group, n = 36) for 15 weeks. Pilot studies confirmed that this dosage produced significant inhibition of LV tissue ACE in vivo. Animals were monitored daily, and survival during the 15-week treatment period was assessed by actuarial analysis. At 15 weeks, in vivo LV systolic and diastolic pressures and heart rate were measured. To assess contractile function, the force-calcium relation was evaluated by use of the isovolumic buffer-perfused, balloon-in-LV heart preparation at comparable coronary flow rates per gram LV weight. Quantitative morphometry was performed. Mortality during the 15-week trial was significantly less in the Fos/LVH group than in the LVH group (3% versus 31%, P < .005). No deaths occurred in the Sham group. In vivo LV systolic pressure was similar between Fos/LVH and LVH hearts (223 +/- 10 versus 232 +/- 9 mm Hg) and significantly higher than the Sham group (99 +/- 3 mm Hg, P < .05). In vivo LV diastolic pressure was significantly lower in Fos/LVH hearts than in LVH hearts (10 +/- 2 versus 15 +/- 2 mm Hg), and both were significantly higher than in the Sham group (5 +/- 1 mm Hg, P < .05). Heart rate was similar among all groups. Despite equivalent elevation of LV systolic pressure, fosinopril resulted in regression of myocyte hypertrophy in Fos/LVH versus LVH (myocyte cell width, 14.8 +/- 0.5 versus 20.8 +/- 2.2 microns, P < .05) to normal levels (Sham, 16.3 +/- 0.9 microns). Quantitative morphometry demonstrated that the regression of LV myocyte hypertrophy in the Fos/LVH group was associated with a relative increase in the fractional volume of fibrillar collagen and noncollagen interstitium. In the isolated heart experiments, LV systolic developed pressure relative to perfusate [Ca2+] was significantly higher in Fos/LVH hearts than in LVH hearts. The improvement in systolic function was not related to any difference in myocardial high-energy phosphate levels, since LV ATP and creatine phosphate levels were similar in Fos/LVH and LVH hearts.

CONCLUSIONS

In rats with ascending aortic stenosis, chronic ACE inhibition with fosinopril improved survival, decreased the extent of LV hypertrophy, and improved cardiac function despite persistent elevation of LV systolic pressure. The favorable effects of fosinopril may be related in part to inhibition of the effects of cardiac ACE on myocyte hypertrophy rather than to systemic hemodynamic mechanisms.

Distribution and function of cardiac angiotensin AT1- and AT2-receptor subtypes in hypertrophied rat hearts

To determine distribution and function of cardiac angiotensin (ANG) II receptor AT1 and AT2 subtypes in left ventricular (LV) hypertrophy (LVH), ANG II (10(-8) M) was infused into isolated rat hearts with hypertrophy from aortic banding and into sham-operated controls. ANG II was infused alone or in the presence of AT1 inhibitor [losartan (10(-5) M) or CL-329167 (10(-7) M)] or AT2 inhibitor [CG-42112A (10(-8) M]. ANG II alone caused less increase in coronary vascular resistance (CVR) in LVH compared with control hearts (19 vs. 39%; P < 0.01), although baseline CVR was higher in LVH hearts. This was prevented by AT1 but not AT2 antagonists. ANG II also increased LV end-diastolic pressure in LVH hearts, signifying decreased diastolic relaxation that was prevented by AT1 but not AT2 inhibition. Characterization of ANG II binding sites in LV membrane preparations revealed similar dissociation constants between groups (1.6 +/- 0.95 vs. 2.2 +/- 2.0 nM; not significant) but lower maximum binding capacity in the LVH group (21.1 +/- 5.9 vs. 33.5 +/- 3.0 fmol/mg protein; P < 0.05). Competition assays demonstrated that control left ventricles contain predominantly the AT1 subtype (68.8 +/- 20%), whereas LVH ventricles contain primarily the putative AT2 subtype (59.8% +/- 10.8%; P < 0.05). This suggests that receptor subtype redistribution occurs in LVH with AT1 subtype down-regulation. Nonetheless, the AT1 subtype mediates the effects of ANG II on coronary tone and diastolic dysfunction in pressure-overload hypertrophy.

Association between a deletion polymorphism of the angiotensin-converting-enzyme gene and left ventricular hypertrophy

BACKGROUND

Epidemiologic studies have shown that left ventricular hypertrophy is often found in the absence of an elevated cardiac workload. To investigate whether such hypertrophy is determined in part by genetic factors, we studied the association between this condition, as assessed by electrocardiographic criteria, and a deletion (D)-insertion (I) polymorphism of the angiotensin-converting-enzyme (ACE) gene.

METHODS

A population-based random sample of 711 women and 717 men 45 to 59 years of age was studied cross-sectionally in Augsburg, Germany. Electrocardiographic indexes, including the Sokolow-Lyon index, Minnesota Code 3.1, and the Rautaharju equations, were used to detect left ventricular hypertrophy. The status of the ACE gene with respect to the deletion-insertion allele was determined by the polymerase chain reaction in all subjects with left ventricular hypertrophy and an identical number of control subjects without the condition who were matched for age, sex, and blood-pressure status.

RESULTS

We identified 141 women and 149 men with evidence of left ventricular hypertrophy. Among these subjects, an excess were homozygous for the D allele of the ACE gene (odds ratio, 1.76; 95 percent confidence interval, 1.22 to 2.53; P = 0.003). The association of the DD genotype with left ventricular hypertrophy was stronger in men (odds ratio, 2.63; 95 percent confidence interval, 1.50 to 4.64; P < 0.001) than in women and was most prominent when blood-pressure measurements were normal (odds ratio, 4.05; 95 percent confidence interval, 1.76 to 9.28; P = 0.001). This association was evident for each of the scores recorded in the electrocardiographic testing for left ventricular hypertrophy.

CONCLUSIONS

The findings suggest that left ventricular hypertrophy is partially determined by genetic disposition. They identify the DD genotype of ACE as a potential genetic marker associated with an elevated risk of left ventricular hypertrophy in middle-aged men.

Effects of brief repetitive ischemia on contractility, relaxation, and coronary flow. Exaggerated postischemic diastolic dysfunction in pressure-overload hypertrophy

The recovery of systolic and diastolic function during unstable angina may be modified by the repetition of brief episodes of ischemia and by the presence of left ventricular hypertrophy (LVH). We studied the effects of six consecutive 5-minute cycles of no-flow ischemia and reperfusion followed by 25 minutes of recovery in isovolumic red blood cell-perfused hearts from aortic-banded rats with chronic LVH (n = 8) and sham-operated control rats (n = 8). At baseline (left ventricular end-diastolic pressure [LVEDP], 10 mm Hg), left ventricular developed pressure (123 +/- 5 versus 114 +/- 5 mm Hg/g) and coronary flow [2.5 +/- 0.3 versus 2.2 +/- 0.2 (mL/min)/g] were similar in LVH versus control rats. Repetitive ischemia was associated with progressive depression of postischemic recovery of left ventricular systolic function, and the recovery of left ventricular developed pressure after the final 25-minute reperfusion period was similar in LVH versus control rats (61 +/- 6% versus 72 +/- 4% of baseline, P = NS). Although there was no increase in isovolumic LVEDP during the initial cycle of transient ischemia, both groups showed a rapid and similar rise in LVEDP during subsequent ischemic cycles (delta 82 +/- 8 versus delta 89 +/- 7 mm Hg/g in response to the final ischemia cycle for LVH versus control rats, respectively; P = NS). The control hearts showed complete restoration of LVEDP to baseline during final reperfusion, whereas the LVH hearts showed prolonged and severe postischemic diastolic dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of 2,3-butanedione monoxime to estimate nonmechanical VO2 in rabbit hearts

The purpose of the present study was to evaluate the feasibility of partitioning myocardial O2 consumption (VO2) into mechanical and nonmechanical components in the whole heart preparation using a negative inotrope, 2,3-butanedione monoxime (BDM), which has been reported to have a selective effect on the contractile proteins in a low concentration range (< 6 mM). In six isolated bovine red blood cell-perfused rabbit hearts, VO2 and force-time integral (FTI) were measured during infusion of varying concentrations of BDM at a constant left ventricular volume chosen such that control left ventricular peak isovolumic pressure was approximately 100 mmHg. The VO2-FTI relation with BDM concentrations < or = 5 mM was highly linear (median r = 0.98). Its VO2-axis intercept at zero FTI had a positive value (mean 23% of control, 0.014 ml O2.beat-1 x 100 g-1). To confirm the selective effect of BDM on the contractile proteins, the intracellular free Ca2+ transient was measured with the fluorescent indicator indo 1 in three isolated buffer-perfused rabbit hearts. The amplitude of the Ca2+ transient was not altered by BDM at concentrations < or = 10 mM, although left ventricular developed pressure was markedly depressed. This finding indicates that BDM < or = 10 mM does not affect excitation-contraction coupling. We conclude that the VO2-axis intercept value of the VO2-FTI relation during BDM infusion in a low concentration range represents VO2 for nonmechanical energy utilization. The BDM method to partition VO2 into mechanical and nonmechanical components is thus feasible in the whole rabbit heart.

Selective changes in cardiac gene expression during compensated hypertrophy and the transition to cardiac decompensation in rats with chronic aortic banding

Left ventricular hypertrophy (LVH) is associated with reinduction of the fetal program of gene expression. It is unclear whether this pattern of cardiac gene expression changes with the development of left ventricular decompensation and failure. To answer these questions, we quantified steady-state levels of mRNA by the polymerase chain reaction in the left ventricular myocardium of rats 8 and 20 weeks after ascending aortic banding. Clinical and hemodynamic assessment identified two distinct groups of animals 20 weeks after aortic banding. The first group (20-week nonfailed LVH) demonstrated substantial LVH but no depression in systolic developed pressure per gram left ventricular weight compared with the age-matched control group. In contrast, a second group of rats exhibited clinical signs of congestive failure as well as a marked diminution in left ventricular developed pressure per gram. Assessment of the levels of mRNA encoding a panel of cardiac proteins demonstrated a greater than twofold increase in beta-myosin heavy chain mRNA and an approximately sixfold increase in atrial natriuretic factor mRNA in left ventricular myocardium of all three groups (8-week LVH, 20-week nonfailed LVH, 20-week failed LVH) when compared with appropriate age-matched control groups. In contrast, Ca(2+)-ATPase mRNA levels were decreased by 50% only in the left ventricular myocardium of animals with both clinical signs and hemodynamic indexes consistent with cardiac decompensation (20-week failed LVH). These results suggest that in rats with ascending aortic banding the hypertrophic phenotype is associated with a selective reinduction of the fetal gene program, which persists even after the development of left ventricular failure.(ABSTRACT TRUNCATED AT 250 WORDS)