The aim was to examine the relationship between changes in myocyte function to changes in protein and mRNA content of components of the beta adrenergic system with tachycardia induced cardiomyopathy.
...Contractile function and beta adrenergic responsiveness were measured in isolated myocytes from control pigs (n = 6) and in pigs subjected to three weeks of pacing induced supraventricular tachycardia (n = 6). beta Receptor density and affinity, the relative content of the stimulatory (Gs) and inhibitory (Gi) subunits of the G protein complex, and adenylate cyclase activity were determined from sarcolemmal preparations. In order to determine whether these changes were accompanied by alterations in steady state mRNA levels for specific components of the beta adrenergic system, mRNA content for the beta 1 adrenergic receptor and the G alpha s and G alpha i2 subunits of the G protein complex was measured.
Chronic supraventricular tachycardia caused a 36% increase in left ventricular end diastolic dimension and a 61% decrease in left ventricular fractional shortening compared to controls. The velocity of isolated myocyte shortening was 50% lower in myocytes from hearts with tachycardia cardiomyopathy than in control myocytes. In the presence of 50 nM isoprenaline or 2 microM forskolin, the velocity of myocyte shortening was 65% lower in the myopathic myocytes than in the controls. With the development of tachycardic cardiomyopathy, beta adrenergic receptor density fell by 25% with no change in affinity, Gs decreased by 35%, and Gi increased by over 50% compared to controls. Basal adenylate cyclase activity and isoprenaline and forskolin stimulated adenylate cyclase activity fell by over 50% with supraventricular tachycardia compared to controls. The relative content of G alpha i2 mRNA increased threefold with the development of tachycardic cardiomyopathy with no change in the relative abundance of mRNA for the beta 1 receptor or G alpha s when compared with controls.
The changes in myocyte beta adrenergic responsiveness with the development of tachycardic cardiomyopathy are due to alterations in cellular mechanisms (decreased beta receptor and Gs density, increased Gi) and in molecular mechanisms (increased Gi mRNA content).
Standard mitral valve replacement (MVR) in patients with chronic mitral regurgitation consistently results in a decrease in postoperative left ventricular (LV) ejection performance. This fall in ...ejection performance has been attributed, at least in part, to unfavorable loading conditions imposed by the elimination of the low-impedance pathway for LV emptying into the left atrium. In contrast to standard MVR in which the chordae tendineae are severed, however, MVR with chordal preservation (MVR-CP) does not usually decrease LV ejection performance despite similar removal of the low-impedance pathway. The purpose of the present study was to define the mechanisms responsible for this discordance in postoperative ejection performance between MVR with and without chordal preservation.
Echocardiography and sphygmomanometer blood pressures were obtained in 15 patients with pure chronic mitral regurgitation before and 7-10 days after mitral valve surgery. These measurements were used to calculate ventricular volume, wall stress, and ejection fraction. Seven patients underwent MVR with chordal transection (MVR-CT), and eight patients underwent MVR-CP. MVR-CT resulted in no postoperative change in LV end-diastolic volume, a significant increase in LV end-systolic volume, a significant increase in end-systolic stress, from 89 +/- 9 to 111 +/- 12 g/cm2 (p < 0.05), and a significant decrease in ejection fraction, from 0.60 +/- 0.02 to 36 +/- 0.02 (p < 0.05). In contrast, patients who underwent MVR-CP had a significant decrease in LV end-diastolic and end-systolic volumes. End-systolic wall stress actually fell from 95 +/- 6 to 66 +/- 6 g/cm2 (p < 0.05), and ejection fraction was unchanged (0.63 +/- 0.01 before and 0.61 +/- 0.02 after mitral valve surgery) instead of reduced.
MVR-CT resulted in a decrease in ejection performance caused in part by an increase in end-systolic stress, which in turn increased end-systolic volume. Conversely, MVR-CP resulted in a smaller LV size, allowing a reduced end-systolic stress and preservation of ejection performance despite closure of the low-impedance left atrial ejection pathway.
The PARAGON-HF (Prospective Comparison of ARNI with ARB Global Outcomes in HF With Preserved Ejection Fraction) trial is designed to determine the efficacy and safety of the angiotensin receptor ...neprilysin inhibitor sacubitril/valsartan compared with valsartan in patients with chronic heart failure and preserved ejection fraction (HFpEF).
HFpEF is highly prevalent, associated with substantial morbidity and mortality, and in need of effective therapies that improve outcomes. The angiotensin receptor neprilysin inhibitor (ARNI) sacubitril/valsartan, which has been shown to benefit patients with heart failure (HF) and reduced ejection fraction, demonstrated favorable physiologic effects in a phase II HFpEF trial.
The PARAGON-HF trial is a randomized, double-blind, parallel group, active-controlled, event-driven trial comparing the long-term efficacy and safety of valsartan and sacubitril/valsartan in patients with chronic HFpEF (left ventricular ejection fraction ≥45%), New York Heart Association functional class II to IV symptoms, elevated natriuretic peptides, and evidence of structural heart disease. Before randomization, all patients entered sequential single-blind run-in periods to ensure tolerability of both drugs at half the target doses (i.e., valsartan titrated to 80 mg bid followed by sacubitril/valsartan 49/51 mg 100 mg bid). The primary outcome is the composite of cardiovascular death and total (first and recurrent) HF hospitalizations.
PARAGON-HF will determine whether sacubitril/valsartan is superior to angiotensin receptor blockade alone in patients with chronic symptomatic HFpEF. (Efficacy and Safety of LCZ696 Compared to Valsartan, on Morbidity and Mortality in Heart Failure Patients With Preserved Ejection Fraction PARAGON-HF; NCT01920711)
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In vivo studies show that beta3-integrin-mediated focal adhesion formation (FAF) causes recruitment of nonreceptor tyrosine kinases to the cytoskeleton in pressure-overloaded myocardium. To define ...the mechanism of beta3-integrin-mediated signaling, we developed a cell culture model (adult feline cardiocytes embedded in a 3-dimensional matrix of native type 1 collagen, fibronectin, and vitronectin) wherein beta3-integrin-mediated focal adhesion kinase occurs. Focal adhesion kinase was analyzed immunocytochemically using confocal microscopy. Initial studies suggested that cardiocytes cultured in a 3-dimensional matrix formed focal adhesions consisting of both beta3-integrin and the muscle-specific isoform, beta1-integrin (beta1D). The focal adhesions were associated with focal adhesion kinase on both costameres and intercalated disks. To determine the cause of beta1D-integrin-mediated focal adhesion kinase in this model, time course studies were done. Beta3-integrin-mediated focal adhesion kinase occurred within 30 minutes after embedding cardiocytes and persisted for >24 hours, whereas beta1D-integrin-mediated focal adhesion kinase was present from the outset. Because confocal microscopy showed that laminin was present on the surface of freshly isolated cardiocytes, we hypothesized that this was causative of beta1D-integrin-mediated focal adhesion kinase. Freshly isolated cardiocytes washed with acidic medium (2 minutes, pH 3.0) to remove laminin and then embedded in a 3-dimensional matrix showed complete absence of beta1D-integrin-mediated focal adhesion kinase, but beta3-integrin-mediated focal adhesion kinase occurred with a time course similar to that seen in cultured, unwashed cardiocytes. Acid washing did not alter the binding ability of beta1D-integrin, because acid-washed cardiocytes in the presence of laminin showed beta1D-integrin-mediated focal adhesion kinase. Thus, cardiocytes embedded in a 3-dimensional matrix show beta3-integrin-mediated focal adhesion kinase and provide an in vitro model to study beta3-integrin-mediated signaling in response to hemodynamic cardiac loading.
Variability is a major complicating factor in analysis by two-dimensional gel electrophoresis. Improvements in methodologies have focused on improving individual gel quality rather than ...reproducibility. We homogenized rat cardiac tissue and rehydrated using a matrix of buffers to determine the optimal sample conditions. Six buffers were used to solubilize the proteins. Solubilized proteins were separated by isoelectric focusing using four buffers. Gels were run in triplicate to assess the method of preparation yielding the least variability. Number of spots and variability were different between conditions. Proteins solubilized in a buffer containing 5 M urea, 2 M thiourea, 2% CHAPS, 2% SB 3-10, ampholytes, DTT, and protease inhibitors and focused in a buffer containing 9 M urea and 4% NP40 had the lowest coefficient of variation. Variability was compared across isoelectric point ranges and was different. Minimizing technical variability in two-dimensional polyacrylamide gel electrophoresis is critical to identify differences between conditions. Sample preparation should be optimized to minimize variability as well as to maximize the number of spots seen.
Independent studies have shown either ubiquitin‐mediated protein degradation or the mammalian target of rapamycin (mTOR) is necessary for increased ventricular mass and survival signaling for ...compensated hypertrophy in pressure‐overloaded (PO) myocardium. We tested whether the ubiquitin‐mediated regulation of growth and survival in hypertrophic myocardium is linked to the mTOR pathway. For in vivo studies, right ventricle pressure overload (RVPO) in rats was conducted by pulmonary artery banding; the normally loaded LV served as an internal control. Rapamycin (0.75 mg/kg/day) or vehicle alone was administered intraperitoneally for 3 days or 2 wk. Ubiquitinated proteins increased in cardiomyocytes following 48 h PO and were further enhanced by rapamycin. Rapamycin pretreatment also significantly increased PO‐induced Akt phosphorylation at S473, confirmed in cardiomyocytes in vitro to be downstream of mTORC2. In vivo prosurvival signaling showed rapamycin increased PO‐induced degradation of phosphorylated inhibitor of κB (IκB), enhanced expression of cellular inhibitor of apoptosis protein 1 (cIAP1), and decreased active caspase‐3. Long term rapamycin treatment in 2 wk PO myocardium blunted hypertrophy, improved contractile function, and reduced caspase‐3 and calpain activation. Therefore, rapamycin may have cardioprotective benefits for hypertensive patients.
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