Effects Of Chronic Pressure Overload Research Articles

Stabilization of RyR2 maintains right ventricular function, reduces the development of ventricular arrhythmias, and improves prognosis in pulmonary hypertension.

Right ventricular (RV) dysfunction and its associated arrhythmias are recognized as important determinants of the prognosis of pulmonary arterial hypertension (PAH). Here, we aimed to investigate whether direct pharmacological intervention in the RV muscle with dantrolene (DAN), a stabilizer of the cardiac ryanodine receptor (RyR2), has a protective effect against RV dysfunction and arrhythmia in a monocrotaline (MCT)-induced PAH rat model. Male 8-week-old Sprague-Dawley rats were injected with MCT for the induction of PAH. Induction of ventricular tachycardia (VT) by catecholamines was also evaluated in association with RyR2-mediated Ca2+ release properties in isolated cardiomyocytes. A pulmonary artery-banding model has also been established to assess the independent effects of chronic pressure overload on RV morphology and function. In the MCT-induced PAH rat model, RV hypertrophy, dilation, and functional decline were observed, with a survival rate of 0% 2 months after MCT induction. In contrast, chronic DAN treatment improved all these RV parameters and increased survival by 80%. Chronic DAN treatment also prevented the dissociation of calmodulin from RyR2, thereby inhibiting Ca2+ sparks and spontaneous Ca2+ transients in MCT-induced hypertrophied RV cardiomyocytes. Epinephrine induced VT in more than 50% of rats with MCT-induced PAH, but complete suppression of VT was achieved by chronic DAN treatment. Stabilization of RyR2 by DAN has potential as a new therapeutic agent against the development of RV dysfunction and fatal arrhythmia associated with PAH.

Alpha-lipoic acid protects against pressure overload-induced heart failure via ALDH2-dependent Nrf1-FUNDC1 signaling

Alpha-lipoic acid (α-LA), a well-known antioxidant, was proved to active ALDH2 in nitrate tolerance and diabetic animal model. However, the therapeutic advantage of α-LA for heart failure and related signaling pathway have not been explored. This study was designed to examine the role of α-LA–ALDH2 in heart failure injury and mitochondrial damage. ALDH2 knockout (ALDH2−/−) mice and primary neonatal rat cardiomyocytes (NRCMs) were subjected to assessment of myocardial function and mitochondrial autophagy. Our data demonstrated α-LA significantly reduced the degree of TAC-induced LV hypertrophy and dysfunction in wild-type mice, not in ALDH2−/− mice. In molecular level, α-LA significantly restored ALDH2 activity and expression as well as increased the expression of a novel mitophagy receptor protein FUNDC1 in wild-type TAC mice. Besides, we confirmed that ALDH2 which was activated by α-LA governed the activation of Nrf1–FUNDC1 cascade. Our data suggest that α-LA played a positive role in protecting the heart against adverse effects of chronic pressure overload.

Rats are Protected from Chronic Pressure Overload Compared with Mice Through Angiogenesis, but not Myogenesis.

It is generally assumed that rats and mice respond to cardiovascular stress similarly. The first goal of this investigation was to compare the effects of chronic pressure overload, induced by 4 weeks of transverse aortic constriction (TAC), in Sprague Dawley rats and C57/BL/6J mice. TAC, after 1 day, induced similar left ventricular (LV) pressure gradients in both rats and mice (113 ± 5.4 vs. 103 ± 11.5 mmHg), and after 4weeks a similar amount of LV hypertrophy (LV/tibial length increase: 51 ± 6.0 vs. 51 ± 5.7). After 4 weeks of TAC, LV systolic and diastolic function were preserved in rats, whereas LV ejection fraction decreased in mice (19 ± 2%), along with increases in LV end diastolic pressure (159 ± 54%), LV systolic wall stress (90 ± 12%), and LV diastolic wall stress (102 ± 41%). The second goal was to determine whether angiogenesis or myogenesis was the mechanism protecting against chronic pressure overload. Immunofluorescent Ki67 staining of capillaries revealed greater increases in angiogenesis with TAC in rats (10 ± 2 positive cells/field) than in mice (6 ± 1 positive cells/field). Myocardial blood flow fell by 55 ± 15% in mice but was preserved in rats. Coronary reserve, the increase in blood flow to the heart with adenosine, was preserved in rats, whereas it fell by 28% in mice with TAC. The next goal was to determine if myogenesis, through generation of stem cells, mediated these differences. This was accomplished by staining the myocardium with c‐kit. More c‐kit positive cells were found in rats with TAC compared to mice with TAC (0.30 ± 0.03 vs. 0.07 ± 0.02 cells/mm2). Surprisingly, these c‐kit positive cells were located not in myocytes, but in the interstitial space and were all negative for Troponin I. However, some of these c‐kit positive cells were positive for CD31, i.e., endothelial cells, which could be involved in mediation of the angiogenesis. Thus, rats tolerate severe pressure overload better than mice, with mechanisms involving increased angiogenesis, but not myogenesis.

Alpha-Lipoic Acid Protects Against Pressure Overload-induced Heart Failure <i>via</i> ALDH2-Dependent Nrf1-FUNDC1 Signaling

Background: Acetaldehyde dehydrogenase 2 (ALDH2) could protect the heart against pressure overload-induced heart failure in mice. Alpha-lipoic acid (α-LA), a well-known antioxidant, was capable of activating ALDH2. However, impact of α-LA on pressure overload-induced heart failure remains unknown now. Methods: α-LA on pressure overload-induced heart failure were assessed using ALDH2 knockout (ALDH2-/-) mice and primary neonatal rat cardiomyocytes (NRCMs). TAC-induced left ventricular hypertrophy and contractile function were assessed by echocardiography and cell shortening/relengthening system. Heart histological measurement were using H&E, WGA, Masson’s trichrome, DHE and TUNEL. Mitochondrial mass and morphology were visualized using TEM. The target proteins and their interactions was investigated by bioinformatic analysis, luciferase reporter and chromatin immunoprecipitation (ChIP) assays. Findings: In vivo, we found that supplement of α-LA significantly reduced transverse aortic constriction (TAC)-induced LV hypertrophy and dysfunction in wild-type mice, as evidenced by preserved LV ejection fraction, a more favorable histologic change and restoration of mitochondrial normality. Whereas, α-LA did not affect TAC induced LV hypertrophy and dysfunction in ALDH2 gene knockout (KO) mice. In molecular level, α-LA significantly restored ALDH2 activity and expression as well as upregulated the expression of FUN14 domain containing 1 (FUNDC1), an activator of hypoxia-induced mitophagy, in wild type TAC mice, again, these effects were not observed in ALDH2 gene KO mice undergoing TAC. In angiotensin II –induced hypertrophy in vitro model of neonatal rat cardiomyocytes (NRCMs), we confirmed that α-LA could activate ALDH2 and nuclear respiratory factor 1 (Nrf1) - FUNDC-1 cascade. Interpretation: These data supported the notion that α-LA treatment could protect the heart against adverse effects of chronic pressure overload via ALDH2-dependent Nrf1-FUNDC1 signaling pathway. Funding Statement: This work was supported by the National Science Fund for Distinguished Young Scholars to AS (81725002) and a grant of Innovative Research Groups of the National Natural Science Foundation of China (81521001). Declaration of Interests: The authors have declared that no conflict of interest exists. Ethics Approval Statement: All of the mice experiments were performed under protocols approved by the Institutional Animal Care and Use Committee of the Fudan University.

Worse cardiac remodeling in response to pressure overload in type 2 diabetes mellitus

BackgroundDiabetic cardiomyopathy is characterized by cardiac structural and functional abnormalities. Additionally, chronic pressure overload conditions are highly prevalent amongst diabetic population and this association leads to a more severe myocardial impairment. The differences in myocardial pathophysiology between type 1 and type 2 diabetes mellitus (DM) still remain to be clarified. Thus, we aimed to investigate biventricular structural and functional changes promoted by the two types of DM and the impact of concomitant chronic pressure overload. MethodsWistar rats were injected with streptozotocin (Type 1 DM, T1DM) or fed with a hypercaloric diet (Type 2 DM, T2DM). Pressure overload was imposed in DM animals by aortic constriction and after 5weeks of DM the cardiac function and structure were evaluated. ResultsBoth types of DM promoted hypertrophy, increased fibrosis and advanced glycation end-products deposition, in the two ventricles. Interestingly, the induced myocardial alterations were distinct. While T1DM stimulated a pronounced hypertrophy and extracellular matrix remodeling, T2DM induced functional impairment. The negative impact of the association of DM with aortic constriction was more pronounced in T2DM, promoting impaired function and increased stiffness, particularly in the right ventricle. ConclusionsOur study demonstrated that the two types of diabetes induce distinct cardiac alterations per se or when combined with chronic pressure overload. T1DM promoted a more extensive remodeling in cardiac structure while T2DM significantly impaired ventricular function. The impact of pressure overload was more notorious in T2DM as observed by worse myocardial remodeling, suggesting a higher susceptibility to the deleterious effects of chronic pressure overload, namely hypertension, among this diabetic population.

Abnormal right ventricular relaxation in pulmonary hypertension.

Left ventricular diastolic dysfunction is a well-described complication of systemic hypertension. However, less is known regarding the effect of chronic pressure overload on right ventricular (RV) diastolic function. We hypothesized that pulmonary hypertension (PHT) is associated with abnormal RV early relaxation and that this would be best shown by invasive pressure measurement. Twenty-five patients undergoing right heart catheterization for investigation of breathlessness and/or suspected PHT were studied. In addition to standard measurements, RV pressure was sampled with a high-fidelity micromanometer, and RV pressure/time curves were analyzed. Patients were divided into a PHT group and a non-PHT group on the basis of a derived mean pulmonary artery systolic pressure of 25 mmHg. Eleven patients were classified to the PHT group. This group had significantly higher RV minimum diastolic pressure ([Formula: see text] vs. [Formula: see text] mmHg, [Formula: see text]) and RV end-diastolic pressure (RVEDP; [Formula: see text] vs. [Formula: see text] mmHg, [Formula: see text]), and RV τ was significantly prolonged ([Formula: see text] vs. [Formula: see text] ms, [Formula: see text]). There were strong correlations between RV τ and RV minimum diastolic pressure ([Formula: see text], [Formula: see text]) and between RV τ and RVEDP ([Formula: see text], [Formula: see text]). There was a trend toward increased RV contractility (end-systolic elastance) in the PHT group ([Formula: see text] vs. [Formula: see text] mmHg/mL, [Formula: see text]) and a correlation between RV systolic pressure and first derivative of maximum pressure change ([Formula: see text], [Formula: see text]). Stroke volumes were similar. Invasive measures of RV early relaxation are abnormal in patients with PHT, whereas measured contractility is static or increasing, which suggests that diastolic dysfunction may precede systolic dysfunction. Furthermore, there is a strong association between measures of RV relaxation and RV filling pressures.

Metformin Protects Against Systolic Overload–Induced Heart Failure Independent of AMP-Activated Protein Kinase α2

Activation of AMP-activated protein kinase (AMPK)-α2 protects the heart against pressure overload-induced heart failure in mice. Although metformin is a known activator of AMPK, it is unclear whether its cardioprotection acts independently of an AMPKα2-dependent pathway. Because the role of AMPKα1 stimulation on remodeling of failing hearts is poorly defined, we first studied the effects of disruption of both the AMPKα1 and AMPKα2 genes on the response to transverse aortic constriction-induced left ventricular (LV) hypertrophy and dysfunction in mice. AMPKα2 gene knockout significantly exacerbated the degree of transverse aortic constriction-induced LV hypertrophy and dysfunction, whereas AMPKα1 gene knockout had no effect on the degree of transverse aortic constriction-induced LV hypertrophy and dysfunction. Administration of metformin was equally effective in attenuating transverse aortic constriction-induced LV remodeling in both wild-type and AMPKα2 knockout mice, as evidenced by reduced LV and lung weights, a preserved LV ejection fraction, and reduced phosphorylation of mammalian target of rapamycin (p-mTOR(Ser2448)) and its downstream target p-p70S6K(Thr389). These data support the notion that activation of AMPKα1 plays a negligible role in protecting the heart against the adverse effects of chronic pressure overload, and that metformin protects against adverse remodeling through a pathway that seems independent of AMPKα2.

Adult Cardiac Expression of the Activating Transcription Factor 3, ATF3, Promotes Ventricular Hypertrophy

Cardiac hypertrophy is an adaptive response to various mechanophysical and pathophysiological stresses. However, when chronic stress is sustained, the beneficial response turns into a maladaptive process that eventually leads to heart failure. Although major advances in the treatment of patients have reduced mortality, there is a dire need for novel treatments for cardiac hypertrophy. Accordingly, considerable efforts are being directed towards developing mice models and understanding the processes that lead to cardiac hypertrophy. A case in point is ATF3, an immediate early transcription factor whose expression is induced in various cardiac stress models but has been reported to have conflicting functional significance in hypertrophy. To address this issue, we generated a transgenic mouse line with tetracycline-regulated ATF3 cardiac expression. These mice allowed us to study the consequence of ATF3 expression in the embryo or during the adult period, thus distinguishing the effect of ATF3 on development versus pathogenesis of cardiac dysfunction. Importantly, ATF3 expression in adult mice resulted in rapid ventricles hypertrophy, heart dysfunction, and fibrosis. When combined with a phenylephrine-infusion pressure overload model, the ATF3 expressing mice displayed a severe outcome and heart dysfunction. In a complementary approach, ATF3 KO mice displayed a lower level of heart hypertrophy in the same pressure overload model. In summary, ectopic expression of ATF3 is sufficient to promote cardiac hypertrophy and exacerbates the deleterious effect of chronic pressure overload; conversely, ATF3 deletion protects the heart. Therefore, ATF3 may serve as an important drug target to reduce the detrimental consequences of heart hypertrophy.

Pulmonary Hypertension is Associated With Right Ventricular Diastolic Dysfunction

Purpose: The effect of chronic pressure overload on right ventricular (RV) diastolic function is unknown. We examined invasive measures of RV diastolic function in patients with a range of pulmonary pressures. Methods: Twenty-five patients (seven male, mean age 57.6) underwent right heart catheterisation for investigation of dyspnoea and/or suspected pulmonary hypertension (PH). These included nine patients with left ventricular diastolic dysfunction (LVDD), seven patients with scleroderma, two patients with scleroderma and LVDD, one patient with IPAH, one patient with severe mitral stenosis, one patient with interstitial lung disease and four ostensibly healthy subjects. RV pressure was sampled by a Radi PressureWire. RV systolic pressure (RVSP), RV minimum diastolic pressure (RVDP), RV dP/dt max and RV dP/dt min were obtained. RV end diastolic pressure (RVEDP) was defined as the pressure at 10% RV dP/dt max. RV isovolumic relaxation time (IVRT) was defined as the time between RV dP/dt min and the time at RVEDP during initial pressure decay. RV tau was determined using the method of Weiss. Patients were divided into a PH group (mPAP > 25 mmHg) and a non-PH group. Results: Eleven patients had mPAP > 25 mmHg. This group had higher RVSP, RVDP, RVEDP and longer RV tau. There was a trend to a longer IVRT. RV dP/dt min was greater in the PH group, reflecting the after load dependence of this measure. In contrast, RV dP/dt max (a surrogate of contractility) was similar.Tabled 1RVSP (mmHg)RVDP (mmHg)RV EDP (mmHg)dP/dt min (mmHg/s)dP/dt max (mmHg/s)RV tau (ms)IVRT (ms)PH56.0 ± 21.55.1 ± 6.611.0 ± 6.3−530 ± 219521 ± 20953 ± 3252 ± 25Non−PH30.0 ± 5.2−0.1 ± 3.33.8 ± 3.7−304 ± 78436 ± 14631 ± 1338 ± 16p0.0020.030.0040.0060.270.040.13 Open table in a new tab Conclusion: Pulmonary hypertension is associated with abnormal measures of RV active relaxation and increased RVEDP.

Right Ventricular Tau is an Important Determinant of Right Ventricular End Diastolic Pressure

Purpose: The effect of chronic pressure overload on the diastolic function of the right ventricle (RV) has not been well studied in humans. We explored the relationship between invasive measures of RV diastolic function and RV pressure across a range of patients with and without pulmonary hypertension. Methods: Eighteen patients undergoing diagnostic right heart catheterisation were studied. Six patients had left ventricular diastolic dysfunction (LVDD), six had scleroderma, two had LVDD and scleroderma, two had idiopathic pulmonary arterial hypertension and two patients were found to be normal after investigation. RV pressure was measured invasively by a Radi PressureWire sampling at 100 Hz. Afterload was measured by peak RV systolic pressure (RVSP). Diastolic function parameters of minimum RV diastolic pressure (minRVDP) and RV (dP/dt)min and RV end diastolic pressure (RVEDP) were derived. RV tau was calculated using the method of Weiss. All measurements were averaged over five cardiac cycles. Results:Tabled 1Parameter (range)RVSP (18.4–69.3 mmHg)minRVDP (−5.9 to 10.2 mmHg)RVEDP (−2.5 to 15.2 mmHg)RV tau (9–80 ms)r = 0.32p = nsr = 0.91p < 0.0001r = 0.94p < 0.0001RV (dP/dt)min (−200 to −856 mmHg/s)r = −0.89p < 0.0001r = −0.15p = nsr = −0.12p = ns Open table in a new tab RV tau was strongly associated with minRVDP and RVEDP but not with RVSP. RV (dP/dt)min was strongly correlated with RVSP but not minRVDP or RVEDP. Conclusion: RV tau is an afterload independent measure of RV relaxation, while RV (dP/dt)min is strongly inversely associated with peak RV systolic pressure. Early RV relaxation as measured by RV tau is an important determinant of RVEDP as well as minimum RV diastolic pressure.

Long-term use of low-dose spironolactone in spontaneously hypertensive rats: Effects on left ventricular hypertrophy and stiffness

AbstractThe aim of the present study was to evaluate the effect of low-dose spironolactone initiated during the early stages of hypertension development and to assess the effects of chronic pressure overload on ventricular remodeling in rats. Male spontaneously hypertensive rats (SHRs) (4 weeks) were randomized to receive daily spironolactone (20mg/kg) or vehicle (mineral oil) from 4 weeks to 8 months of age. Systolic blood pressure was measured non-invasively by tail-cuff pletysmography at baseline, 4 and 8 months. Hemodynamic assessment was performed at the end of treatment by arterial and ventricular catheterization. An in situ left ventricular pressure-volume curve was created to evaluate dilatation and wall stiffness. Systolic blood pressure at 1 month of age was higher in SHRs than in the Wistar group; it increased throughout the follow-up period and remained elevated with treatment (Wistar: 136±2, SHR: 197±6.8, SHR-Spiro: 207±7.1mmHg; p<0.05). Spironolactone reduced cardiac hypertrophy (Wistar: 1.25±0.03 SHR: 1.00±0.03, SHR-Spiro: 0.86±0.02g; p<0.05) and left ventricular mass normalized to body weight (Wistar: 2.51±0.06, SHR: 2.70±0.08, 2.53±0.07mg/g; p<0.05). Moreover, the left ventricular wall stiffness that was higher in SHRs was partially reduced by spironolactone treatment (Wistar: 0.370±0.032; SHR: 0.825±0.058; SHR-Spiro: 0.650±0.023mmHg/ml; p<0.05). Our results show that long-term spironolactone treatment initiated at the early stage of hypertension development reduces left ventricular hypertrophy and wall stiffness in SHRs.

Effects of cardiac overexpression of type 6 adenylyl cyclase affects on the response to chronic pressure overload.

Adenylyl cyclase (AC) type 5 (AC5) and AC type 6 (AC6) are the two major AC isoforms in the heart. Cardiac overexpression of AC6 has been shown to be protective in response to several interventions. In this investigation, we examined the effects of chronic pressure overload in AC6 transgenic (TG) mice. In the absence of any stress, AC6 TG mice exhibited enhanced contractile function compared with their wild-type (WT) littermates, i.e., increased (P < 0.05) left ventricular (LV) ejection fraction (EF) (75 +/- 0.9 vs. 71 +/- 0.5%) and LV dP/dt (7,850 +/- 526 vs. 6,374 +/- 315 mmHg/s). Forskolin (25 microg x kg(-1) x min(-1) for 5 min) increased LVEF more (P < 0.05) in AC6 TG mice (14.8 +/- 1.0%) than in WT mice (7.7 +/- 1.0%). Also, isoproterenol (0.04 microg x kg(-1) x min(-1) for 5 min) increased LVEF more (P < 0.05) in AC6 TG mice (18.0 +/- 1.2%) than in WT mice (11.6 +/- 2.1%). Pressure overload, induced by 4 wk of transverse aortic constriction (TAC), increased the LV weight-to-body weight ratio and myocyte cross-sectional area similarly in both groups, but reduced LVEF more in AC6 TG mice (22%) compared with WT mice (9%), despite the higher starting level of LVEF in AC6 TG mice. LV systolic wall stress increased more in AC6 TG mice than in WT mice, which could be responsible for the reduced LVEF in AC6 TG mice with chronic pressure overload. In addition, LV dP/dt was no longer elevated in AC6 TG mice after TAC compared with WT mice. LV end-diastolic diameter was also greater (P < 0.05) in AC6 TG mice (3.8 +/- 0.07 mm) than in WT mice (3.6 +/- 0.05 mm) after TAC. Thus, in contrast to other interventions previously reported to be salutary with cardiac AC6 overpression, the response to chronic pressure overload was not; actually, AC6 TG mice fared worse than WT mice. The mechanism may be due to the increased LV systolic wall stress in AC6 TG mice with chronic pressure overload.

Genetic inhibition of calcineurin induces diastolic dysfunction in mice with chronic pressure overload

Calcineurin is a Ca(2+)/calmodulin-dependent protein phosphatase that induces myocardial growth in response to several physiological and pathological stimuli. Calcineurin inhibition, induced either via cyclosporine or genetically, can decrease myocardial hypertrophy secondary to pressure overload without affecting left ventricular (LV) systolic function. Since hypertrophy can also affect LV diastolic function, the goal of this study was to examine the effects of chronic pressure overload (2 wk aortic banding) in transgenic (Tg) mice overexpressing Zaki-4beta (TgZ), a specific endogenous inhibitor of calcineurin, on LV diastolic function. As expected, in the TgZ mice with calcineurin inhibitor overexpression, aortic banding reduced the degree of LV hypertrophy, as assessed by LV weight-to-body weight ratio (3.5 + or - 0.1) compared with that in non-Tg mice (4.6 + or - 0.2). LV systolic function remained compensated in both groups with pressure overload. However, the LV end-diastolic stress-to-LV end-diastolic dimension ratio, an index of diastolic stiffness and LV pressure half-time and isovolumic relaxation time, two indexes of isovolumic relaxation, increased significantly more in TgZ mice with aortic banding. Protein levels of phosphorylated phospholamban (PS16), sarco(endo)plasmic reticulum Ca(2+)-ATPase 2a, phosphorylated ryanodine receptor, and the Na(+)/Ca(2+) exchanger were also reduced significantly (P < 0.05) in the banded TgZ mice. As expected, genetic calcineurin inhibition inhibited the development of LV hypertrophy with chronic pressure overload but also induced LV diastolic dysfunction, as reflected by both impaired isovolumic relaxation and increased myocardial stiffness. Thus genetic calcineurin inhibition reveals a new mechanism regulating LV diastolic function.

Abstract 392: Increased Oxidative Stress and Apoptosis as Mechanisms for Adverse Effects of Chronic Pressure Overload and Catecholamine Stress in Mice with Cardiac Overexpression of Type 5 Adenylyl Cyclase

Studies with cardiac overexpression of type 6 adenylyl cyclase (AC6) suggest it protects against cardiac stress. Less is known about cardiac overexpression of AC5. We generated transgenic (Tg) mice with cardiac specific overexpression of AC5 and examined both the effects of pressure overload induced by 1 wk of transverse aortic banding (TAC) and 1 wk of chronic isoproterenol (ISO) delivered by osmotic mini-pump (n=8/group). TAC induced greater, p&lt;0.05, left ventricular (LV) hypertrophy, as assessed by LV/body weight, in AC5 Tg (4.9±0.2) compared with wild type (WT) (4.0±0.1) and exhibited a significant decrease, p&lt;0.05, in LV ejection fraction (LVEF) (58±4%) where LVEF was maintained in WT (75±1%). TUNEL analysis shows that apoptosis in AC5 Tg was twice that in WT, p&lt;0.05. This was confirmed by a 2-fold increase in activity of caspase 3 in AC5 Tg compared to WT mice, p&lt;0.05. The AC5 Tg began to develop heart failure as reflected by increased, p&lt;0.05, lung/body weight (10.2±1.6) vs WT (6.4±0.2). In the heart, the antioxidant manganese superoxide dismutase (MnSOD), quantified by western blotting, was decreased by 40% in AC5 Tg compared to WT mice, p&lt;0.05, after 1 wk of aortic banding. Chronic ISO also induced a greater, p&lt;0.05, decrease in LVEF (48±4%) compared to WT (60±2%). 100 microM of ISO stimulation increased cell viability by 36% and decreased apoptosis by 34% (p&lt;0.05 vs LacZ control). MnSOD was upregulated by 2.9-fold in AC5 knockdown myocytes after treatment with ISO for 48 hrs. These results demonstrate that cardiac overexpression of AC5 exerts adverse effects on oxidative stress and apoptosis in response to both chronic pressure overload and catecholamine stress.

Abstract 540: Effects Of Altered Levels Of Adenylyl Cyclase Type 5 In Cardiac Myocytes From Chimeric Mice

The role of adenylyl cyclase (AC) isoforms in the heart has remained controversial in regards to their ability to enhance or impair cardiac function. We examined the effects of chronic pressure overload (aortic banding) in transgenic (TG) mice with cardiac overexpressed AC isoform type 5 (AC5TG), a major cardiac AC isoform. In AC5TG, the hypertrophic response, as assessed by LV/tibia length (TL), was greater, p&lt;0.05, in AC5TG (6.6±0.2) than wildtype (WT) (5.1±0.2). In addition, cardiac decompensation occurred, as reflected by decreased LV ejection fraction and increased lung/body weight, which could exert systemic effects through reflexes and hormones. We sought to examine whether the effects of overexpressed AC5 on the response to pressure overload is due to the affects on the myocyte or its environment. Chimeric mice from fusion between embryos from the transgenic overexpressed AC5 parents and the Rosa26 parents, which ubiquitously express beta-galactosidase in all tissues and can be identified histologically with X-gal staining, were developed. The proportion of the AC5TG (FVB background) cells in the myocardium ranged from 2% to 75% (n=9). We subjected these animals to 2 wk aortic banding at 4 – 6 months of age and examined the physiological and histological changes in the heart. There was a direct correlation (r= 0.91) between the percentage of AC5OE cells and LV hypertrophy index (LV weight/BW) including LV end diastolic and systolic wall thickness (r=0.98 and 0.92, respectively). We then determined the myocyte cross-sectional cell size from different cell origin micrographically. After 2wk banding, myocytes originating from the Rosa26 (C57/BL6) and FVB background were similar in size, but myocytes overexpressing AC5 were significantly larger (33%, p&lt;0.05). Conversely, there was a negative correlation between the amount of AC5OE cells and heart function: LV ejection fraction and contractility decreased in mice with a higher percentage of AC5OE myocytes (r = −0.89 and r = −0.81, respectively). Thus, overexpression of AC5 even in only a small fraction of total myocytes in the heart induced myocyte hypertrophy independent of any systemic influences.

Left ventricular regional variations in myosin isoform shift in Dahl salt-sensitive hypertensive rats.

To evaluate the effects of chronic pressure overload on different parts of the left ventricle (LV), we examined a myosin isoform shift from V1 to V3 as a biochemical marker of LV hypertrophy in Dahl salt-sensitive (DS) rats. Six-week-old DS rats were fed an 8% (high salt, HS; n = 24) or a 0.3% (low salt, LS; n = 12) NaCl diet. After 2 or 4 weeks, the hearts were dissected and the LVs were separated into four parts (the base and mid-portion of the interventricular septum (IVS), and the base and mid-portion of the LV free wall) for isomyosin analysis. The myosin isoform shift was analyzed by pyrophosphate gel electrophoresis. Both blood pressure and LV/body weight ratio were clearly increased in the HS group. The myosin isoform shift from V1 to V3, which was measured as a decrease in the percentage of V1 isomyosin, was demonstrated only in the base of LV, with significant predominance in the IVS at 2 weeks and in all four parts at 4 weeks in the HS group. In the LS group, a myosin isoform shift was demonstrated only in the basal portion of the LV at 4 weeks. We concluded that, in rats with salt-induced hypertension, the myosin isoform shift from V1 to V3 starts at the base of the LV, and particularly at the base of the IVS, and then spreads across the entire LV. These results suggest that pressure overload from hypertension may be strongest at the base of the IVS, and that LV hypertrophy may originate at the IVS base.

Diminished neuropeptide Y and dopamine beta-hydroxylase immunoreactivity in a guinea pig model of left ventricular hypertrophy.

The aims of the study were to determine the effect of chronic pressure overload of the left ventricle on the density and distribution of neuropeptide-Y-like immunoreactive (NPY-LI) nerve fibres in heart and to compare any changes to those observed in adrenergic nerve fibres, identified by dopamine beta-hydroxylase immunoreactivity. Pressure overload was produced in female adult guinea pigs by constriction of the abdominal aorta, using a modified Weck haemoclip. The same operation was performed on a separate group of animals except that no clip was placed around the aorta. Five weeks after surgery, animals were anaesthetised, and the hearts were fixed by perfusion for immunohistochemistry. Cryostat sections were stained, using an indirect peroxidase/antiperoxidase method, for NPY or dopamine beta-hydroxylase. Aortic stenosis caused a 45% increase in left ventricular weight and a 58% increase in left atrial weight at 5 weeks postsurgery. Pulmonary oedema, a sign of cardiac failure, was evident in most of the animals with aortic stenosis. Immunohistochemical studies showed that in atria and right ventricles from animals with abdominal aortic stenosis the distribution and density of NPY-LI nerve fibres were similar to those in the sham operated guinea pigs. However, the left ventricles obtained from the animals with aortic stenosis were nearly devoid of NPY-LI nerve fibres. The density of dopamine beta-hydroxylase-LI nerve fibres was also substantially reduced in the hypertrophied left ventricles. Aortic stenosis resulting in left ventricular hypertrophy caused a nearly complete loss of NPY-LI and dopamine beta-hydroxylase-LI nerve fibres from the left ventricle. The parallel reduction in both neuropeptide Y and dopamine beta-hydroxylase is in accordance with the association of neuropeptide Y with sympathetic (adrenergic) nerve fibres in the left ventricle and suggests that chronic left ventricular hypertrophy causes a severe degeneration of sympathetic axons supplying this chamber and/or reduces the ability of these sympathetic neurones to maintain normal levels of neurotransmitter related enzymes and neuropeptides.

Synergistic effects of diabetes mellitus and renovascular hypertension on the rat heart--stereological investigations on papillary muscles.

The effects of combined renovascular hypertension and diabetes mellitus on the rat heart were investigated in order to detect possible synergistic effects of the two conditions. Hypertensive diabetic and hypertensive nondiabetic young male Wistar rats were compared with diabetic and non-diabetic controls. Since the normal body weight increase of the diabetic animals was markedly suppressed a weight-matched nondiabetic control group was introduced in addition. Hypertension was established for eight weeks by a surgical stenosis of the left renal artery, diabetes mellitus was maintained for four weeks after a single intraperitoneal injection of 75 mg/kg streptozotocin. Light and electron microscopic stereological parameters were obtained for the left ventricular papillary muscles. The whole hearts were also investigated histologically. Qualitative morphology failed to substantiate synergistic effects in the hypertensive diabetic rats. Vascular abnormalities were not observed. The stereological parameters, however, revealed microstructural reactions which were observed exclusively in the hypertensive diabetic group: the volume ratio of mitochondria-to-myofibrils was decreased, the surface-to-volume ratio of mitochondria was increased (reduction of mitochondrial size) and the mean cross sectional area of capillaries was decreased. Similar quantitative mitochondrial changes have been frequently described in long-standing hypertension, but in the present investigation, they were not found in the nondiabetic hypertensive group. It is therefore concluded that diabetes mellitus potentiates the effects of chronic pressure overload on myocardial cells. However, the myocardial fibrosis which has been found by other groups at later stages of hypertension and/or diabetes mellitus was not detected in the present study. The reduced mean cross sectional area of capillaries in hypertensive-diabetic rats may be correlated with early molecular changes of the myocardial interstitium or with early abnormalities of small arteries. Thus our stereological results support the hypothesis that a non-coronary hypertensive diabetic cardiomyopathy occurs in mammalian hearts.

Systemic hypertension induces disparate localized left ventricular action potential lengthening and altered sensitivity to verapamil in left ventricular myocardium

Previously, we demonstrated that acute exposure to superfusate containing verapamil suppresses action potential plateau to a greater degree in cells at the tip of the anterior papillary muscle compared to those at its base in normal cat left ventricle (LV) studied in tissue bath. To determine the effects of chronic pressure overload brought about by renal hypertension on papillary muscle electrophysiology and regional sensitivity to verapamil, LV were isolated from cats subjected to unilateral nephrectomy and contralateral kidney wrapping. After 3 months, systemic hypertension (mean increase = 60.2 +/- 1.4 mmHg) was associated with moderate LV hypertrophy of approximately equal to 18% (LV weight/body weight). Transmembrane action potentials recorded from the endocardial surface (including anterior papillary muscle) in pressure overloaded LV in vitro (800 ms stimulus cycle length) showed increased action potential duration at 25, 75 and 90% of repolarization (APD25, APD75 and APD90, respectively) relative to controls (LV from normal and sham operated cats). With respect to the anterior papillary muscle in pressure overloaded LV, APD25, APD75 and APD90 were increased to a greater extent in cells at the base of the muscle compared to those increases observed at the tip (P less than 0.05). In contrast to its effects in controls, verapamil (2 micrograms/ml) significantly reduced APD25 at both the base and the tip of the papillary muscle in pressure overloaded preparations, but particularly at the base; also, the disparities between the APD75 or APD90 at tip and base were decreased. Thus, regional electrophysiologic disparities were induced in systemic hypertension, and these differences were subsequently reduced by verapamil.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Chronic Pressure Overload on the Maximal Rate of Pressure Fall of the Right Ventricle

The maximal rate of fall in right ventricular pressure (negative dp/dt) was evaluated in 34 patients. Eight had normal pulmonary arterial pressure. Seventeen had pulmonary arterial hypertension, and nine had pulmonary arterial hypertension with right ventricular failure. The right ventricular maximal negative dp/dt in patients with normal pulmonary arterial pressure was 170 +/- 20 mm Hg/sec. In patients with pulmonary arterial hypertension not accompanied by right ventricular failure, this value was 670 +/- 60 mm Hg/sec; and in patients with right ventricular failure, it was also 670 +/- 60 mm Hg/sec. This was higher than in control subjects (P less than 0.001). The maximal positive dp/dt was also higher in patients with pulmonary hypertension, regardless of the presence of right ventricular failure. Right ventricular maximal negative dp/dt correlated with right ventricular maximal positive dp/dt (r = 0.72). Right ventricular maximal negative dp/dt in patients who were not in right ventricular failure correlated linearly with pulmonary arterial systolic pressure (r = 0.83) and pulmonary arterial diastolic pressure (r = 0.83). At any level of pulmonary arterial systolic pressure, right ventricular maximal negative dp/dt in patients with right ventricular failure was lower than in patients with the same level of pulmonary arterial hypertension who were not in failure. These observations indicate that right ventricular maximal negative dp/dt is dependent on load. Even in the presence of right ventricular failure, right ventricular maximal negative dp/dt exceeded values in control subjects.