Left Ventricular Hypertrophy Hearts Research Articles

Transplant Outcomes in Hearts with Moderate to Severe Left Ventricular Hypertrophy After the 2018 OPTN/UNOS Allocation Changes

<h3>Purpose</h3> After the 2018 OPTN/UNOS heart transplant (HT) allocation changes, there has been an increase in graft ischemia time, a factor shown to worsen HT outcomes in recipients of hearts with left ventricular hypertrophy (LVH). We compare HT outcomes in moderate to severe LVH defined by left ventricular wall thickness ≥ 1.4cm and non-LVH hearts and determine if there were changes in LVH HT outcomes after 2018. <h3>Methods</h3> The UNOS database was queried for all HT recipients ages >18 from 2016 to 2020. Multi-organ transplants were excluded. Demographic, donor, and recipient information were compared between LVH and non-LVH hearts. The primary outcome was post-transplant survival with secondary outcomes of rejection, cardiac allograft vasculopathy (CAV), and post-transplant ejection fraction, all at one year. Comparisons were made using Chi-squared and Wilcoxon rank-sum. Multiple logistic and linear regression models were used to discern the predictors of survival and the effect of LVH on outcomes. <h3>Results</h3> 10,175 HTs were analyzed: 491 LVH and 9784 non-LVH. After the 2018 changes, compared to non-LVH HT donors, LVH HT donors were older, had higher BMI, more often had HTN, were male, and had kidney disease. LVH HT recipients were older, higher BMI, and had greater HLA mismatch. Graft ischemia time, survival, and secondary outcomes were similar. Examining the LVH cohort specifically before and after the 2018 changes, there were no differences in survival or most secondary outcomes (decrease in CAV) despite increases in recipient BMI, recipient prior cardiac surgery, and graft ischemia time, which were independent predictors of worse outcomes in the overall cohort. LVH was not a predictor of survival or any secondary outcome. <h3>Conclusion</h3> Outcomes for recipients of hearts with moderate to severe LVH were not negatively impacted by the 2018 OPTN/UNOS changes despite longer graft ischemia time, and outcomes for recipients of LVH hearts were similar to those receiving hearts without LVH.

Inhibition of GTPase Rac1 expression by vitamin D mitigates pressure overload-induced cardiac hypertrophy.

1, 25-dihydroxy Vitamin D3 (VitD) attenuates left ventricular hypertrophy (LVH), but the mechanisms remain to be portrayed in-depth. The small GTPase Rac1 plays a pivotal role in cardiovascular pathology, especially LVH. Here, we tested whether VitD exerts its anti-LVH effects by counteracting the small GTPase Rac1 expression. In Wistar rats, pressure overload-induced LVH was created by abdominal aortic banding. The animals were intraperitoneally administered VitD (0.1µg/kg/d). Blood pressure was measured via carotid artery cannulation. Real-time RT-PCR and Western blotting were performed to assess the mRNA and protein expression, respectively. Myocardium was stained for determination of cardiomyocytes area and fibrosis. Lipid peroxidation levels and the activities of antioxidant enzymes were measured in left ventricular tissue. VitD significantly reduced hypertrophy markers (blood pressure, heart-to-body weight ratio, cardiomyocytes area, fibrosis as well as atrial and brain natriuretic peptides mRNA levels) compared to untreated groups (P<0.05). VitD also improved the activity of antioxidant enzymes and reduced lipid peroxidation levels in the myocardium (P<0.05). LVH hearts of untreated animals displayed a significant increase in Rac1 expression compared with the control group (P<0.05). In contrast, cardiac Rac1, at either mRNAs or protein levels, was markedly lower in LVH animals receiving VitD compared with their untreated counterparts (P<0.05). Our findings attest that VitD mitigates hallmarks of LVH imparted by pressure overload. Notably, VitD appears to perform its anti-LVH function partly through small GTPase Rac1 suppression. This, in turn, provides a robust incentive to consider VitD before LVH culminates in HF devastating disease.

Abstract 140: BMI- and Gender-specific Increase of MAP2K3/p38 Activity in Human Cardiac Hypertrophy

Introduction: MAP2K3 is a stress-induced kinase and its role cardiac hypertrophy has been controversial: while in vitro studies have displayed a positive correlation in activity with hypertrophy, in vivo studies have shown a negative association. Its direct downstream target, p38α MAPK, has been shown to be in activated in hypertrophic and failed hearts, but this has not been explored with regard to gender or BMI. Hypothesis: Early activation of p38 MAPK in hypertrophy is influenced by gender and BMI. Methods: Human heart samples were grouped into non-failed (NF), left ventricular hypertrophy (LVH), and NF without LVH (control). BMI &lt; 25 was considered “lean”, 25 &lt; BMI &lt; 30 was considered overweight, and BMI &gt; 30 was considered “obese”. RNA-Seq was used to generate cardiac gene expression profiles. Immunoblots were used to examine protein expression of MAP2K3, p38, and activated p38 (pp38; phospho-T180 and Y182). Results: We found that MAP2K3 mRNA levels were increased in obese males by 134% with LVH compared to non-LVH controls (FPKM: LVH = 19.2±3.5, n=3; non-LVH = 8.2±1.9, n=3; FPKM = Fragments Per Kilobase of transcript per Million mapped reads), without statistical significance (p&gt;0.05). MAP2K3 protein expression was 5-fold higher in LVH (1.24±0.20, n=9) versus non-LVH hearts (0.25±0.03, n=15) (p&lt;0.0001). Within all LVH hearts sampled, MAP2K3 protein expression is higher only in male overweight or obese (1.21±0.22, n=7) over lean (0.52±0.04, n=6) (p&lt;0.05). No differences were detected in gene expression profiles of the four isoforms of p38 and total p38 protein expression levels between LVH and NF groups (p&gt;0.05). Activated-p38 was detected in LVH without failure. Levels of p38 activation are higher in overweight/obese than in lean male group (pp38/p38 ratio: M_BMI&gt;25 = 0.63 ± 0.03 (n=7), M_BMI&lt;25 = 0.41 ± 0.12 (n=3), p&lt;0.05). For BMI&gt;25, levels of activated p38 are also higher in male (0.63 ± 0.03, n=7) than in female (0.08 ± 0.01, n=3) (p&lt;0.0001), independent of LVH. Conclusions: We found increased protein expression of MAP2K3 and phosphorylation of p38 in cardiac hypertrophy positively associated with male obese human hearts.

Myocardial ATP hydrolysis rates in vivo: a porcine model of pressure overload-induced hypertrophy.

Left ventricular (LV) hypertrophy (LVH) and congestive heart failure are accompanied by changes in myocardial ATP metabolism. However, the rate of ATP hydrolysis cannot be measured in the in vivo heart with the conventional techniques. Here, we used a double-saturation phosphorous-31 magnetic resonance spectroscopy-magnetization saturation transfer protocol to monitor ATP hydrolysis rate in swine hearts as the hearts became hypertrophic in response to aortic banding (AOB). Animals that underwent AOB (n = 22) were compared with animals that underwent sham surgery (n = 8). AOB induced severe LVH (cardiac MRI). LV function (ejection fraction and systolic thickening fraction) declined significantly, accompanied by deferent levels of pericardial effusion, and wall stress increased in aorta banded animals at week 1 after AOB, suggesting acute heart failure, which recovered by week 8 when concentric LVH restored LV wall stresses. Severe LV dysfunction was accompanied by corresponding declines in myocardial bioenergetics (phosphocreatine-to-ATP ratio) and in the rate of ATP production via creatine kinase at week 1. For the first time, the same linear relationships of the rate increase of the constants of the ATP hydrolysis rate (kATP→Pi) vs. the LV rate-pressure product increase during catecholamine stimulation were observed in vivo in both normal and LVH hearts. Collectively, these observations demonstrate that the double-saturation, phosphorous-31 magnetic resonance spectroscopy-magnetization saturation transfer protocol can accurately monitor myocardial ATP hydrolysis rate in the hearts of living animals. The severe reduction of LV chamber function during the acute phase of AOB is accompanied by the decrease of myocardial bioenergetic efficiency, which recovers as the compensated LVH restores the LV wall stresses.

Synthetic Phosphopeptides Enable Quantitation of the Content and Function of the Four Phosphorylation States of Phospholamban in Cardiac Muscle

We have studied the differential effects of phospholamban (PLB) phosphorylation states on the activity of the sarcoplasmic reticulum Ca-ATPase (SERCA). It has been shown that unphosphorylated PLB (U-PLB) inhibits SERCA and that phosphorylation of PLB at Ser-16 or Thr-17 relieves this inhibition in cardiac sarcoplasmic reticulum. However, the levels of the four phosphorylation states of PLB (U-PLB, P16-PLB, P17-PLB, and doubly phosphorylated 2P-PLB) have not been measured quantitatively in cardiac tissue, and their functional effects on SERCA have not been determined directly. We have solved both problems through the chemical synthesis of all four PLB species. We first used the synthetic PLB as standards for a quantitative immunoblot assay, to determine the concentrations of all four PLB phosphorylation states in pig cardiac tissue, with and without left ventricular hypertrophy (LVH) induced by aortic banding. In both LVH and sham hearts, all phosphorylation states were significantly populated, but LVH hearts showed a significant decrease in U-PLB, with a corresponding increase in the ratio of total phosphorylated PLB to U-PLB. To determine directly the functional effects of each PLB species, we co-reconstituted each of the synthetic peptides in phospholipid membranes with SERCA and measured calcium-dependent ATPase activity. SERCA inhibition was maximally relieved by P16-PLB (the most highly populated PLB state in cardiac tissue homogenates), followed by 2P-PLB, then P17-PLB. These results show that each PLB phosphorylation state uniquely alters Ca(2+) homeostasis, with important implications for cardiac health, disease, and therapy.

Compensatory remodeling of coronary microvasculature maintains shear stress in porcine left-ventricular hypertrophy

Hypertension-induced left-ventricular hypertrophy (LVH) is generally accompanied with coronary neovascularization. The extent of vascular growth or rarefaction depends on many factors (e.g. age, duration of hypertension, degree of hypertrophy). Here, we hypothesize that there is a compensatory vascular growth that maintains uniform wall shear stress (WSS) in perfusion arterioles (diameters of 8-60 μm) in LVH of young porcine. To test this hypothesis, we investigated LVH in young porcine after 5 weeks of supravalvular aortic stenosis (3 months of age). The morphometry (diameters, lengths, number and connectivity of vessels) of the entire left circumflex (LCx) arterial tree was determined and a hemodynamic network analysis was used to calculate the distribution of pressure, flow and WSS throughout the tree in the control and LVH groups. It was found that the number of vessels and the weight of left ventricle (LV) in hypertrophy increased 1.5 and 1.2 times, respectively, and the length of the LCx main trunk increased by 3 cm (36% increase), as compared with those in control group. There were similar myocardial blood flows of 0.87 ± 0.24 and 0.94 ± 0.38 ml/min per g in control and LVH hearts, respectively. The compensatory remodeling in early LVH restores WSS in the smaller perfusion arterioles, but not in the larger epicardial branches. The present findings quantify the structural and functional remodeling in the entire LCx arterial tree in response to LVH, which reflect heterogeneity in vascular morphometry and hemodynamics from small to large vessels. These conclusions enhance our understanding of compensatory vascular remodeling in LVH of pediatric heart.

Seamless networks of myocardial bioenergetics

Seamless networks of myocardial bioenergetics

Compromised Myocardial Energetics in Hypertrophied Mouse Hearts Diminish the Beneficial Effect of Overexpressing SERCA2a

The sarcoplasmic reticulum calcium ATPase (SERCA) plays a central role in regulating intracellular Ca(2+) homeostasis and myocardial contractility. Several studies show that improving Ca(2+) handling in hypertrophied rodent hearts by increasing SERCA activity results in enhanced contractile function. This suggests that SERCA is a potential target for gene therapy in cardiac hypertrophy and failure. However, it raises the issue of increased energy cost resulting from a higher ATPase activity. In this study, we determined whether SERCA overexpression alters the energy cost of increasing myocardial contraction in mouse hearts with pressure-overload hypertrophy using (31)P NMR spectroscopy. We isolated and perfused mouse hearts from wild-type (WT) and transgenic (TG) mice overexpressing the cardiac isoform of SERCA (SERCA2a) 8 weeks after ascending aortic constriction (left ventricular hypertrophy (LVH)) or sham operation. We found that overexpressing SERCA2a enhances myocardial contraction and relaxation in normal mouse hearts during inotropic stimulation with isoproterenol. Energy consumption was proportionate to the increase in contractile function. Thus, increasing SERCA2a expression in the normal heart allows an enhanced inotropic response with no compromise in energy supply and demand. However, this advantage was not sustained in LVH hearts in which the energetic status was compromised. Although the overexpression of SERCA2a prevented the down-regulation of SERCA protein in LVH hearts, TG-LVH hearts showed no increase in inotropic response when compared with WT-LVH hearts. Our results suggest that energy supply may be a limiting factor for the benefit of SERCA overexpression in hypertrophied hearts. Thus, strategies combining energetic support with increasing SERCA activity may improve the therapeutic effectiveness for heart failure.

Multiplex Analysis of Cardiac Hypertrophic Signaling: Reduced in vivo Phosphorylation of Glycogen Synthase Kinase-3&#946; and Proline-Rich Akt Substrate (PRAS40)

The serine/threonine kinase Akt (PKB) is activated in response to growth factors, cytokines and other growth promoting stimuli and is involved in the regulation of a number of cellular processes including metabolism, cell growth, proliferation and survival. To study intracellular metabolic effects of left ventricular hypertrophy (LVH) induced by chronic aortic banding in a recently established swine model, protein arrays can be used to analyze changes in cytosolic protein phosphorylation levels such as cell signal transduction and protein kinase pathways. Miniaturized sandwich immunoassays allow the simultaneous analysis of several parameters in a single experiment. Bead-based protein array systems or suspension microarrays are well-established multiplex sandwich immunoassay formats. Cytosolic proteins were extracted from pig hearts. Using the bead-based Luminex system, multiplexed sandwich immunoassays have been developed to analyze the phosphorylated proteins IR[pYpY1162/1163], IGF-1R[pYpY1135 /1136], IRS-1[pS312], Akt[pS473], PRAS40[pT246], p70S6K[pTpS421/424], and GSK-3β[pS9], which were measured simultaneously in extracted myocardial tissue homogenates with the Akt Pathway Phospho 7-Plex Panel using a Luminex 100 IS system. Using this assay, tissue homogenates derived from myocardial tissue samples from 28 individual porcine in vivo model experiments in normal hearts (n=17) and LVH hearts (n=11) were analyzed for phosphorylated protein concentrations. Results obtained allowed grouping of myocardial tissue samples into a LVH and a normal group. Two candidate molecules: PRAS40 (normal vs. LVH two-tailed probability P= 0.0022) and GSK-3β (P=0.003), had lower concentrations in LVH pigs than in normal animals, suggesting loss of GSK-3β inhibitory activity and contributing to speculation of altered insulin sensitivity associated with LVH. Keywords: Cardiac hypertrophy, akt/protein kinase B, glycogen synthase (GSK)-3β, proline-rich akt substrate (PRAS40), multiplex analysis, animal model, phosphatidyli-nositol 3-kinase (PI3K) pathway, sandwich immunoassay flow cytometry, sevoflurane anesthesia, IR, IGF-1R, IRS-1, Akt, PRAS40, p70S6K, GSK-3, IR[pYpY1162/1163], IGF-1R[pYpY1135/1136], IRS-1[pS312], Akt[pS473], pT246, GSK-3[pS9], Ambulatory transthoracic ultrasound examinations

Myocardial Energetics in Left Ventricular Hypertrophy

The heart carries out its pumping function by converting the chemical energy stored in fatty acids and glucose into the mechanical energy of actin-myosin interaction of myofibrils. Development of congestive heart failure is usually preceded by a period of compensated left ventricular hypertrophy (LVH) and alterations in myocardial bioenergetics have been considered to play an important role in this transition. Myocardial energetic state that is reflected by the ratio of Phosphocreatine to Adenosine Triphosphate (PCr/ATP) is significantly decreased in hearts with LVH. The severity of this abnormality is linearly related to the severity of cardiac hypertrophy as well as left ventricular (LV) dysfunction, and is independent of a persistent myocardial ischemia. The decrease in PCr/ATP is accompanied by a decrease in creatine kinase flux and alterations in substrate utilization in LVH hearts. Moreover, there is a profound heterogeneity in alterations in myocardial energy metabolism in hearts with post-infarction hypertrophy with the most severe abnormality present in the inner layers of the periscar border zone (BZ). This review will discuss various aspects of myocardial energetics in animal models of three different types of LVH (pressure-overload, volume overload and post-infarction) with a brief description of myocardial energetics in humans with LVH.

Emergent Critical Phenomena in the Evolution of Heart Failure

The failing heart is hypothesized to suffer from energy supply inadequate for supporting normal cardiac function. This study aims at quantitatively determining the energy state, represented by the cytoplasmic ATP hydrolysis potential (δGATPase), in the failing heart. Biopsy measurements and 31P‐Magnetic Resonance Spectroscopy experimental data show that at basal conditions total creatine pool (CRtot), ATP, and CrP decrease in left ventricular hypertrophy (LVH) hearts. These decreases are proportional to the degree of LVH, but not associated with cardiac underperfusion. By incorporating these changes into a recently developed computational model of cardiac energetics [Wu et al., J. Physiol. 586:4193‐4208, 2008], we are able to simulate local metabolite and ion concentrations and thus δGATPase in the LVH hearts. The simulations reveal the impacts of CRtot, total exchangeable phosphate, and total adenine nucleotides (TAN) on δGATPase at the maximal cardiac work rate. Model predictions indicate that the evolution of heart failure involves two distinct energetic stages: an early stage with relative stable cardiac reserve and a late stage with rapidly deteriorated energetics. Analysis reveals a critical phenomenon in which low and moderate reductions in TAN have no impact on oxidative capacity while reductions in TAN beyond the critical point lead to severely compromised energy state.

Modulation of contractility by myocyte-derived arginase in normal and hypertrophied feline myocardium

L-Arginine, the sole substrate for the nitric oxide (NO) synthase (NOS) enzyme in producing NO, is also a substrate for arginase. We examined normal feline hearts and hearts with compensated left ventricular (LV) hypertrophy (LVH) produced by ascending aorta banding. Using Western blot analysis, we examined the abundance of arginase isozymes in crude homogenates and isolated cardiac myocytes obtained from the LVs of normal and LVH hearts. We examined the functional significance of myocyte arginase via measurement of shortening and intracellular calcium in isolated myocytes in the presence and absence of boronoethyl chloride (BEC), a specific pharmacological inhibitor of arginase. Both arginase I and II were detected in crude myocardial homogenates, but only arginase I was present in isolated cardiac myocytes. Arginase I was downregulated in LVH compared with normal. Inhibition of arginase with BEC reduced fractional shortening, maximal rate of shortening (+dL/dt) and relengthening (-dL/dt), and the peak of the free cytosolic calcium transient in normal myocytes but did not affect these parameters in LVH myocytes. These negative inotropic actions of arginase inhibition were associated with increases in cGMP generation. These studies indicate that only arginase I is present in cardiac myocytes where it tends to limit NO and cGMP production with the effect of supporting basal contractility. In experimental LVH induced by pressure overload, our studies demonstrate reduced arginase I expression and reduced functional significance, allowing greater arginine substrate availability for NO/cGMP signaling.

Oxidative capacity in failing hearts.

Although high-energy phosphate metabolism is abnormal in failing hearts [congestive heart failure (CHF)], it is unclear whether oxidative capacity is impaired. This study used the mitochondrial uncoupling agent 2,4-dinitrophenol (DNP) to determine whether reserve oxidative capacity exists during the high workload produced by catecholamine infusion in hypertrophied and failing hearts. Left ventricular hypertrophy (LVH) was produced by ascending aortic banding in 21 swine; 9 animals developed CHF. Basal myocardial phosphocreatine (PCr)/ATP measured with 31P NMR spectroscopy was decreased in both LVH and CHF hearts (corresponding to an increase in free [ADP]), whereas ATP was decreased in hearts with CHF. Infusion of dobutamine and dopamine (each 20 microg. kg-1. min-1 iv) caused an approximate doubling of myocardial oxygen consumption (MVO2) in all groups and decreased PCr/ATP in the normal and LVH groups. During continuing catecholamine infusion, DNP (2-8 mg/kg iv) caused further increases of MVO2 in normal and LVH hearts with no change in PCr/ATP. In contrast, DNP caused no increase in MVO2 in the failing hearts; the associated decrease of PCr/ATP suggests that DNP decreased the mitochondrial proton gradient, thereby causing ADP to increase to maintain adequate ATP synthesis.

Myocardial creatine kinase kinetics and isoform expression in hearts with severe LV hypertrophy.

Left ventricular (LV) hypertrophy (LVH) results in a fetal shift in myocardial creatine kinase (CK) expression. Because CK plays an important role in intracellular energy production, transport, and utilization, this study was performed to characterize changes in CK expression and CK flux in severe pressure-overload LVH. Ascending aortic banding in 8-wk-old dogs resulted in LVH with a 92% increase in relative LV mass. In LVH hearts, CK-M isoform mRNA was decreased by 40% (P = 0.05) and protein was decreased by 50% (P < 0.01), whereas mitochondrial CK protein was decreased by 22% (P < 0.05). CK-B isoform mRNA was undetectable in normal hearts but was prominently expressed in LVH (P < 0.01); CK-B protein was increased by more than 10-fold in LVH (P < 0.01). Despite these changes, total CK activity was normal in LVH. Myocardial CK flux was examined using (31)P magnetic resonance spectroscopy magnetization transfer. The CK forward rate constant was similar in normal and LVH hearts at baseline and did not change in either group during dobutamine treatment. In hearts with LVH, the CK forward flux rate was reduced by approximately 60% (P < 0.05) and decreased further during dobutamine. Thus, although pressure-overload LVH caused alterations of expression of both CK mRNA and protein levels, LV performance and oxygen consumption in response to dobutamine were normal. However, myocardial free ADP was increased in LVH hearts. This finding suggests that the CK alterations result in a need for higher ADP levels to maintain ATP synthesis in the hypertrophied heart.

High-energy phosphate metabolism and creatine kinase in failing hearts: a new porcine model.

This study aimed to create a pig model of heart failure secondary to severe aortic stenosis and to examine the relationship between the alterations in myocardial high-energy phosphate (HEP) metabolism and protein expression of creatine kinase (CK) isoforms. Sixteen pigs with left ventricular hypertrophy (LVH) secondary to ascending aortic banding and 10 normal pigs (N) were studied. Myocardial protein levels of CK isoforms (Western blot), HEP levels, and CK kinetics ((31)P MR spectroscopy) were measured under basal conditions. Nine of the 16 animals with LVH developed congestive heart failure (CHF), as evidenced by ascites (100 to 2000 mL). LV weight/body weight ratio (g/kg) was 2.18+/-0.15 in N hearts, 3.04+/-0.14 in hearts with LVH (P<0.01), and 4.23+/-0.36 in hearts with CHF (P<0.01 versus LVH). Right ventricle weight/body weight ratio and LV end-diastolic pressure were significantly higher in hearts with CHF (each P<0.01 versus N or LVH). Myocardial phosphocreatine/ATP ratios and the CK forward flux rates were decreased in LVH hearts, most severely in hearts with CHF. CK-M/beta-actin ratios were 2.21+/-12 (N), 1.69+/-0.15 (LVH), and 1.39+/-0.27 (CHF, P<0.05 versus N). CK-mitochondria (CK-Mt)/beta-actin ratios were 1.40+/-0.09 (N), 1.24+/-0.09 (LVH), and 1.02+/-0.08 (CHF, P<0.05 versus N or LVH). The severity of the reduction of CK flux rate was linearly related to the severity of the decrease of CK-Mt/beta-actin (r=0.68, P<0.01). In this new model of heart failure/hypertrophy, the abnormal myocardial HEP metabolism is related to the decreased CK-Mt protein level, which in turn is related to the severity of the hypertrophy.

The cardiac endothelin system in established pressure overload left ventricular hypertrophy.

In normal hearts, endothelin-1 (ET-1) has been shown to initiate myocyte growth and to modulate cardiac function. However, regulation of the various components of the system and the functional effects of ET-1 in established left ventricular hypertrophy (LVH) are less clear. We thus studied ET-1, ET(A) receptor, and endothelin converting enzyme (ECE-1) mRNA regulation as well as the effects of ET-1 on coronary resistance, LV contractility and relaxation in hypertrophied rat hearts. Cardiac pressure overload, secondary to banding of the ascending aorta, resulted in a transient increase of cardiac ET-1 and ET(A) receptor mRNAs that reached a maximum at 2 days (+75% and +40%, respectively, P<0.05, each). ET-1 mRNA levels reached a second peak at 84 days of pressure overload (+60%, P<0.05), at the later time point in conjunction with elevated ECE-1 mRNA levels (+20%, P<0.05). The functional implications of ET-1 were examined in a study of isolated perfused hearts. Both hearts with established LVH and sham control hearts responded to ET-1 perfusion (10(-1)] to 10(-9) M) with an increase of coronary perfusion pressure (CPP; +85+/-15 and +75+/-8 mm Hg; P<0.001 each) and a slight decrease of LV systolic pressure (LVP; -12+/-9 and -9+/-7 mm Hg; P = NS). In contrast, ET-1 increased LV end-diastolic pressure (LVEDP) only in LVH hearts (+22+/-7 mm Hg, P<0.05 versus baseline and +20+/-7 mm Hg, P<0.05 versus sham). Direct stimulation of protein kinase C mimicked the effects of ET-1, whereas inhibition of this kinase or the Na+ -H+ exchanger blunted the effects of ET-1 on CPP, LVP, and LVEDP. Interestingly, coadministration of the vasodilator and the nitric oxide (NO) donor nitroglycerin not only prevented the increase of CPP and LVEDP, but also uncovered a slight positive inotropic effect of ET-1 in LVH hearts. Thus, the cardiac expression of ET-1, ET(A), and ECE-1 mRNAs displays a distinct pattern during early and advanced cardiac pressure overload. Furthermore, ET-1 mediates a slight depression of systolic, and a profound depression of diastolic, functional parameters in hearts with established LVH, effects that appear to be secondary to ET-1-related coronary vasoconstriction. The data suggest a functional role of the endothelin system in hearts with established pressure overload hypertrophy.

Gender differences in molecular remodeling in pressure overload hypertrophy

OBJECTIVESThe 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.BACKGROUNDClinical 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.METHODSMale (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.RESULTSThe 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.CONCLUSIONSThere 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.

Myocardial oxygenation at high workstates in hearts with left ventricular hypertrophy.

High cardiac workloads produced by catecholamine infusion result in loss of myocardial phosphocreatine (PCr) and accumulation of inorganic phosphate (Pi) which are more prominent in heart with left ventricular hypertrophy (LVH) than in normal hearts. Since ischemia can cause changes in phosphorylated compounds similar to those during catecholamine stimulation, this study tested the hypothesis that the exaggerated depletion of PCr and accumulation of Pi during high workloads in LVH is the result of impaired myocyte oxygenation. 31P- and 1H-NMR spectroscopy were used to determine myocardial high energy phosphate levels and myoglobin desaturation, respectively, in eight normal dogs and nine dogs with LVH produced by ascending aortic banding. The mean LV weight/body weight ratio was approximately twice normal in the LVH group. Infusion of dobutamine (15 and 30 micrograms/kg/min), and dobutamine + dopamine (each 20 micrograms/kg/min) caused progressive similar increases in the heart rate x systolic LV pressure product to a maximum of 57.4 +/- 3.3 x 10(3) in normal and 63.9 +/- 2.7 x 10(3) in LVH animals, while myocardial oxygen consumption increased from 0.09 +/- 0.01 to 0.24 +/- 0.04 in normals and from 0.10 +/- 0.02 to 0.25 +/- 0.03 ml/min/g in LVH. PCr/ATP ratios during basal conditions were lower in LVH hearts (1.73 +/- 0.10, 1.61 +/- 0.09 and 1.51 +/- 0.09 in subepicardium, midwall and subendocardium, respectively) as compared with normals (2.24 +/- 0.09, 2.01 +/- 0.08 and 1.89 +/- 0.07; each p < 0.01 normal vs. LVH). Catecholamine infusions caused dose-related decreases in PCr/ATP and appearance of Pi which was more marked in LVH than in normal hearts. 1H-NMR spectroscopy did not detect deoxymyoglobin in either normal or LVH hearts even during the highest workloads. In contrast, occlusion of the anterior descending coronary artery resulted in a large deoxymyoglobin signal. Increases of cardiac work produced by catecholamine stimulation resulted in greater decreases of PCr and greater increases of Pi in hypertrophied than in normal hearts. These abnormalities were not the result of inadequate intracellular oxygen availability and consequently cannot be ascribed to demand ischemia.

Effect of treadmill exercise on transmural distribution of blood flow in hypertrophied left ventricle.

Pressure-overload left ventricular (LV) hypertrophy (LVH) is associated with increased vulnerability to subendocardial hypoperfusion during exercise. Abnormal perfusion could be the result of failure of the coronary vessels to grow in proportion to the degree of myocyte hypertrophy or could be due to increased extravascular forces acting on the intramural coronary vasculature. This study assessed the contribution of extravascular forces by examining the effect of exercise on the distribution of myocardial blood flow when coronary vasomotor tone was abolished with a maximal vasodilating dose of intracoronary adenosine. One year after ascending aortic banding in six dogs, the LV-to-body weight ratio was 7.80 +/- 0.38 g/kg compared with 4.57 +/- 0.20 g/kg in nine normal dogs (P < 0.01). Under awake resting conditions blood flow in LVH hearts increased from 1.17 +/- 0.27 ml . min-1 . g-1 during basal conditions to 5.78 +/- 1.06 ml . min-1 . g-1 during adenosine (at a coronary pressure of 100 +/- 6 mmHg), whereas in normal dogs blood flow increased from 1.22 +/- 0.17 to 5.26 +/- 0.71 ml . min-1 . g-1 (at a coronary pressure of 62 +/- 4 mmHg). At rest the transmural distribution of blood flow during adenosine was not different between hypertrophied and normal hearts, with subendocardial-to-subepicardial (Endo-to-Epi) blood flow ratios of 1. 01 +/- 0.09 and 1.14 +/- 0.13, respectively (P = not significant). During adenosine infusion, treadmill exercise to produce heart rates of 200-220 beats/min caused redistribution of blood flow away from the subendocardium that was much more marked in LVH (Endo-to-Epi blood flow ratio = 0.35 +/- 0.04) than in normal hearts (Endo-to-Epi blood flow ratio = 0.76 +/- 0.09, P < 0.05 vs. LVH). In comparison with normal, the exaggerated decrease in subendocardial blood flow produced by exercise in LVH hearts resulted from abnormally increased extravascular compressive forces, including a greater decrease in diastolic duration and an increase in LV end-diastolic pressure.

Positive Functional Effects of Milrinone and Methylene Blue Are Not Additive in Control and Hypertrophic Canine Hearts

This study was designed to test whether increased inotropy caused by raising intracellular cAMP would add to the positive inotropy caused by reducing cGMP and whether this relationship was affected by experimental hypertrophy. We used open chest anesthetized dogs with left ventricular hypertrophy (LVH) induced by valvular aortic stenosis and age matched controls (CON). Hearts were instrumented to measure local segment shortening, force, and regional work. Milrinone (MIL), a selective cyclic AMP-phosphodiesterase inhibitor, and methylene blue (MB), a guanylate cyclase inhibitor, were used to alter cAMP and cGMP levels. Ten CON and 11 LVH animals were randomly assigned to receive first either MIL (1 μg/kg/min) or MB (2 mg/kg/min) intracoronary (i.c.) infusion. After 10 min, simultaneous i.c. infusion of the other agent was begun. MIL increased regional minute work (g × mm/min) in both CON (1311 ± 207 to 2072 ± 285) and LVH (1052 ± 136 to 1371 ± 351) hearts. MB did not increase work significantly, but did increase contractile force. MIL + MB increased work from baseline; however, the combination did not increase work more than either agent alone (1961 ± 510 CON; 1390 ± 285 LVH). Myocardial cAMP levels (pmol/g) were significantly increased by MIL in both CON (329 ± 53 to 437 ± 13) and LVH hearts (351 ± 67 to 538 ± 32), and the addition of MB further raised cAMP (879 ± 115 CON; 741 ± 96 LVH). MB resulted in decreased myocardial cGMP (pmol/g) (3.20 ± 0.61 to 2.16 ± 0.92 CON; 5.21 ± 1.15 to 2.46 ± 0.56 LVH), while MIL increased cGMP (3.20 ± 0.61 to 6.24 ± 1.79 CON; 5.21 ± 1.15 to 6.53 ± 0.41 LVH). Both MIL and MB caused increases in O2consumption, with MIL + MB together increasing O2consumption further. The current findings demonstrate a potentiation of cAMP production in the presence of MIL + MB above either agent alone, but this did not lead to potentiation of positive functional effects. High levels of cGMP caused by milrinone may have limited the positive functional effects of cAMP.