Left Ventricular Hypertrophy In Response Research Articles

Dysferlin facilitates the de novo biogenesis of tubular membranes in hypertrophic remodelling

Abstract Introduction Ferlins are transmembrane proteins with multiple C2 domains that may mediate Ca2+ dependent membrane fusion and repair events. In ventricles, Dysferlin expression is dominant, and patient mutations have been associated with cardiomyopathies. Hence, we hypothesized that Dysferlin is essential for the functional integrity of the tubular endomembrane system in ventricular myocytes (VM), and may facilitate the cellular hypertrophic remodelling in pressure-overload. Results In 30 weeks old Dysferlin knockout (KO) mice, echocardiography revealed dilative cardiomyopathy with reduced left-ventricular ejection fractions (difference between means KO vs. wildtype (WT) −13.45±2.17%, p<0.001, n=16/20 mice). Asking for the subcellular relevance of Dysferlin, we investigated VM nanodomains by immunolabelling in STimulated Emission Depletion (STED) nanoscopy and visualized punctual Dysferlin clusters decorating the T-tubule system of mouse and human VM. Precisely, Dysferlin clusters localized to junctions of the tubular system and the sarcoplasmic reticulum (SR) in nanometric proximity to RyR2 Ca2+ release units. Complexome profiling (LC-MS/MS) also suggested interactions of Dysferlin with RyR2 and the SR membrane-tethering protein Junctophilin-2 (JP2) in high molecular weight complexes. In JP2-overexpressing mice, live-cell STED membrane imaging captured polyadic junctional membrane structures in VM, specifically surrounded by dense Dysferlin clusters, which proposes Dysferlin as stabilizing protein of tubule-SR junctions. Further, we studied the ultrastructural remodelling of the tubular system in a mouse model of cardiac hypertrophy and heart failure induced by transaortic constriction (TAC). Interestingly, mortality four weeks post TAC was not increased in KO mice. However, echocardiography uncovered that Dysf-KO prevents left-ventricular hypertrophy in response to pressure-overload, which was confirmed by single cell measurements (VM area: WT 3559±120 μm2 vs. KO 2671±87 μm2, n=163/158 VM, p<0.001). Thus, we assumed Dysferlin to mediate tubular network proliferation during hypertrophic remodelling. Indeed, WT VM showed an augmented Dysferlin expression post TAC (158±0,125%, p=0,005, n=7/7 mice), and immunofluorescence STED nanoscopy detected an increased Dysferlin network complexity. In detail, we visualized highly abundant Dysferlin clusters decorating newly shaped axial tubules, which were quantified by component-specific tubule network analysis. Conclusion Nanoscale imaging proposes Dysferlin as stabilizer of tubule-SR junctions, thereby promoting functional excitation-contraction coupling, and demonstrates the crucial importance of Dysferlin in pressure-overload induced hypertrophic remodelling, facilitating the de novo biogenesis of axial tubule membranes and tubule-SR junctions necessary for VM growth. Thus, Dysferlin may emerge as potential novel therapeutic rationale to control subcellular membrane remodelling in cardiac diseases. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Multiscale Bioimaging Cluster of Excellence: From Molecular Machines to Networks of Excitable Cells;German Research Foundation (DFG) - Collaborative Research Centre 1002 (SFB 1002): Modulatory Units in Heart Failure

The Ca2+-activated cation channel TRPM4 is a positive regulator of pressure overload-induced cardiac hypertrophy.

Pathological left ventricular hypertrophy (LVH) occurs in response to pressure overload and remains the single most important clinical predictor of cardiac mortality. The molecular pathways in the induction of pressure overload LVH are potential targets for therapeutic intervention. Current treatments aim to remove the pressure overload stimulus for LVH, but do not completely reverse adverse cardiac remodelling. Although numerous molecular signalling steps in the induction of LVH have been identified, the initial step by which mechanical stretch associated with cardiac pressure overload is converted into a chemical signal that initiates hypertrophic signalling remains unresolved. In this study, we show that selective deletion of transient receptor potential melastatin 4 (TRPM4) channels in mouse cardiomyocytes results in an approximately 50% reduction in the LVH induced by transverse aortic constriction. Our results suggest that TRPM4 channel is an important component of the mechanosensory signalling pathway that induces LVH in response to pressure overload and represents a potential novel therapeutic target for the prevention of pathological LVH.

Abstract P112: Decreased α-Myosin Expression is Associated with Left Ventricular Hypertrophy in Hypertensive Caribbean Vervets

Caribbean vervets ( Chlorocebus aethiops sabeus ) develop hypertension (HT; Systolic Blood Pressure ≥ 140 mmHg) in over 30% (125/345) of the outbred population. Elevated total peripheral resistance in HT increases cardiac afterload, which may lead to left ventricular hypertrophy (LVH) and cardiac remodeling. We hypothesize that prolonged spontaneous HT is associated with LVH, cardiac and aortic fibrosis, as well as differential transcription of myocardial contractile proteins. Vervets were characterized as HT (SBP = 170 ± 25.3 mmHg; n=125) or normotensive (NT, SBP = 99 ± 14.5 mmHg; n=148) using forearm plethysmography (ketamine sedated;15 mg/kg i.m.). Cardiomyocyte cross-sectional area was greater in HT compared to NT animals (HT 283 ± 52 μm 2 , n=9 vs NT 114 ± 8 μm 2 , n=10; p<0.01). Average collagen stained as a function of tissue area was similar in left ventricular myocardium of HT and NT animals (HT 14.17 ± 3.13% or 0.17/1.21 mm 2 , n=9 vs NT 12.22 ± 0.80% or 0.16/1.27 mm 2 , n=10; p>0.05). Aortic adventia collagen area was greater in HT compared to NT vervets (HT 66.12 ± 4.22% or 0.60/0.90 mm 2 , n=6 vs NT 54.53 ± 2.21% or 0.56/1.02 mm 2 , n=10; p<0.05). Total tissue collagen was estimated using a hydroxyproline assay. Collagen content was not different between HT and NT vervets for left ventricular myocardium (HT 194.02 ± 8.61 μg/mL, n=11 vs NT 201.70 ± 18.89 μg/mL, n=10; p=0.71) or aorta (HT 745.64 ± 44.49 μg/mL, n=11 vs NT 668.39 ± 31.06 μg/mL, n=11; p=0.17). Myosin gene expression (α and β) was estimated using RT-PCR of mRNA in left ventricular myocardium of NT (SBP = 98.91 ±10.89 mmHg; n=20) and HT (SBP = 171.51 ± 30.28 mmHg; n=17) vervets. α-myosin was downregulated in HT compared to NT vervets (HT RQ = 0.10 ± 0.03 vs. NT RQ = 0.22 ± 0.04; p<0.05), while β-myosin expression was not different (HT RQ = 0.22 ± 0.17 vs. NT RQ = 0.20 ± 0.16; p=0.83). Thus, spontaneous HT in outbred vervets induces LVH in response to factors other than cardiac fibrosis. Myosin gene expression may shift from α-myosin to other contractile protein isoforms, characteristic of human heart failure. In this nonhuman primate model, HT does not induce significant aortic fibrosis that may occur in aged animals. Future studies will further characterize contractile and pro-inflammatory proteins in LVH of spontaneous HT vervets.

Deletion of Interleukin-6 Attenuates Pressure Overload-Induced Left Ventricular Hypertrophy and Dysfunction.

The role of interleukin (IL)-6 in the pathogenesis of cardiac myocyte hypertrophy remains controversial. To conclusively determine whether IL-6 signaling is essential for the development of pressure overload-induced left ventricular (LV) hypertrophy and to elucidate the underlying molecular pathways. Wild-type and IL-6 knockout (IL-6(-/-)) mice underwent sham surgery or transverse aortic constriction (TAC) to induce pressure overload. Serial echocardiograms and terminal hemodynamic studies revealed attenuated LV hypertrophy and superior preservation of LV function in IL-6(-/-) mice after TAC. The extents of LV remodeling, fibrosis, and apoptosis were reduced in IL-6(-/-) hearts after TAC. Transcriptional and protein assays of myocardial tissue identified Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and signal transducer and activator of transcription 3 (STAT3) activation as important underlying mechanisms during cardiac hypertrophy induced by TAC. The involvement of these pathways in myocyte hypertrophy was verified in isolated cardiac myocytes from wild-type and IL-6(-/-) mice exposed to prohypertrophy agents. Furthermore, overexpression of CaMKII in H9c2 cells increased STAT3 phosphorylation, and exposure of H9c2 cells to IL-6 resulted in STAT3 activation that was attenuated by CaMKII inhibition. Together, these results identify the importance of CaMKII-dependent activation of STAT3 during cardiac myocyte hypertrophy via IL-6 signaling. Genetic deletion of IL-6 attenuates TAC-induced LV hypertrophy and dysfunction, indicating a critical role played by IL-6 in the pathogenesis of LV hypertrophy in response to pressure overload. CaMKII plays an important role in IL-6-induced STAT3 activation and consequent cardiac myocyte hypertrophy. These findings may have significant therapeutic implications for LV hypertrophy and failure in patients with hypertension.

Activation of Cardiac Fibroblast Growth Factor Receptor 4 Causes Left Ventricular Hypertrophy

Chronic kidney disease (CKD) is a worldwide public health threat that increases risk of death due to cardiovascular complications, including left ventricular hypertrophy (LVH). Novel therapeutic targets are needed to design treatments to alleviate the cardiovascular burden of CKD. Previously, we demonstrated that circulating concentrations of fibroblast growth factor (FGF) 23 rise progressively in CKD and induce LVH through an unknown FGF receptor(FGFR)-dependent mechanism. Here, we report that FGF23 exclusively activates FGFR4 on cardiac myocytes to stimulate phospholipase Cγ/calcineurin/nuclear factor of activated Tcell signaling. A specific FGFR4-blocking antibody inhibits FGF23-induced hypertrophy of isolated cardiac myocytes and attenuates LVH in rats with CKD. Mice lacking FGFR4 do not develop LVH in response to elevated FGF23, whereas knockin mice carrying an FGFR4 gain-of-function mutation spontaneously develop LVH. Thus, FGF23 promotes LVH by activating FGFR4, thereby establishing FGFR4 as a pharmacological target for reducing cardiovascular risk in CKD.

Impact of left ventricular hypertrophy on impaired coronary microvascular dysfunction

Left ventricular hypertrophy (LVH) has been recognized as a marker of hypertension-related target organ damage, and a strong independent risk factor for adverse cardiovascular (CV) outcomes. CV risk increases with increasing LV mass, and decreases with regression of LVH in response to antihypertensive treatment [1]. However, the exact mechanisms underlying the CV events in patients with LVH have not yet been elucidated. Although coronary microvascular (MV) dysfunction (CMD) with structural abnormalities has been pathologically recognized as a possible cause of adverse outcomes in patients with hypertrophic cardiomyopathy (HCM) and in those with arterial hypertension [2], there has been no clinically-available technique that enables direct measurement of coronary microcirculation in vivo in humans.

PM303 Gender Differences In Left Ventricular Hypertrophy In Response To Increased Body Weight

PM303 Gender Differences In Left Ventricular Hypertrophy In Response To Increased Body Weight

Overexpression of ornithine decarboxylase decreases ventricular systolic function during induction of cardiac hypertrophy

Ornithine decarboxylase (ODC), the first enzyme of polyamine metabolism, is rapidly upregulated in response to agents that induce a pathological cardiac hypertrophy. Transgenic mice overexpressing ODC in the heart (MHC-ODC mice) experience a much more dramatic left ventricular hypertrophy in response to β-adrenergic stimulation with isoproterenol (ISO) compared to wild-type (WT) controls. ISO also induced arginase activity in transgenic hearts but not in controls. The current work studies the cooperation between the cardiac polyamines and L-arginine (L-Arg) availability in MHC-ODC mice. Although ISO-induced hypertrophy is well-compensated, MHC-ODC mice administered L-Arg along with ISO showed a rapid onset of systolic dysfunction and died within 48 h. Myocytes isolated from MHC-ODC mice administered L-Arg/ISO exhibited reduced contractility and altered calcium transients, suggesting an alteration in [Ca(2+)] homeostasis, and abbreviated action potential duration, which may contribute to arrhythmogenesis. The already elevated levels of spermidine and spermine were not further altered in MHC-ODC hearts by L-Arg/ISO treatment, suggesting alternative L-Arg utilization pathways lead to dysregulation of intracellular calcium. MHC-ODC mice administered an arginase inhibitor (Nor-NOHA) along with ISO died almost as rapidly as L-Arg/ISO-treated mice, while the iNOS inhibitor S-methyl-isothiourea (SMT) was strongly protective against L-Arg/ISO. These results point to the induction of arginase as a protective response to β-adrenergic stimulation in the setting of high polyamines. Further, NO generated by exogenously supplied L-Arg may contribute to the lethal consequences of L-Arg/ISO treatment. Since considerable variations in human cardiac polyamine and L-Arg content are likely, it is possible that alterations in these factors may influence myocyte contractility.

Proteasome inhibition in hypertrophied myocardium

Proteasome inhibition in hypertrophied myocardium

Left Ventricular Hypertrophy and Clinical Outcomes in Hypertensive Patients

The prevalence of left ventricular hypertrophy (LVH) rises with severity of hypertension (HT), age, and obesity. Its prevalence ranges from 20% in mildly hypertensive patients to almost 100% in those with severe or complicated HT. However, the diagnosis of LVH is not straightforward, and the definitions and criteria used in clinical studies lack consistency. While many factors play a role in the onset and progression of LVH, blood pressure (BP) is recognized as a central factor. Twenty-four-hour BP measurements are more closely related to LVH than conventional BP readings taken in the clinician's office. Increased renin-angiotensin system (RAS) activity also plays an important role in the development of LVH, and various studies show a correlation between plasma renin activity and left ventricular mass (LVM). LVH is a recognized marker of HT-related target organ damage, and a strong and independent risk factor for adverse cardiovascular (CV) outcomes. CV risk increases with increasing LVM, and decreases with regression of LVH in response to antihypertensive treatment. Therefore the detection, prevention, and reversal of LVH are important goals in HT management. Most antihypertensive drugs can attenuate BP and LVH. However, each drug class may induce LVH regression to a different extent and these extents seldom correlate with the degree of BP reduction achieved. Data from the few large comparative studies in this area suggest that certain classes of antihypertensive drugs and/or their combinations are more effective than others. In particular, calcium channel blockers and drugs that target the RAS, such as angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs), appear to have a specific effect on LVH, independent of BP reduction. Guidelines, therefore, have recommended these drug classes for the treatment of hypertensive patients with LVH.

Left ventricular hypertrophy: beyond the image and defining the human cardiac phenotype in hypertension

IntroductionLeft ventricular hypertrophy (LVH) has proven to be a very useful risk marker in hypertension. It indicates a higher risk of cardiovascular events and particularly sudden death [1,2]. It defines the effects of hypertension on an important target organ, the heart, and is one step along th

Histopathological study of time course changes in inter‐renal aortic banding‐induced left ventricular hypertrophy of mice

The left ventricular hypertrophy (LVH) in response to pressure overload is an important risk factor in cardiac morbidity and mortality. To investigate the time course of histopathological alterations in the LVH in response to pressure overload, histopathological and immunohistochemical examination was performed using the aortic banding-induced mouse LVH model. Five-week-old male CD-1 mice were subjected to the inter-renal aortic banding. Major organs were sampled on 3, 10, 14, 21, 28 or 42 days after banding. Haematoxylin and eosin (H&E) staining, Masson's trichrome staining and immunohistochemistry for proliferating cell nuclear antigen (PCNA), alpha-smooth muscle actin (aSMA), ICAM-1, type I collagen and CD31 was performed and microscopically examined. Three days after aortic banding, acute inflammatory changes, such as macrophages/neutrophil infiltration and vascular wall injury were observed on/around the coronary arteries/arterioles of both ventricles. Intense ICAM-1 immunostaining was observed on the endothelium of the coronary arteries/arterioles. After day 10, vascular wall thickening and perivascular fibrosis was induced on the coronary arteries/arterioles. Immunohistochemistry for aSMA and PCNA demonstrated the proliferation of vascular smooth muscle cells in the media. After day 28, minimal cardiomyocyte hypertrophy was observed at the light microscope level. In the inter-renal aortic banding LVH model, histopathological alterations in early phase were mainly observed on coronary arteries/arterioles. These early phase alterations were thought to be hypertension-related changes in the coronary vasculatures. The cardiomyocyte hypertrophy observed in later phase was minimal at the light microscope level. These evidences would facilitate the understanding of pathophysiology of pressure overload LVH.

Impact of Diabetes Mellitus on Regression of Electrocardiographic Left Ventricular Hypertrophy and the Prediction of Outcome During Antihypertensive Therapy

Diabetes mellitus is associated with increased cardiovascular (CV) morbidity and mortality and with greater ECG left ventricular hypertrophy (LVH); however, it is unclear whether diabetes attenuates regression of hypertensive LVH and whether regression of ECG LVH has similar prognostic value in diabetic and nondiabetic hypertensive individuals. A total of 9193 hypertensive patients (1195 with diabetes) in the Losartan Intervention For Endpoint (LIFE) Reduction in Hypertension Study were treated with losartan- or atenolol-based regimens and followed up with serial ECG and blood pressure determinations at baseline and 6 months and then yearly until death or study end. ECG LVH was defined with gender-adjusted Cornell voltage-duration product (CP) criteria >2440 mm . ms. After a mean follow-up of 4.8+/-0.9 years, patients with diabetes had less regression of CP LVH (-138+/-866 versus -204+/-854 mm . ms, P<0.001), remained more likely to have LVH by CP (56.0% versus 48.1%, P<0.001), and had higher rates of CV death, myocardial infarction, stroke, and all-cause mortality and of the LIFE composite end point of CV death, myocardial infarction, or stroke. In multivariable Cox proportional hazards models, in-treatment regression or absence of ECG LVH by CP was associated with between 17% and 35% reductions in event rates in patients without diabetes but did not significantly predict outcome in patients with diabetes. Hypertensive patients with diabetes have less regression of CP LVH in response to antihypertensive therapy than patients without diabetes, and regression of ECG LVH is less useful as a surrogate marker of outcomes in hypertensive patients with diabetes. These findings may in part explain the higher CV morbidity and mortality in hypertensive patients with diabetes, and the absence of a demonstrable improvement in prognosis in diabetic patients in response to regression of ECG LVH suggests a more complex interrelation between underlying LV structural and functional abnormalities and outcome in these patients.

Variation at the Beta-1Adrenoceptor Gene Locus is Associated with Left Ventricular Mass in Endurance Athletes

0714 Left ventricular hypertrophy in response to endurance training is a common feature in athletes. Twin studies, as well as association studies have shown that genetic factors play a role in the determination of the so called athlete's heart. In two recent studies, variants of the gene encoding the Beta-1 adrenoceptor (B1AR) has been associated with enlargement of the left ventricle in two different cohorts of sedentary subjects. PURPOSE: The aim of our study was to investigate the role of B1AR genetic polymorphisms for the development of left ventricular hypertrophy in endurance athletes. METHODS: We studied a cohort of 198 male Caucasian athletes involved in different endurance sports with a training history of at least 5 years (Tab. 1). Left ventricular mass was determined using M-mode echocardiography. Left ventricular mass index (LVMI) was calculated using Devereux's formula with correction for the body surface area. Subjects were typed for two single nucleotide polymorphisms (SNPs) that result in serine/glycine (Ser49Gly) and arginine/glycine (Arg389Gly) amino acid substitutions at residues 49 and 389 in the B1AR gene, respectively.Tab. 1: Characteristics of subjects (mean +/− std)RESULTS: Genotype distributions for both polymorphisms were in Hardy-Weinberg equilibrium. A significant association was found for Ser49Gly genotype and LVM (p = 0.036). Further analysis revealed a higher LVMI in carriers of the Gly-Allele compared to subjects homozygote for the Ser-Allele (LVMI 154g/m-2 vs. 145g/m-2, p = 0.014). No association was seen between the Arg389Gly polymorphism and LVM or LVMI (p = 0.093 and 0.232, respectively). CONCLUSION: In summary, we found evidence that the Ser49Gly polymorphism in the gene encoding for the B1AR may play a role in the development of left ventricular hypertrophy in highly trained endurance athletes.

Gender differences in regression of electrocardiographic left ventricular hypertrophy in response to antihypertensive therapy: The LIFE study

Gender differences in regression of electrocardiographic left ventricular hypertrophy in response to antihypertensive therapy: The LIFE study

Hypertensive patients with diabetes have less regression of electrocardiographic left ventricular hypertrophy in response to antihypertensive therapy: The LIFE study

Hypertensive patients with diabetes have less regression of electrocardiographic left ventricular hypertrophy in response to antihypertensive therapy: The LIFE study

Induction of cardiac angiotensin I-converting enzyme with dietary NaCl-loading in genetically hypertensive and normotensive rats.

We have recently shown that the angiotensin I converting enzyme (ACE) gene is linked to NaCl-loaded blood pressure in the stroke-prone spontaneously hypertensive rat (SHRSP), and that high-NaCl loading selectively stimulates ACE in the aorta of SHRSP but not in normotensive Wistar-Kyoto (WKY) rats. We therefore investigated the relationship between cardiac ACE and the development of hypertension and left ventricular hypertrophy in response to normal- and high-NaCl diet in these rats. ACE mRNA and ACE activity were measured in left ventricular tissue after completion of hemodynamic characterization of the animals. While SHRSP rats increased blood pressure (P < 0.0001) and heart rate (P < 0.005) in response to high NaCl, blood pressure remained unchanged in WKY. Similarly, relative left ventricular weight increased only in SHRSP after high NaCl (P < 0.002). A significant two- to threefold increase of cardiac ACE mRNA and fourfold stimulation of ACE enzyme activity in response to high NaCl was found in both WKY and SHRSP rats (P < 0.005). The induction of ACE gene expression was significantly more pronounced in SHRSP compared to WKY (P < 0.02), whereas no significant strain differences in left ventricular ACE activity were found after either normal- or high-NaCl diet. Thus, arterial blood pressure and left ventricular weight remained unchanged in the WKY rats despite the activation of left ventricular ACE activity after high-NaCl exposure. These results demonstrate that left ventricular ACE activity is equally upregulated in response to high-NaCl in the normotensive and hypertensive strain, independently from the development of hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Blockade of the renin-angiotensin system in cardiac pressure-overload hypertrophy in rats.

Left ventricular hypertrophy in response to pressure overload may be modified by neurohumoral activation. To investigate the contribution of the renin-angiotensin system, we studied rats after banding of the ascending aorta that developed severe left ventricular hypertrophy associated with normal plasma renin but elevated cardiac angiotensin-converting enzyme (ACE) levels. Rats were treated with vehicle, ACE inhibitor (ramipril), angiotensin II type 1 receptor antagonist (losartan), or vasodilator (hydralazine) during weeks 7 through 12 after aortic banding. A significant regression of left ventricular mass index as determined by serial echocardiography was observed in ramipril- and losartan-treated groups during weeks 9 through 12 after banding, whereas hypertrophy further increased in vehicle- and hydralazine-treated groups. Twelve weeks after banding, relative left ventricular weights and myocyte widths were markedly increased in vehicle- and hydralazine-treated groups, whereas ramipril and losartan significantly reduced these parameters. In addition, molecular adaptations in left ventricular hypertrophy, such as upregulation of left ventricular atrial natriuretic peptide and downregulation of sarcoplasmic reticulum Ca(2+)-ATPase mRNA levels, were blunted by ramipril or losartan treatment. Hypertrophic regression was associated with reduced mortality in rats treated with ramipril (11%) and losartan (13%) versus hydralazine (20%) and vehicle (31%). Thus, the renin-angiotensin system may be involved in the maintenance of chronic left ventricular hypertrophy. Blockade of the system may result in regression of the hypertrophic phenotype and improve survival in rats despite persistent pressure overload.

Regression of left ventricular hypertrophy in a transplanted heart

A woman with advanced coronary artery disease underwent heart transplantation. The donor heart had left ventricular hypertrophy. The electrocardiographic and echocardiographic evidence, of left ventricular hypertrophy regressed during follow up; estimated left ventricular mass decreased from 393 g to 171 g. The adaptation of myocardial mass and performance after transplantation is not fully understood. This case illustrates the potential for regression of left ventricular hypertrophy in response to altered loading conditions.

Age-related differences in the expression of proto-oncogene and contractile protein genes in response to pressure overload in the rat myocardium.

Cardiac adaptation to hemodynamic stress involves both quantitative (hypertrophy) and qualitative (pattern of gene expression) changes. Our previous studies have shown that advancing age in the rat is associated with diminished capacity to develop left ventricular hypertrophy in response to either ascending aortic constriction (AoC). In this study, we examined whether the expression of protooncogenes and contractile protein genes in response to AoC differs between adult (9-mo-old) and old (18-mo-old) rats. RNA was isolated from the left ventricles of AoC animals of both age groups subjected to a similar hemodynamic stress. Immediately after AoC, the levels of the ventricular expression of c-fos and c-jun protooncogenes were markedly lower in the old rats than in the adult animals. 5 d after the operation, the ratio of beta- to alpha-myosin heavy chain mRNAs increased significantly after AoC in both age groups. In contrast, AoC was associated with a marked reduction in the levels of mRNAs encoding sarcoplasmic reticulum Ca(2+)-ATPase (by 69%) and cardiac calsequestrin (by 49%) in the old rats but not in the adults. The mRNAs encoding atrial natriuretic factor and skeletal alpha-actin increased in response to AoC only in the adult rats. There were no significant differences in expression of the cardiac alpha-actin mRNA among the experimental groups. These data suggest that (a) the expression of protooncogenes in response to acute pressure overload is significantly reduced in the aged rats and (b) the pattern of expression of the contractile protein gene in response to AoC in the old rats differs qualitatively as well as quantitatively from that in younger animals. These age-related differences may play a role in the higher frequency of heart failure in the aged during hemodynamic stress.