Pressure-overloaded Rat Research Articles

Pioglitazone attenuates inflammatory atrial fibrosis and vulnerability to atrial fibrillation induced by pressure overload in rats

Inflammatory processes are involved in the pathogenesis of atrial fibrillation (AF). The purpose of this study was to test the hypothesis that atrial fibrosis and enhanced vulnerability to AF evoked by pressure overload can be attenuated by pioglitazone, a peroxisome proliferator-activated receptor-γ agonist, via suppression of inflammatory profibrotic signals. Male Sprague-Dawley rats were subjected to abdominal aortic constriction (AAC). Pioglitazone 3 mg/kg/day or vehicle was orally administered for 4 weeks. Western blot analysis revealed that AAC enhanced expression of monocyte chemoattractant protein (MCP)-1, transforming growth factor-β1 and α-smooth muscle actin in the left atrium (LA), which was suppressed by pioglitazone. Messenger RNA expression of collagen type 1 and atrial natriuretic peptide in the LA was increased by AAC, which was suppressed by pioglitazone. Gelatin zymography demonstrated that activity of matrix metalloproteinase-9 was increased by AAC, which was suppressed by pioglitazone. Pioglitazone attenuated AAC-induced LA fibrosis. In isolated-perfused heart experiments, AAC did not alter the refractory period of the LA or the right atrium (RA), but it did prolong the interatrial conduction time. Programmed extrastimuli from the RA induced AF in all of the AAC-treated rats (8/8 [100%]). This was suppressed by pioglitazone (2/8 [25%], P <.05) with normalization to interatrial conduction time. The results of this study suggest that inflammatory profibrotic mechanisms are involved in this pressure-overloaded AF model. The results also suggest that pioglitazone is effective at attenuating atrial fibrosis, possibly via suppression of MCP-1-mediated inflammatory profibrotic processes.

E0113 Effects of Captopril on myocardial energy metabolism in chronic pressure overload rats

ObjectiveTo investigate the effect of Captopril on cardiac function and levels of energy-rich phosphates in pressure overload induced left ventricular hypertrophy rats.MethodsTotally, 120 SD rats were randomly divided into three...

Effects of polydatin on attenuating ventricular remodeling in isoproterenol-induced mouse and pressure-overload rat models

The study was designed to examine the effects of polydatin on ventricular remodeling induced by isoproterenol in mice and by abdominal aortic banding in rats. Polydatin reduced cardiac weight indexes in mice and rats, lowered the contents of cyclic AMP and angiotensin II in mice. It also decreased the size of cardiomyocyte, the levels of aldosterone, tumor necrosis factor-α, angiotensin II and endothelin-1, reduced ventricular collagen volume and decreased blood pressure in rats. The results demonstrate that polydatin has the beneficial effects on attenuating ventricular remodeling, which are associated with its inhibiting the activation of neurohormone, especially in rennin-angiotensin-aldosterone system.

Effect of sodium houttuyfonate on inhibiting ventricular remodeling induced by abdominal aortic banding in rats

Ventricular remodeling is an independent risk factor for many cardiovascular events. Inhibiting ventricular remodeling early may be an effective way to postpone heart failure for patients with cardiovascular illness. The study was designed to examine the effect of sodium houttuyfonate on ventricular remodeling induced by pressure overload in rats, as well as to explore the mechanisms involved. The model rats in which ventricular remodeling was induced abdominal aortic banding (AAB) were randomly divided into 4 groups: AAB control, AAB plus captopril (40 mg/kg), AAB plus low dose of sodium houttuyfonate (50 mg/kg), and AAB plus high dose of sodium houttuyfonate (100 mg/kg). One month after operation, hemodynamic parameters, heart mass indexes, size of cardiomyocytes, myocardial collagen volume, angiotensin II content in ventricular tissue, and serum concentrations of aldosterone and tumor necrosis factor (TNF)-alpha were evaluated. Sodium houttuyfonate significantly reduced heart mass indexes, the size of cardiomyocytes, and the myocardial collagen volume and decreased the levels of angiotensin II, aldosterone, and TNF-alpha. At the high dose, it decreased blood pressure and heart rate. In conclusion, sodium houttuyfonate attenuates ventricular remodeling induced by pressure overload in rats. The beneficial effects are in part associated with its alleviating the activation of renin-angiotensin-aldosterone system and decreasing the TNF-alpha level. Furthermore, its function seems to correlate with reduced blood pressure and heart rate.

Myocardial performance (Tei) index is normal in diastolic and systolic heart failure induced by pressure overload in rats

Myocardial performance index (MPI), or Tei index, is a Doppler echocardiographic parameter defined as the sum of the isovolumic contraction and relaxation times divided by the ejection time. It is considered a reliable parameter for global left ventricular function. However, the interpretation of this index is not fully clear in diastolic dysfunction. We measured MPI in a pressure-overload model of rats with severe diastolic with or without systolic dysfunction and examined its usefulness as a parameter for cardiac function in a hypertensive heart failure model. Pressure overload was created by placement of a metal clip around the thoracic aorta [transverse aortic constriction (TAC)] at a weight of 40-50 g. Transthoracic echocardiography including Doppler analysis and invasive left ventricular catheter examination were performed 10 and 20 weeks after TAC (n = 6 for each time point). While left ventricular ejection fraction was over 50% in all TAC animals after 10 weeks (56.3 ± 2.3%), it was below 50% in all TAC animals after 20 weeks (45.4 ± 1.0%). E/E' was significantly larger in the TAC groups at both time points and the time constant τ by Millar catheter was also elevated in the TAC groups. On the other hand, MPI was not different compared with the control groups (10 weeks: 0.47 ± 0.09 vs. 0.44 ± 0.04; 20 weeks: 0.38 ± 0.03 vs. 0.46 ± 0.07). MPI is not a reliable parameter for the assessment of contractile function in pressure-overload heart failure. It is normal in diastolic dysfunction with or without preserved ejection fraction.

Effect of inhibition of glycogen synthase kinase-3 on cardiac hypertrophy during acute pressure overload

A large number of diverse signaling molecules in cell and animal models participate in the stimulus-response pathway through which the hypertrophic growth of the myocardium is controlled. However, the mechanisms of signaling pathway including the influence of lithium, which is known as an inhibitor of glycogen synthase kinase-3beta, in pressure overload hypertrophy remain unclear. The aim of our study was to determine whether glycogen synthase kinase-3beta inhibition by lithium has acute effects on the myocyte growth mechanism in a pressure overload rat model. First, we created a rat model of acute pressure overload cardiac hypertrophy by abdominal aortic banding. Protein expression time courses for beta-catenin, glycogen synthase kinase-3beta, and phosphoserine9-glycogen synthase kinase-3beta were then examined. The rats were divided into four groups: normal rats with or without lithium administration and pressure-overloaded rats with or without lithium administration. Two days after surgery, Western blot analysis of beta-catenin, echo-cardiographic evaluation, left ventricular (LV) weight, and LV atrial natriuretic peptide mRNA levels were evaluated. We observed an increase in the level of glycogen synthase kinase-3beta phosphorylation on Ser 9. A significant enhancement of LV heart weight (P < 0.05) and interventricular septum and posterior wall thickness (P < 0.05) with pressure-overloaded hypertrophy in animals treated with lithium were also observed. Atrial natriuretic peptide mRNA levels were significantly increased with pressure overload hypertrophy in animals treated with lithium. We have shown in an animal model that inhibition of glycogen synthase kinase-3beta by lithium has an additive effect on pressure overload cardiac hypertrophy.

Resveratrol Arrests and Regresses the Development of Pressure Overload- but Not Volume Overload-Induced Cardiac Hypertrophy in Rats1–3

Cardiac hypertrophy is a compensatory enlargement of the heart due to either volume overload (VO) and/or pressure overload (PO) that develops into heart failure if left untreated. The polyphenol resveratrol has been reported to regress PO-induced cardiac hypertrophy in rats. Our aim in this study was to assess the effectiveness of resveratrol on VO-induced cardiac hypertrophy. Sprague Dawley rats were subjected to aortocaval shunt and abdominal aortic banding surgeries to create VO and PO, respectively; sham-operated rats served as controls. To arrest the development of cardiac hypertrophy, daily resveratrol treatment (2.5 mg/kg body weight) was started 2 d postsurgery for 26 d and assessed by echocardiography at 2, 14, and 28 d postsurgery. Similarly, to regress cardiac hypertrophy resveratrol treatment was started after structural and functional abnormalities developed (14 d postsurgery) for 14 d and assessed by echocardiography at 14 and 28 d postsurgery. VO surgeries induced eccentric hypertrophy characterized by increased left ventricle internal dimensions (LVID) without wall thickening. Conversely, PO induced concentric hypertrophy with increased wall thickness without change in LVID. Lipid peroxidation, a marker for oxidative stress, was significantly elevated in both PO and VO rats. Resveratrol treatment arrested the development and regressed abnormalities in cardiac structure and function in PO but not VO rats. Treatment with resveratrol also significantly reduced oxidative stress in cardiac tissue of PO and VO rats. The results on cardiac structure and function demonstrate a potential for resveratrol in the treatment of cardiac hypertrophy due to PO but not VO.

Salutary effects of Corydalis yanhusuo extract on cardiac hypertrophy due to pressure overload in rats

We have evaluated the effects of an alcohol extract from the rhizome of Corydalis yanhusuo W. T. (CY), a well-known traditional Chinese medicinal herb, on pressure-overloaded cardiac hypertrophy induced by transverse abdominal aorta constriction (TAAC) in rats. Rats were given vehicle or CY extract (200 or 50 mg kg(-1) per day) from the second week after induction of pressure overload, for a period of 7 weeks. Haemodynamic parameters, relative heart weight and myocyte cross-sectional area were measured in each group. We also estimated left ventricular (LV) collagen volume fraction (CVF) using Masson trichrome staining, and type I collagen expression by Western blot assay. Chronic TAAC caused notable cardiac hypertrophy and heart dysfunction. Significant collagen deposition and greater type I collagen expression were found in model control rats. These changes were not significantly reversed after treatment with 50 mg kg(-1) CY, whereas 200 mgkg(-1) significantly improved heart function and prevented cardiac hypertrophy, with parallel reductions in myocardial fibrosis, as evidenced by reduced LV CVF and reduced levels of type I collagen. In conclusion, chronic treatment of rats with CY extract attenuated development of cardiac hypertrophy.

Chronic pressure overload in rats reduces mitochondrial respiratory capacity but not coupling to ATP-production

Chronic pressure overload in rats reduces mitochondrial respiratory capacity but not coupling to ATP-production

A Potential Role of Alpha-7 Nicotinic Acetylcholine Receptor in Cardiac Angiogenesis in a Pressure-Overload Rat Model

This work investigated the expression of alpha-7 nicotinic acetylcholine receptor (α7nAChR) in the left ventricle and its putative role in cardiac angiogenesis in a pressure overload rat model induced by abdominal aorta coarctation. Blood pressure and protein levels of α7nAChR were measured at 4, 8, 12, and 16 weeks after surgery. mRNA levels of α7nAChR, cardiac vagus nerve function, cardiac hypertrophy, and microvessel density of the left ventricle were determined at the final 16-week period. The role of α7nAChR in angiogenesis was evaluated. It was found that systolic blood pressure above the coarctation site was greater at 16 weeks after coarctation and expression of α7nAChR was significantly increased at both mRNA and protein levels in the left ventricle compared with the control. Positive staining for receptors was mainly focused around vessels and among the degenerated cardiomyocytes. Cardiac vagus nerve function was significantly attenuated; microvessel density was markedly increased and was associated with cardiac hypertrophy. Activation of α7nAChR induced tube formation of cultured human umbilical vein endothelial cells (HUVECs). We conclude that expression of α7nAChR was increased at 16 weeks after coarctation, and this might be a compensatory response to decreased vagus nerve function and cardiac hypertrophy and may also play a role in cardiac angiogenesis.

Pressure-independent effects of pharmacological stimulation of soluble guanylate cyclase on fibrosis in pressure-overloaded rat heart

Cardiac fibrosis is a hallmark of cardiovascular remodeling associated with hypertension. The purpose of this study was to explore the effect and mechanism of soluble guanylate cyclase (sGC) stimulator BAY 41-2272, leading to intracellular cyclic guanosine monophosphate (cGMP) elevation, on the remodeling process induced by pressure overload. Seven-week-old male Wistar rats with hypertension induced by suprarenal aortic constriction (AC) were treated orally with 2 mg kg(-1) day(-1) of BAY 41-2272 for 14 days. BAY 41-2272 had no effects on blood pressure, but decreased AC-induced collagen accumulation in the left ventricle (LV), inhibiting the number of myofibroblasts and gene expressions of transforming growth factor-beta1 and type 1 collagen. In addition, the antifibrotic action of BAY 41-2272 was accompanied by reducing AC-induced angiotensin-converting enzyme (ACE) mRNA and its enzymatic activity, and angiotensin II concentration in LV. In cultured cardiac fibroblasts, BAY 41-2272 inhibited ACE synthesis and myofibroblast transformation, accompanied by elevating the intracellular cGMP concentration. These results suggest that sGC stimulator BAY 41-2272 might be effective to reduce fibrosis in hypertensive heart disease by attenuating angiotensin II generation through myofibroblast transformation.

FAK signalling mediates NF-κB activation by mechanical stress in cardiac myocytes

Background Nuclear Factor (NF)-κB and Focal Adhesion Kinase (FAK) signalling are implicated in cardiomyocyte hypertrophy. We investigated whether FAK signalling contributed towards NF-κB activation by mechanical stress in cardiac myocytes. Methods Experiments were performed with pressure overload rat left ventricle and isolated cardiac myocytes from adult rats and isolated neonatal rat ventricular myocytes (NRVMs) underwent in vitro stretching. Results Pressure overload induced NF-κB increase in myocardial cell nuclear extracts. Adult rat isolated cardiac myocyte confocal microscopy analysis showed NF-κB detected into nuclei. Cyclic stretch increased the amount and NF-κB DNA-binding activity in NRVMs nuclear extracts. NRVMs confocal microscopy confirmed NF-κB subcelullar relocation in stretched cells. Changes in NF-κB subcelular location and DNA-binding activity in stretched NRVMs were paralleled by increased FAK phosphorylation, detected in stretched NRVMs by anti-phosphospecific antibody directed to Tyr397. NRVMs treatment with FAK/Src pharmacological inhibitor attenuated NF-κB subcelullar relocation and increased DNA binding activity induced by cyclic stretch in cardiac myocytes. Conclusions FAK signalling coordinates cardiac myocyte NF-κB activation in response to mechanical stress. Further studies are needed to elucidate the influence of this signalling pathway on gene transcription regulation, and cardiac myocyte phenotypic changes in response to mechanical stress.

Olmesartan improves left ventricular function in pressure-overload hypertrophied rat heart by blocking angiotensin II receptor with synergic effects of upregulation of angiotensin converting enzyme 2

It is not clear how the blocking effect of angiotensin II receptors by olmesartan affects the functional recovery of pressure-overload hypertrophied heart. Hypertrophied heart was created by abdominal aortic banding above the celiac artery in Wistar rats at the age of eight weeks. Hypertrophied heart was excised and studied at 10 and 16 weeks after the operation (HT groups). For the last four weeks before the experiment, olmesartan (0.2 mg/kg per day) was administered subcutaneously by osmotic minipumps (Olm groups). Left ventricular function was measured by Langendorff perfusion. The levels of mRNA for angiotensin-converting enzyme (ACE), ACE2 and extracellular signal-regulated kinases (ERKs) in myocardium were analyzed by RT-PCR. Left ventricular systolic (+dP/dt(max), left ventricular systolic pressure) and diastolic functions (-dP/dt(max), tau) were impaired in HT groups, while in Olm groups they were significantly improved. The left ventricle to body weight (LV/BW) ratio increased significantly in HT groups, but in Olm groups the LV/BW ratio decreased significantly in comparison with HT groups. The ACE2 mRNA level was significantly higher in Olm groups as compared with HT groups. Plasma angiotensin II and the ERK mRNA level in HT groups increased significantly, but decreased in Olm groups in comparison with HT groups significantly. Olmesartan improved left ventricular function and hypertrophy through the increase of the ACE2 mRNA and decrease of both angiotensin II and ERK mRNA in pressure-overload rat heart.

Quercetin Prevents Cardiac Hypertrophy Induced by Pressure Overload in Rats

Inhibition of cardiac hypertrophy leads to a significant reduction in cardiovascular mortality and morbidity. Quercetin is by far the most abundant flavonoid and believed to ameliorate cardiovascular disease. Therefore, we investigated whether quercetin supplementation could attenuate the development of cardiac hypertrophy induced by pressure overload. Three weeks after suprarenal transverse abdominal aortic constriction, heart to body weight (HW/BW) ratio increased compared to the sham group (3.40 +/- 0.06 mg/g versus 2.83 +/- 0.02 mg/g, P<0.001). The quercetin administered group showed complete inhibition of cardiac hypertrophy (2.85 +/- 0.01 mg/g, P<0.001). Malonyldialdehyde production induced by pressure overload was suppressed by quercetin. The activities of extracellular signal-regulated kinase (ERK1/2), p38 MAP kinase, Akt and GSK-3beta were significantly increased with pressure overload and attenuated by quercetin treatment. We conclude that quercetin appears to block the development of cardiac hypertrophy induced by pressure overload in rats and that these effects may be mediated through reduced oxidant status and inhibition of ERK1/2, p38 MAP kinase, Akt and GSK-3beta activities.

Letter by Csont and Ferdinandy Regarding Article, “Biglycan Is Required for Adaptive Remodeling After Myocardial Infarction”

To the Editor: We read with great interest the article by Westermann et al1 in which the authors showed that biglycan expression was strongly increased in the myocardium after permanent coronary occlusion in wild-type mice. In the hearts of bgn −/ 0 mice 21 days after coronary occlusion, however, collagen matrix organization was impaired, and several parameters of left ventricular function were deteriorated. Furthermore, these animals showed increased mortality rates after infarction. The authors conclude that the complete absence of biglycan is deleterious and prevents the establishment of a stable infarct scar and hemodynamic adaptation, suggesting that biglycan is required for proper infarct healing. Although the observations of the authors are most valuable, the major conclusion of the authors1 is …

All-transretinoic acid prevents development of cardiac remodeling in aortic banded rats by inhibiting the renin-angiotensin system

This study was designed to determine the effect of all-trans retinoic acid (RA) on the development of cardiac remodeling in a pressure overload rat model. Male Sprague-Dawley rats were subjected to sham operation and the aortic constriction procedure. A subgroup of sham control and aortic constricted rats were treated with RA for 5 mo after surgery. Pressure-overloaded rats showed significantly increased interstitial and perivascular fibrosis, heart weight-to-body weight ratio, and gene expression of atrial natriuretic peptide and brain natriuretic peptide. Echocardiographic analysis showed that pressure overload induced systolic and diastolic dysfunction, as evidenced by decreased fractional shortening, ejection fraction, stroke volume, and increased E-to-E(a) ratio and isovolumic relaxation time. RA treatment prevented the above changes in cardiac structure and function and hypertrophic gene expression in pressure-overloaded rats. RA restored the ratio of Bcl-2 to Bax, inhibited cleavage of caspase-3 and -9, and prevented the decreases in the levels of SOD-1 and SOD-2. Pressure overload-induced phosphorylation of ERK1/2, JNK, and p38 was inhibited by RA, via upregulation of mitogen-activated protein kinase phosphatase (MKP)-1 and MKP-2. The pressure overload-induced production of angiotensin II was inhibited by RA via upregulation of expression of angiotensin-converting enzyme (ACE)2 and through inhibition of the expression of cardiac and renal renin, angiotensinogen, ACE, and angiotensin type 1 receptor. Similar results were observed in cultured neonatal cardiomyocytes in response to static stretch. These results demonstrate that RA has a significant inhibitory effect on pressure overload-induced cardiac remodeling, through inhibition of the expression of renin-angiotensin system components.

Effect of Yiqi Huoxue Recipe (益气活血方) on cardiac function and ultrastructure in regression of pressure overload-induced myocardial hypertrophy in rats

To investigate the effect of Yiqi Huoxue Recipe (YHR) on the cardiac function and ultrastructure during the regression of myocardial hypertrophy induced by pressure overload in rats. The model of myocardial hypertrophy was established by abdominal aortic banding. Eighty male Wistar rats were divided into six groups, the normal control group I (n=20), the normal control group II (n=12), the hypertension model group I (n=12), the hypertension model group II (n=12), the YHR group (n=12) and the Captopril group (n=12). The observation was carried out in the normal control group I and the hypertension model group I after 4 weeks of modeling, and the other four groups were observed after 16 weeks of modeling (12 weeks of administration). The cardiac function was measured with a multichannel biological signal analysis system, and the myocardium ultrastructure was observed by a transmission electron microscope. (1) Compared with the normal control group I, the systolic blood pressure and cardiac coefficient (left ventricular weight/body weight) in the model I group was higher (P<0.05, P<0.01). (2) In the YHR group, cardiac coefficient and -dp/dt(max) were lower, left ventricular systolic pressure and +dp/dt(min) were higher when compared with the model group II and the Captopril group (P<0.05 or P<0.01). In the Captopril group, only cardiac coefficient was lower when compared with the mode group II (P<0.05). (3) Compared with the normal control group II, +dp/dt(max) was higher (P<0.01) -dp/dt(max) and isovolumetric contraction time (ICT) was lower (P<0.05, P<0.01) in both the YHR group and the Captopril group. (4) Results of the myocardium ultrastructure showed edema under myocardium plasmalemma, enlarged sarcoplasmic reticulum and T tube, and significantly enlarged intercalated disc of the cardiac muscle in the model groups. In the Captopril group, the extension of sarcoplasmic reticulum and T tube as well as the pathological changes of intercalated disc were lighter, with slight edema under the myocardium plasmalemma. In the YHR group, the expansion of the sarcoplasmic reticulum was less than in the Captopril group, part of the pathological changes of intercalated discs was slightly more severe than that in the Captopril group, the dissolution of nuclear chromatin was not found, which was similar to that of the Captopril group, and no injury of the nucleus was found, either. YHR could reverse myocardial hypertrophy in rats with abdominal aortic banding and improve the systolic and diastolic function of the left ventricle. The ultrastructure of the myocardium such as arcoplasmic reticulum, intercalated disc, and cell nucleus in abdominal aortic banding rats could be partly reversed by the recipe.

The absence of endogenous lipid oxidation in early stage heart failure exposes limits in lipid storage and turnover

Intramyocardial lipid handling in pressure-overload-induced heart failure remains poorly understood, and the balance between endogenous and exogenous lipid utilization for mitochondrial ATP production is essentially unknown. In this study, we determined the contribution of endogenous triacylglycerols (TAG) to mitochondrial oxidation relative to that of exogenous palmitate, glucose, and endogenous glycogen in the failing, pressure-overloaded rat heart. TAG content and turnover were also assessed to determine if lipid availability and mobility were altered. Dynamic-mode 13C NMR was performed in intact hearts from aortic banded and sham operated Spraque-Dawley rats perfused with 13C-labeled palmitate or glucose to assess TAG turnover rate and palmitate oxidation rate. The fractional contributions from palmitate, glucose, glycogen, and TAG to mitochondrial ATP production were determined from NMR analysis of heart extracts. TAG oxidation was not evident in HF, whereas the contribution of TAG to oxidative ATP production was significant in shams. TAG content was 39% lower in HF compared to sham, and TAG turnover rate was 60% lower in HF. During adrenergic challenge, TAG sources were again not oxidized in the HF group. In early cardiac failure, endogenous TAG oxidation was reduced in parallel to increased carbohydrate oxidation, with no change in exogenous palmitate oxidation. This finding was consistent with reduced TAG storage and mobilization. These data further elucidate the role of intermediary and lipid metabolism in the progression of LVH to failure, and contribute to emerging evidence linking the disruption of myocardial substrate use to cardiomyopathies.

Effects of sex differences on constitutive nitric oxide synthase expression and activity in response to pressure overload in rats

Clinical studies have documented sex differences in left ventricular (LV) hypertrophy patterns, but the mechanisms are so far poorly defined. This study aimed to determine whether 1) severe pressure overload altered expression and/or activity of cardiac constitutive nitric oxide synthase (NOS1 and NOS3) and 2) these changes were modulated according to sex. Analyses were performed 0.4-20 wk after thoracic aortic constriction (TAC) in male and female Wistar rats. Male rats with TAC exhibited early signs of cardiac dysfunction, as shown by echocardiographic and LV end-diastolic pressure measurements, whereas females with TAC exhibited higher LV hypertrophy (+96% vs. males at 20 wk; P < 0.05). After TAC, cardiac NOS1 expression was rapidly induced (0.4 wk) and stable afterward in males (P < 0.05 vs. sham groups), whereas it was delayed in females. Accordingly, specific NOS1 activity was increased by 2 wk in male rats with TAC (+122%; P < 0.001 vs. sham groups) and only by 20 wk in females (+220%; P < 0.001 vs. sham groups). NOS1 activity was correlated with NOS1 level. Regarding cardiac NOS3, expression was unaffected by TAC, and the decrease in activity observed at early and late times in male and female rats with TAC, respectively, is shown to be related to NOS3 allosteric regulator caveolin-1 level. The data demonstrated a unique sex-dependent regulation of the constitutive NOSs in response to TAC in rats; such a difference might play a role in the sex-dependent adaptability of the heart in response to pressure overload.

Endogenous inhibitors of hypertrophy in concentric versus eccentric hypertrophy

Left ventricular (LV) hypertrophy (LVH) is an adaptive response to hemodynamic overload, but also contributes to the pathogenesis of heart failure. LVH can be concentric (cLVH) but subsequent dilatation and progression to eccentric hypertrophy (eLVH) may lead to global pump failure. Recently, several endogenous molecular inhibitors of hypertrophy have been identified. Using real-time PCR, we compared the myocardial mRNA expression of these inhibitors in pressure-overload induced cLVH (severe aortic stenosis) and in volume overload-induced eLVH (severe mitral regurgitation) in patients, and during the progression from cLVH to eLVH in pressure overload in rat. Each of these genes showed a unique temporal expression profile. Strikingly, except for SOCS-3, changes in gene expression of these negative regulators in rat cLVH and eLVH vs sham were recapitulated in human cLVH and eLVH. In particular, VDUP-1 and MCIP-1 were high in cLVH but expression levels were normal in eLVH, both in rat and human. These data indicate that during the progression of LVH, both in pressure and volume overload, expression levels of endogenous inhibitors of hypertrophy are modified and that these changes may have pathophysiological significance. In particular, MCIP-1 (the endogenous calcineurin inhibitor) and VDUP-1 (the endogenous inhibitor of thioredoxin) are potential molecular switches in the progression of LV hypertrophy.