Chronic N(G)-nitro-L-arginine methyl ester-induced hypertension : novel molecular adaptation to systolic load in absence of hypertrophy

Antihypertensive effect of the stem bark aqueous extract of Garcinia lucida Vesque (Clusiaceae) in L-NAME-treated rats: Contribution of endothelium-dependent and -independent vasorelaxation

Garcinia lucida is used in Cameroonian folk medicine to handle a variety of ailments, including arterial hypertension. This study aimed at determining the phytochemical profile and the antihypertensive effect of the stem bark aqueous extract of G. lucida (AEGL). AEGL was subjected to LC-MS analysis, and its effect (75, 150, and 300 mg/kg/day; by gavage) was evaluated against Nω-nitro-L-arginine methyl ester (L-NAME; 40 mg/kg)-induced hypertension in adult male Wistar rats for four consecutive weeks. Blood pressure and heart rate were monitored weekly using tail-cuff plethysmography. The vasorelaxant effect of cumulative concentrations (3-10-30-100-300 μg/mL) of AEGL was examined on endothelium-intact and denuded thoracic aorta rings which were precontracted with KCl (90 mM) or norepinephrine (NE; 10-5 M), and in the absence or presence of L-NAME (10-4 M), indomethacin (10-5 M), methylene blue (10-6 M), tetraethylammonium (TEA, 5 × 10-6 M), glibenclamide (10 × 10-6 M) or propranolol (5 × 10-6 M). The influence of AEGL on the response to NE, KCl, and CaCl2 was also investigated. Six compounds, including Garcinia biflavonoids GB1 and GB2, were identified. AEGL prevented the development of hypertension (p < 0.01 and p < 0.001) without affecting the heart rate. AEGL induced a concentration-dependent relaxation of aortic rings precontracted with NE (EC50 = 7.915 μg/mL) that was significantly inhibited by the removal of the endothelium, L-NAME, or methylene blue (p < 0.05-0.001). Indomethacin, propranolol, TEA, and glibenclamide did not affect AEGL-evoked vasorelaxation. Preincubation of aortic rings with AEGL reduced the magnitude of contraction elicited by CaCl2 but did not alter that of KCl or NE. AEGL possesses an antihypertensive effect that is mediated by both endothelium-dependent and endothelium-independent mechanisms. The activation of the NO/sGC/cGMP pathway accounts for the endothelium-dependent vasorelaxation. These pharmacological effects of AEGL could be attributed to the presence of the Garcinia biflavonoids GB1 and GB2.

Recent Developments in Drug Targets and Combination Therapy for the Clinical Management of Hypertension

Raised blood pressure is the most common complication worldwide that may lead to atherosclerosis and ischemic heart disease. Unhealthy lifestyles, smoking, alcohol consumption, junk food, and genetic disorders are some of the causes of hypertension. To treat this condition, numerous antihypertensive medications are available, either alone or in combination, that work via various mechanisms of action. Combinational therapy provides a certain advantage over monotherapy in the sense that it acts in multi mechanism mode and minimal drug amount is required to elicit the desired therapeutic effect. Such therapy is given to patients with systolic blood pressure greater than 20 mmHg and/or diastolic blood pressure exceeding 10 mmHg beyond the normal range, as well as those suffering from severe cardiovascular disease. The selection of antihypertensive medications, such as calcium channel blockers, angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), and low-dose diuretics, hinges on their ability to manage blood pressure effectively and reduce cardiovascular disease risks. This review provides insights into the diverse monotherapy and combination therapy approaches used for elevated blood pressure management. In addition, it offers an analysis of combination therapy versus monotherapy and discusses the current status of these therapies, from researchbased findings to clinical trials.

Early Development of Cardiac Fibrosis in Young Old-Father Offspring

Cardiac aging is characterized by progressive fibrosis. Epidemiological studies have found that advanced paternal age is associated with an increased risk of heart failure in the next generation. This study is aimed at evaluating the effect of paternal age, in the young male rat progeny, on cardiac phenotype under circulatory stress conditions. Offspring rats were obtained by mating old males (24 months old) with young females (two months old) and by mating young males (two months old) with the same young females. Hypertension was induced in old father offspring (OFO) rats and young old father (YFO) offspring rats using L-NAME (N(ω)-nitro-L-arginine methyl ester). The OFO L-NAME rats showed a high blood pressure phenotype associated with substantial cardiac hypertrophy and an exacerbation of cardiac fibrosis compared to the YFO L-NAME rats. Histological analysis of heart tissue showed an expansion of the extracellular matrix, with fibroblasts displaying markers of epicardial origin (Tcf21, Tbx18, and Wt1) in the OFO group. Moreover, western blot and protein phosphorylation antibody array identified the TGF-β2 receptor pathway as preferentially activated in aged hearts as well as in OFO cardiac tissue treated with L-NAME. In addition, old father offspring rats (OFO+OFO L-NAME) had increased cardiac DNA methylation. In young hypertensive progeny, advanced paternal age at conception may be a risk factor for early progression towards cardiac fibrosis. An intergenerational transmission may be behind the paternal age-related cardiac remodeling in the young offspring.

Tetrahydrobiopterin enhances mitochondrial biogenesis and cardiac contractility via stimulation of PGC1α signaling

Tetrahydrobiopterin (BH4) shows therapeutic potential as an endogenous target in cardiovascular diseases. Although it is involved in cardiovascular metabolism and mitochondrial biology, its mechanisms of action are unclear. We investigated how BH4 regulates cardiovascular metabolism using an unbiased multiple proteomics approach with a sepiapterin reductase knock-out (Spr-/-) mouse as a model of BH4 deficiency. Spr-/- mice exhibited a shortened life span, cardiac contractile dysfunction, and morphological changes. Multiple proteomics and systems-based data-integrative analyses showed that BH4 deficiency altered cardiac mitochondrial oxidative phosphorylation. Along with decreased transcription of major mitochondrial biogenesis regulatory genes, including Ppargc1a, Ppara, Esrra, and Tfam, Spr-/- mice exhibited lower mitochondrial mass and severe oxidative phosphorylation defects. Exogenous BH4 supplementation, but not nitric oxide supplementation or inhibition, rescued these cardiac and mitochondrial defects. BH4 supplementation also recovered mRNA and protein levels of PGC1α and its target proteins involved in mitochondrial biogenesis (mtTFA and ERRα), antioxidation (Prx3 and SOD2), and fatty acid utilization (CD36 and CPTI-M) in Spr-/- hearts. These results indicate that BH4-activated transcription of PGC1α regulates cardiac energy metabolism independently of nitric oxide and suggests that BH4 has therapeutic potential for cardiovascular diseases involving mitochondrial dysfunction.

5-Lipoxagenase deficiency attenuates L-NAME-induced hypertension and vascular remodeling

BACKGROUND

Abnormalities of the L-arginine-nitric oxide pathway induce hypertension. 5-Lipoxygenase (5-LO) is the key enzyme involved in synthesis of leukotrienes (LTs). However, whether nitricoxide synthase dysfunction induces hypertensive vascular remodeling by regulating 5-LO activity and its downstream inflammatory metabolites remains unknown.

METHODS AND RESULTS

Six-week L-NAME treatment significantly induced hypertension and vascular remodeling in both wild-type (WT) and 5-LO-knockout (5-LO-KO) mice, and blood pressure in caudal and carotid arteries was lower in 5-LO-KO than WT mice with L-NAME exposure. On histology, L-NAME induced less media thickness, media-to-lumen ratio, and collagen deposition and fewer Ki-67-positive vascular smooth muscle cells (VSMCs) but more elastin expression in thoracic and mesenteric aortas of 5-LO-KO than L-NAME-treated WT mice. L-NAME significantly increased LT content, including LTB4 and cysteinyl LT (CysLTs), in plasma and neutrophil culture supernatants from WT mice. On immunohistochemistry, L-NAME promoted the colocalization of 5-LO and 5-LO-activating protein on the nuclear envelope of cultured neutrophils, which was accompanied by elevated LT content in culture supernatants. In addition, LTs significantly promoted BrdU incorporation, migration and phenotypic modulation in VSMCs.

CONCLUSION

L-NAME may activate the 5-LO/LT pathway in immune cells, such as neutrophils, and promote the products of 5-LO metabolites, including LTB4 and CysLTs, which aggravate vascular remodeling in hypertension. 5-LO deficiency may protect against hypertension and vascular remodeling by reducing levels of 5-LO downstream inflammatory metabolites.

Comparison between characteristics of severe and very severe aortic stenosis

OBJECTIVES

Patients with very severe aortic stenosis (AS) have extremely poor clinical outcomes even if they are asymptomatic compared to those with severe AS, but the clinical and echocardiographic characteristics of patients with very severe AS remain unclear.

METHODS

The Asian Valve Registry is a prospective, multicenter, multinational registry for the study and identification of the incidence, natural course, clinical outcomes, and prognostic factors for patients with significant AS at 9 centers in Asian countries. Severe AS was observed in 367 of 1066 patients with AS, and 212 were classified as very severe AS, defined as a peak aortic valve velocity ≥5.0 m/s or a mean aortic valve gradient ≥60 mm Hg.

RESULTS

The prevalence of NYHA functional class II-IV among patients with very severe AS was significantly higher than that among patients with severe AS (67.9% vs 51.5%, P < .001). As for echocardiographic parameters, it was noteworthy that left ventricular mass index (LVMI) and left atrial volume index (LAVI) for patients with very severe AS were significantly larger than those for patients with severe AS (LVMI: 145.1 ± 36.4 g/m² vs 119.2 ± 32.1 g/m² , P < .0001; LAVI: 56.1 ± 24.6 mL/m² vs 49.8 ± 22.6 mL/m² , P = .002). Moreover, multivariate logistic regression analysis showed that LVMI was the only independently associated with NYHA functional class II-IV in patients with very severe AS.

CONCLUSIONS

Our findings may well have clinical implications for better management of patients with AS and lead to better understanding of poor outcomes for patients with very severe AS.

Expression of Class I and Class II a/b Histone Deacetylase is Dysregulated in Hypertensive Animal Models

Background and Objectives

Dysregulation of histone deacetylase expression and enzymatic activity is associated with a number of diseases. It has been reported that protein levels of histone deacetylase (HDAC)1 and HDAC5 increase during human pulmonary hypertension, and that the enzymatic activity of HDAC6 is induced in a chronic hypertensive animal model. This study investigated the protein expression profiles of class I and II a/b HDACs in three systemic hypertension models.

Subjects and Methods

We used three different hypertensive animal models: (i) Wistar-Kyoto rats (n=8) and spontaneously hypertensive rats (SHR; n=8), (ii) mice infused with saline or angiotensin II to induce hypertension, via osmotic mini-pump for 2 weeks, and (iii) mice that were allowed to drink L-N^G-nitro-L-arginine methyl ester (L-NAME) to induce hypertension.

Results

SHR showed high systolic, diastolic, and mean blood pressures. Similar increases in systolic blood pressure were observed in angiotensin II or L-NAME-induced hypertensive mice. In SHR, class IIa HDAC (HDAC4, 5, and 7) and class IIb HDAC (HDAC6 and 10) protein expression were significantly increased. In addition, a HDAC3 protein expression was induced in SHR. However, in L-NAME mice, class IIa HDAC protein levels (HDAC4, 5, 7, and 9) were significantly reduced. HDAC8 protein levels were significantly reduced both in angiotensin II mice and in SHR.

Conclusion

These results indicate that dysregulation of class I and class II HDAC protein is closely associated with chronic hypertension.

Effects of carvedilol or amlodipine on target organ damage in L-NAME hypertensive rats: their relationship with blood pressure variability

The aim of the study was to compare the effects of chronic oral treatment with carvedilol or amlodipine on blood pressure, blood pressure variability and target organ damage in N-nitro-l-arginine methyl ester (L-NAME) hypertensive rats. Wistar rats were treated with L-NAME administered in the drinking water for 8 weeks together with oral administration of carvedilol 30 mg/kg (n = 6), amlodipine 10 mg/kg (n = 6), or vehicle (n = 6). At the end of the treatment, echocardiographic evaluation, blood pressure, and short-term variability measurements were performed. Left ventricular and thoracic aortas were removed to assess activity of metalloproteinase 2 and 9 and expression levels of transforming growth factor β, tumor necrosis factor α, and interleukin 6. Histological samples were prepared from both tissues. Carvedilol and amlodipine induced a comparable reduction of systolic and mean arterial pressure and its short-term variability in L-NAME rats. The expression of transforming growth factor β, tumor necrosis factor α, and interleukin 6 decreased in both organs after carvedilol or amlodipine treatment and the activity of metalloproteinase was reduced in aortic tissue. Treatment with carvedilol or amlodipine completely prevented left ventricular collagen deposition and morphometric alterations in aorta. Oral chronic treatment with carvedilol or amlodipine significantly attenuates blood pressure variability and reduces target organ damage and biomarkers of tissue fibrosis and inflammation in L-NAME hypertensive rats.

Evaluation of anti-hypertensive activity of Ulmus wallichiana extract and fraction in SHR, DOCA-salt- and L-NAME-induced hypertensive rats

ETHNOPHARMACOLOGICAL RELEVANCE

Ulmus wallichiana Planchon (Himalayan Elm), a traditional medicinal plant, used in fracture healing in folk tradition of Uttarakhand, Himalaya, India. It is also used as diuretic. U. rhynchophylla, native to China, known as Gou Teng in Chinese medicine, is used for hypertension (WHO). U. macrocarpa has antihypertensive and vasorelaxant activity. However, no detailed studies related to hypertension have been reported previously, so we have explored the antihypertensive activity of U. wallichiana.

AIM OF THE STUDY

To investigate the pharmacological effect of ethanolic extract (EE) and butanolic fraction (BF) of U. wallichiana in hypertensive rats.

MATERIALS AND METHODS

SHR, DOCA-salt- and L-NAME-induced hypertension models were used. Treatment was performed by oral administration of EE and BF of U. wallichiana (500mg/kg/day and 50mg/kg/day) for 14 days. Then blood pressure was measured by non-invasive blood pressure (NIBP) measurement technique. Invasive blood pressure (IBP) was also reported to support the NIBP data. Concentrations of plasma renin, angiotensin II (Ang II), nitrate/nitrite (NO), cGMP were estimated. Angiotensin-converting enzyme (ACE) activity and ROS activity were also estimated.

RESULTS

Blood pressure was significantly higher in SHR as compared to normotensive wistar group (170.59±0.83mmHg vs 121.54±1.24mmHg, respectively). SBP was increased in DOCA-salt induced group compared to their control (132.77±3.90mmHg vs 107.85±5.95mmHg, respectively) and L-NAME-induced group compared to their control (168.55±5.07mmHg vs 113.03±4.13mmHg, respectively). The treatment of extract and fraction of U. wallichiana significantly decreased the blood pressure in SHR+EE (151.26±1.85mmHg, p<0.001), SHR+BF (140.44±1.16mmHg, p<0.001); DOCA+EE (113.43±5.44mmHg, p<0.05), DOCA+BF (105.09±5.12mmHg, p<0.05) and L-NAME+EE (119.76±4.39mmHg, p<0.001), L-NAME+BF (117.50±7.27mmHg, p<0.001) compared to their respective diseased control groups. The plasma renin, Ang II and ACE activity were also significantly decreased and augmented the NO and cGMP levels. It also down regulated the expression of Renin, ACE, NOS3 and TGF-β1 at mRNA levels.

CONCLUSIONS

The EE and BF probably reducing the BP via Renin-angiotensin-aldosterone system and NO/cGMP signaling pathway. The decrease in blood pressure may be due to presence of quercetin analogue flavonoids (2S,3S)-(+)-3',4',5,7-tetrahydroxydihydroflavonol-6-C-β-D-glucopyranoside; 6-Glucopyranosyl-3,3',4',5,7-pentahydroxyflavone; 6-Glucopyranosyl-4',5,7-trihydroxyflavanone and (2S,3S)-(+)-4',5,7-trihydroxydihydroflavonol-6-C-β-D-glucopyranoside, may be due to its antioxidant activity. Thus EE and BF of U. wallichiana found to have the potential ability to be used as herbal medicament to treat hypertension.

Reversal of cardiovascular remodelling with candesartan

Cardiovascular remodelling, defined as ventricular and vascular hypertrophy together with fibrosis, characterises hypertension following inhibition of the production of the endogenous vasodilator, nitric oxide (NO). This study has determined whether the cardiovascular remodelling following chronic NO synthase inhibition can be reversed by administration of the selective angiotensin II AT1-receptor antagonist, candesartan. Male Wistar rats were treated with L-nitroarginine methyl ester (L-NAME, 400 mg/l in drinking water) for eight weeks and with candesartan cilexetil (2 mg/kg/day by oral gavage) for the last four weeks. L-NAME-treated rats became hypertensive with systolic blood pressure increasing from 110±4 mmHg (control) to 170±10 mmHg. Rats developed left ventricular hypertrophy (control 1.70±0.06; L-NAME 2.10±0.04 mg/kg body wt) with markedly increased deposition of perivascular and interstitial collagen. Candesartan returned blood pressure, left ventricular weights and collagen deposition to control values. Echocardiographic assessment showed concentric hypertrophy with an increased fractional shortening; this was reversed by candesartan treatment. Heart failure was not evident. In the isolated Langendorff heart, diastolic stiffness increased in L-NAME-treated rats while the rate of increase in pressure (+dP/dt) increased after eight weeks only; candesartan reduced collagen deposition and normalised +dP/dt. In isolated left ventricular papillary muscles, the potency (negative log EC50) of noradrenaline as a positive inotropic compound was unchanged, (control 6.56±0.14); maximal increase in force before ectopic beats was reduced from 5.0±0.4 mN to 2.0±0.2 mN. Noradrenaline potency as a vasoconstrictor in thoracic aortic rings was unchanged, but maximal contraction was markedly reduced from 25.2±2.0 mN to 3.0±0.3 mN; this was partially reversed by candesartan treatment. Thus, chronic inhibition of NO production with L-NAME induces hypertension, hypertrophy and fibrosis with increased toxicity and significant decreases in vascular responses to noradrenaline. These changes were at least partially reversible by treatment with candesartan, implying a significant role of AT1-receptors in L-NAME-induced cardiovascular changes.

Arterial Smooth Muscle Mitochondria Amplify Hydrogen Peroxide Microdomains Functionally Coupled to L-Type Calcium Channels

RATIONALE

Mitochondria are key integrators of convergent intracellular signaling pathways. Two important second messengers modulated by mitochondria are calcium and reactive oxygen species. To date, coherent mechanisms describing mitochondrial integration of calcium and oxidative signaling in arterial smooth muscle are incomplete.

OBJECTIVE

To address and add clarity to this issue, we tested the hypothesis that mitochondria regulate subplasmalemmal calcium and hydrogen peroxide microdomain signaling in cerebral arterial smooth muscle.

METHODS AND RESULTS

Using an image-based approach, we investigated the impact of mitochondrial regulation of L-type calcium channels on subcellular calcium and reactive oxygen species signaling microdomains in isolated arterial smooth muscle cells. Our single-cell observations were then related experimentally to intact arterial segments and to living animals. We found that subplasmalemmal mitochondrial amplification of hydrogen peroxide microdomain signaling stimulates L-type calcium channels, and that this mechanism strongly impacts the functional capacity of the vasoconstrictor angiotensin II. Importantly, we also found that disrupting this mitochondrial amplification mechanism in vivo normalized arterial function and attenuated the hypertensive response to systemic endothelial dysfunction.

CONCLUSIONS

From these observations, we conclude that mitochondrial amplification of subplasmalemmal calcium and hydrogen peroxide microdomain signaling is a fundamental mechanism regulating arterial smooth muscle function. As the principle components involved are fairly ubiquitous and positioning of mitochondria near the plasma membrane is not restricted to arterial smooth muscle, this mechanism could occur in many cell types and contribute to pathological elevations of intracellular calcium and increased oxidative stress associated with many diseases.

Brain BDNF levels elevation induced by physical training is reduced after unilateral common carotid artery occlusion in rats

We investigated the contribution of blood flow elevation in the cerebrovasculature to physical training-induced brain-derived neurotrophic factor (BDNF) levels elevation in the brain. Brain-derived neurotrophic factor protein levels were measured in the motor cortex 24 h after the last session of a forced treadmill walking (30 minutes a day, 18 m/minute for 7 consecutive days). Unilateral common carotid artery occlusion and modulation of exercise intensity (0 versus -10% inclination of the treadmill) were used as strategies to reduce the (normal) elevation of flow in the cerebrovasculature occurring during exercise. Administration of N-nitro-L-arginine methyl ester (L-NAME, 60 mg/kg before each exercise sessions) and genetic hypertension (spontaneously hypertensive rats) were used as approaches to reduce stimulation of nitric oxide production in response to shear stress elevation. Vascular occlusion totally and partially abolished the effect of physical training on BDNF levels in the hemisphere ipsilateral and contralateral to occlusion, respectively. BDNF levels were higher after high than low exercise intensity. In addition, both genetic hypertension and L-NAME treatment blunted the effects of physical training on BDNF. From these results, we propose that elevation of brain BDNF levels elicited by physical training involves changes in cerebral hemodynamics.

Apelin elevates blood pressure in ICR mice with L‑NAME‑induced endothelial dysfunction

Apelin is the endogenous ligand of APJ, which belongs to the family of G protein-coupled receptors. Apelin and APJ are highly expressed in various cardiovascular tissues, including the heart, kidney and vascular endothelial and smooth muscle cells. Although apelin exerts hypotensive effects via activation of endothelial nitric oxide synthase (eNOS), the ability of apelin to regulate blood pressure under pathological conditions is poorly understood. In the current study, N^G-nitro-L-arginine methyl ester (L-NAME), a potent NOS inhibitor, was administered chronically, to induce peripheral vascular damage in mice. L-NAME-treated mice exhibited hypertension, increased vascular cell adhesion molecule-1 and plasminogen activator inhibitor-1 mRNA levels in the aorta and impaired vasodilatation associated with decreased aortic eNOS expression, consistent with endothelial damage. Three days following withdrawal of L-NAME treatment, the blood pressure response to apelin stimulation was assessed. Although apelin reduced blood pressure in non-treated mice, it was found to transiently elevate blood pressure in L-NAME-treated mice. These results indicate that apelin functions as a vasopressor peptide under pathological conditions, including vascular endothelial dysfunction in mice.

Antidiabetic and antihypertensive effect of a polyphenol-rich fraction of Thymelaea hirsuta L. in a model of neonatal streptozotocin-diabetic and N(G) -nitro-l-arginine methyl ester-hypertensive rats

BACKGROUND

  The present study examined the effect of the polyphenol-rich fraction from Thymelaea hirsuta (PRF-Th) in a rat model of streptozotocin (STZ)-diabetes and nitric oxide (NO)-deficient hypertension.

METHODS

  Diabetes was induced by a single dose of STZ (90 mg/kg, i.p.). To induce NO-deficient hypertension, rats were treated with the NO synthase inhibitor N(G) -nitro-l-arginine methyl ester; l-NAME; 30 mg/kg per day, p.o. for 3 weeks. The effects of 21 days treatment with 80 mg/kg per day PRF-Th in the drinking water were evaluated in diabetic-hypertensive (DH) rats. In all groups (n = 6 in each), glycemia and systolic blood pressure were determined weekly. At the end of the experiment, hepatic glycogen was determined.

RESULTS

  Blood glucose levels decreased gradually from baseline until the end of the experiment in untreated DH rats (from 1.92 ± 0.09 to 1.3 ± 0.1 g/L; P < 0.05). Administration of PRF-Th concomitantly with l-NAME prevented the blood pressure increase in rats. After 21 days, blood pressure in PRF-Th + l-NAME- and l-NAME-treated rats was 132 ± 1 and 157 ± 1 mmHg, respectively (P < 0.001). Administration of 2 mL/kg per day PRF-Th to DH rats significantly increased hepatic glycogen levels compared with levels in untreated DH rats (13.65 ± 1.84 vs 6.34 ± 0.75 mg/g tissue, respectively; P < 0.01). Moreover, PRF-Th significantly reduced the amount of glucose absorbed in in situ perfused jejunum segments compared with control (by 33.6%; P <0.001). This effect of PRF-Th was comparable with that of acarbose, an α-glucosidase inhibitor.

CONCLUSIONS

  The findings of the present study indicate that T. hirsuta has antidiabetic and antihypertensive activity in STZ-diabetic, NO-deficient hypertensive rats. This effect seems to be due to its rich polyphenol content. Therefore, T. hirsuta may be useful as a food supplement for the prevention of type 2 diabetes and hypertension.

Animal models for the study of arterial hypertension

Hypertension is one of the leading causes of disability or death due to stroke, heart attack and kidney failure. Because the etiology of essential hypertension is not known and may be multifactorial, the use of experimental animal models has provided valuable information regarding many aspects of the disease, which include etiology, pathophysiology, complications and treatment. The models of hypertension are various, and in this review, we provide a brief overview of the most widely used animal models, their features and their importance.

Tension cost correlates with mechanical and biochemical parameters in different myocardial contractility conditions

OBJECTIVES

Tension cost, the ratio of myosin ATPase activity to tension, reflects the economy of tension development in the myocardium. To evaluate the mechanical advantage represented by the tension cost, we studied papillary muscle contractility and the activity of myosin ATPase in the left ventricles in normal and pathophysiological conditions.

METHODS

Experimental protocols were performed using rat left ventricles from: (1) streptozotocin-induced diabetic and control Wistar rats; (2) N-nitro-L-arginine methyl ester (L-NAME) hypertensive and untreated Wistar rats; (3) deoxycorticosterone acetate (DOCA) salt-treated, nephrectomized and salt- and DOCA-treated rats; (4) spontaneous hypertensive rats (SHR) and Wistar Kyoto (WKY) rats; (5) rats with myocardial infarction and shamoperated rats. The isometric force, tetanic tension, and the activity of myosin ATPase were measured.

RESULTS

The results obtained from infarcted, diabetic, and deoxycorticosterone acetate-salt-treated rats showed reductions in twitch and tetanic tension compared to the control and sham-operated groups. Twitch and tetanic tension increased in the N-nitro-L-arginine methyl ester-treated rats compared with the Wistar rats. Myosin ATPase activity was depressed in the infarcted, diabetic, and deoxycorticosterone acetate salt-treated rats compared with control and sham-operated rats and was increased in N-nitro-L-arginine methyl ester-treated rats. These parameters did not differ between SHR and WKY rats. In the studied conditions (e.g., post-myocardial infarction, deoxycorticosterone acetate salt-induced hypertension, chronic N-nitro-L-arginine methyl ester treatment, and streptozotocin-induced diabetes), a positive correlation between force or plateau tetanic tension and myosin ATPase activity was observed.

CONCLUSION

Our results suggest that the myocardium adapts to force generation by increasing or reducing the tension cost to maintain myocardial contractility with a better mechanical advantage.

The effect of indapamide on development of myocardial hypertrophy and fibrosis in L-NAME-induced hypertension in rat

The aim of this study was to analyze the effect of indapamide and its combination with ACE inhibitor (captopril) and antioxidant (Provinols™) on both myocardial hypertrophy and fibrosis. Wistar rats were treated with L-NAME (40 mg/kg/day, L); L-NAME plus indapamide (1 mg/kg/day), or captopril (10 mg/kg/day), or Provinols™ (40 mg/kg/day), or combination of indapamide with captopril, and indapamide with Provinols™ for 7 weeks. Blood pressure (BP), LV hypertrophy and fibrosis were determined. The content of collagens type I and III was evaluated morphometrically after picrosirius red staining. L-NAME treatment led to increased BP, LV hypertrophy, total fibrosis and relative content of collagens without the change in collagen type I/III ratio. Indapamide and captopril decreased BP, LV hypertrophy and the collagen ratio without affecting total fibrosis, while Provinols™ reduced BP, the collagen ratio and fibrosis without affecting LV hypertrophy. The combinations decreased all the parameters. Decrease of LV hypertrophy was achieved by drugs with the best reducing effect on BP, fibrosis reduction was reached by the antioxidant treatment with only partial effect on BP. Thus, the combination of antihypertensive and antioxidant treatment may represent a powerful tool in preventing myocardial remodeling induced by hypertension.

Chronic ( − )-epicatechin improves vascular oxidative and inflammatory status but not hypertension in chronic nitric oxide-deficient rats

The present study analysed the effects of the flavanol ( − )-epicatechin in rats after chronic inhibition of NO synthesis with NG-nitro-l-arginine methyl ester (l-NAME), at doses equivalent to those achieved in the studies involving human subjects. Wistar rats were randomly divided into four groups: (1) control-vehicle, (2) l-NAME, (3) l-NAME-epicatechin 2 (l-NAME-Epi 2) and (4) l-NAME-epicatechin 10 (l-NAME-Epi 10). Rats were daily given by oral administration for 4 weeks: vehicle, ( − )-epicatechin 2 or 10 mg/kg. Animals in the l-NAME groups daily received l-NAME 75 mg/100 ml in drinking-water. The evolution in systolic blood pressure and heart rate, and morphological and plasma variables, proteinuria, vascular superoxide, reactivity and protein expression at the end of the experiment were analysed. Chronic ( − )-epicatechin treatment did not modify the development of hypertension and only weakly affected the endothelial dysfunction induced by l-NAME but prevented the cardiac hypertrophy, the renal parenchyma and vascular lesions and proteinuria, and blunted the prostanoid-mediated enhanced endothelium-dependent vasoconstrictor responses and the cyclo-oxygenase-2 and endothelial NO synthase (eNOS) up-regulation. Furthermore, ( − )-epicatechin also increased Akt and eNOS phosphorylation and prevented the l-NAME-induced increase in systemic (plasma malonyldialdehyde and urinary 8-iso-PGF2α) and vascular (dihydroethidium staining, NADPH oxidase activity and p22phox up-regulation) oxidative stress, proinflammatory status (intercellular adhesion molecule-1, IL-1β and TNFα up-regulation) and extracellular-signal-regulated kinase 1/2 phosphorylation. The present study shows for the first time that chronic oral administration of ( − )-epicatechin does not improve hypertension but reduced pro-atherogenic pathways such as oxidative stress and proinflammatory status of the vascular wall induced by blockade of NO production.

Metformin attenuates ventricular hypertrophy by activating the AMP-activated protein kinase-endothelial nitric oxide synthase pathway in rats

1. Metformin is an activator of AMP-activated protein kinase (AMPK). Recent studies suggest that pharmacological activation of AMPK inhibits cardiac hypertrophy. In the present study, we examined whether long-term treatment with metformin could attenuate ventricular hypertrophy in a rat model. The potential involvement of nitric oxide (NO) in the effects of metformin was also investigated. 2. Ventricular hypertrophy was established in rats by transaortic constriction (TAC). Starting 1 week after the TAC procedure, rats were treated with metformin (300 mg/kg per day, p.o.), N(G)-nitro-L-arginine methyl ester (L-NAME; 50 mg/kg per day, p.o.) or both for 8 weeks prior to the assessment of haemodynamic function and cardiac hypertrophy. 3. Cultured cardiomyocytes were used to examine the effects of metformin on the AMPK-endothelial NO synthase (eNOS) pathway. Cells were exposed to angiotensin (Ang) II (10⁻⁶ mol/L) for 24 h under serum-free conditions in the presence or absence of metformin (10⁻³ mol/L), compound C (10⁻⁶ mol/L), L-NAME (10⁻⁶ mol/L) or their combination. The rate of incorporation of [³H]-leucine was determined, western blotting analyses of AMPK-eNOS, neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) were undertaken and the concentration of NO in culture media was determined. 4. Transaortic constriction resulted in significant haemodynamic dysfunction and ventricular hypertrophy. Myocardial fibrosis was also evident. Treatment with metformin improved haemodynamic function and significantly attenuated ventricular hypertrophy. Most of the effects of metformin were abolished by concomitant L-NAME treatment. L-NAME on its own had no effect on haemodynamic function and ventricular hypertrophy in TAC rats. 5. In cardiomyocytes, metformin inhibited AngII-induced protein synthesis, an effect that was suppressed by the AMPK inhibitor compound C or the eNOS inhibitor L-NAME. The improvement in cardiac structure and function following metformin treatment was associated with enhanced phosphorylation of AMPK and eNOS and increased NO production. 6. The findings of the present study indicate that long-term treatment with metformin could attenuate ventricular hypertrophy induced by pressure overload via activation of AMPK and a downstream signalling pathway involving eNOS-NO.

Biomechanical strain causes maladaptive gene regulation, contributing to Alport glomerular disease

Patients with Alport's syndrome develop a number of pro-inflammatory cytokine and matrix metalloproteinase (MMP) abnormalities that contribute to progressive renal failure. Changes in the composition and structure of the glomerular basement membranes likely alter the biomechanics of cell adhesion and signaling in these patients. To test if enhanced strain on the capillary tuft due to these structural changes contributes to altered gene regulation, we subjected cultured podocytes to cyclic biomechanical strain. There was robust induction of interleukin (IL)-6, along with MMP-3, -9, -10, and -14, but not MMP-2 or -12 by increased strain. Neutralizing antibodies against IL-6 attenuated the strain-mediated induction of MMP-3 and -10. Alport mice treated with a general inhibitor of nitric oxide synthase (L-NAME) developed significant hypertension and increased IL-6 and MMP-3 and -10 in their glomeruli relative to those of normotensive Alport mice. These hypertensive Alport mice also had elevated proteinuria along with more advanced histological and ultrastructural glomerular basement membrane damage. We suggest that MMP and cytokine dysregulation may constitute a maladaptive response to biomechanical strain in the podocytes of Alport patients, thus contributing to glomerular disease initiation and progression.

Nitric oxide synthase inhibition in rats: Melatonin reduces blood pressure and ischemia/reperfusion-induced infarct size

Reduction in the synthesis or bioavailability of nitric oxide plays a significant role in the development of myocardial infarction and hypertension. Numerous studies suggest that melatonin reduces blood pressure (BP) and ischemia/reperfusion (I/R) injury in rats. The effects of melatonin on the BP and I/R-induced cardiac infarct size in L-NAME-induced hypertensive rats remains unknown. This study was designed to investigate the effects of melatonin on BP and the I/R-induced infarct size in chronic nitric oxide synthase inhibited rats by L-NAME. Rats received L-NAME for 15 days to produce hypertension and melatonin the last 5 days before I/R studies. To produce cardiac damage, the left coronary artery was occluded for 30 min, followed by 120 min reperfusion. L-NAME led to a significant increase in BP. Melatonin administration (10 mg/kg) to L-NAME treated rats significantly reduced BP and infarct size. Also, melatonin attenuated the mortality resulting from I/R, but this was not statistically significant. Melatonin administration would seem important to reduce BP and infarct size resulting from I/R in L-NAME-induced hypertensive rats.

Ginsenoside Rg(1) inhibits rat left ventricular hypertrophy induced by abdominal aorta coarctation: involvement of calcineurin and mitogen-activated protein kinase signalings

Ginsenoside Rg(1) (Rg(1)), one of the active components of Panax ginseng, has been reported to inhibit proliferation of vascular smooth muscle cells induced by tumor necrosis factor-alpha. This study aims to investigate whether Rg(1) has protective effect on rat left ventricular hypertrophy and to probe its protective mechanisms. The rat left ventricular hypertrophy was induced by abdominal aorta coarctation and Rg(1) (3.75, 7.5 and 15 mg/kg/day) was given the day after surgery for 21 consecutive days. The left ventricular hypertrophy induced by abdominal aorta coarctation was evidenced by histopathology, electromicroscopy, and by determining the elevated left ventricular weight and the expression of atrial natriuretic peptide. Rg(1) significantly ameliorated left ventricular hypertrophy induced by abdominal aorta coarctation in a dose-dependent manner. To examine the mechanism of protection, the expressions of calcineurin, CnA (the catalytic subunit of calcineurin), extracellular signal-regulated kinase-1, and mitogen-activated protein (MAP) kinase phosphatase-1 were determined at the transcript and protein levels. The abdominal aorta coarctation induced increases in calcineurin, CnA, and extracellular signal-regulated kinase-1 expressions were suppressed, but the expression of MAP kinase phosphatase-1 was increased by Rg(1). These results demonstrate that Rg(1) alleviates left ventricular hypertrophy induced by abdominal aorta coarctation, and the protection appears to be due, at least in part, to its inhibitory effects on calcineurin and MAP kinase signaling pathways.

Lipopolysaccharide induces cellular hypertrophy through calcineurin/NFAT-3 signaling pathway in H9c2 myocardiac cells

Evidences suggest that lipopolysaccharide (LPS) participates in the inflammatory response in the cardiovascular system; however, it is unknown if LPS is sufficient to cause the cardiac hypertrophy. In the present study, we treated H9c2 myocardiac cells with LPS to explore whether LPS causes cardiac hypertrophy, and to identify the precise molecular and cellular mechanisms behind hypertrophic responses. Here we show that LPS challenge induces pathological hypertrophic responses such as the increase in cell size, the reorganization of actin filaments, and the upregulation of hypertrophy markers including atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) in H9c2 cells. LPS treatment significantly promotes the activation of GATA-4 and the nuclear translocation of NFAT-3, which act as transcription factors mediating the development of cardiac hypertrophy. After administration of inhibitors including U0126 (ERK1/2 inhibitor), SB203580 (p38 MAPK inhibitor), SP600125 (JNK1/2 inhibitor), CsA (calcineurin inhibitor), FK506 (calcineurin inhibitor), and QNZ (NFkappaB inhibitor), LPS-induced hypertrophic characteristic features, such as increases in cell size, actin fibers, and levels of ANP and BNP, and the nuclear localization of NFAT-3 are markedly inhibited only by calcineurin inhibitors, CsA and FK506. Collectively, these results suggest that LPS leads to myocardiac hypertrophy through calcineurin/NFAT-3 signaling pathway in H9c2 cells. Our findings further provide a link between the LPS-induced inflammatory response and the calcineurin/NFAT-3 signaling pathway that mediates the development of cardiac hypertrophy.

Nuclear factor-kappaB signaling contributes to severe, but not moderate, angiotensin II-induced left ventricular remodeling

OBJECTIVE

The transcription factor nuclear factor-kappaB (NF-kappaB) has been implicated in cardiomyocyte hypertrophy in vitro as well as in vivo; however, it is unknown if activation of NF-kappaB plays a mandatory role in the hypertrophic process. Here we characterize the importance of NF-kappaB signaling in moderate and severe left ventricular (LV) hypertrophy in rats with chronic pressure overload induced by angiotensin II (Ang II) infusion.

METHODS AND RESULTS

Electrophoretic mobility shift assay analysis revealed that Ang II infusion (2.5 microg/kg per min) for 6 days increased LV NF-kappaB/DNA-binding activity in a biphasic manner in Sprague-Dawley rats. Pyrrolidine dithiocarbamate (PDTC) (100 mg/kg per day), an NF-kappaB inhibitor, abolished Ang II-induced NF-kappaB activation and concomitant increase in tumor necrosis factor-alpha gene expression, while activator protein-1/DNA binding was not affected. Inhibition of NF-kappaB signaling for 6 days significantly attenuated Ang II-induced increases in LV/body weight ratio, LV mean wall thickness and cardiomyocyte cross-sectional area, without compromising LV systolic function. Moreover, PDTC abolished Ang II-induced cardiomyocyte apoptosis and interstitial fibrosis, and attenuated the gene expression of type I collagen. In contrast, a moderate LV hypertrophy induced by Ang II at a lower dose (0.5 microg/kg per min) was not associated with a significant activation of NF-kappaB, and PDTC treatment had no effect on the hypertrophic indices.

CONCLUSION

Our in-vivo data indicate a critical role of NF-kappaB signaling in the advanced stage of the remodeling process, whereas development of moderate LV hypertrophy is not dependent on NF-kappaB activation.

Efeito da administração oral de arginina sobre a pressão arterial e parâmetros cardíacos em ratos submetidos ao bloqueio crônico da síntese de óxido nítrico

Já está claramente estabelecido, que a inibição crônica da síntese de óxido nítrico resulta em hipertensão sustentada, remodelamento cardíaco e fibrose. Além disso, resultados de nosso grupo demonstraram que a suplementação oral com L-arginina foi capaz de aumentar a resistência da musculatura esquelética a fadiga muscular localizada em humanos. O tratamento experimental de ratos com L-NAME é um dos modelos mais comumente utilizados para se induzir hipertensão. A resposta compensatória esperada contra o aumento da resistência vascular sistêmica seria a hipertrofia ventricular esquerda; entretanto, isso tem sido um ponto bastante controverso na literatura. O objetivo do presente estudo foi verificar os efeitos da inibição do óxido nítrico pela administração oral de L-NAME sobre o tecido cardíaco de ratos e a possível reversão pela L-arginina. Foram utilizados 30 ratos Wistar machos (250-350g), mantidos em condições de temperatura, luz e umidade controlada, e com água e comida ad libitum. Ao final de quatro semanas, os animais foram sacrificados por inalação de CO2 e os corações foram removidos e imediatamente dissecados, sendo separados átrios e ventrículos, obtendo-se os pesos total e parcial. Os valores foram corrigidos em função do peso corporal obtido na última semana de tratamento e expressos como índice cardíaco. O L-NAME foi capaz de induzir hipertensão e aumento significativo do duplo produto, porém sem resultados significativos sobre os pesos cardíacos, não sendo observada hipertrofia do órgão. Os aumentos de pressão arterial e duplo produto foram revertidos pela administração concomitante de arginina, de maneira dependente da dose. Dados preliminares não publicados demonstraram a reversão da fibrose cardíaca induzida pelo L-NAME, nos animais que receberam tratamento com arginina. Podemos concluir que a arginina pode vir a ser uma ferramenta valiosa na prevenção da hipertensão e do remodelamento cardíaco, principalmente nos casos relacionados a disfunções vasculares e, ainda, produzindo efeitos adicionais em atividades atléticas.

Ouabain-induced hypertension enhances left ventricular contractility in rats

Chronic ouabain treatment produces hypertension acting on the central nervous system and at vascular levels. However, cardiac effects in this model of hypertension are still poorly understood. Hence, the effects of hypertension induced by chronic ouabain administration ( approximately 8 microg day(-1), s.c.) for 5 weeks on the cardiac function were studied in Wistar rats. Ouabain induces hypertension but not myocardial hypertrophy. Awake ouabain-treated rats present an increment of the left ventricular systolic pressure and of the maximum positive and negative dP/dt. Isolated papillary muscles from ouabain-treated rats present an increment in isometric force, and this effect was present even when inotropic interventions (external Ca(2+) increment and increased heart rate) were performed. However, the sarcoplasmic reticulum activity and the SERCA-2 protein expression did not change. On the other hand, the activity of myosin ATPase increased without changes in myosin heavy chain protein expression. In addition, the expression of alpha(1) and alpha(2) isoforms of Na(+), K(+)-ATPase also increased in the left ventricle from ouabain-hypertensive rats. The present results showed positive inotropic and lusitropic effects in hearts from awake ouabain-treated rats, which are associated with an increment of the isometric force development and of the activity of myosin ATPase and expression of catalytic subunits of the Na(+), K(+)-ATPase.

Differential expression of components of the cardiomyocyte adrenomedullin/intermedin receptor system following blood pressure reduction in nitric oxide-deficient hypertension

Adrenomedullin (AM) and intermedin (IMD; adrenomedulln-2) are vasodilator peptides related to calcitonin gene-related peptide (CGRP). The actions of these peptides are mediated by the calcitonin receptor-like receptor (CLR) in association with one of three receptor activity-modifying proteins. CGRP is selective for CLR/receptor activity modifying protein (RAMP)1, AM for CLR/RAMP2 and -3, and IMD acts at both CGRP and AM receptors. In a model of pressure overload induced by inhibition of nitric-oxide synthase, up-regulation of AM was observed previously in cardiomyocytes demonstrating a hypertrophic phenotype. The current objective was to examine the effects of blood pressure reduction on cardiomyocyte expression of AM and IMD and their receptor components. Nomega-nitro-L-arginine methyl ester (L-NAME) (35 mg/kg/day) was administered to rats for 8 weeks, with or without concurrent administration of hydralazine (50 mg/kg/day) and hydrochlorothiazide (7.5 mg/kg/day). In left ventricular cardiomyocytes from L-NAME-treated rats, increases (-fold) in mRNA expression were 1.6 (preproAM), 8.4 (preproIMD), 3.4 (CLR), 4.1 (RAMP1), 2.8 (RAMP2), and 4.4 (RAMP3). Hydralazine/hydrochlorothiazide normalized systolic blood pressure (BP) and abolished mRNA up-regulation of hypertrophic markers sk-alpha-actin and BNP and of preproAM, CLR, RAMP2, and RAMP3 but did not normalize cardiomyocyte width nor preproIMD or RAMP1 mRNA expression. The robust increase in IMD expression indicates an important role for this peptide in the cardiac pathology of this model but, unlike AM, IMD is not associated with pressure overload upon the myocardium. The concordance of IMD and RAMP1 up-regulation indicates a CGRP-type receptor action; considering also a lack of response to BP reduction, IMD may, like CGRP, have an anti-ischemic function.

Upregulation of adrenomedullin and its receptor components during cardiomyocyte hypertrophy induced by chronic inhibition of nitric oxide synthesis in rats

Adrenomedullin may provide a compensatory mechanism to attenuate left ventricular hypertrophy (LVH). Nitric oxide synthase inhibition, induced by chronic administration of N(omega)-nitro-L-arginine methyl ester (L-NAME) to rats, induces cardiac hypertrophy in some, but not all cases; there are few reports of direct assessment of cardiomyocyte parameters. The objective was to characterize hypertrophic parameters in left (LV) and right ventricular (RV) cardiomyocytes after administration of L-NAME to rats for 8 wk and to determine whether adrenomedullin and its receptor components were upregulated. After treatment with L-NAME (20 and 50 mg x kg(-1) x day(-1)), compared with nontreated animals, 1) systolic blood pressure increased (by 34.2 and 104.9 mmHg), 2) heart weight-to-body wt ratio increased 24.1% at the higher dose (P < 0.05), 3) cardiomyocyte protein mass increased (P = NS), 4) cardiomyocyte protein synthesis ([14C]phenylalanine incorporation) increased (P < 0.05), 5) expression of skeletal alpha-actin, atrial natriuretic peptide, brain natriuretic peptide, and ET-1 mRNAs was enhanced (P < 0.05) in LV but not RV cardiomyocytes at 20 and 50 mg x kg(-1) x day(-1), respectively, and 6) expression of adrenomedullin, receptor activity-modifying protein 3 (RAMP3), and RAMP2 (but not calcitonin receptor-like receptor and RAMP1) mRNAs was increased by L-NAME (20 mg x kg(-1) x day(-1)) in LV. In conclusion, L-NAME enhanced protein synthesis in both LV and RV cardiomyocytes but elicited a hypertrophic phenotype accompanied by altered expression of the counterregulatory peptide adrenomedullin and receptor components (RAMP2, RAMP3) in LV only, indicating that the former is due to impaired nitric oxide synthesis, whereas the phenotypic changes are due to pressure overload.

L-arginine fails to protect against myocardial remodelling in L-NAME-induced hypertension

BACKGROUND

We investigated whether the substrate for nitric oxide synthesis L-arginine is able to modify hypertension and left ventricular hypertrophy development induced by chronic blockade of nitric oxide synthase activity by NG-nitro-L-arginine-methyl ester (L-NAME).

MATERIAL AND METHODS

Four groups of rats were investigated: control, L-arginine 1.5 g kg-1, L-NAME 40 mg kg-1, and L-NAME +L-arginine in corresponding doses. Systolic blood pressure was measured by non-invasive tail-cuff plethysmography each week. After 4 weeks, the animals were sacrificed and hydroxyproline and coenzyme Q9 and Q10 concentrations in the left ventricle, and nitric oxide synthase activity in the left ventricle, kidney and brain were investigated.

RESULTS

In the L-NAME group, nitric oxide synthase activity was decreased in the left ventricle, kidney and brain, and hypertension, left ventricular hypertrophy and fibrosis developed. Heart remodelling was associated with the decrease of coenzyme Q9 and Q10 concentrations in the left ventricle. Simultaneous treatment with L-NAME and L-arginine prevented nitric oxide synthase activity diminution in the left ventricle but not in the kidney and brain, and completely failed to prevent hypertension, left ventricular hypertrophy and fibrosis. Nevertheless, l-arginine prevented the diminution of coenzyme Q9 and Q10 concentrations in the left ventricle.

CONCLUSIONS

We conclude that L-arginine failed to prevent hypertension, left ventricular hypertrophy and fibrosis development despite restoration of nitric oxide synthase activity in the left ventricle. However, L-arginine prevented the diminution of coenzyme Q levels in the left ventricle.

Oxidant stress from nitric oxide synthase-3 uncoupling stimulates cardiac pathologic remodeling from chronic pressure load

Cardiac pressure load stimulates hypertrophy, often leading to chamber dilation and dysfunction. ROS contribute to this process. Here we show that uncoupling of nitric oxide synthase-3 (NOS3) plays a major role in pressure load-induced myocardial ROS and consequent chamber remodeling/hypertrophy. Chronic transverse aortic constriction (TAC; for 3 and 9 weeks) in control mice induced marked cardiac hypertrophy, dilation, and dysfunction. Mice lacking NOS3 displayed modest and concentric hypertrophy to TAC with preserved function. NOS3(-/-) TAC hearts developed less fibrosis, myocyte hypertrophy, and fetal gene re-expression (B-natriuretic peptide and alpha-skeletal actin). ROS, nitrotyrosine, and gelatinase (MMP-2 and MMP-9) zymogen activity markedly increased in control TAC, but not in NOS3(-/-) TAC, hearts. TAC induced NOS3 uncoupling in the heart, reflected by reduced NOS3 dimer and tetrahydrobiopterin (BH4), increased NOS3-dependent generation of ROS, and lowered Ca(2+)-dependent NOS activity. Cotreatment with BH4 prevented NOS3 uncoupling and inhibited ROS, resulting in concentric nondilated hypertrophy. Mice given the antioxidant tetrahydroneopterin as a control did not display changes in TAC response. Thus, pressure overload triggers NOS3 uncoupling as a prominent source of myocardial ROS that contribute to dilatory remodeling and cardiac dysfunction. Reversal of this process by BH4 suggests a potential treatment to ameliorate the pathophysiology of chronic pressure-induced hypertrophy.

Left ventricular hypertrophy in aortic valve stenosis: preventive or promotive of systolic dysfunction and heart failure?

AIMS

In aortic stenosis (AS), left ventricular (LV) hypertrophy is considered a compensatory response helping maintain systolic function. Recent research in experimental AS suggests, however, that LV hypertrophy is not necessary to sustain LV contractions but may in fact be maladaptive. The present work aimed to clarify the role of LV hypertrophy in AS-related heart failure (HF) in man.

METHODS AND RESULTS

We studied 137 adult patients with isolated AS undergoing pre-operative echocardiography and cardiac catheterization. HF was diagnosed by the European criteria and LV hypertrophy by sex-specific limits of echocardiographic LV mass. The higher the LV mass was, the poorer was the LV ejection fraction (beta=-0.26, P< 0.001, linear regression) and the greater the likelihood of HF independent of the severity of AS (P< 0.001, logistic regression). In the subgroup of critical AS (valve area <0.4 cm(2)/m(2), n=85), patients with absent LV hypertrophy (n=19) had better preserved ejection fraction (mean+/-SE, 64+/-3 vs. 57+/-2%, P=0.045) and less HF (16 vs. 48%, P=0.025) than patients with LV hypertrophy (n=66).

CONCLUSION

In isolated AS, increased LV mass predicts the presence of systolic dysfunction and HF independent of the severity of valvular obstruction. LV hypertrophy may be maladaptive rather than beneficial in AS in man.

Gene expression of energy and protein metabolism in hearts of hypertensive nitric oxide- or GSH-depleted mice

Hypertension demands cardiac synthetic and metabolic adaptations to increased afterload. We studied gene expression in two models of mild hypertension without overt left ventricular hypertrophy using the NO synthase inhibitor nitro-L-arginine (L-NNA) and the glutathione depletor buthionine-S,R-sulfoximine (BSO). Mice were administered L-NNA, BSO, or water for 8 weeks. RNA of left ventricles was pooled per group, reverse transcribed, Cy3 and Cy5 labeled, and hybridized to cDNA microarrays. Normalized log(2) Cy3/Cy5 ratios of > or =0.7 or < or =-0.7 were considered significant. L-NNA and BSO both caused hypertension. Gene expression was regulated in cytoskeletal components in both models, protein synthesis in L-NNA-treated mice, and energy metabolism in BSO-treated mice. Energy metabolism genes shared several common transcription factor-binding sites such as Coup-Tf2, of which gene expression was increased in BSO-treated mice, and COMP-1. Characterization of the left ventricular adaptations as assessed with gene expression profiles reveals differential expression in energy and protein metabolism related to the pathogenetic background of the hypertension.

Chronic Nitric Oxide Synthase Inhibition Prevents New Coronary Capillary Generation

L-NAME-induced hypertension has been shown to produce concentric (eutrophic) remodeling of the heart despite an enhanced afterload. We postulated that nitric oxide synthase inhibition could limit coronary capillary growth to explain the nature of remodeling. To test our hypothesis, we aimed at determining the effect of endogenous and exogenous nitric oxide on coronary neovascularization. Aortic and coronary rings from normotensive animals were incubated in a three-dimensional type I collagen matrix in the presence of L-NAME or the nitric oxide donor SNAP. L-NAME inhibited, while SNAP stimulated, neovascularization from aortic and coronary rings after 12 days of in vitro incubation. In arterial rings harvested from rats treated with L-NAME for 14 days and in which no further in vitro treatment was added, only coronary rings showed a reduction in new capillary generation. While confirming that chronic L-NAME-treated rats develop concentric remodeling, the evaluation of capillary density did not reveal any difference as compared with the controls in 3 areas of the myocardium. In conclusion, chronic inhibition of nitric oxide synthesis in vivo produces a long-lasting reduction in the capacity of coronary arteries to generate new capillaries in vitro. Thus, our results lend support to the hypothesis that an inhibition of new capillary formation could prevent the development of compensatory ventricular hypertrophy, in favor of concentric remodeling.

Reduced left ventricular compliance and mechanical efficiency after prolonged inhibition of NO synthesis in conscious dogs

Acute inhibition of NO synthesis decreases left ventricular (LV) work and external efficiency, but it is unknown whether compensatory mechanisms can limit the alterations in LV mechanoenergetics after prolonged NO deficiency. Eight chronically instrumented male mongrel dogs received 35 mg kg-1 day-1 of Nomega-nitro-L-arginine methyl ester orally for 10 days to inhibit NO synthesis. At spontaneous beating frequency, heart rate, coronary blood flow, peak LV pressure, end-diastolic LV pressure and the maximum derivative of LV pressure (dP/dtmax) were not significantly different vs. baseline, whereas LV end-diastolic diameter (32.5 +/- 1.0 vs. 37.6 +/- 1.4 mm) and LV stroke work (515 +/- 38 vs. 650 +/- 44 mmHg mm), were reduced (all P < 0.05). The slope of the LV end-systolic pressure-diameter relationship was increased at 10 days vs. baseline (13.9 +/- 1.0 vs. 9.6 +/- 0.9 mmHg mm-1, P < 0.05), while the end-diastolic LV diameter was smaller at matched LV end-diastolic pressures. At fixed heart rate (130 beats min-1), cardiac oxygen consumption was increased (12.2 +/- 1.5 vs. 9.9 +/- 1.0 ml min-1), and the ratio between stroke work and oxygen consumption was decreased by 33 +/-7 % (all P < 0.05) after NO inhibition. We conclude that sustained inhibition of NO synthesis in dogs causes a decrease in LV work despite an increased contractility, which is most probably due to reduced diastolic compliance and a decrease in external efficiency. Thus, prolonged NO deficiency is not compensated for on the level of LV mechanoenergetics in vivo.

Inhibition of left ventricular remodelling preserves chamber systolic function in pressure-overloaded mice

Controversy exists whether the development of left-ventricular hypertrophy (LVH) is a mechanism able to prevent cardiac dysfunction under conditions of pressure overload. In the present study we re-assessed the long-term effects of attenuating LVH by using L- and D-propranolol, which are equally able to inhibit the development of LVH induced by aortic banding. The aortic arch was banded proximal to the left common carotid artery in 71 CD-1 mice that were then assigned randomly to receive L-propranolol, D-propranolol (both 80 mg/kg per day) or vehicle. Concurrently, sham-operated mice were given L-propranolol, D-propranolol or vehicle. LV dimension and performance were evaluated under isoflurane anaesthesia by cine-magnetic resonance imaging, echocardiography and cardiac catheterization up to 8 weeks after surgery. After 2 weeks of pressure overload, the vehicle-treated banded mice had enhanced LV weight, normal chamber size and increased relative wall thickness (concentric hypertrophy), whereas L-propranolol- or D-propranolol-banded mice showed a markedly blunted hypertrophic response, i.e. normal chamber size and normal relative wall thickness, as well as preserved systolic LV chamber function. After 4 weeks, the vehicle-treated banded mice showed LV enlargement with a reduced relative wall thickness (eccentric remodelling) and a clear-cut deterioration in LV systolic function. In contrast, L-propranolol- or D-propranolol-treated banded mice showed normal chamber size with a normal relative wall thickness and preserved systolic function. A distinct histological feature was that in banded mice, L-or D-propranolol attenuated the development of cardiomyocyte hypertrophy but not the attendant myocardial fibrosis. At the 8-week stage, LV dysfunction was present in propranolol-treated banded mice although it was much less severe than in vehicle-treated banded mice. It is concluded that (i) deterioration of LV systolic performance is delayed if LV hypertrophy is inhibited, (ii) banding-induced deterioration of LV systolic function is associated with LV eccentric remodelling and (iii) the antihypertrophic effect of propranolol is due to a selective action on cardiomyocytes rather than on collagen accumulation

Cardiac hypertrophy: the good, the bad, and the ugly

Cardiac hypertrophy is the heart's response to a variety of extrinsic and intrinsic stimuli that impose increased biomechanical stress. While hypertrophy can eventually normalize wall tension, it is associated with an unfavorable outcome and threatens affected patients with sudden death or progression to overt heart failure. Accumulating evidence from studies in human patients and animal models suggests that in most instances hypertrophy is not a compensatory response to the change in mechanical load, but rather is a maladaptive process. Accordingly, modulation of myocardial growth without adversely affecting contractile function is increasingly recognized as a potentially auspicious approach in the prevention and treatment of heart failure. In this review, we summarize recent insights into hypertrophic signaling and consider several novel antihypertrophic strategies.

Chronic inhibition of nitric oxide synthase induces hypertension and cardiomyocyte mitochondrial and myocardial collagen remodelling in the absence of hypertrophy

OBJECTIVES

To evaluate the morphometric and ultrastructural alterations of the heart produced by long-term inhibition of nitric oxide (NO) synthase with N(omega)-nitro-l-arginine methyl ester (l-NAME) and to examine whether the changes are caused by l-NAME-induced hypertension or a lack of NO.

METHODS

Male Wistar rats were divided randomly into three sets: control group, standard diet/l-NAME-treated group, and standard diet/l-NAME + captopril-treated group.

RESULTS

Chronic inhibition of NO synthesis with l-NAME given for 4 weeks promoted a time-dependent hypertensive response which was not accompanied by an increase in cardiac mass, myocellular hypertrophy or other evidence of myocyte damage. However, this response was associated with left ventricular cardiomyocyte mitochondrial remodelling and discrete interstitial fibrosis in both the left and right ventricles. The remodelling was characterized by an increase in the number and size of mitochondria. Importantly, systolic pressure overload did not result in left ventricle decompensation. The concomitant treatment with l-NAME and captopril abolished the development of hypertension and left ventricular cardiomyocyte subcellular remodelling, but not the discrete interstitial fibrosis in the left and right ventricle.

CONCLUSIONS

The present study suggests that, in the l-NAME model of hypertension, decreased NO production could be an important means of controlling cardiovascular hypertensive stress by regulating mitochondrial biogenesis and function in the tissue. On the other hand, discrete interstitial ventricular myocardial fibrosis observed in l-NAME-treated rats, either hypertensive or rendered normotensive with captopril, clearly indicates that this response depends on a process associated with NO insufficiency.

Colchicine attenuates left ventricular hypertrophy but preserves cardiac function of aortic-constricted rats

To investigate the effects of colchicine on left ventricular (LV) function and hypertrophy (LVH) of rats subjected to constriction of transverse aorta (TAoC), we evaluated SO (sham operated, vehicle; n = 25), SO-T (sham operated, colchicine 0.4 mg/kg body wt ip daily; n = 38), TAoC (vehicle; n = 37), and TAoC-T (TAoC, colchicine; n = 34) on the 2nd, 6th, and 15th day after surgery. Colchicine attenuated LVH of TAoC-T compared with TAoC rats, as evaluated by ratio between LV mass (LV(M)) and right ventricular mass, LV wall thickness, and average diameter of cardiac myocytes. Systolic gradient across TAoC ( approximately 45 mmHg), LV systolic pressure, LV end-diastolic pressure, and rate of LV pressure increase (+dP/dt) were comparable in TAoC-T and TAoC rats. However, the baseline and increases of LV systolic pressure-to-LV(M) and +dP/dt-to-LV(M) ratios induced by phenylephrine infusion were greater in TAoC-T and SO-T compared with SO rats. Baseline and increases of +dP/dt-to-LV(M) ratio were reduced in TAoC compared with SO rats. TAoC rats increased polymerized fraction of tubulin compared with SO, SO-T, and TAoC-T rats. Our results indicate that colchicine treatment reduced LVH to pressure overload but preserved LV function.

Myocardial fibrosis blunts nitric oxide synthase-related preload reserve in human dilated cardiomyopathy

The purpose of the study was to investigate interactions between myocardial nitric oxide synthase (NOS) and myocardial fibrosis, both of which determine left ventricular (LV) preload reserve in patients with nonischemic dilated cardiomyopathy (DCM). In previous animal experiments, chronic inhibition of NOS induced myocardial fibrosis and limited LV preload reserve. Twenty-eight DCM patients underwent LV catheterization, balloon caval occlusions (BCO; n = 8), intracoronary substance P infusion (n = 8), and procurement of LV endomyocardial biopsies for determinations of collagen volume fraction (CVF), of gene expression of NOS2, NOS3, heme oxygenase (HO)-1, and TNF-alpha, and of NOS2 protein. CVF was unrelated to the intensity of NOS2, NOS3, HO-1, or TNF-alpha gene expression or of NOS2 protein expression. Preload recruitable LV stroke work (PR-LVSW) correlated directly with NOS2 gene expression (P = 0.001) and inversely with CVF (P = 0.04). High CVF (>10%) reduced baseline LVSW and PR-LVSW at each level of NOS2 gene expression. In DCM, myocardial fibrosis is unrelated to the intensity of myocardial gene expression of NOS, antioxidative enzymes (HO-1), or cytokines (TNF-alpha) and blunts NOS2-related recruitment of LV preload reserve.

Impact of hydroxymethylglutaryl coenzyme a reductase inhibition on left ventricular remodeling after myocardial infarction: an experimental serial cardiac magnetic resonance imaging study

OBJECTIVES

We sought to assess the influence of long-term hydroxymethylglutaryl coenzyme A reductase inhibition (statin) therapy on left ventricular (LV) remodeling after myocardial infarction (MI) by use of serial cardiac magnetic resonance imaging (CMRI) studies.

BACKGROUND

Statin therapy has been shown to reduce cardiac hypertrophy in vitro and in vivo, but the influence on LV post-MI remodeling is largely unknown.

METHODS

The CMRI measurements were taken four and 12 weeks after left coronary artery ligation in a 7.05-tesla Biospec. The MI size, LV mass and volumes, cardiac output (CO), and ejection fraction were determined. Rats were treated for 12 weeks with either placebo (P), cerivastatin (C; 0.6 mg/kg body weight per day) as a dietary supplement, or cerivastatin plus the nitric oxide synthase (NOS) inhibitor N-methyl-L-arginine methyl ester (L-NAME, 76 mg/100 ml) and hydralazine (8 mg/100 ml) in drinking water (CLH) to assess the contribution of endogenous nitric oxide formation.

RESULTS

Administration of cerivastatin attenuated hypertrophy after MI, and this effect was completely abolished by NOS inhibition (increase of LV mass from 4 to 12 weeks after MI: 235.3 +/- 33.7 mg with P vs. 59.8 +/- 20.5 mg with C vs. 239.5 +/- 16.0 mg with CLH; p < 0.05 vs. P and CLH). Left ventricular dilation was not changed (increase of end-diastolic volume from 4 to 12 weeks after MI: 108.7 +/- 28.8 with P vs. 126.6 +/- 20.5 with C vs. 173.7 +/- 25.1 with CLH; p = NS). The CO was higher in the cerivastatin group (12 weeks: 76.1 +/- 2.9 ml/min with P vs. 95.8 +/- 4.8 ml/min with C; p < 0.05). The effects of cerivastatin were abolished by NOS inhibition in the CLH group (CO at 12 weeks: 69.3 +/- 2.8 ml/min, p < 0.05 vs. C).

CONCLUSIONS

Left ventricular remodeling was profoundly changed by statin treatment. Hypertrophy was attenuated, and global function was improved. These positive effects were abolished by NOS inhibition.

Hypertension plus diabetes mimics the cardiomyopathy induced by nitric oxide inhibition in rats

STUDY OBJECTIVES

We compared the myocardial lesions caused by the long-term inhibition of nitric oxide (NO) biosynthesis with those associated with renovascular hypertension (two-kidney, one-clip model [2K-1C]) and superimposed streptozotocin-induced diabetes mellitus (DM).

DESIGN

Prospective trial.

SETTING

University laboratory.

INTERVENTIONS

Male Wistar rats were classified into the following groups: (1) a control group; (2) the L-NAME group (treatment with the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester [L-NAME], 75 micro mol per rat per day, orally); (3) the 2K-1C group (renovascular hypertension); (4) the DM group (treatment with streptozotocin, 60 mg/kg via intraperitoneal route); and (5) the 2K-1C plus DM group (renovascular hypertension and streptozotocin-induced DM). Arterial BP was measured by a tail-cuff method for 3 weeks, after which histologic and stereological analysis of the heart was done and cardiac NO synthase type 3 (NOS3) levels were assessed by Western blotting. The circulating levels of nitrates/nitrites and thromboxane B(2) (TXB(2), the stable metabolite of thromboxane A(2)) were also measured.

RESULTS

In DM and 2K-1C rats, the myocardial lesions consisted mainly of recent myocardial infarcts, which were more severe in the 2K-1C plus DM group. In L-NAME-treated rats, multiple foci of reparative fibrosis and fresh myocardial necrosis resembled the severe lesions found in the 2K-1C plus DM group. Although NOS3 protein expression increased (19 to 44%; p < 0.05) in all treated groups, serum nitrate/nitrite levels decreased only in the L-NAME group and the 2K-1C plus DM group. These two groups also showed a more pronounced increase in TXB(2) concentrations.

CONCLUSIONS

These results indicate that the association of hypertension and DM mimics the alterations induced by L-NAME in rats, which suggests a role for NO in the pathophysiology of hypertensive-diabetic cardiomyopathy.

Protective effects of the flavonoid quercetin in chronic nitric oxide deficient rats

OBJECTIVES

The present study analysed, for the first time, the effects of the flavonoid quercetin in rats after chronic inhibition of nitric oxide (NO) synthesis with Nomega-nitro-L-arginine methyl ester (L-NAME).

DESIGN

Rats were divided randomly into five different treatment groups for 6 weeks: (1) vehicle (control, 1 ml of 1% methylcellulose once daily); (2) vehicle plus L-NAME (75 mg/100 ml in drinking water); (3) quercetin (10 mg/kg p.o. once daily); (4) quercetin (5 mg/kg p.o.) plus L-NAME; and (5) quercetin (10 mg/kg p.o.) plus L-NAME.

METHODS

The evolution of systolic blood pressure, morphological variables, proteinuria, plasma malondialdehyde and nitrite and nitrate concentrations, hepatic glutathione and malondialdehyde content, glutathione enzymes activity and vascular reactivity at the end of the experiment were analysed.

RESULTS

Quercetin markedly inhibited the development of L-NAME-induced hypertension. This effect was accompanied by a partial or full prevention of most of the effects induced by L-NAME, such as: (1) increases in the left ventricular and kidney weight indices; (2) proteinuria; (3) renal histological lesions, including hyaline arteriopathy and thickening of the vascular wall with moderate decrease of the lumen; (4) increased endothelium-dependent contraction; (5) increased vascular thromboxane B2 (TXB2) synthesis; (6) reduced plasma concentrations of nitrites plus nitrates (NOx); (7) increased plasma and hepatic malondialdehyde (MDA) concentrations; and (8) reduced glutathione peroxidase activity. In most cases these effects were dose dependent, but none of them were observed in normotensive animals.

CONCLUSIONS

This study confirms and extends the previous evidence about the antihypertensive effects and end-organ protection of the flavonoid quercetin in animal models of hypertension.

N(G)-nitro-L-arginine methyl ester-induced hypertension and natriuretic peptide gene expression: inhibition by angiotensin II type 1 receptor antagonism

This study examined the role of angiotensin II in the increase of blood pressure, activation of cardiac natriuretic peptide gene expression, left ventricular hypertrophy, and vascular changes in nitric oxide-deficient hypertension. N(G)-nitro->L-arginine methyl ester (>L-NAME, 20 mg/kg/d), angiotensin II type 1 receptor (AT ) antagonist losartan (20 mg/kg/d), or their combination were administered orally for 8 weeks in Wistar rats. >L-NAME elevated systolic blood pressure, which reached its maximum within 4 weeks (200 +/- 4 mm Hg). Despite hypertension, >L-NAME administration for 8 weeks did not induce left ventricular hypertrophy. Losartan treatment significantly decreased the development of hypertension induced by >L-NAME and decreased left ventricular hypertrophy in untreated rats. In contrast, losartan did not prevent the hypertrophic remodeling of the mesenteric resistance arteries induced by >L-NAME. >L-NAME treatment increased ventricular atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) mRNA levels and immunoreactive BNP levels significantly. Losartan therapy decreased the >l-NAME-induced ventricular ANP gene expression by 69% (p < 0.05) and also reduced ventricular BNP mRNA levels so that it did not differ from control. Losartan treatment alone decreased ventricular immunoreactive ANP and BNP levels by 30% (p < 0.05). These results show that ventricular ANP and BNP gene expression are dissociated from the increased ventricular mass in nitric oxide deficiency-induced hypertension. Results suggest that >l-NAME-induced hypertension and the associated activation of ventricular ANP and BNP gene expression are, at least in part, mediated by angiotensin II, whereas the resistance vessel hypertrophy following nitric oxide synthase inhibition is angiotensin II independent.