Rat Model Of Monocrotaline-induced Pulmonary Hypertension Research Articles

Abstract 4123631: Significance of collagen triple helix repeat-containing protein 1 as a right ventricular biomarker in pulmonary hypertension

Background: Right ventricular failure is a major prognostic determinant of pulmonary hypertension and progresses with myocardial fibrosis. Extracellular matrix proteins play a major role in myocardial fibrosis. Right ventricular biomarkers for right ventricular function and fibrosis are poorly examined in pulmonary hypertension. This study investigated the significance of collagen triple helix repeat-containing protein 1 (CTHRC1), one of the extracellular matrix proteins, as a right ventricular biomarker. Methods and Results: A monocrotaline-induced pulmonary hypertension rat model was used in this study. CTHRC1 expression in the right ventricle was higher in rats with monocrotaline-induced pulmonary hypertension than in controls. CTHRC1 was associated with fibrosis in the rat's right ventricle. Next, human circulating CTHRC1 levels were evaluated in controls (n = 20), pulmonary arterial hypertension (PAH, n = 46), and chronic thromboembolic pulmonary hypertension (CTEPH) patients (n = 64). Human circulating CTHRC1 levels were higher in PAH (P = 0.006) and CTEPH patients (P = 0.011) than in controls (Figure). Human circulating CTHRC levels were correlated with tricuspid lateral annular peak systolic velocity (R = -0.213, P = 0.029), right ventricular fractional area change (R = -0.225, P = 0.017), and right ventricular global longitudinal strain evaluated by magnetic resonance imaging (R = 0.429, P = 0.009). In addition, human circulating CTHRC1 levels were decreased after balloon pulmonary angioplasty (P < 0.001) in CTEPH patients. Conclusions: CTHRC1 could be a novel biomarker associated with right ventricular failure and fibrosis in pulmonary hypertension patients.

In Vivo Anti-Inflammatory Activity of D-Limonene in a Rat Model of Monocrotaline-Induced Pulmonary Hypertension: Implications to the Heart Function.

D-limonene (D-L) is the major monocyclic monoterpene in citrus plants with anti-inflammatory properties. Pulmonary hypertension (PH) can cause right heart dysfunction and increases the risk of death, partially due to inflammatory response in the heart. To evaluate the possible protective effect of D-L on cardiac function in a rat model of monocrotaline-induced PH (MCT-PH). Electrocardiogram was monitored in vivo. Masson Trichrome technique was deployed to verify fibrosis in the heart. Contractility function of isolated atrial tissue was studied using organ bath chamber. Real-time quantitative PCR was applied to quantify inflammation in the right ventricle. The MCT-PH group showed electrical and structural heart remodeling, with the presence of fibrosis in the cardiac tissue and in vivo electrocardiographic changes. Treatment with D-L partially prevented the development of tissue fibrosis and the increase in P wave duration in the MCT-PH group. The contraction and relaxation velocity of isolated right and left atrium were accelerated in CTR and MCT-PH animals treated with D-L. Finally, D-L was able to prevent the abnormal expression of the key inflammatory cytokines (interleukin 1-β, interleukin 6 and tumor necrosis factor-α) in the right ventricle of MCT-PH animals. D-L was able to enhance the production of the anti-inflammatory cytokine Interleukin-10. Our results showed that in vivo administration of D-L partially prevented the molecular, structural and functional remodeling of the heart in the MCT-PH model with attenuation of the inflammatory response in the heart.

Collagen Triple Helix Repeat-Containing Protein 1 Is a Novel Biomarker of Right Ventricular Involvement in Pulmonary Hypertension

BackgroundPulmonary hypertension leads to right ventricular failure, which is a major determinant of prognosis. Circulating biomarkers for right ventricular function are poorly explored in pulmonary hypertension. This study aimed to clarify the significance of collagen triple helix repeat-containing protein 1 (CTHRC1) as a biomarker of right ventricular failure in pulmonary hypertension. MethodsA monocrotaline-induced pulmonary hypertension rat model was used to evaluate right ventricular CTHRC1 expression and its relationship with fibrosis. Next, human plasma CTHRC1 levels were measured in controls (n = 20), pulmonary arterial hypertension (n = 46), and patients with chronic thromboembolic pulmonary hypertension (CTEPH) (n = 64) before the first and after the final balloon pulmonary angioplasty. ResultsCTHRC1 expression was higher in the right ventricles of rats with monocrotaline-induced pulmonary hypertension than in those of controls. CTHRC1 was colocalized with vimentin and associated with fibrosis in the right ventricles. Plasma CTHRC1 levels were higher in human patients with pulmonary arterial hypertension (P = 0.006) and CTEPH (P = 0.011) than in controls. Plasma CTHRC levels were correlated with B-type natriuretic peptide (R = 0.355, P < 0.001), tricuspid lateral annular peak systolic velocity (R = –0.213, P = 0.029), and right ventricular fractional area change (R = –0.225, P = 0.017). Finally, plasma CTHRC1 levels were decreased after the final balloon pulmonary angioplasty (P < 0.001) in CTEPH. ConclusionsCTHRC1 can be a circulating biomarker associated with right ventricular function and fibrosis in pulmonary hypertension and might reflect the therapeutic efficacy of balloon pulmonary angioplasty in CTEPH.

Ranolazine exerts atrial antiarrhythmic effects in a rat model of monocrotaline-induced pulmonary hypertension.

Atrial arrhythmias are a hallmark of heart diseases. The antiarrhythmic drug ranolazine with multichannel blocker properties is a promising agent to treat atrial arrhythmias. We therefore used the rat model of monocrotaline-induced pulmonary-hypertension to assess whether ranolazine can reduce the incidence of ex vivo atrial arrhythmias in isolated right atrium. Four-week-old Wistar rats were injected with 50 mg/kg of monocrotaline, and isolated right atrium function was studied 14 days later. The heart developed right atrium and right ventricular hypertrophy, and the ECG showed an increased P wave duration and QT interval, which are markers of the disease. Moreover, monocrotaline injection caused enhanced chronotropism and faster kinetics of contraction and relaxation in isolated right atrium. Additionally, in a concentration-dependent manner, ranolazine showed chronotropic and ionotropic effects upon isolated right atrium, with higher potency in the control when compared with experimental model. Using a burst pacing protocol, the isolated right atrium from the monocrotaline-treated animals was more susceptible to develop arrhythmias, and ranolazine was able to attenuate the phenotype. Thus, we concluded that the rat model of monocrotaline-induced pulmonary-hypertension develops right atrium remodelling, which increased the susceptibility to present ex vivo atrial arrhythmias, and the antiarrhythmic drug ranolazine ameliorated the phenotype.

HNRNPA2B1: RNA-Binding Protein That Orchestrates Smooth Muscle Cell Phenotype in Pulmonary Arterial Hypertension.

RNA-binding proteins are master orchestrators of gene expression regulation. They regulate hundreds of transcripts at once by recognizing specific motifs. Thus, characterizing RNA-binding proteins targets is critical to harvest their full therapeutic potential. However, such investigation has often been restricted to a few RNA-binding protein targets, limiting our understanding of their function. In cancer, the RNA-binding protein HNRNPA2B1 (heterogeneous nuclear ribonucleoprotein A2B1; A2B1) promotes the pro-proliferative/anti-apoptotic phenotype. The same phenotype in pulmonary arterial smooth muscle cells (PASMCs) is responsible for the development of pulmonary arterial hypertension (PAH). However, A2B1 function has never been investigated in PAH. Through the integration of computational and experimental biology, the authors investigated the role of A2B1 in human PAH-PASMC. Bioinformatics and RNA sequencing allowed them to investigate the transcriptome-wide function of A2B1, and RNA immunoprecipitation and A2B1 silencing experiments allowed them to decipher the intricate molecular mechanism at play. In addition, they performed a preclinical trial in the monocrotaline-induced pulmonary hypertension rat model to investigate the relevance of A2B1 inhibition in mitigating pulmonary hypertension severity. They found that A2B1 expression and its nuclear localization are increased in human PAH-PASMC. Using bioinformatics, they identified 3 known motifs of A2B1 and all mRNAs carrying them. In PAH-PASMC, they demonstrated the complementary nonredundant function of A2B1 motifs because all motifs are implicated in different aspects of the cell cycle. In addition, they showed that in PAH-PASMC, A2B1 promotes the expression of its targets. A2B1 silencing in PAH-PASMC led to a decrease of all tested mRNAs carrying an A2B1 motif and a concomitant decrease in proliferation and resistance to apoptosis. Last, in vivo A2B1 inhibition in the lungs rescued pulmonary hypertension in rats. Through the integration of computational and experimental biology, the study revealed the role of A2B1 as a master orchestrator of the PAH-PASMC phenotype and its relevance as a therapeutic target in PAH.

Abstract P3001: Hnrnpa2b1 An Rna-binding Protein That Orchestrates Smooth Muscle Cell Phenotype In Pulmonary Arterial Hypertension.

Background: RNA-binding proteins (RPBs) are master orchestrators of gene expression regulation. RBPs regulate hundreds of transcripts at once by recognizing specific motifs. Characterizing RBP targets is critical to harvest their full therapeutic potential. However, such investigation has often been restricted to a few RBP targets, limiting our understanding of their function. In cancer, the RBP HNRNPA2B1 (A2B1) promotes the pro-proliferative / anti-apoptotic phenotype. The same phenotype in pulmonary arterial smooth muscle cells (PASMC) is responsible for the development of pulmonary arterial hypertension (PAH). However, A2B1 function has never been investigated in PAH. Methods: Through the integration of computational and experimental biology, we investigated the role of A2B1 in human PAH-PASMC. Bioinformatics and RNA-sequencing allowed us to investigate the transcriptome-wide function of A2B1, while RNA immunoprecipitation and A2B1 silencing experiments in vitro allowed us to decipher the intricate molecular mechanism at play. In addition, we performed a pre-clinical trial in the monocrotaline-induced pulmonary hypertension rat model to investigate the relevance of A2B1 inhibition in mitigating pulmonary hypertension severity. Results: In the present study, we found that A2B1 is up-regulated in human PAH-PASMC. We also show that A2B1 localization shifts in PAH-PASMC from cytoplasmic to nuclear mainly due to significantly higher expression of B1 isoform compared to A2 isoform of A2B1. Using bio-informatics, we identified three known motifs of A2B1 and all mRNAs carrying them. In PAH-PASMC, we demonstrated the complementary non-redundant function of A2B1 motifs as all motifs are implicated in different aspect of the cell cycle. In addition, we showed that in PAH-PASMC, A2B1 promotes the expression of its targets. A2B1 silencing in PAH-PASMC lead to a decrease of all tested mRNAs carrying an A2B1 motif, and an according decrease in proliferation and resistance to apoptosis. Finally, in vivo A2B1 inhibition in the lungs rescued pulmonary hypertension in rats. Conclusion: Through the integration of computational and experimental biology, our study revealed the role of A2B1 as a master orchestrator of the PAH-PASMC phenotype and its relevance as a therapeutic target in PAH.

Echocardiographic assessment of right ventricular function in experimental pulmonary hypertension.

Echocardiography, a non-invasive and cost-effective method for monitoring cardiac function, is commonly used for evaluation and pre-clinical diagnostics of pulmonary hypertension (PH). Previous echocardiographic studies in experimental models of PH are fragmentary in terms of the evaluation of right ventricle (RV) function. In this study, three rodent models of PH: a mouse model of hypoxia-induced PH, a rat model of hypoxia+Sugen induced PH and a rat model of monocrotaline-induced PH, were employed to measure RV fractional area change (RVFAC), RV free wall thickness (RVFWT), pulmonary acceleration time (PAT), pulmonary ejection time (PET), and tricuspid annular plane systolic excursion (TAPSE). We found that, in these models, RVFWT significantly increased, but RVFAC, PAT, or PAT/PET ratios and TAPSE values significantly decreased. Accurate and complete TAPSE patterns were demonstrated in the three rodent models of PH. The RV echocardiography data matched the corresponding invasive hemodynamic and heart histologic data in each model. This serves as a reference study for real-time and non-invasive evaluation of RV function in rodent models of PH using echocardiography.

Therapeutic effects of the selective farnesoid X receptor agonist obeticholic acid in a monocrotaline-induced pulmonary hypertension rat model

Activation of the farnesoid X receptor (FXR), a member of the nuclear receptor steroid superfamily, leads to anti-inflammatory and anti-fibrotic effects in several tissues, including the lung. We have recently demonstrated a protective effect of the farnesoid X receptor (FXR) agonist obeticholic acid (OCA) in rat models of monocrotaline (MCT)-induced pulmonary arterial hypertension (PAH) and bleomycin-induced pulmonary fibrosis. The aim of the present study was to investigate whether the positive effects of OCA treatment could be exerted also in established MCT-induced PAH, i.e., starting treatment 2weeks after MCT administration. Rats with MCT-induced PAH were treated, 2weeks after MCT administration, with OCA or tadalafil for two additional weeks. Pulmonary functional tests were performed at week 2 (before treatment) and four (end of treatment). At the same time points, lung morphological features and expression profile of genes related to smooth muscle relaxation/contraction and tissue remodeling were also assessed. 2weeks after MCT-induced injury, the treadmill resistance (a functional parameter related to pulmonary hypertension) was significantly decreased. At the same time point, we observed right ventricular hypertrophy and vascular remodeling, with upregulation of genes related to inflammation. At week 4, we observed a further worsening of the functional and morphological parameters, accompanied by dysregulation of inflammatory and extracellular matrix markers mRNA expression. Administration of OCA (3 or 10mg/kg/day), starting 2weeks after MCT-induced injury, significantly improved pulmonary function, effectively normalizing the exercise capacity. OCA also reverted most of the lung alterations, with a significant reduction of lung vascular wall thickness, right ventricular hypertrophy, and restoration of the local balance between relaxant and contractile pathways. Markers of remodeling pathways were also normalized by OCA treatment. Notably, results with OCA treatment were similar, or even superior, to those obtained with tadalafil, a recently approved treatment for pulmonary hypertension. The results of this study demonstrate a significant therapeutic effect of OCA in established MCT-induced PAH, improving exercise capacity associated with reduction of right ventricular hypertrophy and lung vascular remodeling. Thus, OCA dosing in a therapeutic protocol restores the balance between relaxant and contractile pathways in the lung, promoting cardiopulmonary protective actions in MCT-induced PAH.

Proteinase-activated receptor 1 antagonism ameliorates experimental pulmonary hypertension.

Pulmonary hypertension (PH) is characterized by progressive increases in pulmonary vascular resistance (PVR). Thrombotic lesions are common pathological findings. The pulmonary artery has a unique property regarding the vasoconstrictive response to thrombin, which is mediated by proteinase-activated receptor 1 (PAR1). We aim to elucidate the role of PAR1 in the development and progression of PH. A rat model of monocrotaline-induced PH and a mouse model of hypoxia (Hx)-induced PH were used to investigate the effects of atopaxar (a PAR1 antagonist) and PAR1 knockout on haemodynamic parameters, right ventricular hypertrophy (RVH), vascular remodelling and survival. In perfused lung preparations, the pressor response to PAR1 agonist was significantly augmented in monocrotaline-induced PH. Both the preventive and therapeutic administration of atopaxar significantly inhibited the increase in PVR and the development of RVH and prolonged survival. A real-time PCR revealed that the level of PAR1 mRNA in the pulmonary artery was significantly higher than that in any of the systemic arteries examined in control rats, and the level was significantly up-regulated in monocrotaline-induced PH. PAR1 gene knockout significantly attenuated the haemodynamic and histological findings in the mouse model of Hx-induced PH. The specific expression of PAR1 in the pulmonary artery and its up-regulation were suggested to play a critical role in the development and progression of experimental PH in murine models. PAR1 is a potential therapeutic target for the treatment of PH.

Urantide improves the structure and function of right ventricle as determined by echocardiography in monocrotaline-induced pulmonary hypertension rat model.

Urotensin II (UII) has been reported to playa key role in pulmonary arterial hypertension (PAH) development. Doppler echocardiography, a noninvasive and simple tool, is recommended for diagnosing PAH. This study was designed to investigate the effect of urantide, a UII receptor antagonist, on the structure and function of the right ventricle in PAH rat models by Doppler echocardiography. A total of 60 male rats were divided into two groups: early- and late-treatment groups. Rats in the urantide and MCT (monocrotaline) subgroups were injected with 10μg/kg urantide in the urantide group or an equal amount of normal saline in the MCT group 1week after PAH model construction in the early-treatment group and 4weeks after the construction in the late-treatment group. Rats in the control group received an equal volume of normal saline solution. PAH-related indexes were measured by echocardiography. PAH rat models exhibited higher right ventricular diastolic diameter and lower time to peak, ejection time, and peak flow velocity of pulmonary artery than controls (P < 0.05). However, compared with the MCT group, all abovementioned indexes were improved in the urantide group (P < 0.05). No significant differences in pulmonary artery diameter and left ventricular ejection fraction were noted among the groups. Compared with the MCT group, systolic pulmonary arterial pressure (SPAP) and mean pulmonary arterial pressure (mPAP) were significantly lower in the urantide group (P < 0.05). SPAP examined by echocardiography was correlated with mPAP by catheterization (P < 0.05). Urantide treatment improved right heart failure parameters in MCT-induced PAH rats, thus providing a potential new strategy for treating PAH.

Modafinil improves monocrotaline-induced pulmonary hypertension rat model.

Pulmonary arterial hypertension (PAH) progressively leads to increases in pulmonary vasoconstriction. Modafinil plays a role in vasorelaxation and blocking KCa3.1 channel with a result of elevating intracellular cyclic adenosine monophosphate (cAMP) levels. The purpose of this study is to evaluate the effects on modafinil in monocrotaline (MCT)-induced PAH rat. The rats were separated into three groups: the control group, the monocrotaline (M) group (MCT 60 mg/kg), and the modafinil (MD) group (MCT 60 mg/kg + modafinil). Reduced right ventricular pressure (RVP) was observed in the MD group. Right ventricular hypertrophy was improved in the MD group. Reduced number of intra-acinar pulmonary arteries and medial wall thickness were noted in the MD group. After the administration of modafinil, protein expressions of endothelin-1 (ET-1), endothelin receptor A (ERA) and KCa3.1 channel were significantly reduced. Modafinil suppressed pulmonary artery smooth muscle cell (PASMC) proliferation via cAMP and KCa3.1 channel. Additionally, we confirmed protein expressions such as Bcl-2-associated X, vascular endothelial growth factor, tumor necrosis factor-α, and interleukin-6 were reduced in the MD group. Modafinil improved PAH by vasorelaxation and a decrease in medial thickening via ET-1, ERA, and KCa3.1 down regulation. This is a meaningful study of a modafinil in PAH model.

Development of a servo pump system for in vivo loading of pathological pulmonary artery impedance on the right ventricle of normal rats.

Pulmonary artery (PA) impedance provides detailed information on right ventricular (RV) afterload in pulmonary hypertension (PH). This study aimed to examine PA impedance in a rat model of monocrotaline-induced PH (MCT-PH) and to develop an experimental system for in vivo loading of pathological PA impedance on the RV of normal rats. PA impedance was quantified in normal (n= 10) and MCT-PH rats (n= 10) using a three-element Windkessel (3-WK) model. Compared with normal rats, MCT-PH rats had higher characteristic impedance (ZC) and peripheral pulmonary resistance (RP) (ZC: 0.121 ± 0.039 vs. 0.053 ± 0.017 mmHg·min·ml(-1), P< 0.001; RP: 0.581 ± 0.334 vs. 0.252 ± 0.105 mmHg·min·ml(-1), P= 0.013) and lower pulmonary artery compliance (CP) (0.242 ± 0.131 vs. 0.700 ± 0.186 ml/mmHg, P< 0.001). In another group of 10 normal rats, a computer-controlled servo pump was connected to the left PA for loading PA impedance with parameters in pathological ranges designed by the 3-WK model. Activation of the servo pump decreased the error of measured vs. target PA impedance (modulus: from 0.047 ± 0.020 without pump activation to 0.019 ± 0.007 with pump activation,P< 0.001; phase: 0.085 ± 0.028 to 0.043 ± 0.012 radians,P< 0.001). In conclusion, MCT-PH increases ZC and RP and decreases CP Our servo pump system, which is capable of imposing arbitrary PA impedance with pathological parameters, may offer a unique opportunity to delineate the pathological significance of PA impedance in PH.

An inhibitory effect of tumor necrosis factor-alpha antagonist to gene expression in monocrotaline-induced pulmonary hypertensive rats model

PurposeTumor necrosis factor (TNF)-α is thought to contribute to pulmonary hypertension. We aimed to investigate the effect of infliximab (TNF-α antagonist) treatment on pathologic findings and gene expression in a monocrotaline-induced pulmonary hypertension rat model.MethodsSix-week-old male Sprague-Dawley rats were allocated to 3 groups: control (C), single subcutaneous injection of normal saline (0.1 mL/kg); monocrotaline (M), single subcutaneous injection of monocrotaline (60 mg/kg); and monocrotaline + infliximab (M+I), single subcutaneous injection of monocrotaline plus single subcutaneous injection of infliximab (5 mg/kg). The rats were sacrificed after 1, 5, 7, 14, or 28 days. We examined changes in pathology and gene expression levels of TNF-α, endothelin-1 (ET-1), endothelin receptor A (ERA), endothelial nitric oxide synthase (eNOS), matrix metalloproteinase (MMP)2, and tissue inhibitor of matrix metalloproteinase (TIMP).ResultsThe increase in medial wall thickness of the pulmonary arteriole in the M+I group was significantly lower than that in the M group on day 7 after infliximab treatment (P<0.05). The number of intra-acinar muscular arteries in the M+I group was lower than that in the M group on days 14 and 28 (P<0.05). Expression levels of TNF-α, ET-1, ERA, and MMP2 were significantly lower in the M+I group than in the M group on day 5, whereas eNOS and TIMP expressions were late in the M group (day 28).ConclusionInfliximab administration induced early changes in pathological findings and expression levels of TNF-α, and MMP2 in a monocrotaline-induced pulmonary hypertension rat model.

Inhibition of MicroRNA-17 Improves Lung and Heart Function in Experimental Pulmonary Hypertension

MicroRNAs (miRs) control various cellular processes in tissue homeostasis and disease by regulating gene expression on the posttranscriptional level. Recently, it was demonstrated that the expression of miR-21 and members of the miR-17-92 cluster was significantly altered in experimental pulmonary hypertension (PH). To evaluate the therapeutic efficacy and antiremodeling potential of miR inhibitors in the pathogenesis of PH. We first tested the effects of miR inhibitors (antagomirs), which were specifically designed to block miR-17 (A-17), miR-21 (A-21), and miR-92a (A-92a) in chronic hypoxia-induced PH in mice and A-17 in monocrotaline-induced PH in rats. Moreover, biological function of miR-17 was analyzed in cultured pulmonary artery smooth muscle cells. In the PH mouse model, A-17 and A-21 reduced right ventricular systolic pressure, and all antagomirs decreased pulmonary arterial muscularization. However, only A-17 reduced hypoxia-induced right ventricular hypertrophy and improved pulmonary artery acceleration time. In the monocrotaline-induced PH rat model, A-17 treatment significantly decreased right ventricular systolic pressure and total pulmonary vascular resistance index, increased pulmonary artery acceleration time, normalized cardiac output, and decreased pulmonary vascular remodeling. Among the tested miR-17 targets, the cyclin-dependent kinase inhibitor 1A (p21) was up-regulated in lungs undergoing A-17 treatment. Likewise, in human pulmonary artery smooth muscle cells, A-17 increased p21. Overexpression of miR-17 significantly reduced p21 expression and increased proliferation of smooth muscle cells. Our data demonstrate that A-17 improves heart and lung function in experimental PH by interfering with lung vascular and right ventricular remodeling. The beneficial effects may be related to the up-regulation of p21. Thus, inhibition of miR-17 may represent a novel therapeutic concept to ameliorate disease state in PH.

Changes of Pulmonary Pathology and Gene Expressions After Simvastatin Treatment in the Monocrotaline-Induced Pulmonary Hypertension Rat Model

Background and ObjectivesSimvastatin's properties are suggestive of a potential pathophysiologic role in pulmonary hypertension. The objectives of this study were to investigate changes of pulmonary pathology and gene expressions, including endothelin (ET)-1, endothelin receptor A (ERA), inducible nitric oxide synthase (NOS2), endothelial nitric oxide synthase (NOS3), matrix metalloproteinase (MMP) 2, tissue inhibitor of matrix metalloproteinases (TIMP) and caspase 3, and to evaluate the effect of simvastatin on monocrotaline (M)-induced pulmonary hypertension.Materials and MethodsSix week old male Sprague-Dawley rats were treated, as follows: control group, subcutaneous (sc) injection of saline; M group, sc injection of M (60 mg/kg); and simvastatin group, sc injection of M (60 mg/kg) plus 10 mg/kg/day simvastatin orally.ResultsOn day 28, right ventricular hypertrophy (RVH) significantly decreased in the simvastatin group compared to the M group. Similarly, right ventricular pressure significantly decreased in the simvastatin group on day 28. From day 7, the ratio of medial thickening of the pulmonary artery was significantly increased in the M group, but there was no significant change in the simvastatin group. The number of muscular pulmonary arterioles was significantly reduced in the simvastatin group. On day 5, gene expressions of ET-1, ERA, NOS2, NOS3, MMP and TIMP significantly decreased in the simvastatin group.ConclusionAdministration of simvastatin exerted weak inhibitory effects on RVH and on the number of muscular pulmonary arterioles, during the development of M-induced pulmonary hypertension in rats. Simvastatin decreased gene expressions on day 5.