Contractile performance of papillary muscles of renovascular hypertensive and isoproterenol-pretreated rats

Simvastatin prevents isoproterenol-induced cardiac hypertrophy through modulation of the JAK/STAT pathway

Simvastatin (SIM) is a lipid-soluble inhibitor of hydroxy-3-methylglutaryl coenzyme A reductase with multiple reported therapeutic benefits. The present study was designed to investigate the effect of pretreatment with SIM on isoproterenol (ISO)-induced cardiac hypertrophy in rats. Twenty-four male albino Wistar rats weighing 180–200 g were divided into four groups. Groups I and III received normal saline while groups II and IV received SIM (10 mg/kg body weight) for 30 days per gavage. In the last 7 days, rats of groups III and IV were administered ISO (5 mg/kg) intraperitoneally to induce cardiac hypertrophy. Administration of ISO induced an increase in heart-to-body weight (HW/BW) ratio, an increase in serum interleukin-6, and elevated systolic and diastolic blood pressure. Serum levels of lipids, cardiovascular risk indices, and cardiac troponin I and creatine phosphokinase-MB showed significant increase in ISO-induced hypertrophic rats. Histopathological examination of heart tissue revealed focal areas of subendocardium degeneration, mononuclear cellular infiltrations, fibrous tissue deposition, and increased thickness of the myocardium of left ventricle. In addition, ISO-administered rats exhibited significant upregulation of cardiac Janus kinase, phosphorylated signal transducer and activator of transcription, and nuclear factor-kappa B. Pretreatment with SIM significantly prevented ISO-induced cardiac hypertrophy, alleviated the altered biochemical parameters, and improved the heart architecture. In conclusion, our study provides evidence that SIM prevented the development of cardiac hypertrophy via modulation of the Janus kinase/signal transducer and activator of transcription-signaling pathway in the heart of ISO-administered animals.

Inhibition of phosphodiesterase 5 restores endothelial function in renovascular hypertension

Background

The clipping of an artery supplying one of the two kidneys (2K1C) activates the renin-angiotensin (Ang) system (RAS), resulting in hypertension and endothelial dysfunction. Recently, we demonstrated the intrarenal beneficial effects of sildenafil on the high levels of Ang II and reactive oxygen species (ROS) and on high blood pressure (BP) in 2K1C mice. Thus, in the present study, we tested the hypothesis that sildenafil improves endothelial function in hypertensive 2K1C mice by improving the NO/ROS balance.

Methods

2K1C hypertension was induced in C57BL/6 mice. Two weeks later, they were treated with sildenafil (40 mg/kg/day, via oral) or vehicle for 2 weeks and compared with sham mice. At the end of the treatment, the levels of plasma and intrarenal Ang peptides were measured. Endothelial function and ROS production were assessed in mesenteric arterial bed (MAB).

Results

The 2K1C mice exhibited normal plasma levels of Ang I, II and 1–7, whereas the intrarenal Ang I and II were increased (~35% and ~140%) compared with the Sham mice. Sildenafil normalized the intrarenal Ang I and II and increased the plasma (~45%) and intrarenal (+15%) Ang 1–7. The 2K1C mice exhibited endothelial dysfunction, primarily due to increased ROS and decreased NO productions by endothelial cells, which were ameliorated by treatment with sildenafil.

Conclusion

These data suggest that the effects of sildenafil on endothelial dysfunction in 2K1C mice may be due to interaction with RAS and restoring NO/ROS balance in the endothelial cells from MAB. Thus, sildenafil is a promising candidate drug for the treatment of hypertension accompanied by endothelial dysfunction and kidney disease.

Exploration of pharmacological interventions to prevent isoproterenol-induced myocardial infarction in experimental models

High incidences of myocardial infarction associated with high morbidity and mortality, are a major concern and economic burden on industrialized nations. Persistent β-adrenergic receptor stimulation with isoproterenol leads to the development of oxidative stress, myocardial inflammation, thrombosis, platelet aggregation and calcium overload, which ultimately cause myocardial infarction. Therapeutic agents that are presently employed for the prevention and management of myocardial infarction are beta-blockers, antithrombotics, thrombolytics, statins, angiotensin converting enzyme inhibitors, angiotensin II type 1 receptor blockers, calcium channel blockers and nitrovasodilators. In spite of effective available interventions, the mortality rate of myocardial infarction is progressively increasing. Thus, there has been a regular need to develop effective therapies for the prevention and management of this insidious disease. In this review, the authors give an overview of the consequences of isoproterenol in the pathogenesis of cardiac disorders and various therapeutic possibilities to prevent these disorders.

Exercise training can prevent cardiac hypertrophy induced by sympathetic hyperactivity with modulation of kallikrein-kinin pathway and angiogenesis

Sympathetic hyperactivity induces adverse effects in myocardial. Recent studies have shown that exercise training induces cardioprotection against sympathetic overload; however, relevant mechanisms of this issue remain unclear. We analyzed whether exercise can prevent pathological hypertrophy induced by sympathetic hyperactivity with modulation of the kallikrein-kinin and angiogenesis pathways. Male Wistar rats were assigned to non-trained group that received vehicle; non-trained isoproterenol treated group (Iso, 0.3 mg kg(-1) day-(1)); and trained group (Iso+Exe) which was subjected to sympathetic hyperactivity with isoproterenol. The Iso rats showed hypertrophy and myocardial dysfunction with reduced force development and relaxation of muscle. The isoproterenol induced severe fibrosis, apoptosis and reduced myocardial capillary. Interestingly, exercise blunted hypertrophy, myocardial dysfunction, fibrosis, apoptosis and capillary decreases. The sympathetic hyperactivity was associated with high abundance of ANF mRNA and β-MHC mRNA, which was significantly attenuated by exercise. The tissue kallikrein was augmented in the Iso+Exe group, and kinin B1 receptor mRNA was increased in the Iso group. Moreover, exercise induced an increase of kinin B2 receptor mRNA in myocardial. The myocardial content of eNOS, VEGF, VEGF receptor 2, pAkt and Bcl-2 were increased in the Iso+Exe group. Likewise, increased expression of pro-apoptotic Bad in the Iso rats was prevented by prior exercise. Our results represent the first demonstration that exercise can modulate kallikrein-kinin and angiogenesis pathways in the myocardial on sympathetic hyperactivity. These findings suggest that kallikrein-kinin and angiogenesis may have a key role in protecting the heart.

Spironolactone prevents alterations associated with cardiac hypertrophy produced by isoproterenol in rats: involvement of serum- and glucocorticoid-regulated kinase type 1

Persistent β-adrenergic receptor stimulation with isoproterenol is associated with cardiac hypertrophy as well as cardiac synthesis of angiotensin II. Serum- and glucocorticoid-regulated kinase type 1 (SGK-1) is a key mediator in structural, functional and molecular cardiac effects of aldosterone in rats. This study was designed to investigate the cardiac effects of the mineralocorticoid receptor antagonist spironolactone on the response to isoproterenol treatment in rats, as well as the involvement of the main mediator of cellular aldosterone action, SGK-1, in the heart. Male Wistar rats received isoproterenol (3 mg kg(-1) day(-1)) or vehicle for 15 days. Half of the animals in each group were simultaneously treated with spironolactone (200 mg kg(-1) day(-1)). Systolic and diastolic blood pressures were not significantly different among groups. Treatment with spironolactone normalized the increased left ventricular end-diastolic pressure observed in isoproterenol-treated rats. Isoproterenol treatment induced cardiac hypertrophy and increased collagen content, both of which were normalized by spironolactone treatment. The mRNA levels of transforming growth factor β, connective tissue growth factor, matrix metalloprotease 2, matrix metalloprotease inhibitor 2, tumour necrosis factor α, interleukin 1β, p22phox and xanthine dehydrogenase were increased (P < 0.05) in isoproterenol-treated rats, and this effect was prevented by spironolactone (P < 0.05). Spironolactone also reduced the elevated SGK-1 expression in isoproterenol-treated rats. The observed reduction of the principal mediator of aldosterone cellular actions, SGK-1, by spironolactone in hearts from isoproterenol-treated rats suggests a role of mineralocorticoids in the cardiac hypertrophy, fibrosis, inflammation, oxidation and diastolic dysfunction induced by isoproterenol treatment in rats.

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.

Exercise training inhibits inflammatory cytokines and more than prevents myocardial dysfunction in rats with sustained beta-adrenergic hyperactivity

Myocardial hypertrophy and dysfunction occur in response to excessive catecholaminergic drive. Adverse cardiac remodelling is associated with activation of proinflammatory cytokines in the myocardium. To test the hypothesis that exercise training can prevent myocardial dysfunction and production of proinflammatory cytokines induced by beta-adrenergic hyperactivity, male Wistar rats were assigned to one of the following four groups: sedentary non-treated (Con); sedentary isoprenaline treated (Iso); exercised non-treated (Ex); and exercised plus isoprenaline (Iso+Ex). Echocardiography, haemodynamic measurements and isolated papillary muscle were used for functional evaluations. Real-time RT-PCR and Western blot were used to quantify tumour necrosis factor alpha, interleukin-6, interleukin-10 and transforming growth factor beta(1) (TGF-beta(1)) in the tissue. NF-B expression in the nucleus was evaluated by immunohistochemical staining. The Iso rats showed a concentric hypertrophy of the left ventricle (LV). These animals exhibited marked increases in LV end-diastolic pressure and impaired myocardial performance in vitro, with a reduction in the developed tension and maximal rate of tension increase and decrease, as well as worsened recruitment of the Frank-Starling mechanism. Both gene and protein levels of tumour necrosis factor alpha and interleukin-6, as well as TGF-beta(1) mRNA, were increased. In addition, the NF-B expression in the Iso group was significantly raised. In the Iso+Ex group, the exercise training had the following effects: (1) it prevented LV hypertrophy; (ii) it improved myocardial contractility; (3) it avoided the increase of proinflammatory cytokines and improved interleukin-10 levels; and (4) it attenuated the increase of TGF-beta(1) mRNA. Thus, exercise training in a model of beta-adrenergic hyperactivity can avoid the adverse remodelling of the LV and inhibit inflammatory cytokines. Moreover, the cardioprotection is related to beneficial effects on myocardial performance.

Effects of isoproterenol treatment for 7 days on inflammatory mediators in the rat aorta

The aim of the present study was to evaluate the effect of overstimulation of beta-adrenoceptors on vascular inflammatory mediators. Wistar rats were treated with the beta-adrenoceptor agonist isoproterenol (0.3 mg.kg(-1).day(-1) sc) or vehicle (control) for 7 days. At the end of treatment, the right carotid artery was catheterized for arterial and left ventricular (LV) hemodynamic evaluation. Isoproterenol treatment increased LV weight but did not change hemodynamic parameters. Aortic mRNA and protein expression were quantified by real-time RT-PCR and Western blot analysis, respectively. Isoproterenol enhanced aortic mRNA and protein expression of IL-1beta (124% and 125%) and IL-6 (231% and 40%) compared with controls but did not change TNF-alpha expression. The nuclear-to-cytoplasmatic protein expression ration of the NF-kappaB p65 subunit was increased by isoproterenol treatment (51%); in addition, it reduced the cytoplasmatic expression of IkappaB-alpha (52%) in aortas. An electrophoretic mobility shift assay was performed using the aorta, and increased NF-kappaB DNA binding (31%) was observed in isoproterenol-treated rats compared with controls (P < 0.05). Isoproterenol treatment increased phenylephrine-induced contraction in aortic rigs (P < 0.05), which was significantly reduced by superoxide dismutase (150 U/ml) and sodium salicylate (5 mM). Cotreatment with thalidomide (150 mg.kg(-1).day(-1) for 7 days) also reduced hyperreactivity to phenylephrine induced by isoproterenol. In conclusion, overstimulation of beta-adrenoceptors increased proinflammatory cytokines and upregulated NF-kappaB in the rat aorta. Moreover, local oxidative stress and the proinflammatory state seem to play key roles in the altered vascular reactivity of the rat aorta induced by chronic beta-adrenergic stimulation.

Changes in vascular reactivity following administration of isoproterenol for 1 week: a role for endothelial modulation

1. The aim of this study was to assess the effects of treatment with isoproterenol (ISO, 0.3 mg kg-1 day-1, s.c.) for 7 days on the vascular reactivity of rat-isolated aortic rings. Additionally, potential mechanisms underlying the changes that involved the endothelial modulation of contractility were investigated. 2. Treatment with ISO induced cardiac hypertrophy without changes in haemodynamic parameters. Aortic rings from ISO-treated rats showed an increase in the contraction response to phenylephrine (PHE) and serotonin, but did not change relaxations produced by acetylcholine or isoproterenol. Removal of the endothelium increased the responses to PHE in both groups. However, this procedure was less effective in ISO-treated as compared with control rats. Endothelial cell removal abolished the increase in the response to PHE in ISO-treated rats. The presence of Nomega-nitro-L-arginine methyl ester shifted the concentration-response curve to PHE to the left in both groups of rats. However, this effect was more pronounced in the ISO group. In addition, aminoguanidine (50 microM) potentiated the actions of PHE only in the ISO group. ISO treatment increased nitric oxide synthase (NOS) activity and neuronal NOS and endothelial NOS protein expression in the aorta. 3. Neither losartan (10 microM) nor indomethacin (10 microM) abolished the effects of ISO on the actions of PHE. Superoxide dismutase (SOD, 150 U ml-1) and L-arginine (5 mM), but neither catalase (300 U ml-1) nor apocynin (100 microM), blocked the effect of ISO treatment. In addition, we observed an increase in superoxide anion levels as measured by ethidium bromide fluorescence and of copper and zinc superoxide dismutase protein expression in ISO-treated rats. 4. In conclusion, our data suggest that ISO treatment alters the endothelial cell-mediated modulation of the contraction to PHE in rat aorta. The increased maximal response of PHE seems to be due to an increase in superoxide anion generation, which inactivates some of the basal NO produced and counteracts NO-mediated negative modulation even in the presence of high NO production and antioxidant defence.

Isoproterenol-induced hypertrophy may result in distinct left ventricular changes

1. The aim of the present study was to analyse the possible lack of uniformity in isoproterenol (ISO)-induced myocardial hypertrophy. 2. Data obtained for isovolumic hearts isolated from 20 rats treated with ISO (0.3 mg/kg over 8 days) were divided into two groups (H1, n = 10; H2, n = 10) according to the volume (mean+/-SD) needed to change left ventricle diastolic pressure from 0 to 40 mmHg (H1, 184+/-30 microL; H2, 108+/-14 microL). Eight control rats (C; 165+/-37 microL) were used for comparison. 3. In addition to ventricular distensibility differences, the groups differed in terms of myocardial mass (mean+/-SEM: H1, 181+/-3 mg > H2, 166+/-3 mg > C, 136+/-3 mg; P < 0.001), of relaxation constant (H2, 43+/-4 msec > H1, 28+/-2 msec; P = 0.0012) and of maximum developed circumferential stress (C, 145+/-9 kdyn/cm2 = H1, 137+/-6 kdyn/cm2 > H2, 110+/-4 kdyn/cm2; P = 0.002). 4. Our results show that ISO-induced myocardial hypertrophy is not homogeneous. Data obtained for H2, taken as a whole and compared with H1 (smaller myocardial mass and impairment of relaxation, elastic stiffness and force generation), suggest that, in some animals, myocardial necrosis and reparative fibrosis may prevail over the stimulus for myocyte growth. The lack of uniformity of ISO-induced myocardial hypertrophy has not been previously reported and may have contributed to the divergence observed in the literature regarding the functional characteristics of the present model.

Developed pressure data may provide misinformation when used alone to evaluate systolic function in isovolumetric left ventricle preparations

We report data showing that developed pressure (DPmax) may lead to opposite conclusion with respect to maximal developed circumferential wall stress (sigma max) when used to assess contractile function in left ventricle isovolumic preparations. Isovolumetric left ventricle preparations of rats with cardiac hypertrophy (H; N = 10) induced by isoproterenol administration showed higher DPmax (174 +/- 14 mmHg) than control (C; N = 8) animals (155 +/- 12 mmHg) or rats with regression (R; N = 8) of hypertrophy (144 +/- 11 mmHg). In contrast, the estimated sigma max for C (145 +/- 26 kdynes/cm2) and R (133 +/- 17 kdynes/cm2) was higher than for H (110 +/- 13 kdynes/cm2). According to Laplace's law, the opposite results of DPmax and sigma max may depend on the increased mass/volume left ventricle ratio of the hypertrophied hearts, which favored pressure generation. These results clearly show that DPmax should be used with caution to analyze systolic function.

Effects of isoproterenol on the mechanical activity of isolated papillary muscles and perfused rat hearts in various calcium concentrations

The aim of the study was to examine, in papillary muscles and in a whole heart preparation, the effects of isoproterenol on the myocardial mechanical activity at different extracellular Ca2+ concentrations. Papillary muscles from left ventricles, contracting isometrically, and rat hearts perfused by the Langendorff technique developing isovolumetric pressure at a fixed rate (200 bpm) and diastolic pressure of 5 mmHg were studied at different Ca2+ concentrations for analysis of the effects of increasing doses of isoproterenol. Papillary muscles were treated with isoproterenol (0.5 to 8 ng ml-1) at four extracellular Ca2+ concentrations (0.25, 0.5, 1.25 and 2.5 mM) and Langendorff perfused hearts were stimulated by isoproterenol (0.05 ng ml-1 to 0.8 ng ml-1), also at four extracellular Ca2+ concentrations (0.5, 1.25, 2.5 and 3.75 mM). Both papillary muscles and perfused hearts showed that force and isovolumetric systolic pressure increase in response to isoproterenol at low Ca2+ concentrations. As Ca2+ concentration is increased, isoproterenol's positive inotropic effect subsides. However, papillary muscle isometric contractions showed a similar time to peak tension decrease in response to isoproterenol at all external Ca2+ concentrations used. The results suggest that the positive inotropic response to isoproterenol, in isolated preparations, changes as a function of extracellular Ca2+ concentration decreasing as external Ca2+ increases. Time to peak tension reduction reinforces the idea that this small positive inotropic response to isoproterenol of the rat myocardium, at the physiological Ca2+ concentration, is due to the Ca2+ saturation of the mechanical activity.

Myocardial depression produced by unilateral nephrectomy in rats

Previous experiments using 15 days renovascular hypertensive rats and their sham operated uninephrectomized controls suggested a decrease in contractile force developed by the papillary muscles from uninephrectomized rats. Because of the implications of such findings two sets of experiments were performed. The first set 15 days after operations, compared four groups of Wistar male rats: uninephrectomized, sham operated controls and renovascular hypertensive 1K1C and 2K1C. In the second set of experiments the time course effects of uninephrectomy was analysed. The first four groups of animals showed that mean blood pressure was normal in both controls and uninephrectomized rats, but the 1K1C and 2K1C groups were hypertensive. Contractile performance was analysed 24 hours after hemodynamic studies from isometric contracting left ventricle papillary muscles. Results showed similar force development in controls, 1K1C and in 2K1C muscles. However, the muscles from uninephrectomized rats showed a significant contractile depression when compared to the other groups, even under different inotropic interventions, like isoproterenol or post-rest potentiation. The study of the time course effects of uninephrectomy showed that the contractile activity is depressed 7, 15 and 30 days after unilateral nephrectomy. The results suggest that the mechanical depression, whatever its underlying mechanism, is located at the contractile machinery level.