Shengbo Yu

Ghrelin inhibits post-infarct myocardial remodeling and improves cardiac function through anti-inflammation effect

Ghrelin is a novel growth hormone-releasing peptide, which has been shown to exert beneficial cardiac effects on chronic heart failure (CHF) recently. In this study, we attempted to investigate the mechanisms for the effect of ghrelin on ventricular remodeling following acute myocardial infarction (MI). Ligation of a coronary artery was used to create an MI in rats. One week after MI, ghrelin (100 microg/kg) or saline was injected subcutaneously twice a day for 4 weeks. When compared to sham groups, ghrelin administration significantly decreased left ventricular (LV) remodeling in post-MI rats, as indicated by increased LV maximum rate of pressure, LV fractional shortening and scar thickness; and decreased LV end-diastolic pressure, LV end-systolic diameter, LV end-diastolic diameter and cardiocytocytes apoptosis. Moreover, ghrelin inhibited the inflammatory response, as shown by decreased mRNA and protein levels of interleukin (IL)-1beta and tumor necrosis factor-alpha (TNF-alpha). Subsequently, the expression of matrix metalloproteinase (MMP)-2 and MMP-9 were also inhibited by ghrelin injection. Ghrelin alleviates LV dysfunction and ventricular remodeling in post-MI rats. This suggests that the beneficial effects of ghrelin on CHF may result from an inhibition of the inflammatory response.

Effect of renal sympathetic denervation on atrial substrate remodeling in ambulatory canines with prolonged atrial pacing.

We have previously demonstrated that catheter-based renal sympathetic denervation (RSD) could suppress atrial fibrillation (AF) in canines with short-time rapid right atrial pacing (RAP). However, the role of renal denervation on atrial remodeling is unclear. The aim of the present study was to explore the long-term effect of RSD on the atrial remodeling during prolonged RAP. Twenty mongrel dogs were implanted with a high-frequency cardiac pacemaker with a transvenous lead inserted into the right atrial appendage. The dogs were divided into three groups: a sham-operated group (n = 6), the chronic RAP (CRAP) group (n = 7), and the CRAP+RSD group (n = 7). In the CRAP+RSD group, a pacemaker was implanted 6 weeks after RSD was performed bilaterally for recovery. RAP was maintained for 5 weeks in CRAP group and CRAP+RSD group. The plasma levels of Angiotensin II and aldosterone were significantly increased in CRAP group compared with sham-operated group, but the increasing trend was inhibited in CRAP+RSD group compared with CRAP group (P<0.05). Similarly, RSD suppressed the increasing trend that prolonged RAP produced in the left atrial levels of ANP, TNF-α and IL-6. Compared with the sham-operated group, the CRAP group had significantly increased levels of caspase-3, bax and Cx40 whereas the level of Bcl-2 decreased (P<0.05). RSD markedly reduced the upregulation of caspase-3, bax and Cx40 and the downregulation of Bcl-2 expression compared with the CRAP group (P<0.05). Picric acid–sirius red staining study suggested that RSD could markedly alleviate the lesion degree of cardic fibrosis induced by CRAP (P<0.05). Immunohistochemistry results showed that the densities of TH- and GAP43- positive nerves were significantly elevated in the CRAP group compared with the sham-operated group, while RSD operation signicantly inhibited the these changes produced by CRAP. These findings suggest that renal denervation could suppress the atrial remodeling after prolonged RAP in ambulatory canines.

Effects of renal sympathetic denervation on the development of atrial fibrillation substrates in dogs with pacing-induced heart failure.

The present study examined the effect of catheter-based renal sympathetic denervation (RSD) on atrial fibrillation (AF) vulnerability and atrial substrate remodeling in a canine high-rate ventricular pacing model. Animal handling was performed in accordance with theWuhan Directive for Animal Research and the current Guidelines for the Care and Use of Laboratory Animals published by the National Institutes of Health (NIH publication no. 85-23, revised 1996). The ethics committee at Wuhan University approved the study protocol. Nineteen adult mongrel dogs were divided into three groups. The pacemakers in the sham-operated group were implanted in a subcutaneous pocket and attached to a pacing lead (Medtronic, Inc., Capture Sense, 4574, USA) in the right ventricular apex. All of the animals recovered for 3 weeks without pacing. The pacemakers were implanted in the heart failure (HF) group, and the dogs underwent ventricular rapid pacing at 240 beats per minute (bpm) for 3 weeks. The dogs in the HF+ RSD group underwent renal artery ablation (RAA) prior to ventricular rapid pacing [1]. After 8 weeks, pacemakers were implanted, and the dogs underwent ventricular rapid pacing for 3 weeks. The femoral artery blood pressure, electrophysiological measurements, echocardiography, left ventricular end-systolic pressure (LVESP), and left ventricular end-diastolic pressure (LVEDP) were measured in all of the animals at baseline and after 3 weeks of pacing. The BNP, Ang II and TNF-α levels were measured in the atrial tissue samples using ELISA and TGF-β was measured using the Western blot. Massons trichrome staining was used to identify increased concentration of interstitial fibrosis.

Atrial autonomic innervation remodelling and atrial fibrillation inducibility after epicardial ganglionic plexi ablation

AIMS The effects of ganglionated plexi (GP) ablation on atrial fibrillation (AF) inducibility and atrial autonomic innervation remodelling have not been elucidated. METHODS AND RESULTS Thirteen dogs were randomly divided into sham-operated group and GP ablation group. All animals underwent a right thoracotomy at the fourth intercostal space. Atrial fibrillation inducibility was assessed by burst rapid pacing at right atrium (RA). After anterior right GP and inferior right GP ablation, AF inducibility was assessed in the GP ablation group. The animals were allowed to recover for 8 weeks, after which, AF was measured again. The levels of atrial natriuretic peptide (ANP) in blood and atrial tissues were examined by radioimmunoassay. Immunocytochemical staining of cardiac nerves was performed in tissues from the dogs. Atrial fibrillation was induced easily in the GP ablation group after 8 weeks although AF was not observed in the sham-operated group, and after instant GP ablation. Compared with that in the sham-operated group, the levels of ANP in the blood and RA increased significantly 8 weeks after GP ablation (111.4 +/- 18.2 vs. 175.1 +/- 25.9; 184.9 +/- 36.3 vs. 299.1 +/- 32.5; P < 0.05). In the GP ablation group, the density of growth-associated protein 43-positive, tyrosine hydroxylase-positive, and choline acetyltransferase-positive nerves in the RA was 821 +/- 752, 481 +/- 627, and 629 +/- 644 per mm(2), respectively, which was significantly (P < 0.01) lower than the nerve density in sham-operated tissues (2590 +/- 841, 1752 +/- 605, and 3147 +/- 886 per mm(2), respectively). CONCLUSION Atrial autonomic innervations remodelling may be the mechanism of induced AF after GP ablation.

Effect of isoprenaline chronic stimulation on APD restitution and ventricular arrhythmogenesis

BACKGROUND Isoprenaline (ISO) acts through β-adrenergic receptors to increase the intracellular Ca(2+), which has effects on action potential duration (APD) restitution and arrhythmogenesis. Thus, we investigated the effect of chronic stimulation with isoprenaline on APD restitution and ventricular tachyarrhythmias (VA) in the rabbit heart. METHODS AND RESULTS Rabbits were randomly selected to receive an injection of isoprenaline (ISO group) or an equal volume of 0.9% saline (CTL group). The S(1)-S(2) protocol (n=15) and S(1) dynamic pacing (n=15) were performed to construct APD restitution and to induce APD alternans or arrhythmia in 10 sites of Langendorff-perfused hearts. Compared with the same sites in the control group, long-term ISO administration (7 days) shortened the APD(90) and the effective refractory period (ERP), and greatly increased the spatial dispersion of APD and ERP (p<0.01). Compared to CTL group, the APD restitution curves were significantly changed (p<0.01) and showed increased spacial dispersion of maximal slope (S(max)) among each site in the ISO group (p<0.05). In induction of VA and APD alternans, the threshold of VA and alternans was both decreased in each site of the ISO group. CONCLUSION Chronic stimulation with ISO facilitated VA, possibly through the increased spatial dispersion of APD restitution.

Effects of Intrinsic and Extrinsic Cardiac Nerves on Atrial Arrhythmia in Experimental Pulmonary Artery Hypertension.

Atrial arrhythmia, which includes atrial fibrillation (AF) and atrial flutter (AFL), is common in patients with pulmonary arterial hypertension (PAH), who often have increased sympathetic nerve activity. Here, we tested the hypothesis that autonomic nerves play important roles in vulnerability to AF/AFL in PAH. The atrial effective refractory period and AF/AFL inducibility at baseline and after anterior right ganglionated plexi ablation were determined during left stellate ganglion stimulation or left renal sympathetic nerve stimulation in beagle dogs with or without PAH. Then, sympathetic nerve, &bgr;-adrenergic receptor densities and connexin 43 expression in atrial tissues were assessed. The sum of the window of vulnerability to AF/AFL was increased in the right atrium compared with the left atrium at baseline in the PAH dogs but not in the controls. The atrial effective refractory period dispersion was increased in the control dogs, but not in the PAH dogs, during left stellate ganglion stimulation. The voltage thresholds for inducing AF/AFL during anterior right ganglionated plexi stimulation were lower in the PAH dogs than in the controls. The AF/AFL inducibility was suppressed after ablation of the anterior right ganglionated plexi in the PAH dogs. The PAH dogs had higher sympathetic nerve and &bgr;1-adrenergic receptor densities, increased levels of nonphosphorylated connexin 43, and heterogeneous connexin 43 expression in the right atrium when compared with the control dogs. The anterior right ganglionated plexi play important roles in the induction of AF/AFL. AF/AFL induction was associated with right atrium substrate remodeling in dogs with PAH.

Electrophysiological effect of rotigaptide in rabbits with heart failure.

Introduction Rotigaptide is a new anti-arrhythmic peptide, which has recently been found to increase junctional conductance and prevent ischemia-induced ventricular tachycardia. In this study, we attempted to investigate the effects and mechanisms of rotigaptide on the vulnerability to ventricular arrhythmias in rabbits with heart failure (HF). Material and methods Chronic volume-pressure overload was used to induce HF. After rotigaptide infusion, an electrophysiological study was performed to record monophasic action potential (MAP), determine the effective refractory period (ERP) and ventricular fibrillation threshold (VFT), and assess the susceptibility to ventricular arrhythmia. Finally, real-time PCR was used to detect the changes of connexin 43 (Cx43) mRNA expression. Results HF rabbits exhibited significant down-regulation of Cx43 mRNA, increase of effective refractory period (ERP) and decrease of VFT (p < 0.05, respectively). These changes resulted in an increase of vulnerability to ventricular tachyarrhythmias (VT/VF). Rotigaptide administration shortened ERP (113.3 ±8.6 ms vs. 131.7 ±12.5 ms, p < 0.05), restored VFT (15.0 ±2.0 V vs. 6.3 ±1.4 V, p < 0.05), and decreased the vulnerability to VT/VF. However, short-term rotigaptide treatment had no significant effect on MAP duration (MAP duration at 90% repolarization: 169.3 ±6.0 ms vs. 172.7 ±6.2 ms, p > 0.05) or connexin 43 mRNA expression (p > 0.05). Conclusions Rotigaptide decreases the ERP, elevates VFT, and reduces the vulnerability to ventricular arrhythmias without changing Cx43 expression in rabbits with HF. It may be a promising antiarrhythmic drug for preventing ventricular arrhythmia in HF.

Inflammation abnormalities and inducibility of atrial fibrillation after epicardial ganglionated plexi ablation

BACKGROUND Epicardial ganglionated plexi (GP) ablation can prevent atrial fibrillation inducibility. However, the long-term effects of GP ablation on atrial fibrillation have not been elucidated. METHODS Thirteen adult dogs of either sex, weighing 13-17kg, were randomly assigned to a sham-operated group (n=6) or a GP ablation group (n=7). After right thoracotomy, the atrial effective refractory period (AERP) was measured and atrial fibrillation was induced by right atrial rapid burst pacing. Atrial fibrillation and AERP were remeasured after anterior right and inferior right GP ablation in the GP ablation group. The animals were allowed to recover for 8 weeks, after which atrial fibrillation and AERP were measured again. Concentrations of C-reactive protein, tumour necrosis factor-alpha (TNF-α) and interleukin-6 were measured in the blood and atrial tissues. RESULTS After 8 weeks, atrial fibrillation was induced in all animals in the GP ablation group. AERP and dispersion of AERP (dAERP; maximum AERP minus minimum AERP) were increased after GP ablation but AERP recovered after 8 weeks. There were no significant differences in the concentrations of C-reactive protein, TNF-α or interleukin-6 in venous blood between the two groups and the concentration of C-reactive protein in the atrium did not change before and after GP ablation. However, the concentrations of TNF-α and interleukin-6 in the atrium increased significantly 8 weeks after GP ablation (P<0.05). CONCLUSION Increased concentrations of TNF-α and interleukin-6 in the atrium after GP ablation provide a new causative factor in terms of atrial fibrillation vulnerability.

ASSA13-03-7 Renal Sympathetic Denervation Changes the Distribution of Atrial Substrate and Inhibites the Inducibility of Atrial Fibrillation

Objective Whether renal sympathetic denervation has effect on changes of atrial substrate and inducilibity of atrial fibrillation is unknown. The purpose of this study was to determine the effect of renal denervation on the inducibility atrial fibrillation. Methods Thirteen dogs were randomly divided into control group (7 dogs) and renal artery ablation group (6 dogs). In control group, at first, atrial fibrillation was induced by anterior right ganglionated plexi stimulation. Then, rapid atrial pacing was performed for 7 hours. Atrial effective refractory period and atrial fibrillation were measured each hour. In renal artery ablation group, after renal artery ablation, dogs were raised for 6 weeks. After that, the procedure of pacing and electrophysiological measurement was same as in the control group. Results The voltage in the sinus rate slowing response and the threshold of inducilibity atrial fibrillation increased during ganglionated plexi stimulation after renal artery ablation (3.5 ± 1.6V vs 1.6 ± 0.3V; 5.1V ± 1.0V vs 2.1V ± 0.7V, P = 0.03). Induced number of times and duration of atrial fibrillation was higher in control group than that in renal artery ablation group after cessation of pacing. Levels of ANP in right atrium and densities of Cx43 were lower in renal artery ablation group than that in control group (ANP: 220.5 ± 37.6 pg/mg vs 164.4 ± 22.0 pg/mg, P = 0.02; Cx43: 0.52, 0.63, 0.87 vs 1, 1.02, 1.91, P < 0.01). Conclusions Renal sympathetic denervation results in changes of atrial substrate and markedly decrease the inducilibity of atrial fibrillation by inhibiting activity of renin-angiotensin-aldosterone system.

ASSA13-03-6 Effects of Renal Sympathetic Denervation on the Development of Atrial Fibrillation Substrates in Dogs with Pacing-Induced Heart Failure

Objective We examined the role of renal denervation on the inducibility of AF in dogs with pacing-induced HF. Background Atrial fibrillation (AF) and heart failure (HF) are common interrelated conditions that are associated with renin-angiotensin-aldosterone system activity. Methods and Results Nineteen dogs were randomised into sham-operated (7 dogs), HF (6 dogs) and HF+renal artery ablation (RAA, 6 dogs) groups. Sham-operated dogs were implanted with transvenous cardiac pacemakers without pacing. Dogs in the HF group were implanted with pacemakers and underwent right ventricular pacing for 3 weeks at 240 bpm to induce HF. The dogs in the HF+RAA group received double renal artery ablation. The dogs recovered for 8 weeks and underwent the same HF-inducing procedure. Compared to the baseline, the atrial dimensions increased and the right atrial ERP (131 ± 14 ms to 112 ± 12 ms, p = 0.02) decreased significantly after 3 weeks in the HF dogs but not the HF+RAA dogs. A greater number of AFs were induced in the HF dogs than the HF+RAA dogs (2.2 ± 0.6 vs. 0.3 ± 0.3, p = 0.03). The atrium from HF hearts revealed a large amount of fibrosis, whereas control and HF+RAA dogs showed minimal fibrous tissue. The levels of BNP, Ang II, TNF-α and expression of TGF-β and Cx43 in atrial tissue were increased in the HF dogs compared to the sham-operated and HF+RAA dogs. Conclusion RAA suppressed the atrial substrate remodelling and the AF vulnerability that was induced by long-term rapid ventricular pacing.