Losartan but not enalaprilat acutely reduces reperfusion ventricular tachyarrhythmias in hypertrophied rat hearts after low-flow ischaemia

Acute effects of urocortin 2 on cardiac function and propensity for arrhythmias in an animal model of hypertension-induced left ventricular hypertrophy and heart failure

AIMS

To test acute effects of the corticotropin-releasing factor-related peptide urocortin 2 (Ucn2) on left ventricular (LV) function and the propensity for ventricular arrhythmias in the isolated heart of an animal model of hypertension-induced heart failure.

METHODS AND RESULTS

Hearts from Dahl salt-sensitive rats with severe LV dysfunction were perfused according to Langendorff. Left ventricular developed pressure and the positive and negative derivatives of LV pressure were analysed before and after perfusion with Ucn2 (n = 15) or normal perfusion solution (control, n = 9). Intracellular calcium cycling parameters were assessed by surface fluorometry. Furthermore, monophasic action potential duration (MAPD) and ventricular fibrillation threshold (VFT) were determined, the latter by a train-of-pulses method at increasing voltage to scan the vulnerable period of repolarization. Urocortin 2 significantly affected intracellular calcium cycling and improved LV contractile function and relaxation. Compared with baseline values, Ucn2 significantly decreased MAPD at 30, 50, and 90% repolarization and significantly increased VFT compared with baseline values. No changes were observed in control experiments.

CONCLUSION

Administration of Ucn2 rapidly improves LV function and increases VF threshold in failing, isolated rat hearts with increased propensity for ventricular arrhythmias. These observations suggest a potential use of Ucn2 as a safe and novel agent for the treatment of acute heart failure.

The renin-angiotensin-aldosterone system (RAAS) and cardiac arrhythmias

The role of the renin-angiotensin-aldosterone system (RAAS) in many cardiovascular disorders, including hypertension, cardiac hypertrophy, and atherosclerosis, is well established, whereas its relationship with cardiac arrhythmias is a new area of investigation. Atrial fibrillation and malignant ventricular tachyarrhythmias, especially in the setting of cardiac hypertrophy or failure, seem to be examples of RAAS-related arrhythmias because treatment with RAAS modulators, including angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and mineralocorticoid receptor blockers, reduces the incidence of these arrhythmias. RAAS has a multitude of electrophysiological effects and can potentially cause arrhythmia through a variety of mechanisms. We review new experimental results that suggest that RAAS has proarrhythmic effects on membrane and sarcoplasmic reticulum ion channels and that increased oxidative stress is likely contributing to the increased arrhythmic incidence. A summary of ongoing clinical trials that will address the clinical usefulness of RAAS modulators for prevention or treatment of arrhythmias is presented.

Dimethyl fumarate, a small molecule drug for psoriasis, inhibits Nuclear Factor-kappaB and reduces myocardial infarct size in rats

Persistent Nuclear Factor-kappaB (NF-kappaB) activation is hypothesized to contribute to myocardial injuries following ischemia-reperfusion. Because inhibition or control of NF-kappaB signaling in the heart probably confers cardioprotection, we determined the potency of the NF-kappaB inhibitor dimethyl fumarate (DMF) in cardiovascular cells, and determined whether administration of DMF translates into beneficial effects in an animal model of myocardial infarction. In rat heart endothelial cells (RHEC), we analysed inhibitory effects of DMF on NF-kappaB using shift assay and immunohistofluorescence. In in vivo experiments, male Sprague Dawley rats undergoing left coronary artery occlusion for 45 min received either DMF (10 mg/kg body weight) or vehicle 90 min before ischemia as well as immediately before ischemia. After 120 min of reperfusion, the hearts were stained with phthalocyanine blue dye and triphenyltetrazolium chloride. Additionally, acute hemodynamic and electrophysiologic effects of DMF were determined in dose-response experiments in isolated perfused rat hearts. DMF inhibited TNF-alpha-induced nuclear entry of NF-kappaB in RHEC. In in vivo experiments, myocardial infarct size was significantly smaller in rats that had received DMF (20.7%+/-9.7% in % of risk area; n=17) than in control rats (28.2%+/-6.2%; n=15). Dose-response experiments in isolated perfused rat hearts excluded acute hemodynamic or electrophysiologic effects as mechanisms for the effects of DMF. DMF inhibits nuclear entry of NF-kappaB in RHEC and reduces myocardial infarct size after ischemia and reperfusion in rats in vivo. There was no indication that the beneficial effects of DMF were due to acute hemodynamic or electrophysiologic influences.

The protective effect of H2-receptor activation against the duration of myocardial hypoxia/reoxygenation-induced ventricular fibrillation in sensitized guinea-pig hearts

Patients with high serum immunoglobulin E levels were reported to be protected against sudden death during acute myocardial infarction. The protection mechanism might be attributed to the facilitation of histamine release from sensitized mast cells; however, this remains to be clarified. In this study, we examined the influence of sensitization on ventricular fibrillation (VF) induced by myocardial hypoxia/reoxygenation (H/R). Guinea pigs were actively sensitized by subcutaneous injection of ovalbumin in Bordetella pertussis vaccine. Hearts isolated from non-sensitized and sensitized guinea pigs were subjected to 30-min hypoxia / 30-min reoxygenation using a Langendorff apparatus. The amount of histamine released in the sensitized guinea-pig hearts was elevated, and the duration of VF was found to be reduced. The treatment with a histamine H2-receptor antagonist inhibited the reduction of VF duration. Treatment of the non-sensitized hearts with the histamine H2-receptor agonist resulted in the decrease of VF duration to the same level as that in the sensitized hearts. In conclusion, these results suggest that the risk of sudden death during myocardial H/R may be attenuated in the sensitized hearts and that histamine H2-receptor activation due to the released histamine may be involved in the protective effect.