Cholinergic signaling exerts protective effects in models of sympathetic hyperactivity-induced cardiac dysfunction.

Cholinergic control of the heart is exerted by two distinct branches; the autonomic component represented by the parasympathetic nervous system, and the recently described non-neuronal cardiomyocyte cholinergic machinery. Previous evidence has shown that reduced cholinergic function leads to deleterious effects on the myocardium. Yet, whether conditions of increased cholinergic signaling can offset the pathological remodeling induced by sympathetic hyperactivity, and its consequences for these two cholinergic axes are unknown. Here, we investigated two models of sympathetic hyperactivity: i) the chronic beta-adrenergic receptor stimulation evoked by isoproterenol (ISO), and ii) the α2A/α2C-adrenergic receptor knockout (KO) mice that lack pre-synaptic adrenergic receptors. In both models, cholinergic signaling was increased by administration of the cholinesterase inhibitor, pyridostigmine. First, we observed that isoproterenol produces an autonomic imbalance characterized by increased sympathetic and reduced parasympathetic tone. Under this condition transcripts for cholinergic proteins were upregulated in ventricular myocytes, indicating that non-neuronal cholinergic machinery is activated during adrenergic overdrive. Pyridostigmine treatment prevented the effects of ISO on autonomic function and on the ventricular cholinergic machinery, and inhibited cardiac remodeling. α2A/α2C-KO mice presented reduced ventricular contraction when compared to wild-type mice, and this dysfunction was also reversed by cholinesterase inhibition. Thus, the cardiac parasympathetic system and non-neuronal cardiomyocyte cholinergic machinery are modulated in opposite directions under conditions of increased sympathetic drive or ACh availability. Moreover, our data support the idea that pyridostigmine by restoring ACh availability is beneficial in heart disease.

Cardiac dysfunction in rats prone to audiogenic epileptic seizures.

PURPOSE: Cardiac dysfunction is one of the possible causes of sudden unexpected death in epilepsy (SUDEP). Therefore, the objective of this study was to evaluate cardiac and electrocardiographic parameters in rats with audiogenic epileptic seizures (WAR--Wistar audiogenic rats). METHODS: In vivo arterial pressure, heart rate (HR), autonomic tone and electrocardiography (ECG) were measured in awake animals in order to examine cardiac function and rhythm. Ex vivo, the Langendorff technique was used to analyze the cardiac function and the severity of reperfusion arrhythmias. In vitro, confocal microscopy was used to evaluate calcium transient parameters of isolated ventricular cardiomyocytes. RESULTS: In vivo autonomic tone evaluation revealed enhanced sympathetic activity, changes in cardiac function with increased systolic arterial pressure and higher basal HR in WAR. In addition, ECG analysis demonstrated electrical alterations with prolongation of the QT interval and QRS complex in these animals. Ex vivo, we observed a decrease in systolic tone and HR and an increase in the duration of ischemia/reperfusion arrhythmias in WAR. Moreover, intracellular Ca2+ handling analysis revealed an increase in the peak of calcium and calcium transient decay in audiogenic rats. Treatment with atenolol (ß1-adrenergic antagonist) normalized the systolic tone, reduced cardiac hypertrophy and the associated increase in the susceptibility to reperfusion arrhythmias observed in WAR. CONCLUSION: We present evidence that chronic disturbances in sympathetic tone in WAR cause increases the risk to life-threatening arrhythmias. Our results support a relationship between seizures, cardiac dysfunction and cardiac arrhythmias, which may contribute to the occurrence of SUDEP.

Cardiovascular and electrocardiographic parameters after tonin administration in Wistar rats.

In order to understand the mechanisms of interaction between tonin-angiotensin and renin-angiotensin systems (RAS) we evaluated, "in vivo" and "in vitro", in Wistar rats, cardiovascular and electrocardiographic parameters after tonin administration. Arterial pressure (AP) and electrocardiogram (ECG) were recorded in awake animals before and after tonin administration. Langendorff technique was used to analyze cardiac function in isolated heart in the presence of tonin and video motion edge detection system was used to evaluate the effect of tonin upon contractile function of isolated rat ventricular cardiomyocytes. After tonin infusion rats presented significantly higher diastolic and mean arterial pressure (MAP) and heart rate (HR) as compared with control. The ECG analysis revealed shorter RR interval, increase in the low-frequency (LF) range of the heart rate variability (HRV) power (%) and decrease in the high-frequency (HF) of HRV power (%). Isolated hearts perfused with tonin presented an increase in the arterial coronary pressure (ACP) and decline in the ventricular systolic tension (ST), maximal (dT/dt+) and minimal (dT/dt) contractility. The rates of contraction and relaxation of isolated ventricular cardiomyocytes were significantly increased due to the presence of tonin. The angiotensin II (Ang II) levels in the coronary sinus effluent increased in the presence of tonin in a dose-dependent manner and the effect of tonin upon ACP was completely blocked by candesartan. Tonin is able to generate the vasoconstrictor peptide Ang II in the isolated heart of the rat and the cardiovascular response induced by tonin was completely blocked by candesartan, an indication that the action of Ang II on Ang II type 1 (AT1) receptors is the major mechanism of the heart effects. Tonin affects cardiomyocyte contractile function which may be due to interference with Ca(2+) handling.

Cardiovascular dysautonomia after seizures induced by maximal electroshock in Wistar rats.

BACKGROUND: Cardiac dysfunction is one of the possible causes of sudden unexpected death in epilepsy (SUDEP). Therefore, it was the objective of this study to evaluate the cardiac and electrocardiographic parameters after seizures induced by maximal electroshock (MES) in Wistar rats. METHODS: Electroshock seizures were induced in Wistar rats through a pair of ear-clip electrodes (10 mA at a frequency of 60 Hz applied for one second). In vivo electrocardiography (ECG) was performed in awake animals for analysis of heart rate variability (HRV) and cardiac rhythm. Ex vivo the Langendorff technique was used to analyze cardiac function and observe the incidence and severity of reperfusion arrhythmias. RESULTS: Convulsive seizures triggered by MES induced profound abnormalities in cardiac rhythm with serious electrocardiographic changes including ST-elevation, bundle branch block, atrioventricular nodal escape rhythm and premature ventricular contractions. ECG analysis demonstrated a consistent period of postictal bradyarrhythmia resulting in a transiently irregular cardiac rhythm with highly variable and prolonged QRS complexes and RR, PR, QT and QTc intervals. HRV evaluation revealed an increase in the high-frequency range of the power, suggesting an imbalance in the autonomic control of the heart with a postictal enhancement of parasympathetic tone. In addition, we observed in isolated heart a decrease in systolic tone and an increase in the coronary flow, heart rate and incidence/duration of ischemia-reperfusion arrhythmias. CONCLUSION: The present study supports a relationship betweem seizures, cardiac dysfunction and cardiac arrhythmias. This relationship may partially account for the occurrence of SUDEP.

Antiarrhythmogenic effects of a neurotoxin from the spider Phoneutria nigriventer.

In this study, we evaluated the effects of PhKv, a 4584 Da peptide isolated from the spider Phoneutria nigriventer venom, in the isolated rat heart and in isolated ventricular myocytes. Ventricular arrhythmias were induced by occlusion of the left anterior descending coronary artery for 15 min followed by 30 min of reperfusion. Administration of native PhKv (240 nM) 1 min before or after reperfusion markedly reduced the duration of arrhythmias. This effect was blocked by atropine, thereby indicating the participation of muscarinic receptors in the antiarrhythmogenic effect of PhKv. Notably, recombinant PhKv (240 nM) was also efficient to attenuate the arrhythmias (3.8 ± 0.9 vs. 8.0 ± 1.2 arbitrary units in control group). Furthermore, PhKv induced a significant reduction in heart rate. This bradycardia was partially blunted by atropine and potentiated by pyridostigmine. To further evaluate the participation of acetylcholine on the PhKv effects, we examined the release of this neurotransmitter from neuromuscular junctions. It was found that Phkv (200 nM) significantly increased the release of acetylcholine in this preparation. Moreover, PhKv (250 nM) did not cause any significant change in action potential or Ca(2+) transient parameters in isolated cardiomyocytes. Altogether, these findings show an important acetylcholine-mediated antiarrhythmogenic effect of the spider PhKv toxin in isolated hearts.

Dysautonomia due to reduced cholinergic neurotransmission causes cardiac remodeling and heart failure.

Overwhelming evidence supports the importance of the sympathetic nervous system in heart failure. In contrast, much less is known about the role of failing cholinergic neurotransmission in cardiac disease. By using a unique genetically modified mouse line with reduced expression of the vesicular acetylcholine transporter (VAChT) and consequently decreased release of acetylcholine, we investigated the consequences of altered cholinergic tone for cardiac function. M-mode echocardiography, hemodynamic experiments, analysis of isolated perfused hearts, and measurements of cardiomyocyte contraction indicated that VAChT mutant mice have decreased left ventricle function associated with altered calcium handling. Gene expression was analyzed by quantitative reverse transcriptase PCR and Western blotting, and the results indicated that VAChT mutant mice have profound cardiac remodeling and reactivation of the fetal gene program. This phenotype was attributable to reduced cholinergic tone, since administration of the cholinesterase inhibitor pyridostigmine for 2 weeks reversed the cardiac phenotype in mutant mice. Our findings provide direct evidence that decreased cholinergic neurotransmission and underlying autonomic imbalance cause plastic alterations that contribute to heart dysfunction.

Efeitos agudos da aplicação endovenosa do cogumelo-do-sol (Agaricus blazei Murill) sobre a pressão arterial média e a freqüência cardíaca de ratos anestesiados / Acute effects of the endovenous application of the royal mushroom (Agaricus blazei Murill) on mean arterial pressure and heart rate of anesthetized rats

Este trabalho objetivou verificar os efeitos agudos da aplicação endovenosa do extrato aquoso do Agaricus blazei Murill sobre a pressão arterial média (PAM) e a freqüência cardíaca (FC) de ratos anestesiados. Foram usados Rattus novergicus albinus, n = 6, anestesiados com tiopental sódico, traqueostomizados e canulados através da veia jugular e da artéria carótida. Foram injetadas as concentrações de 1,25 mg/kg, 2,50 mg/kg e 5,00 mg/kg do extrato aquoso em volume de 0,2 mL. A PAM foi registrada com um sistema Biopac, modelo MP100, e a FC com um eletrocardiógrafo ECG-4 Funbec. Os resultados foram obtidos no controle e nos tempos 15, 30, 45, 60 e 120s após a aplicação dos extratos. Os valores foram expressos em média ± EPM e analisados estatisticamente pelos testes "t" de Student-Newman-Keuls e Tukey (p<0,05). O extrato aquoso de A. blazei reduziu a PAM de maneira concentração dependente, sendo que a concentração de 1,25 mg/kg não provocou modificações significativas na PAM nem na FC; a de 2,50 mg/kg provocou diminuição da PAM aos 15s (p<0,01) e da FC aos 30s (p<0,001) e a de 5,00 mg/kg diminuiu a PAM aos 15s (p<0,001) e a FC aos 15 e 30s (p<0,001).

The aim of this paper was to verify the acute effects of the endovenous application of the aqueous extract of Agaricus blazei Murill on mean arterial pressure and heart rate of the anesthetized rats. The injected concentrations were: 1.25 mg/kg, 2.50 mg/kg and 5.00 mg/kg, in volume of 0.2 mL. The rats were anesthetized with sodium thiopental and, after tracheotomy, both jugular vein and carotid artery were cannulated. The MAP was recorded with a Biopac System, model MP100. The HR was obtained with an electrocardiograph model ECG-4 (Funbec). The records were made in the control and 15, 30, 45, 60 and 120s after the application of the different concentrations of the extracts. The values were expressed by mean ± SEM and by paired "t"-Student-Newman-Keuls and Tukey tests (p<0.05). The aqueous extract of the A. blazei decreased the MAP of dependent manner. The concentration of 1.25 mg/kg did not provoke effects; 2.50 mg/kg provoked decrease of the PAM at 15s (p<0.01) and of the HR at 30s (p<0.001) and 5.00 mg/kg provoked decrease of the PAM at 15s (p<0.001) and of the HR at 15 and 30s (p<0.001).