Efeitos antiarritmogênicos da angiotensina-(1-7) em um modelo de arritmias cardíacas in vivo

Abstract

Angiotensin (Ang)-(1-7), a peptide of the renin-angiotensin system, has cardioprotective and antiarrhythmic effects in isolated rat hearts. However, the effects of this peptide on cardiac arrhythmias in vivo and details regarding its mechanisms of action are unknown. The aim of this study was to investigate the effects of Ang-(1-7) on cardiac arrhythmias in vivo and its mechanisms of action. Cardiac arrhythmias were induced in Wistar rats using a combination of halothane (1.5%) and epinephrine (5 to 20g/kg, iv). Electrocardiographic records were made by placing an electrode in each rat limb. A 10-minute period of arrhythmias was followed by an additional 10-minute period of arrhythmias in the presence Ang-(1-7). To analyze the mechanisms of action, we used A-779 [antagonist of Ang-(1-7) receptor], L-NAME (inhibitor of nitric oxide synthases) and DIZE [activator of the ACE2, the main Ang-(1-7)-forming enzyme]. Blood pressure and heart rate were evaluated by a cannula inserted into the femoral artery. Our data showed that Ang-(1-7) significantly reduced cardiac arrhythmias when compared with control [Control: 49±13 and Ang-(1-7): 16±4 arrhythmic events]. This effect was blocked by A-779 and L-NAME, without changes in the hemodynamic parameters. DIZE injection also promoted a significant reduction in the arrhythmic events. To confirm these in vivo antiarrhythmic effects of Ang-(1-7), ventricular cardiomyocytes were isolated from mice and used in three experimental techniques (analysis of contractility, patch clamp and confocal microscopy). Cardiomyocytes were perfused with a solution of halothane plus isoproterenol in order to trigger arrhythmias. Contractility experiments confirmed that Ang-(1-7) and DIZE significantly decrease the amount of arrhythmias without changing the contraction force. To evaluate if this reduction in arrhythmias was associated to alterations in the excitability of cardiomyocytes, we analyzed the action potential. The results showed a shortening of the action potential and a decrease in the resting potential of cardiomyocytes treated with Ang-(1-7) and DIZE. These actions can be considered as cardioprotective effects. Finally, we analyzed the involvement of calcium in these effects using confocal microscopy and it was observed that Ang-(1-7) and DIZE decreased the amount of calcium waves. There were no significant changes in the amplitude of the calcium transient, but considering the transient decay, we observed a significant reduction in this parameter only in cells incubated with Ang-(1-7). Altogether, these results indicate that Ang-(1-7) reduces cardiac arrhythmias in vivo through activation of Mas and nitric oxide release. This effect was confirmed by DIZE. These data suggest that Ang-(1-7) and DIZE might be a feasible therapeutic agent to treat arrhythmogenic syndromes.