Activation of phosphatidylinositol 3-kinase/Akt signaling pathway and endogenous nitric oxide are needed for the antiarrhythmic effect of centrally administered rilmenidine

Activation of imidazoline receptors in the central nervous system has protective effect on several types of arrhythmias. We demonstrated that centrally administered rilmenidine, a selective imidazoline receptor agonist, prevented adrenaline-induced arrhythmias during halothane anaesthesia. However, detailed myocardial signaling of the antiarrhythmic effect remains to be unexplored. The present study was designed to examine a role of pertussis toxin-sensitive G protein, phosphatidylinositol 3-kinase/Akt signaling pathway and endogenous nitric oxide in the antiarrhythmic effect of rilmenidine. Male Sprague–Dawley rats were anaesthetized with halothane and monitored continuously for arterial blood pressure and premature ventricular contractions. The arrhythmogenic dose of adrenaline was defined as the smallest dose producing 3 or more premature ventricular contractions within 15-s period. Firstly, we confirmed that centrally administered rilmenidine prevented adrenaline-induced arrhythmias during halothane anaesthesia and examined the effect of pertussis toxin, wortmannin (a phosphatidylinositol 3-kinase inhibitor), and nitro-l-arginine methyl ester (l-NAME) (a specific nitric oxide synthesis inhibitors), on the antiarrhythmic effect of rilmenidine. We also performed Western blot analysis to determine phosphorylation of Akt and glycogen synthase kinase 3β, a direct Akt downstream target, following the central administration of rilmenidine. The antiarrhythmic effect of rilmenidine was significantly inhibited by pertussis toxin, wortmannin and l-NAME. Rilmenidine increased Akt and glycogen synthase kinase 3β phosphorylation (28 ± 13% and 32 ± 13%, respectively), and this action was abolished by wortmannin. The present results demonstrated that pertussis toxin-sensitive G protein, phosphatidylinositol 3-kinase-Akt-GSK3β signaling pathway and endogenous nitric oxide may play a key role in antiarrhythmic effect of centrally administered rilmenidine.