ANTIARRHYTHMIC ACTION OF RILMENIDINE ON ADRENALINE-INDUCED ARRHYTHMIAVIA CENTRAL IMIDAZOLINE RECEPTORS IN HALOTHANE-ANESTHETIZED DOGS

1 To elucidate the role of central imidazoline receptors in the genesi s of adrenaline-induced arrhythmias under halothane anaesthesia, we in vestigated the effects of rilmenidine, a selective agonist at imidazol ine receptors, on this type of arrhythmia in dogs. Rilmenidine (1, 3, 10 mu g kg(-1), i.v.) did not affect basal haemodynamic parameters (he art rate and blood pressure), but dose-dependently inhibited adrenalin e-induced arrhythmias under halothane anaesthesia. 2 Although, rilmeni dine has a weak affinity for alpha(2)-adrenoceptors, pretreatment with idazoxan (10 mu g kg(-1), intracisternally i.c.), an imidazoline rece ptor antagonist which has also alpha(2)-adrenoceptor blocking potency, blocked the antiarrhythmic effect of rilmenidine (10 mu g kg(-1) i.v. ). In contrast, pretreatment with rauwolscine (20 mu g kg(-1), i.c.), a classical alpha(2)-adrenoceptor antagonist with little affinity for imidazoline receptors, did not affect the effect of rilmenidine (10 mu g kg(-1), i.v.). Furthermore, bilateral vagotomy completely blocked t he antiarrhythmic action of rilmenidine (10 mu g kg(-1), i.v.). 3 It i s suggested that the antiarrhythmic action of rilmenidine is due to th e activation of central imidazoline receptors and that vagal tone is c ritical for this action of rilmenidine.