Antiarrhythmic effects of beta3-adrenergic receptor stimulation in a canine model of ventricular tachycardia

BackgroundBeta3-adrenergic receptor (beta3-AR) stimulation inhibits cardiac contractility.ObjectiveThis study sought to test the hypothesis that beta3-AR stimulation is antiarrhythmic.MethodsWe implanted a radio transmitter for continuous electrocardiogram monitoring in 18 dogs with a tendency for high incidence of spontaneous ventricular tachycardia (VT). Ten of 18 had subcutaneous continuous BRL37344 (beta3-AR agonist) infusion (experimental group) for 1 month. The other dogs were controls. Western blotting studies were performed on tissues sampled from the noninfarcted left ventricular free wall of all dogs that survived the 60-day follow-up period.ResultsPhase 2 VT appeared significantly later in the experimental group than in the control group (P <.05). The number of VT episodes in the experimental group was significantly lower than in the control group during both the first month (0.5 ± 0.95 episodes/day vs. 2.6 ± 2.3 episodes/day) and the second month (0.2 ± 0.2 episode/day vs. 1.2 ± 1.1 episodes/day, P <.05 for both). The experimental group had shorter QTc than control (P <.002). The experimental group had decreased protein levels for sodium calcium exchanger and dihydropyridine receptor, increased beta3-AR expression, without changes in beta1-AR, beta2-AR. The average heart weight and the left ventricular free wall thickness in the experimental group (226 ± 17 g and 15.1 ± 1.2 mm, respectively) was significantly lower than in the control group (265 ± 21 g and 17.4 ± 2.5 mm, respectively, P <.05 for both). There was no difference in the incidences of sudden cardiac death in these 2 groups of dogs.ConclusionBeta3-AR stimulation significantly reduces the occurrence of ventricular tachycardia.