The effect of nifedipine on the sinus and atrioventricular node of the dog heart after beta-adrenergic receptor blockade.

The effect of nifedipine (BAY 1040), a calcium-antagonistic inhibitor of the electromechanical coupling process was tested on atrioventricular conduction and refractoriness of the dog heart in situ by means of His-bundle electrography and programmed electrical stimulation. The animals were anaesthetized with sodium pentobarbital. As the basic effects of the compound can be altered by release of catecholamines from sympathetic nerves of heart and vessels, the dogs were pretreated with acebutolol, a beta-adrenergic receptor blocking agent, which decreased heart rate and prolonged atrioventricular conduction and refractoriness. Nifedipine 1,6 and particularly 30 microgram/kg body weight increased the heart rate and decreased atrioventricular conduction time during atrial pacing, whereas atrioventricular conduction time during sinus rhythm and atrioventricular refractoriness were only affected by nifedipine 30 microgram/kg. In this respect, nifedipine differs distinctly from another calcium antagonistic compound, verapamil.