Effects of isorhynchophylline on heart conduction function in anesthetized rabbits

Isorhynchophylline (Isorhy) is one of the major alkaloids extracted from Chinese traditional medicine, Uncaria rhynchophylla (Miq.) Jackson. By using atrial pacing and recording His bundle electrograms, effects of Isorhy on heart conduction function in anesthetized rabbits were observed. The maximal inhibitory response occurred in 5 min after Isorhy 8 mg �� kg-1 iv and disappeared during 30-120 min. Isorhy, infusion 0-16 mg �� kg-1 at a constant rate, dose-dependently decreased heart rate, prolonged sinus node recovery time, and P-R, A-H, H-V intervals. The depression of Isorhy on heart rate and atrioventricular conduction are marked. Isoprenaline partially antagonized these inhibitory effects of Isorhy, but atropine could not do.