Effects of nifedipine, a potent calcium-antagonistic coronary vasodilator, on atrioventricular conduction and blood flow in the isolated atrioventricular node preparation of the dog.

The effects of the calcium-antagonist nifedipine on atrioventricular (A-V) conduction and blood flow were investigated in comparison with those of verapamil by the use of the isolated, arterially blood-perfused A-V node preparation of the dog. Single injections of 0.3--30 mug of nifedipine and verapamil into the A-V node artery produced a dose-related increase in the A-V conduction time and at 30 mug the two drugs caused second degree block of A-V conduction. The results are compatible with the hypothesis that a slow calcium channel plays an important role in excitation of A-V nodal cells. The rate of blood flow through the A-V node artery was about 10 times more sensitive to nifedipine than was the A-V conduction time and increased in a dose-related manner. In contrast, an increase in blood flow rate by verapamil occurred in almost the same dose range as did impairment of A-V conduction. This indicates that the action of nifedipine is more pronounced on coronary smooth muscle cells than on the A-V nodal cells.