Positive dromotropic effect of dibutyryl cyclic adenosine 3',5'-monophosphate on the atrioventricular node.

The effect of atrioventricular (A-V) conduction of N6-2'-0-dibutyryl cyclic 3',5'-adenosine monophosphate (dibutyryl cyclic AMP) was investigated in comparison with those of norepinephrine, cyclic 3',5'-adenosine monophosphate (cyclic AMP), adenosine-5'-monophosphate (5'-AMP), and adenosine by the use of the isolated, blood-perfused A-V node preparation of the dog. Single injections of dibutyryl cyclic AMP (3-300 micronmol) and norepinephrine (0.1-1 nmol) into the posterior septal artery of the preparation (the upper part of the A-V node is mainly perfused through this artery) produced a dose-dependent decrease in the A-V conduction time. The time to the peak effect and the duration of the effect of dibutyryl cyclic AMP were much longer than with norepinephrine. The positive dromotropic effect of dibutyryl cyclic AMP was resistant to the beta-adrenoceptor blocking action of propranolol. Unlike dibutyryl cyclic AMP, cyclic AMP (above 30 nmol), 5'-AMP and adenosine (above 1 nmol) injected into the posterior septal artery prolonged the A-V conduction time in a dose-dependent manner. The results indicate that dibutyryl cyclic AMP has a mode of action on A-V nodal cells which differs distinctly from that of either norepinephrine or cyclic AMP, 5'-AMP, and adenosine.