Cardiovascular effects of dibutyryl cyclic AMP and milrinone under right heart bypass in anesthetized dogs.

To compare the cardiovascular effects of dibutyryl cyclic AMP (DBcAMP) and milrinone, we used the right heart bypass method in intact anesthetized dogs. The preload of the left ventricle was maintained constant throughout the experiment. Therefore, the effects of DBcAMP and milrinone on cardiac contractility and afterload of the left ventricle were investigated respectively without preload influence. DBcAMP and milrinone exhibited marked positive chronotropic-, positive inotropic-, vasodilative- and diuretic-activity. DBcAMP expressed these effects gradually and continuously, whereas milrinone expressed its pharmacological actions rapidly, but for a short duration of time. Both the afterload-reducing and the cardiac contractile force-enhancing activities of DBcAMP were longer lasting than those of milrinone. Mean arterial pressure was not altered by DBcAMP infusion, whereas it was increased significantly (p < 0.05) by milrinone infusion. The results of this study suggested that DBcAMP appeared to be indicated when there is a need to increase cardiac output by reducing afterload and increasing cardiac contractile force gradually and continuously. On the other hand, milrinone would seem to be indicated when the goal is to raise blood pressure rapidly and to increase cardiac output simultaneously.