Abstract
In blood-perfused isolated canine atrium preparations, single injections of dibutyryl cyclic AMP at a dose range of 1 to 30 mg were made into the cannulated sinus node artery. At doses above 3 mg, dibutyryl cyclic AMP induced a biphasic chronotropic and inotropic response; there was a slight and rapid negative chronotropic and inotropic response, followed by a long-lasting positive chronotropic and inotropic response. The induction of the positive effects was slow, and it took 4 to 8 min to reach a maximum response. These effects continued 20 to 60 min. The ratios of the positive inotropic effects positive chronotropic effect were very similar to those induced by norepinephrine. In this study, it was confirmed that a large dose of dibutyryl cyclic AMP induced a positive chronotropic and inotropic effect on the canine atrium, and the pos-sibility was discussed that cyclic AMP may be involved in the effects of beta-adrenergic amines on the pacemaker and contractile process of the heart.
