Adenosine infusion inhibits adenosine-induced cardiac actions but enhances acetylcholine-induced actions in isolated dog atria.

Using isolated, blood-perfused canine atrial preparations, adenosine was continuously administered at various infusion rates into the cannulated sinus node artery. Adenosine induced negative chrono- and inotropic effects in an infusion-rate related manner. The inotropic responses to the adenosine infusion apparently faded but the chronotropic responses did not. Effects of a bolus injection of adenosine, acetylcholine (ACh), or norepinephrine and effects of intracardiac autonomic nerve stimulation (ICNS) were examined before and during the adenosine infusion. During the adenosine infusion, adenosine-induced effects were significantly reduced but ACh-induced ones were significantly potentiated, and the norepinephrine-induced effects were slightly depressed. ICNS readily induced negative and positive chrono- and inotropic responses which were blocked by atropine and propranolol. These negative responses were enhanced but positive ones were slightly but insignificantly depressed during the adenosine infusion. From these results, it is concluded that adenosine infusion (1) produces a stable continuous bradycardia but in the developed tension an initial decrease is followed by a gradual recovery response showing the fade phenomenon, (2) causes an acute desensitizing action on a subsequent bolus dose of adenosine, and (3) induces a weak antiadrenergic effect, while enhancing cholinergic effects in isolated canine atria.