Further Observations on the Action of Adenosine on the Perfused Heart

Abstract

In an earlier study 3 of the action of adenosine on the perfused heart of the rabbit it was believed that this substance improved the beat of the heart, although records which were obtained by attaching a lever to the ventricle never showed an increase in height of contraction. There was no change in amplitude provided the rate was kept constant. When the normal rhythm was slowed by adenosine there was a decrease in height of contraction due, as Dale 1 has shown, solely to the slowing. Drury 2 later reported that on rare occasions adenosine caused a slight increase in the mechanogram, which usually occurred when the heart was in poor condition, and the coronary outflow was considerably increased by the injection. Wedd and Fenn 4 found that when adenosine was added to a bath in which was suspended an auricle or a strip of heart muscle, either cold-blooded or mammalian, depressed contractility invariably resulted. At times when injected into the rhythmically stimulated perfused heart adenosine has been seen to depress excitability and cause a short period of 2:1 response (Fig. 1). From observations of the effect on the muscle itself, it has been concluded that if adenosine were to improve the beat of the heart it must do so by its vasodilator action.

A series of experiments has recently been undertaken to study the influence of certain choline derivatives on the heart. The technique was similar to that previously employed. The hearts of 35 rabbits and of 7 cats have been perfused. In each experiment from one to 3 injections of adenosine were made to test the reactivity of the coronary vessels. These injections were usually given toward the end of the experiment when the heart was no longer in good condition and the coronary outflow had fallen off.