The Effects of Adenosine on Coronary Conductance, Cardiac Dynamics and Myocardial Metabolism of the Isolated Perfused Cat Heart

The effects of a 5-min infusion of adenosine (2 μg/g heart wet weight/min) in isolated perfused cat hearts (Langendorff preparation) on coronary conductance (coronary flow/perfusion pressure) and cardiac dynamics and metabolism were investigated under two experimental conditions: (1) at constant perfusion pressure (n = 11), and (2) at constant perfusion volume (n = 10). Adenosine increased coronary conductance significantly under both experimental conditions. In the experiments with constant perfusion pressure this increase in coronary conductance was accompanied by an increase in cardiac activity, as evidenced by the significant increase in heart rate and in left ventricular systolic pressure and its maximum rate of pressure rise (dp/dt max.). Concomitant homodirectional changes in myocardial O2 consumption, free CO2 and H+ release and glucose uptake were observed in this group. In the group with constant perfusion volume, on the other hand, the increase in coronary conductance resulting from the significant fall in perfusion pressure led to a significant decrease in cardiac activity and, consequently, a decrease in myocardial O2 consumption, free CO2 and H+ release. Although the glucose uptake was also increased, lactate release remained unchanged under both experimental conditions.