ADENOSINE SYSTEM IN THE HEART

The adenosine system in the heart consists of three components: 1) a mechanism for formation, 2) a receptor-effector coupling system, and 3) a mechanism for degradation. Selective pharmacological modification of this system with drugs such as nucleoside uptake inhibitors and adenosine receptor antagonists results in predictable changes in the cardiac actions of adenosine. The actions of adenosine in the heart are mediated by specific cell surface receptors of at least two subtypes. The A1 receptor subtype mediates the actions of adenosine that decrease O2 consumption (e.g., slowing of heart rate), whereas the A2 receptor subtype mediates the well-known coronary vasodilatory effects of adenosine and thereby increases O2 supply. Adenosine formation is increased when O2 demand exceeds O2 supply. Thus, in the heart adenosine may serve as a negative-feedback signal to adjust myocardial balance between O2 supply and consumption. In this brief review we describe the cardiovascular effects of adenosine, its mechanism(s) of action, and metabolism.