Adenosine--a physiological or pathophysiological agent?

This minireview briefly summarizes the evidence that adenosine, acting on four G-protein coupled receptors, can play physiological roles, but is also critically involved in pathological processes. The factors that decide which of these is the more important in a specific cell or organ are briefly summarized. The fact that drugs that target adenosine receptors in disease will also hit the physiological processes will make drug development more tricky.