Adenosine and pain

© 2003 by Marcel Dekker, Inc. I. INTRODUCTION The endogenous nucleoside adenosine performs multiple functions within the body. It can be progressively phosphorylated to generate the high-energy molecules adenosine mono-, di-, and triphosphate (AMP, ADP, and ATP), and from ATP may be further modified to generate the intracellular second-messenger cyclic-AMP (cAMP). More recently, it has become apparent that adenosine also acts as a chemical-signaling agent or local hormone in its own right. The diversity of responses that are mediated by adenosine in this signaling context is also wide, but as a rule, its effects are generally inhibitory: for example, it reduces heart rate, inhibits fatty acid release from adipocytes, down-regulates the immune response, and acts as a central nervous system (eNS) depressant. The latter response is particularly relevant in understanding the role of adenosine in the physiology of pain.