The bladder uroepithelium transmits information to the underlying nervous and musculature systems, is under constant cyclical strain, expresses all four adenosine receptors (A 1, A2A, A2B, and A3), and is a site of adenosine production. Although adenosine has a welldescribed protective effect in several organs, there is a lack of information about adenosine turnover in the uroepithelium or whether altering luminal adenosine concentrations impacts bladder function or overactivity. We observed that the concentration of extracellular adenosine at the mucosal surface of the uroepithelium was regulated by ecto-adenosine deaminase and by equilibrative nucleoside transporters, whereas adenosine kinase and equilibrative nucleoside transporters modulated serosal levels. We further observed that enriching endogenous adenosine by blocking its routes of metabolism or direct activation of mucosal A 1 receptors with 2-chloro-N 6 -cyclopentyladenosine (CCPA), a selective agonist, stimulated bladder activity by lowering the threshold pressure for voiding. Finally, CCPA did not quell bladder hyperactivity in animals with acute cyclophosphamideinduced cystitis but instead exacerbated their irritated bladder phenotype. In conclusion, we find that adenosine levels at both surfaces of the uroepithelium are modulated by turnover, that blocking these pathways or stimulating A1 receptors directly at the luminal surface promotes bladder contractions, and that adenosine further stimulates voiding in animals with cyclophosphamide-induced cystitis.cyclophosphamide-induced cystitis; voiding ADENOSINE IS A UBIQUITOUSLY occurring nucleoside that is important for the homeostasis of diverse organ systems including the kidneys, heart, lungs, and brain (20,46,55). It is found both intracellularly and in the extracellular space, and its concentration in these compartments is dependent on its biogenesis and turnover (43,44). The intracellular pool of adenosine is synthesized de novo by the hydrolysis of S-adenosylmethionine or is generated from the nucleotidase-dependent breakdown of ATP to ADP to AMP to adenosine. The extracellular pool of adenosine is also formed from the hydrolysis of ATP by ecto-nucleotidases or alkaline phosphatases or by metabolism of cAMPs to AMPs to adenosine. In addition, sodiumcoupled concentrative or equilibrative nucleoside transporters shuttle adenosine in a concentration-dependent manner between the intracellular and extracellular compartments (23). The turnover of extracellular and intracellular adenosine is mediated by two enzymes: adenosine deaminase and adenosine kinase, which decrease adenosine by converting it to inosine or AMP, respectively (13,30,32,52).