Adenosine is a ubiquitous, biologically important nucleoside which is a precursor of other biologically active molecules as well as a component of some co-factors. Moreover, it also has its own distinct physiological functions in the central nervous system, the cardiovascular system, the skeletal muscle and the immune system. One of the principal intracellular actions of adenosine is inhibition of the enzyme phosphodiesterase. Extracellular adenosine has specific neuromodulatory actions on dopamine and glutamate.

Adenosine can act either as a hormone by binding to adenosine receptors or as an intracellular modulator after its translocation into the cell by membrane transport proteins. Four adenosine receptor subtypes have been identified. Notably, adenosine receptors are most widely expressed in the brain and the cardiovascular system, but they also are found in the most of the other tissues: respiratory tract, intestine, kidney, skeletal muscle, pituitary gland, uterus and gonads. Adenosine modulates several physiological effects by stimulating specific cell surface receptors.

In addition, adenosine acts as an endogenous regulator of immune and inflammatory processes. Adenosine exerts multifaceted effects on the heart and blood vessels and is involved in the regulation of the renal function. It works as a universal protective agent against hypoxia, ischemia, excitotoxicity, toxicities induced by other substances and trauma. It is also an effective and safe therapeutic medicine for paroxysmal tachycardias in adult and pediatric patients, with basic electrophysiologic properties of slowing conduction in atrioventricular nodes. The measurement of urinary adenosine can contribute to evaluation of renal injury, metabolic disease or severe respiratory failure, as it was found that unfavorable pathophysiologic conditions are associated with appreciable elevation of adenosine.