Adenosine and the concept of ‘retaliatory metabolites’

Adenosine can modulate a bewildering array of physiological processes including vascular tone, hormone action, neural function, platelet aggregation and lymphocyte differentiation. To explain this diversity, it has been proposed that adenosine is a hormone or a hormone second messenger. However, its unique mechanism of formation suggests instead that adenosine is a new type of cellular regulator for which the term ‘retaliatory metabolite’ is proposed.