Caffeine alters plasma adenosine levels

Since the delights of tea were discovered by Emperor Shen Nung in 2737 BC , methylxanthines have been common in the human diet. Today, the methylxanthine caffeineis the most commonly consumed drug in the world 1 , with actions mediated primarily by adenosine receptor blockade 2 . We now report that caffeine increases plasma adenosine concentration in a manner that is dose-related, saturable, and mimicked by peripheral adenosine receptor blockade. Opposite effects are seen after caffeine withdrawal, indicative of a receptor-mediated effect.