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 world1, with actions mediated primarily by adenosine receptor blockade2. 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.