Adenosine A1 receptors determine effects of caffeine on total fluid intake but not caffeine appetite

Adenosine A1 receptor wild-type (+/+) and knockout (−/−) mice were used to elucidate the role of adenosine A1 receptors in caffeine self-administration in a two-bottle choice test and in the effect of caffeine on total fluid intake and plasma renin concentration. With access to water only, adenosine A1 receptor −/− mice showed greater basal fluid intake and greater plasma renin concentration than +/+ mice. Free access to both water and a caffeinated solution (30 mg/100 ml) for 14 days increased total fluid intake only in adenosine A1 receptor +/+ mice (by 23 ± 3%), and both total fluid intake and plasma renin concentration were no longer different between genotypes. Mean intake of water and caffeinated solution was not different between adenosine A1 receptor +/+ and −/− mice. These data reveal that adenosine A1 receptors do not contribute to caffeine consumption, but determine the effects of caffeine on fluid intake and plasma renin concentration.