Caffeine inhibits forskolin-stimulated cyclic AMP accumulation in rat brain.

Caffeine potently inhibited forskolin-stimulated cyclic AMP accumulation in slices of rat cerebral cortex. The IC50 for this inhibition was 21 +/- 2.9 microM, and 200 microM caffeine almost completely blocked the forskolin response. Theophylline which is a behavioural stimulant mimicked the effect of caffeine. However, there was only a slight inhibition of the forskolin response by theobromine and IBMX (3-isobutyl-1-methylxanthine), both of which lack behavioral stimulant effects.