Inhibitory effect of caffeine on the response to carbachol in rat pancreatic acini

1. Caffeine did not affect by itself the amylase release, nor intracellular calcium concentration in rat pancreatic acini. 2. Concentration of caffeine higher than 1 mM inhibited the amylase released in response to the muscarinic agonist carbamylcholine. This inhibition was also seen on the intracellular calcium elevation: 20 mM caffeine inhibited by 80% the calcium elevation in response to 100 microM carbachol. 3. Caffeine also prevented the specific binding of [3H]-N-methylscopolamine ([3H]-NMS) on rat pancreatic muscarinic receptors. 4. We conclude that caffeine behaves as a muscarinic antagonist.