[Theophylline-induced changes in the presynaptic effects of adenosine, baclofen, clofelin and morphine in the myenteric plexus of the guinea pig].

The experiments on the isolated guinea-pig ileum have shown that the contractions caused by low frequency transmural stimulation are decreased by adenosine, baclofen, clofelin and morphine. Theophylline is a competing antagonist of adenosine and a noncompeting antagonist of baclofen, clofelin and morphine. The effects of the latter are not altered by 1,3-dipropyl-8-phenylxanthine suppressing adenosine effects. It is concluded that presynaptic effects of baclofen, clofelin and morphine depend on cAMP level in cholinergic neurons of myenteric plexus.