Role of adrenergic alpha-receptors in regulation of acetylcholine release evoked by distension of guinea pig ileum.

The significance of adrenergic nerves in the regulation of acetylcholine (ACh) release evoked by distension of the guinea pig ileum was evaluated by pharmacological manipulations. ACh release was measured by bioassay. Release in response to distension was completely abolished by epinephrine and norepinephrine. Tyramine also suppressed the distension-evoked ACh release, while dopamine was ineffective. The release of ACh in the anal segment, adjacent to the distended part, was abolished by epinephrine and norepinephrine. Dibenamine and phentolamine abolished ACh release anal to the distension, but augmented release orally, while dichloroisoproterenol and propranolol were ineffective. The present results give direct evidence that adrenergic nerves modulate cholinergic transmission in the myenteric plexus through alpha-receptors.