Enkephalins modulate inhibitory neuromuscular transmission in circular muscle of human colon via delta‐opioid receptors.

Abstract

1. A sucrose‐gap technique was used to investigate the neuromodulatory actions of enkephalins on non‐adrenergic, non‐cholinergic inhibitory junction potentials (IJPs) in the circular muscle of the human large intestine. 2. The native enkephalins, [Leu5]enkephalin (LENK) and [Met5]enkephalin (MENK) caused a concentration‐dependent reduction in amplitude of IJPs without a significant effect on the smooth muscle membrane. 3. The actions of LENK and MENK were mimicked by the delta‐selective opioid receptor agonists [D‐Pen2, D‐Pen5]enkephalin (DPDPE) and [D‐Ala2, D‐Leu5]enkephalin (DADLE). 4. The actions of LENK, MENK and DPDPE were antagonized to similar extents by the delta‐selective opioid rec..