Endogenous opiate receptor ligand: electrically induced release in the guinea pig ileum.

Opiate receptors mediate the electrically evoked inhibition of the myenteric plexus-longitudinal muscle preparation of the guinea pig ileum. The electrically induced activation of the opiate receptor was produced by a prolonged simulation at 10 hertz and provides the first evidence that an endogenous opiate receptor ligand is released by nerve stimulation. The specificity of the phenomenon was demonstrated by the reversal obtained with the narcotic antagonists naloxone, naltrexone, and GPA 1843; GPA 1847, the (+)-isomer of 1843, did not cause reversal. The model system described should be useful for the study of the storage, synthesis, and release of endorphins.