The effect of enkephalins on the intramural inhibitory non-adrenergic nerve responses of smooth muscle

The study concerned the effect of enkephalins and naloxone on the inhibitory non-adrenergic nerve responses of the taenia coli and the stomach smooth muscle cells of the guinea pig. Met-enkephalin, leu-enkephalin and D-ala-enkephalin (10(-8)10(-5)M) did not affect the muscle tension or membrane potential measured simultaneously using the sucrose-gap method. Naloxone (5x10(-8)--5x10(-6)M) relaxed the stomach strip, but did not modify the inhibitory junction potential. These results indicate that enkephalins are not involved in the nonadrenergic inhibitory nervous system, except possibly as neuromodulators at an interneuronal synaptic level.