Leucine-enkephalin as a modulator of neurotransmission in cat lower esophageal sphincter

Interactions between cholinergic, adrenergic and noncholinergic nonadrenergic inervation in lower esophageal sphincter determine the character of smooth muscle responses to field electrical stimulation. The neurogenic responses of muscle strips from the proximal (LES1), middle (LES2) and lower (LES3) parts of lower esophageal sphincter (LES) are: primary relaxation and secondary contraction in LES1, relaxation in LES2 and primary contraction followed by primary relaxation in LES3. Leucin-enkephalin in concentration of 0.1 microM and 1 microM leads to: increasing of amplitude of the primary relaxation and inhibition of secondary contraction in LES1, enhancing of amplitude of relaxation in LES2 and converts the response in LES3 from two into three component one so that the primary relaxation and the primary contraction are followed by secondary poststimulation relaxation. These effects are most probably the results of inhibition of noradrenaline and acetylcholine releasing under the influence of leucine-enkephalin and of alteration of the correlation between the neurotransmitters. It is assumed that Leucine-enkephalin operates in LES as a neuromodulator inhibiting both the adrenergic and cholinergic neurotransmission.