Leu-enkephalin is an endogenous opioid peptide that acts as an agonist at μ-opioid receptors (μORs) and δ-opioid receptors (δORs). Met-enkephalin exhibits neuromodulatory, antinociceptive/analgesic, and gastrointestinal motility modulating activities. Like other endogenous opioids, leu-enkephalin modulates expression of opioid receptors and plays a role in reward/reinforcement signaling. Leu-enkephalin increases pain thresholds in vivo and inhibits gastrointestinal muscle contractility in other animal models, inhibiting motility and gastric emptying.
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