Morphiceptin

Morphiceptin is a tetrapeptide (Tyr-Pro-Phe-Pro-NH₂) that is a selective μ-opioid receptor agonist. It is derived from β-casomorphin and has over 1,000 times selectivity for μ- over δ-opioid receptors. When injected intracerebroventricularly (into the ventricular system of the brain), morphiceptin had an analgesic ED₅₀ of 1.7 nmol per animal. The analgesic effects of morphiceptin were reversed by naloxone, meaning that the analgesic effect is mediated by the μ-opioid receptor.