Endomorphin 1 (EM1)

Endomorphins are two endogenous opioid peptides. Endomorphin-1 (Tyr-Pro-Trp-Phe-NH₂) and endomorphin-2 (Tyr-Pro-Phe-Phe-NH₂) are tetrapeptides with the highest known affinity and specificity for the opioid receptor. Endomorphin-1 is located in the nucleus of the solitary tract, the periventricular hypothalamus, and the dorsomedial hypothalamus, where it is found within histaminergic neurons and may regulate sedative and arousal behaviors. Endomorphin-1 (EM-1) is a recently isolated endogenous peptide having potent analgesic activity and high affinity and selectivity for the mu-opioid receptor. Endomorphin-1 activates G proteins and inhibits adenylyl cyclase activity in membrane preparations from cells stably expressing the mu opioid receptor, an effect reversed by the mu receptor antagonist CTAP. However, endomorphin-1 appears to have no influence on cells stably expressing the delta opioid receptor.