Endorphin
A class of endogenous opioid peptides produced by the central nervous system and pituitary gland that reduce pain perception and produce feelings of wellbeing. Beta-endorphin is the most studied member, acting primarily on mu opioid receptors. Endorphins are the body's natural counterparts to opioid drugs.
Technical Context
Beta-endorphin (31 aa) is the most pharmacologically significant endorphin, derived from POMC processing in the anterior pituitary (corticotrophs) and hypothalamus. It is co-released with ACTH during stress (explaining the analgesic and euphoric effects of the stress response). Beta-endorphin is a full agonist at mu opioid receptors with 18-33 times the analgesic potency of morphine. Other endorphins (alpha, gamma, sigma) are shorter fragments with different activities. The endorphin system illustrates the concept of endogenous peptide analgesia — the body's own pain management system that therapeutic opioids and peptide drugs like difelikefalin interact with (albeit difelikefalin through the kappa rather than mu pathway).