endorphin /endôr″fin/ [Gk, endon + morphe, shape] , one of the three groups of endogenous opioid peptides composed of many amino acids, elaborated by the pituitary gland and other brain areas, and acting on the central and the peripheral nervous systems to reduce pain. There are three known, designated alpha, beta, and gamma. Beta-endorphin has been isolated in the brain and in the GI tract and seems to be the most potent of the endorphins. Beta-endorphin is composed of 30 amino acids that are identical to part of the sequence of 91 amino acids of the hormone beta-lipotropin, also produced by the pituitary gland. Behavioral tests indicate that beta-endorphin is a powerful analgesic in humans and animals. Brain-stimulated analgesia in humans releases beta-endorphin into the cerebrospinal fluid. Compare enkephalin.
