Endorphins

Endorphins (contracted from endogenous morphine)

Opioid peptides in the brain were first discovered in 1973 by investigators at the University of Aberdeen, John Hughes and Hans Kosterlitz. They isolated "enkephalins" (from the Greek εγκέφαλος, cerebrum) from pig brain, identified as Met-enkephalin and Leu-enkephalin.^{[8][9][10][11]} This came after the discovery of a receptor that was proposed to produce the pain-relieving analgesic effects of morphine and other opioids, which led Kosterlitz and Hughes to their discovery of the endogenous opioid ligands.^[11] Research during this time was focused on the search for a painkiller that did not have the addictive character or overdose risk of morphine.^[11][12]

Rabi Simantov and Solomon H. Snyder isolated morphine-like peptides from calf brain.^[13] Eric J. Simon, who independently discovered opioid receptors, later termed these peptides as endorphins.^[14] This term was essentially assigned to any peptide that demonstrated morphine-like activity.^[15] In 1976, Choh Hao Li and David Chung recorded the sequences of α-, β-, and γ-endorphin isolated from camel pituitary glands for their opioid activity.^[16][17] Li determined that β-endorphin produced strong analgesic effects.^[18] Wilhelm Feldberg and Derek George Smyth in 1977 confirmed this, finding β-endorphin to be more potent than morphine. They also confirmed that its effects were reversed by naloxone, an opioid antagonist.^[19]

Studies have subsequently distinguished between enkephalins, endorphins, and endogenously produced morphine,^[20][21] which is not a peptide. Opioid peptides are classified based on their precursor propeptide: all endorphins are synthesized from the precursor proopiomelanocortin (POMC), encoded by proenkephalin A, and dynorphins encoded by pre-dynorphin.^[12][22]

Etymology

The word endorphin is derived from ἔνδον /

Types

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The class of endorphins consists of three

α-endorphin and γ-endorphin are primarily found in the anterior and intermediate pituitary.[25] While β-endorphin is studied for its opioid activity, α-endorphin and γ-endorphin both lack affinity for opiate receptors and thus do not affect the body in the same way that β-endorphin does. Some studies have characterized α-endorphin activity as similar to that of psychostimulants and γ-endorphin activity to that of neuroleptics separately.^[25]

Synthesis

Endorphin precursors are primarily produced in the

Noradrenaline has been shown to increase endorphins production within inflammatory tissues, resulting in an analgesic effect;^[36] the stimulation of sympathetic nerves by electro-acupuncture is believed to be the cause of its analgesic effects.^[37]

Mechanism of action

Endorphins are released from the pituitary gland, typically in response to pain, and can act in both the

Endorphins play a major role in the body's inhibitory response to pain. Research has demonstrated that meditation by trained individuals can be used to trigger endorphin release.^{[39][failed verification]} Laughter may also stimulate endorphin production and elevate one's pain threshold.^[40]

Endorphin production can be triggered by vigorous