Endorphins, molecules produced by the pituitary and hypothalamus glands to produce pain relief and a sense of well-being. The name derives from “endogenous morphine,” meaning internally produced morphine. A very appropriate description, because the identification of these compounds stemmed from the discovery that that molecules isolated from opium, such as morphine, provided pain relief by stimulating receptors on nerve cells. Receptors are specific protein molecules that are configured to bind to opiates. But why should the body evolve receptors for molecules found in a poppy that grows in the Orient? Perhaps, researchers theorized, morphine just happened to accidentally resemble some sort of molecule that the body itself produced to modulate pain. And in 1975, at the University of Aberdeen, Dr. Hans Kosterlitz and colleague John Hughes found such a molecule. In fact, they found two closely related molecules, both extracted from pigs brains. They called them “enkephalins” from the Greek “in the brain.” The enkephalins turned out to be pentapeptides, molecules composed of five amino acids linked together. Later, longer chains of amino acids, all incorporating the enkephalin structure, were found to stimulate opiate receptors and were termed endorphins.
Today the term endorphin is used to describe all the various peptides that have opiate-like activity. Kosterlitz not only discovered endorphins, he also found that there are subtypes of opiate receptors, raising the possibility that there might be one kind of receptor for pain relief and another one responsible for addiction to opiates. This discovery triggered research into trying to find drugs that might fit one receptor without stimulating the other, perhaps leading to non- addictive opiates. Endorphins are also generated during orgasm and have been linked with the “runners’ high.” Some studies have even suggested that acupuncture needles stimulate endorphin release, based on the observation that naloxone, a drug that block opiate receptors, can negate the effects of acupuncture. There is also some evidence that the placebo effect is due to endorphin release. Patients who gain relief from pain after being treated with a sugar pill, often see a return of the pain after being injected with naloxone.