Endorphins belong to a class of biochemicals commonly referred to as neurohormones
that act by modifying the way in which nerve cells respond to
transmitters. The discovery of this class of biochemicals has an
unusual and interesting history. In the 1960s, biomedical researchers
studying the causes and effects of opium addiction had detected what
they suspected were "opiate receptors" in brain tissue. Since it seemed
quite unlikely that humans (or other vertebrates) would contain a
specific receptor designed for a chemical derived from the poppy plant,
the researchers focused their attention on biochemicals that might be
synthesized in the brain itself. Early in the 1970s, several small
peptides were isolated that appeared to possess natural analgesic
properties, and these were collectively termed enkephalins and endorphins.
The modification of neural transmissions by these biochemicals now
appears to be responsible for the insensitivity to pain that is
experienced by individuals under conditions of great stress or shock.
The effectiveness of analgesic opiate derivatives such as opium,
morphine, and heroin is an accidental side effect that derives from the
ability of these substances to bind to neurohormone receptors despite
their very different structure.
alpha-Endorphin
Four distinct groups of endorphins have been identified to date. They have been termed: alpha-endorphin, a polypeptide with 16 residues; beta-endorphin, a polypeptide with 31 residues; gamma-endorphin, a polypeptide with 17 residues; and sigma-endorphin,
a polypeptide with 27 residues. These different types of endorphins,
like all known polypeptide hormones, are synthesized in a "prepro" form
that is one gigantic polypeptide with a signal sequence and additional
sequences that are cleaved out during posttranslational maturation of
the polypeptide. The most interesting example of this is the pituitary
multihormone precursor termed pro-opiomelanocortin that contains the
sequences for beta-lipotropin, melanocyte-stimulating hormone (MSH), endorphins, enkephalins, and adrenocorticotropic hormone (ACTH).
After synthesis, this peptide is cleaved in the pituitary to generate
ACTH and beta-lipotropin, while processing in the central nervous system
produces endorphins and enkephalins, along with some other products.
beta-Endorphin
Endorphins are most heavily released in the human body during
stressful events or in moments of great pain. The rush of endorphins
into the system at such times is often felt as a queasy or nervous
feeling in the stomach. However, the amount of endorphins released by
individuals varies so that an occurrence that stimulates significant
neurohormone secretion in some people will not necessarily do so in
others. In addition to stress and pain, endorphin secretion may be
triggered by the consumption of certain foods, such as chocolate and
chili peppers. Indeed, the characteristic increase in bodily endorphin
levels caused by chocolate is believed to play a significant role in its
often being turned to as a comfort food in times of stress. Moreover,
due to the endorphin release associated with chili peppers, they have
been utilized in various kinds of medical treatments, especially as part
of therapy for chronic pain, and are sometimes considered an
aphrodisiac. Certain kinds of physical activity have been associated
with endorphin secretion in recent years as well. Undergoing massage
therapy or acupuncture, for example, is believed to stimulate endorphin
release, and the natural painkillers may be responsible for the euphoric
feelings known as "runner's high" and "adrenaline rush."
gamma-Endorphin
Perhaps the most unusual activity believed to be able to stimulate
the body's secretion of endorphins is laughter. Medical studies have
shown that good belly laughter can reduce stress hormones, decrease
pain, lower blood pressure, and even boost the immune system. Due to
such findings, laughter has begun being used as a sort of adjunctive
therapy to other forms of medical treatment. Contemporary interest in
the therapeutic capabilities of laughter was sparked in the 1970s when a
book written by Norman Cousins was published, which related his use of
Marx Brothers films and humorous stories to help alleviate pain he had
been suffering from ankylosing spondylitis, a disease that attacks the
connective tissues of the body. Though Cousins initially received
significant criticism, his work was fully vindicated in 1989 when the
Journal of the American Medical Association published an article by
Swedish scientist Lars Ljungdahl entitled "Laugh If This Is a Joke,"
which argued that "a humor therapy program can increase the quality of
life for patients with chronic problems" and "laughter has an immediate
symptom-relieving effect for these patients, an effect that is
potentiated when laughter is induced regularly over a period." Thus one
might be inclined to agree with the great American humorist Mark Twin
who suggested, "The human race has only one really effective weapon, and
that's laughter."
Inspired by the success in stimulating the natural release of
endorphins in human patients through laughter, some veterinary
practitioners are exploring ways of achieving a similar effect in
animals. Of course, making the family pet chuckle is not an easy task,
so other kinds of activities that secrete endorphins must be used. One
type of endorphin-related animal treatment is known as healing touch
therapy, which involves applying non-invasive touch to a pet to promote
endorphin release, reducing anxiety and pain while promoting healing.
The similar activity of massage is often used in veterinary clinics as
well for analogous purposes. Moreover, acupuncture, offered to humans
for thousands of years, is now also being provided to pets. As with
humans, endorphins are released into an animal's body upon needle or
pressure stimulation of specific points. The neurohormones inhibit pain
perception by causing blood vessels to dilate. In addition to the pain
alleviating effects of this activity, blood flow around joints and
muscles increases, thus augmenting nutrient and oxygen delivery to the
problem areas.
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