SMGr up
A Review of the Current Acupuncture
Mechanisms of Action from Both an Eastern
and Western Perspective
Michael Malone1* and Gary Tsai1
1
Penn State Department of Family and Community Medicine
*Corresponding author: Michael Malone, Penn State Department of Family and Community
Medicine, Email: mmalone@hmc.psu.edu
Published Date: February 09, 2017
INTRODUCTION
Acupuncture is a Chinese medical technique that utilizes stimulation of anatomical points on
the body through a variety of techniques, although it has been synonymously identified with the
use of thin, metallic needles. It has been historically practiced in China several millennia, and has
been gaining popularity in the United States over the past few years [1]. In 2015, National Health
Statistic Reports from the National Health Interview Survey published a report, which included
a comprehensive survey on the use of complementary health approaches by Americans; roughly
3.4 million U.S. adults had used acupuncture in 2012 [2].
Traditionally, acupuncture has been used to treat a wide range of health conditions such as
chronic lower back pain, nausea, headache, among others. However scientific evidence regarding
its efficacy has been limited due to the difficulty of performing double-blinded studies given the
nature of the procedure and appropriate sham placebo treatments [3-5].
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From a Western perspective, acupuncture is typically used to treat a medical diagnosis.
The desired response is a change in the body’s natural processes through biochemical and
physiological effects. Eastern theory for acupuncture, in contrast, is based on the idea that bodily
dysfunction is caused by non-homeostatic flow of Qi/Chi through the body in channels called
meridians. Still, there remains significant controversy and mystery regarding the mechanisms
of how acupuncture works. For the purposes of this article, we will review current Eastern and
Western theories regarding acupuncture’s mechanism of action, including a literature search of
recent scientific literature.
METHODOLOGY
A search of databases including PubMed and Health line were performed including the key
search words: Acupuncture, electro acupuncture, mechanism of action, inflammation, opioid,
endorphin, blood flow, vasodilatation, functional MRI, SPECT, PET, imaging and neurotransmitters.
EASTERN MECHANISM OF ACTION FOR ACUPUNCTURE
In order to understand the eastern mindset regarding acupuncture, it is important that we
discuss Traditional Chinese Medicine (TCM) theory. While it is not possible cover all aspects of
TCM given the vast amount of information and history, we will briefly touch upon the basics.
It is believed that Taoism helped shape the practice of Chinese medicine, which is based on
belief that everything is interdependent and mutually interactive in the universe. In turn, the
body communicates with the universe or environment; when changes occur and the body fails to
adapt, then disease is likely to occur [6].
Compared to Western medicine, Eastern philosophy of medicine involves numerous
interweaving ideas that may be considered foreign or non-scientific in nature. Concepts such as
Qi/Chi (innate vital substance or energy), Yin-Yang Theory, Eight Principles (Interior/Exterior,
Hot/Cold, Full/Empty, Yin/Yang), Five-Element Theory, Meridian system, and several others are
abstract ideas that were used to explain relationships and patterns that occurred in nature [6].
There are no Western equivalents to these ideas, which may contribute to the unfamiliarity and
slow acceptance of TCM outside of Asia.
From the TCM perspective, the body is considered as a whole, made of parts interconnected;
parts that can depend and/or restrict each other physiologically and pathologically. The five
organs (yin organs) make up the core units of the body and are linked through various meridians,
or channels, which are interrelated to yang organs. Although meridians work as a complex system
which carries and distributes qi and blood, they are not blood vessels and have no anatomical
channel structure; nor are they visible [6]. The idea is similar to how a river flows, with obstruction
along the river channels producing illness further downstream in the body. Acupuncture is
therefore able to help restore the flow and return the body to normal through stimulation of
points on the meridian system.
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Table 1: The five organ systems of the body [7].
Organ Paired organs
Heart Small intestine
Liver Gall bladder
Spleen Stomach
Lung Large intestine
Kidney Bladder
Meridians are classified into two groups which correlate with Yin and Yang organs. They are
further delineated with 3 arm yin, 3 arm yang, 3 leg yin, and 3 leg yang meridians.
Table 2: The Meridian System [8].
Channels Organ Pathway
3 Yin Meridians of the Hand Lung, Heart, Pericardium Chest to Hand
3 Yang Meridians of the Hand Large Intestine, Small Intestine, Triple Burner Hand to Face
3 Yang Meridians of the Foot Stomach, Bladder, Gallbladder Face to Foot
3 Yin Meridians of the Foot Spleen, Kidney, Liver Foot to Chest
The triple burner and the pericardium do not refer to anatomical structures, but are functional
units in TCM [9]. The triple burner is considered to be representative of energy centers in the
chest (heart and lungs), abdomen (stomach and spleen), and pelvis (liver, kidney, large intestine,
small intestine, and bladder). It does not refer to the physical location of the organ, but rather
where energy is produced and supplies the rest of the organs [10].
Acupuncture theory involves a system of differentiating disease patterns in the body. It is
generally believed that diseases can be treated when the affected meridians or the affected organs
are cleared. Acupuncture is used as a tool to help move Qi by utilizing meridian points on the body
which are believed to aid in returning the body to its normal state of balance [9].
WESTERN MECHANISM OF ACTION FOR ACUPUNCTURE
Although acupuncture is just one component of traditional Chinese medicine, its precise
effects on the human body remains an area on ongoing investigation. From a Western perspective
acupuncture induces effects on neuropeptides, local circulation, inflammation, and the Central
Nervous System (CNS).
NEUROTRANSMITTERS
Multiple neurotransmitters have been implicated in acupuncture’s mechanism of action from
a Western perspective. The main neurotransmitters mechanisms for acupuncture include an
increase in endogenous opioids and a decrease in substance P.
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Endogenous Opioids
An increase in endogenous opioids in plasma or cerebrospinal fluid has been observed
in humans who receive electro acupuncture [11]. Analgesic relief involves the activation of
endogenous opioid systems and mu-opioid receptors (MOR) has also been shown in animal
models[5,12,13]. Furthermore, part of the response to electro acupuncture is antagonized by
the opioid receptor antagonist naloxone [14]. Han further deciphered that low-frequency (2 Hz)
electro acupuncture induces the activation of mu- and delta-opioid receptors via the release of
enkephalin, beta-endorphin, and endomorph in in supraspinal CNS regions, whereas the effects
of high-frequency (100 Hz) electro acupuncture involve the actions of dynorphin on kappa opioid
receptors in the spinal cord [15]. Studies performed by Harris et al, have shown that acupuncture
therapy evoked not only short-term increases in MOR binding potential, but also long-term
increases in multiple pain and sensory processing regions of the brain. These effects on MOR
binding potentials were absent in the sham acupuncture group [5].
Substance P
Substance P (SP) exists in primary afferents that respond to painful stimuli and appears to
transmit pain information into the central nervous system [16,17]. Electro Acupuncture (EA) and
moxibustion have been shown to down regulate expressions of abnormally increased colonic
mucosa-associated neuropeptide SP in patients with irritable bowel syndrome [17]. Immuno
fluorescence studies of SP in the spinal cord, and dorsal root ganglion tissues in rats also suggest
a possible involvement of the primary SP-positive sensory neurons in the transmission of
acupuncture stimulation signals [19].
Other Possible Neuropeptides involved in Acupuncture’s Mechanism of
Action
Animal studies on the effect of acupuncture and moxibustion interventions in depression rats
suggest an up-regulation response of 5-hydroxytryptamine (5-HT)/ hydroxyindole acetic acid (5-
HIAA), and down-regulation of tryptophan content in the frontal cortex [20]. Another mechanism
by which acupuncture has been reported in the literature is through the up-regulation of the
GIutamate receptor 1 in the amygdala [21].
Direct CNS Effects
Increases in both regional cerebral blood flow and glucose metabolism in the central nervous
system have occurred following both manual acupuncture and electro acupuncture [22,23].
Studies performed within the last decade have shown that acupuncture induces different effects
on the human brain as displayed through the use of a Functional Magnetic Resonance Imaging
machine (FMRI) [24,25]. Acupuncture while utilizing FMRI, Single-Photon Emission Computed
Tomography (SPECT), and Positron Emission Tomography (PET) showed acupuncture altered
brain activity, increased cerebral blood flow, and increased glucose metabolism [26].
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Increase in Local Blood Flow
Acupuncture has been shown to increase the nitric oxide levels in treated regions, resulting
in increased local blood circulation [27-30]. In a RCT acupuncture increased nitric oxide
activity along meridians and the change in circulation was associated with reduced pain [28].
The vasodilatory effects were not seen in noninvasive sham-acupuncture treatments [28].
In another study, acupuncture stimulation was used on patients and showed increase in local
blood flux through the use of laser Doppler flowmetry before, during and after the acupuncture
stimulation [31]. Indocyanine green perfusion imagining has also confirmed the vasoactive effect
of acupuncture [32].
Anti-inflammatory Mechanism of Action
Acupuncture can reduce swelling and local inflammation [33,34]. In animal studies, electro
acupuncture has been shown to reduce chronic inflammatory pain and is hypothesized to be
related to up regulation of MrgprC gene expression which can modulate neurogenic inflammation
[33]. Clinical evidence suggests that acupuncture improves allergic inflammation and symptoms
of allergic rhinitis [35]. This modulation appears to be associated with down-regulation of allergen
specific IgE for house dust mite [36].
Recent animal studies also suggest that electrical acupuncture at ST36 might be a useful and
promising therapeutic for allergic inflammatory as well as Th1-mediated inflammation response
[35]. One study suggests that the therapeutic effects of acupuncture may be mediated through
vagal modulation of inflammatory responses in internal organs via production of TNF-α and c-Fos
[37]. In another recent animal study, acupuncture treatment significantly decreased the levels of
pro-inflammatory cytokines in the hippocampus, prefrontal cortex, and serum suggesting that
that acupuncture’s mechanism of action involves the inhibition of pro-inflammatory cytokines
[38].
CONCLUSION
Acupuncture remains an area where several questions remain to be answered. It’s variety of
effects on the human body are challenging to explain from one perspective. By looking at both the
Eastern and Western proposed mechanisms for acupuncture, we believe one can obtain a better
understanding of ways in which acupuncture likely exerts its effects.
While Western mechanisms are mainly focused on endogenous opioid response, a reduction
in inflammation, increased peripheral blood flow, and metabolic and vascular CNS effects, the
Eastern mechanism focuses on the flow of Qi through meridians. Although without the scientific
rigor, the Eastern (Qi) mechanism of action provides an interesting contrasting perspective that
does not have Western equivalents. Some studies have provided some insight into the mechanisms
of acupuncture, but one can only obtain a holistic view of its mechanism of action by looking at
both the Western and Eastern perspectives.
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International License, which allows users to download, copy and build upon published articles even for commercial
purposes, as long as the author and publisher are properly credited.
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