Neural mechanism of bradycardiac responses elicited by acupuncture-like stimulation to a hind limb in anesthetized rats

Acupuncture modulation of the ACE/Ang II/AT1R and ACE2/Ang(1-7)/MasR pathways in the rostral ventrolateral medulla reduces sympathetic output and prevents cardiac injury caused by SHR hypertension

Acupuncture can reduce blood pressure, heart rate (HR), and ameliorate cardiac damage by modulating the excitability of the sympathetic nervous system, but the exact mechanism of this effect remains unclear. This study investigated the potential mechanisms of acupuncture in the treatment of cardiac damage in hypertension. Spontaneously hypertensive rats (SHR) were used as the hypertension model with Wistar-Kyoto rats as the control. Manual acupuncture, electroacupuncture, and metoprolol were used as interventions. Systolic and diastolic blood pressure (SBP, DBP) plus HR were monitored with cardiac structure determined using Masson staining. Angiotensin II (Ang II) and norepinephrine in myocardium were detected with ELISA as was Ang(1-7) and gamma aminobutyric acid (GABA) in the rostral ventrolateral medulla (RVLM). Expression of mRNA for collagen type I (Col-I), Col-III, actin α1 (ACTA1), and thrombospondin 4 (THBS4) in myocardium was detected using real-time PCR. Expression of angiotensin converting enzyme (ACE), Ang II, angiotensin II type 1 receptor (AT1R), ACE2, and Mas receptor (MasR) proteins in RVLM was monitored using western blot. After manual acupuncture and electroacupuncture treatment, SHRs showed decreased SBP, DBP and HR, reduced myocardial damage. There was decreased expression of the ACE/Ang II/AT1R axis, and increased expression of the ACE2/Ang(1-7)/MasR axis within the RVLM. GABA levels were increased within the RVLM and norepinephrine levels were decreased in myocardial tissue. Metoprolol was more effective than either manual acupuncture or electroacupuncture. Acupuncture directed against hypertensive cardiac damage may be associated with regulation of ACE/Ang II/AT1R and the ACE2/Ang(1-7)/MasR pathway within the RLVM to reduce cardiac sympathetic excitability.

Effects of pre-exercise acupuncture stimulation on heart rate response during short-duration exercise

Background

The purpose of the present study was to investigate the effects of bradycardia induced by pre-exercise acupuncture on heart rate responses during short-duration exercise.

Methods

A total of 29 healthy subjects underwent two protocols: protocol 1 assessed the effects of manual acupuncture on heart rate response during rest, and protocol 2 tested the hypothesis that the bradycardic effects induced by pre-exercise acupuncture continue during low- and high-intensity exercise. Their average age, height, weight, and body mass index were 21.2 ± 2.0 years, 167.2 ± 8.8 cm, 63.8 ± 12.8 kg, and 22.7 ± 3.5 kg/m², respectively. In acupuncture stimulations for protocols 1 and 2, an acupuncture needle was inserted into the lower leg and manual acupuncture stimulation was performed at 1 Hz.

Results

In protocol 1 (resting condition), acupuncture stimulation induced a bradycardic response, which continued for 4 min after the cessation of acupuncture stimulation (p < 0.05). In protocol 2, the bradycardic response induced by pre-exercise acupuncture stimulation remained during low-intensity exercise and in the beginning of high-intensity exercise performed immediately after the cessation of acupuncture stimulation (p < 0.05). However, the effects disappeared when post-acupuncture exercise was performed when the heart rate was approximately 140 beats/min during high-intensity exercise. The rating of perceived exertion after exercise differed significantly between the acupuncture stimulation task (7.9 ± 1.6) and no-stimulation task (8.5 ± 2.0) (p = 0.03) only in the low intensity group.

Conclusion

This study may provide new insights into the effect of acupuncture stimulation on psycho-physiological conditions during exercise.

Effects of a Single Session of Acupuncture Treatment on Blood Pressure and Heart Rate Variability in Patients with Mild Hypertension

Objective: The aim of the present study was to compare the effects of acupuncture treatment on arterial blood pressure (BP) and heart rate (HR) in patients with mild hypertension with high sympathetic tone with those of normotensive patients and to examine the effects on cardiac sympathetic nerve activity (CSNA) and vagal activity using heart rate variability (HRV) analysis. Design: Eight male patients with prehypertension or stage I hypertension and eight normotensive age-matched patients were included in this study. All patients had their systolic BP (SBP), diastolic BP (DBP), HR, and HRV measured. In addition, the ratio of low-frequency (LF) to high-frequency (HF) HRV and the power of the HF of the HRV were recorded. The study was conducted at Kansai University of Health Sciences in Japan. Interventions: Each patient underwent a single, 15-min-long acupuncture session. Acupuncture was applied to PC6, LI4, ST36, LR3 on both sides, and GV20. Results: SBP and HR decreased significantly in the hypertensive group during and after acupuncture compared with the baseline SBP and HR (p < 0.05). LF/HF was significantly reduced during acupuncture (p < 0.05), and HF was significantly increased after acupuncture in the hypertensive group (p < 0.05). However, there were no significant changes in LF/HF or HF in the control group. Conclusions: Acupuncture may reduce the BP and HR in patients with mild hypertension. An HRV analysis suggests that acupuncture may suppress the enhanced basal CSNA activity and increase the vagal nerve activity in patients with mild hypertension. Clinical Trial Registration number: UMIN000041249.

Neuromechanism of acupuncture regulating gastrointestinal motility

Acupuncture has been used in China for thousands of years and has become more widely accepted by doctors and patients around the world. A large number of clinical studies and animal experiments have confirmed that acupuncture has a benign adjustment effect on gastrointestinal (GI) movement; however, the mechanism of this effect is unclear, especially in terms of neural mechanisms, and there are still many areas that require further exploration. This article reviews the recent data on the neural mechanism of acupuncture on GI movements. We summarize the neural mechanism of acupuncture on GI movement from four aspects: acupuncture signal transmission, the sympathetic and parasympathetic nervous system, the enteric nervous system, and the central nervous system.

Spectral Analysis of Heart Rate Variability During Trigger-Point Acupuncture of Various Muscles

Objective: The aim of this research was to clarify changes in cardiovascular autonomic nervous system function due to trigger-point (TP) acupuncture; the current author evaluated differences in responses among acupuncture at TPs of various muscles using spectral analysis of heart rate variability. Materials and Methods: Subjects were 48 healthy men. Before measurements began, subjects were assigned to a TP acupuncture or control group based on presence/absence of referred pain on applying pressure to a taut band within the right extensor digitorum muscle, tibialis anterior muscle, gluteus medius muscle, or masseter muscle. Measurements were conducted in a room with a temperature of 25°C, with subjects in a long sitting position after 10 minutes of rest. Acupuncture needles were retained for 10 minutes at 1 site on the right extensor digitorum muscle, tibialis anterior muscle, gluteus medius muscle, or masseter muscle. Electrocardiography was performed simultaneously with respiratory-cycle measurements. Based on the R-R interval on the electrocardiograms, frequency analysis was performed, low-frequency (LF) and high-frequency (HF) components were extracted, and the ratio of LF to HF components (LF/HF) was evaluated. Results: All subjects in the TP acupuncture group showed a transient increase in the HF component, but no significant changes in heart rate (HR) or LF/HF. In the control group, no significant changes were observed in HR, HF component, or LF/HF. Conclusions: These data suggest that acupuncture stimulation of TPs of the right extensor digitorum muscle, tibialis anterior muscle, gluteus medius muscle, and masseter muscle increases parasympathetic nerve activity transiently.

Acupoint dependence of depressor and bradycardic responses elicited by manual acupuncture stimulation in humans

The cardiovascular effects of the autonomic nervous system (ANS) are modulated by inputs from peripheral sensors and other brain regions. However, it currently remains unknown whether the manual acupuncture (MA) stimulation of different acupuncture points evokes different responses by the heart and vasculature, a phenomenon known as "site specificity". Sixty healthy subjects were randomly divided into a control group and MA stimulation groups at the lower leg, ear, abdomen, and forearm. MA was performed at 1 Hz for 2 min. A depressor response was observed only in the lower leg stimulation group, in which mean blood pressure significantly decreased from 83.4 ± 10.1 to 80.9 ± 11.7 mmHg (p < 0.003). A bradycardic response was elicited in all MA stimulation groups. There was no significant differences in the magnitude of the bradycardic response between groups. MA-induced cardiovascular responses, which may be mediated by the modulation of ANS, differ depending on acupuncture points.

Effects of acupuncture at the ST-36 point on muscle sympathetic nerve activity and blood pressure in normal adults

The aim of the present study was to determine the effects of acupuncture on post-ganglionic muscle sympathetic nerve activity (MSNA) in humans. MSNA was measured in 8 healthy adult males by microneurography evaluation of the left peroneal nerve. Blood pressure (BP) and heart rate (HR) were simultaneously recorded. MSNA was evaluated as the burst rate, with total MSNA, BP and HR normalized to their respective baseline values. After 10min of rest in the supine position, acupuncture was applied to the right ST-36 point in the tibialis anterior muscle for 15min, with recovery then monitored over a 20-min period. While the burst rate and total MSNA remained constant throughout the study, there was a significant decrease in BP during the real but not sham acupuncture procedure (p<0.05). HR did not significantly change throughout the study. The results rule out the role of MSNA in the BP fall during acupuncture at the ST-36 point, and suggest possible involvement of other factors in the fall of BP.

Somatoautonomic reflexes in acupuncture therapy: A review

Oriental therapies such as acupuncture, moxibustion, or Anma, have been used to treat visceral disorders since ancient times. In each of these therapies, stimulation of the skin or underlying muscles leads to excitation of afferent nerves. The sensory information is carried to the central nervous system, where it is transferred to autonomic efferents, thus affecting visceral functions. This neuronal pathway, known as the "somatoautonomic reflex", has been systematically studied by Sato and his colleagues for over a half century. Nearly all their studies were conducted in anesthetized animals, whereas human patients are conscious. Responses in patients or the events following therapeutic somatic stimulation may differ from those observed in anesthetized animals. In fact, it is increasingly apparent that the responses in patients and animals are not always coincident, and the differences have been difficult for clinicians to reconcile. We review the mechanism of the "somatoautonomic reflex" as described in anesthetized animals and then discuss how it can be applied clinically.

Chronic electroacupuncture of the ST36 point improves baroreflex function and haemodynamic parameters in heart failure rats

Electroacupuncture (EA) has been used to treat many diseases, including heart failure (HF). This study aimed to evaluate the effects of chronic stimulation in the ST36 acupuncture point on haemodynamic parameters and baroreflex function in rats with HF. Cardiovascular parameters assessed were heart rate (HR), blood pressure (BP), and the reflex cardiovascular response of HR triggered by stimulation of baroreceptors in animals with HF subsequent to acute myocardial infarction (AMI). Male Wistar rats were divided into three groups: Sham Control - animals without HF and without EA; HF Control group - animals with HF and without EA; and HF EA group - animals with HF that received the EA protocol. Six weeks after surgical induction of AMI, the EA protocol (8 weeks, 5 times a week) was performed. The protocol was applied with EA at the ST36 point, frequency of 2 Hz, pulse of 0.3 ms and intensity of 1-3 mA for 30 min. Haemodynamic parameters and baroreceptor function were assessed. There was no difference between groups in the variables HR, systolic blood pressure (SBP) and diastolic blood pressure (DBP), which were evaluated with awake animals (p>0.05). There was an increase in the mean arterial pressure (MAP) in the HF EA group compared to the HF Control group (p<0.05). The maximum gain of the baroreflex heart rate response (Gain) was higher in the HF EA group than the HF Control and Sham Control groups. Chronic EA in the ST36 point increased the MAP and baroreflex sensitivity in rats with HF.

Hemodynamic changes in the brachial artery induced by acupuncture stimulation on the lower limbs: a single-blind randomized controlled trial

Acupuncture is commonly performed at acupoints. No comparisons of quantitative physiological alterations in the brachial artery (BA) induced by the stimulation of different acupoints in the lower limbs have been performed in humans. Therefore, we investigated changes in blood flow volume (BFV) in the BA as an indicator of the physiological effects induced by stimulation at 3 points. Seventy-five healthy participants aged 33 ± 9 years (mean ± SD) were enrolled and randomly assigned to 3 groups; they received stimulation at 3 different points located on the lower limbs: ST36, LR3, and a non-acupoint. Stimulation was performed bilaterally with manual rotation of the needles. Using ultrasonography, BFV was measured continuously from rest to 180 seconds after stimulation. LR3 stimulation significantly increased BFV compared to that before needle insertion. Meanwhile, stimulation at ST36 and the non-acupoint significantly decreased BFV compared to that before needle insertion. Stimulation at LR3 elicited a significant increase in BFV compared to that at ST36 and the non-acupoint. The results suggest that the stimulation of different points on the lower limbs causes distinct physiological effects on BFV in the BA.

Neural acupuncture unit: a new concept for interpreting effects and mechanisms of acupuncture

When an acupuncture needle is inserted into a designated point on the body and mechanical or electrical stimulation is delivered, various neural and neuroactive components are activated. The collection of the activated neural and neuroactive components distributed in the skin, muscle, and connective tissues surrounding the inserted needle is defined as a neural acupuncture unit (NAU). The traditionally defined acupoints represent an anatomical landmark system that indicates local sites where NAUs may contain relatively dense and concentrated neural and neuroactive components, upon which acupuncture stimulation would elicit a more efficient therapeutic response. The NAU-based local mechanisms of biochemical and biophysical reactions play an important role in acupuncture-induced analgesia. Different properties of NAUs are associated with different components of needling sensation. There exist several central pathways to convey NAU-induced acupuncture signals, Electroacupuncture (EA) frequency-specific neurochemical effects are related to different peripheral and central pathways transmitting afferent signals from different frequency of NAU stimulation. More widespread and intense neuroimaging responses of brain regions to acupuncture may be a consequence of more efficient NAU stimulation modes. The introduction of the conception of NAU provides a new theoretical approach to interpreting effects and mechanisms of acupuncture in modern biomedical knowledge framework.

Neuroanatomical characteristics of acupuncture points: relationship between their anatomical locations and traditional clinical indications

This study examines the relationship between the anatomical location of traditional acupuncture points and their clinical indications as stated in two textbooks of traditional Chinese medicine (TCM). The following relationships are noted: (1) The acupuncture points in the trunk and their stated effects on the internal organs in the trunk have a segmental relationship--that is, acupuncture points within certain spinal segments in the trunk affect the functioning of the organs that receive autonomic innervation from the same spinal segments. This is consistent with the concept of segmental acupuncture and the idea that acupuncture may act via the somatic sympathetic reflex with a spinal pathway to affect the trunk organs. (2) The acupuncture points in the trunk and extremities have a musculoskeletal effect that is local or regional, but not distal. This is consistent with some of the models of acupuncture mechanisms on musculoskeletal effects in the Western medical acupuncture approach. (3) The acupuncture points on the head and neck preferentially affect the nearest organ. This presumably reflects the belief in TCM that acupuncture can somehow regulate the functioning of the proximal organ. No clear relationship can be identified between the myotome level of the acupuncture points in the extremities and their non-musculoskeletal clinical indications.

Involvement of the mechanoreceptors in the sensory mechanisms of manual and electrical acupuncture

The modalities of acupuncture can be broadly classified into manual acupuncture (MA) and electroacupuncture (EA). Although MA has been reported to cause winding of tissue around the needle and subsequent activation of the sensory mechanoreceptors and nociceptors, the sensory mechanisms of acupuncture stimulation are not fully understood. To test the hypothesis that the involvement of the mechanoreceptors in the sensory mechanism is different in MA and EA, we examined the effects of a stretch-activated channel blocker gadolinium on the hemodynamic responses to hind limb MA and EA in anesthetized rats (n = 9). Gadolinium significantly attenuated the MA-induced bradycardic response (-22 ± 5 vs. -10 ± 3 bpm, P<0.05) and tended to attenuate the MA-induced depressor response (-30 ± 5 vs. -18 ± 4 mmHg, P = 0.06). On the other hand, gadolinium significantly attenuated both the EA-induced bradycardic (-22 ± 5 vs. -9 ± 4 bpm, P<0.01) and depressor responses (-32 ± 6 vs. -15 ± 5 mmHg, P<0.01). These results indicate that the mechanoreceptors are involved in the sensory mechanisms for both MA and EA.

Brief effect of acupuncture on the peripheral arterial system of the upper limb and systemic hemodynamics in humans

BACKGROUND

Pulse diagnosis of the peripheral artery is an important technique in Traditional Chinese Medicine, where, in acupuncture therapy, the treatment is adjusted according to the observed changes of the pulse. We investigated the change of blood flow in the peripheral artery and the cardiac index during acupuncture treatment.

OBJECTIVES

The aim of this study is to explore the effect of acupuncture on radial and brachial artery blood flow volume and the cardiac index in healthy subjects.

METHODS

Eighteen (18) healthy volunteers were enrolled. Acupuncture was performed bilaterally on LR-3 with manual rotation of the needles. The blood pressure and heart rate were measured at rest and 180 seconds after acupuncture. Radial and brachial artery blood flow volume was monitored continuously by an ultrasound with an echo-tracking system. Cardiac index was measured by impedance cardiography. The hemodynamic parameters were measured before, during, and 30, 60, 180 seconds after acupuncture.

RESULTS

The peripheral artery blood flow volume decreased significantly during acupuncture (radial; p < 0.01, brachial; p < 0.05) but increased at 180 seconds after acupuncture (radial; p < 0.05, brachial; p < 0.05) compared with before acupuncture. The cardiac index did not change significantly after acupuncture, but systemic vascular resistance index significantly decreased (p < 0.05).

CONCLUSIONS

The present study showed that radial and brachial artery blood flow volume decreased immediately during acupuncture on LR-3 acupoint, but increased at 180 seconds after acupuncture. This reaction is attributed to the change in peripheral vascular resistance.

Radial artery hemodynamic changes related to acupuncture

BACKGROUND

Assessment of the radial pulse by palpation (pulse diagnosis) is an important diagnostic technique in Traditional Chinese Medicine (TCM), but the changes of blood flow volume in the radial artery during and after acupuncture are unknown.

OBJECTIVE

The aim of this study was to explore the changes of radial artery blood flow volume during and after acupuncture in healthy subjects.

DESIGN

This study was conducted as a pilot study utilizing a one-group intervention design.

SETTING

The study was conducted at a TCM outpatient clinic of Tohoku University Hospital.

PARTICIPANTS

Twenty-six healthy volunteers participated in the study.

INTERVENTION

Acupuncture was performed at LR-3 bilaterally with manual rotation of the needles.

OUTCOME MEASURES

Blood pressure was measured at rest and 180 seconds after acupuncture. Radial artery hemodynamics were monitored continuously with a high-resolution ultrasound echo-tracking system. The vessel diameter and blood flow volume of the right radial artery and heart rate were measured at rest, before acupuncture, during acupuncture, and 30, 60, and 180 seconds after acupuncture.

RESULTS

The systolic and diastolic diameter of the radial artery did not significantly change. Radial artery blood flow volume decreased significantly during acupuncture (mean +/- SD, 0.16 +/- 0.11 mL/sec per m(2); P < .01) compared with baseline (0.43 +/- 0.27 mL/sec per m(2)), but was increased at 180 seconds after acupuncture (0.54 +/- 0.28 mL/sec per m(2); P < .01).

CONCLUSIONS

The present study showed that radial artery blood flow volume decreased immediately during acupuncture at the LR-3 acupoint, but was increased at 180 seconds after acupuncture.

Afferent nerve fibers and acupuncture

Acupuncture has been used for analgesia, for treating visceral function disorders and for improving motor functions. It is well established that stimulation of the skin and muscles, either electrically or with noxious or non-noxious stimuli, induces a variety of somato-motor and autonomic responses. This strongly suggests that acupuncture acts by exciting cutaneous and/or muscular afferent nerve fibers. A question of considerable scientific and practical interest is what kinds of somatic afferent fibers are stimulated by acupuncture and are involved in its effects. There are several types of afferent fiber: thick myelinated Aα and Aβ (group I and II), thin myelinated Aδ (group III) and thinner unmyelinated C (group IV) fibers. In recent studies we have tried to establish which ones of these types of somatic afferent fiber are stimulated by acupuncture. In this article we first review the experimental evidence showing that the effects of acupuncture are mediated by the activation of afferent nerve fibers innervating the skin and muscles. Secondly, we discuss what types of afferent nerve fiber are activated by electrical acupuncture, and what types are involved in its effects on somato-motor functions and on visceral functions. Finally, we present some new findings based on recordings from single afferent nerve fibers excited by manual acupuncture.

Neural mechanisms of reflex inhibition of heart rate elicited by acupuncture-like stimulation in anesthetized rats

We briefly review our recent studies on the neural mechanisms of the reflex effects of acupuncture-like stimulation on heart rate in rats. In pentobarbital anesthetized rats, acupuncture-like stimulation of one of various segmental areas of the body (forelimb, chest, abdomen, hindlimb) invariably induces a decrease in heart rate. In the case of the hindlimb, the effect can be produced by stimulation of the muscles alone but not of skin alone, and is abolished by severance of the hindlimb somatic nerves. Electrical stimulation of groups III and IV nerve fibers (in the tibial nerve) decreases heart rate. Decrease in heart rate by acupuncture-like stimulation of a hindlimb is accompanied by a decrease in cardiac sympathetic nerve activity, and is abolished by cardiac sympathectomy but not by vagotomy. High spinal cord transection or infusion of the GABA(A) receptors antagonist, bicuculline, into the cisterna magna is effective in disrupting the reflex bradycardia. Opioid receptor blockade does not disrupt the reflex arc. We conclude that the reflex pathway involved in the decrease of heart rate by acupuncture-like stimulation comprises groups III and IV muscle afferent nerves whose activation stimulates GABAergic neurons in the brainstem and inhibits sympathetic outflow to the heart. When the sympathetic tone is high due to hypercapnia, the induced reduction in both cardiac sympathetic nerve activity and heart rate is not augmented, suggesting that the magnitude of sympatho-inhibitory response to acupuncture-like stimulation does not depend on pre-existing sympathetic tone.

Sympatho-inhibitory response of the heart as a result of short-term acupuncture-like stimulation of the rat hindlimb is not augmented when sympathetic tone is high as a result of hypercapnia

This study examined whether the sympatho-inhibitory response of the heart to acupuncture-like stimulation of a hindlimb in anesthetized rats depends on the sympathetic tone. Observed reductions in both cardiac sympathetic nerve activity and heart rate following short-term acupuncture-like stimulation of a hindlimb were not augmented when the sympathetic tone was high as a result of hypercapnia.

Mechanism of the reflex inhibition of heart rate elicited by acupuncture-like stimulation in anesthetized rats

Acupuncture or acupuncture-like stimulation applied to different body areas can modify autonomic nerve activity to various organs, including gut, bladder, adrenal medulla, and the heart. We studied the reflex bradycardia in response to insertion into the skin and underlying muscles and twisting of an acupuncture needle in pentobarbital-anesthetized rats. We found that acupuncture-like stimulation of forelimb, hindlimb, chest, and abdomen all produced significant heart rate decreases. Rate minima were reached at the end of the 60-second stimulation episode and significant bradycardia persisted for about 40 s after stimulation ended. Heart rate decreases were paralleled by decreases in cardiac sympathetic nerve activity, and could be produced by electrical stimulation of group IV muscle afferent fibers (tibial nerve). Electrical stimulation of the tibial nerve at rates as low as 0.1-2 Hz was effective for eliciting heart rate decreases. Nerve fiber groups were defined by stimulation of and recording from tibial nerve. Activation of groups I, II, or III fiber was ineffective for eliciting the reflex bradycardia. Sympathectomy, high spinal transection, or infusion of the GABA(A) receptor antagonist, bicuculline, into the cisterna magna were all effective for disrupting the reflex bradycardia. Vagotomy and opioid receptor blockade were ineffective for disrupting the reflex pathway. We conclude that the reflex pathway to decrease heart rate by acupuncture-like stimulation consists of mainly group IV muscle afferent fibers whose activity (even very low rate of activity) leads to the activation of GABA-ergic neurons in the brainstem and an inhibition of sympathetic outflow to the heart.