Abstract
OBJECTIVE To investigate physiologic and biochemical effects of electroacupuncture and dexmedetomidine administration to goats.
ANIMALS 30 healthy adult goats.
PROCEDURES Goats were allotted to 5 groups (6 goats/group) and received electroacupuncture, dexmedetomidine (5 or 20 μg/kg, IM), electroacupuncture plus dexmedetomidine (5 μg/kg, IM), or saline (0.9% NaCl) solution (IM [control treatment]). Pain threshold, cardiorespiratory effects, rectal temperature, and hematologic and biochemical variables were assessed.
RESULTS Dexmedetomidine (20 μg/kg) increased pain threshold and decreased heart rate, respiratory rate, and rectal temperature. Pain threshold of goats receiving electroacupuncture plus dexmedetomidine (5 μg/kg) was higher than that of goats receiving electroacupuncture or of goats receiving dexmedetomidine at 5 μg/kg at 30 minutes, but did not differ from that of goats receiving dexmedetomidine at 20 μg/kg. Compared with goats administered dexmedetomidine at 20 μg/kg, goats receiving electroacupuncture plus dexmedetomidine at 5 μg/kg had a higher heart rate from 30 to 60 minutes and a higher respiratory rate from 5 to 60 minutes. Electroacupuncture plus dexmedetomidine (5 μg/kg) did not affect rectal temperature. Serum glucose concentrations of goats receiving electroacupuncture plus dexmedetomidine (5 μg/kg) were higher than for goats receiving dexmedetomidine at 5 μg/kg at 30 minutes but not for goats receiving dexmedetomidine at 20 μg/kg. Creatinine and BUN concentrations, alanine or aspartate aminotransferase activities, and hematologic variables of treated goats did not change.
CONCLUSIONS AND CLINICAL RELEVANCE Electroacupuncture in combination with a low dose of dexmedetomidine (5 μg/kg, IM) administered to goats provided antinociception.
Dexmedetomidine is a synthetic α2-adrenoceptor agonist that is registered for use as a sedative-analgesic agent in veterinary medicine. Because it is a highly selective α2-adrenoceptor agonist, dexmedetomidine has been recommended for use as a premedicant in various species.1–3 However, dexmedetomidine has sympatholytic effects that manifest as decreases in norepinephrine release, blood pressure, and heart rate.4–7 The combination of α2-adrenoceptor agonists and ketamine has been used in ruminants and can reduce the risk of regurgitation and aspiration.8 However, such combinations still cause some adverse effects (eg, suppressed cardiovascular functions, increased respiratory frequency, and decreased rectal temperature) in ruminants.9,10
Electroacupuncture involves electrical stimulation administered via inserted needles. This procedure was first introduced in 1960 and was successfully used to relieve pain during various operations (ie, cesarean section, gastrectomy, enterectomy, and castration) in humans11 and domestic animals12,13 while maintaining a stable physiologic index. Subsequently, the combination of electroacupuncture and drug administration, referred to as acupuncture-drug balanced antinociception, was successfully used during surgeries in humans. This combination improved antinociceptive effects and also minimized some drug-induced adverse effects.14–16 Electroacupuncture, in combination with analgesics, reduces required dosages of analgesics in humans,17 rats,18 and goats19 by 40% to 46%, 50%, and > 75%, respectively, with the same antinociceptive effect as that resulting from a single dose of the analgesics alone. It is clear that the antinociceptive effect induced by electroacupuncture in goats (ruminants) is superior to that in humans or rats. However, effectiveness of the combined use of electroacupuncture and α2-adrenoceptor agonists for ruminants remains unclear.
There is a lack of information concerning antinociception for the combined use of electroacupuncture and dexmedetomidine in ruminants. In rats, electroacupuncture interacts synergistically with some sedatives or analgesics (ie, fentanyl, pethidine, droperidol, perphenazine, and tetrahydrocannabinol) but has antagonistic effects with others (ie, ketamine and diazepam).20,21 The purpose of the study reported here was to investigate the antinociceptic effectiveness of electroacupuncture plus dexmedetomidine and determine the effect of this combination on physiologic (ie, heart rate, respiratory rate, and rectal temperature), hematologic, and biochemical (glucose, creatinine, and BUN concentrations and AST and ALT activities) variables in goats.
Materials and Methods
Animals
Thirty healthy adult female crossbred goats (mean ± SD age, 1.64 ± 0.29 years; mean body weight, 28.41 ± 1.09 kg) were used to investigate the antinociceptive effects of dexmedetomidine and electroacupuncture. Goats were purchased from the Hubei Agricultural Academy of Science and allotted into 5 groups (6 goats/group) by use of a random number table. To reduce stress, goats were allowed to adapt to their surroundings and to restraint (1 h/d) for 2 weeks before the start of the experiment. In particular, efforts were made to maintain all goats under the same management conditions. Feed and water were withheld for 24 and 12 hours, respectively, before the start of the experiment. The experimental protocol was approved by the Animal Care Center, College of Veterinary Medicine, Huazhong Agricultural University.
Experimental design
Each group of goats received 1 of 5 treatments. Treatments consisted of 0.04 mL of saline (0.9% NaCl) solution/kg (IM [control treatment]), electroacupuncture, 2 dosages of dexmedetomidine hydrochloridea (5 or 20 μg/kg, IM), and electroacupuncture plus dexmedetomidine (5 μg/kg, IM). All IM injections were administered into the semimembranosus muscles. Electroacupuncture was administered via stainless steel acupuncture needles as an electric pulse into selected acupuncture points. For goats receiving electroacupuncture plus dexmedetomidine, electroacupuncture and dexmedetomidine were administered at the same time. The induction time for electroacupuncture antinociception (25 to 30 minutes) is similar to that for dexmedetomidine (20 to 30 minutes); thus, the simultaneous administration allowed the strongest antinociceptive effect.
Electroacupuncture
Acupuncture sites were shaved and antiseptically prepared with 10% povidone-iodine solution. The needles were disinfected and inserted into the points by a skilled acupuncturist (MLH). A set of Bai hui (hundred meetings), San tai (3 platforms), Erh gen (ear base), and San yan luo (3 Yang communication) points was selected for electroacupuncture stimulation.19 Anatomic locations of these points have been described for use in veterinary medicine.19,22 The Bai hui point was identified on the dorsal midline between the spinous processes of the last lumbar and the first sacral vertebrae; a needle (diameter, 0.40 mm; length, 50 mm) was inserted perpendicularly into the Bai hui point to a depth of approximately 30 mm. The San tai point was identified on the dorsal midline between the spinous processes of the fourth and fifth thoracic vertebrae; a needle (diameter, 0.45 mm; length, 75 mm) was inserted in a cranioventral direction into the San tai point to a depth of 40 to 50 mm. The Erh gen points were identified bilaterally ventrocaudal to the ear base at the depression between the ear base and cranial border of the transverse process of the atlas; a needle (diameter, 0.45 mm; length, 75 mm) was inserted into the Erh gen point on the right side until it reached the subcutaneous tissue of the right temporal fossa. The San yan luo point was identified approximately 5 cm ventral to the lateral tuberosity of the radius in the groove between the common digital extensor and lateral digital extensor muscles of the right forelimb; a needle (diameter, 0.45 mm; length, 75 mm) was inserted at approximately 30° in a ventromedial direction into the San yan luo point until it reached the subcutaneous tissue on the medial side of the forelimb.
Needles at the Bai hui and San tai points were connected to one of the output ports of a pulse generator,b whereas needles at the Erh gen and San yan luo points were connected to the other output port of the pulse generator. In accordance with results of another study,23 the electroacupuncture frequency was set at 60 Hz and the intensity was maintained constant at 3.2 V throughout the entire electroacupuncture procedure.
Start of the experiment was the moment when electroacupuncture or an injection of dexmedetomidine was administered (time 0). Electroacupuncture was administered for 60 minutes. Then, frequency and intensity settings were returned to 0, the pulse generator was disconnected, and the needles were removed.
Physiologic variables
All goats were positioned in sternal recumbency, with minimal restriction of thoracic excursions. The head of each goat was maintained in a typical upright anatomic position. Goats were allowed to adapt to their surroundings for 30 minutes before the start of each experiment.
Physiologic variables (eg, heart rate, respiratory rate, and rectal temperature) were monitored by use of a 5-lead ECG monitorc and a rectally inserted temperature probe. Measurements were obtained at 0, 5, 10, 15, 20, 30, 45, 60, and 1,440 minutes. Dexmedetomidine-treated goats were injected IV with an α2-adrenoceptor antagonist (atipamezoled; 50 and 200 μg/kg for goats receiving 5 and 20 μg of dexmedetomidine/kg, respectively) at 60 minutes to reverse dexmedetomidine effects.
The pain threshold was determined at 0, 15, 30, 45, 60, and 1,440 minutes. The pain threshold was measured at the center of the left flank. Pain was induced by potassium iontophoresis through gradual increases in potassium ions passing through the skin19; the number of ions was proportional to the increase in voltage or current. An investigator (ZYQ) who had skill in pain evaluation and who was not aware of the treatment administered to each goat evaluated the pain threshold. The site for evaluation of the pain threshold was shaved, washed with soap and water, and rinsed with 75% ethanol. Two electrodes were soaked with saturated potassium chloride and placed 1 to 2 cm apart on the skin. A galvanofaradism apparatuse was used to deliver the pulsed direct current to the electrodes, which forced potassium ions into the subcutaneous tissues. Voltage was continuously increased. Pain threshold voltage was recorded at the moment when obvious contractions of the local skin and muscles, turning of the head toward the abdomen, hunching of the back, and evasive body movements were observed. The current was then turned off.
Measurement of pain threshold was repeated 3 times. Percentage change in the pain threshold was calculated as follows:
where Vn is the mean voltage for the pain threshold during the experiment and V0 is the mean voltage for the pain threshold before the experiment (time 0).
Hematologic and biochemical variables
Biochemical and hematologic variables were determined by use of a 5-mL blood sample collected from an auricular vein with a disposable syringe. Samples were collected at 0, 30, 60, and 1,440 minutes. Hematologic variables (WBC count, RBC count, hemoglobin concentration, Hct, mean corpuscular volume, and mean corpuscular hemoglobin) were analyzed with a hematology analyzer.f Biochemical variables (concentrations of serum glucose, creatinine, and BUN and activities of AST and ALT) were measured with a biochemical analyzer.g
Statistical analysis
Data analysis was performed with a commercially available software program.h Physiologic variables, including pain threshold, heart rate, respiratory rate, rectal temperature, and biochemical and hematologic variables, were analyzed by use of a repeated-measures ANOVA to detect changes over time and between treatments. The Bonferroni test was applied when significant differences were found. Values of P < 0.05 were considered significant.
Results
Sedative and antinociceptive effects
Salivation and calmness were observed at (mean ± SD) 7.66 ± 5.83 minutes; snoring, muscle relaxation, and tongue protrusion were detected at 15.03 ± 5.00 minutes; and closed eyelids were observed at 15.33 ± 8.16 minutes after administration of dexmedetomidine. Teeth grinding and excitement were occasionally observed. Tympany developed in some dexmedetomidine-treated goats. Clinical signs in goats receiving dexmedetomidine at 20 μg/kg were more obvious than those in goats receiving dexmedetomidine at 5 μg/kg.
Calmness with abdominal muscle tension and occasional excitement were first noticed 10.00 ± 3.52 minutes after the start of electroacupuncture stimulation. In goats receiving electroacupuncture and dexmedetomidine, calmness was first noticed at 4.85 ± 2.91 minutes, and other clinical signs were not detected.
Antinociceptive effects of electroacupuncture and dexmedetomidine were expressed on the basis of pain threshold. The Mauchly test of sphericity revealed significant (P = 0.004) differences among the repeated measurements for pain threshold. A repeated-measures ANOVA indicated a significant (P < 0.001) difference among the treatment groups. Compared with the pain threshold for the control treatment, the pain threshold for electroacupuncture-treated goats was significantly increased at 15 to 60 minutes and for goats receiving dexmedetomidine at 20 μg/kg was significantly increased at 15 to 45 minutes. Dexmedetomidine at 5 μg/kg resulted in a significant increase in the pain threshold at 30 minutes, compared with results for the control group. The pain threshold for goats receiving electroacupuncture plus dexmedetomidine (5 μg/kg) was significantly higher at 30 minutes than that for goats receiving dexmedetomidine at 5 μg/kg alone as well as at 30 minutes for goats receiving electroacupuncture alone. There were no significant differences in pain threshold between goats receiving electroacupuncture plus dexmedetomidine and goats receiving dexmedetomidine at 20 μg/kg during the experiment (Table 1).
Effects of electroacupuncture and dexmedetomidine on changes in pain threshold (V) in healthy adult female goats (n = 6 goats/group).
| Group | 15 minutes | 30 minutes | 45 minutes | 60 minutes | 1,440 minutes |
|---|---|---|---|---|---|
| Control treatment* | 6.73 ± 6.69a | 11.60 ± 12.30a,A | 6.59 ± 12.00a | 7.79 ± 9.21a | 3.56 ± 2.87 |
| Dexmedetomidine (5 μg/kg, IM) | 32.82 ± 23.20a,b | 41.47 ± 20.37b | 25.08 ± 29.37 | 19.14 ± 9.77a,b | 4.46 ± 7.10 |
| Dexmedetomidine (20 μg/kg, IM) | 68.66 ± 26.26c | 75.95 ± 33.04c,B | 46.98 ± 30.20b | 34.83 ± 22.56 | 9.69 ± 14.26 |
| Electroacupuncture | 49.04 ± 42.02b,c | 46.18 ± 20.84b,d | 56.56 ± 45.10b | 67.43 ± 40.02c | 5.84 ± 10.51 |
| Electroacupuncture plus dexmedetomidine (5 μg/kg, IM) | 61.69 ± 32.63b,c | 81.11 ± 30.56c,B | 66.02 ± 49.56b | 51.83 ± 40.01b,c | 1.98 ± 9.33 |
Values are mean ± SD. Start of administration of electroacupuncture or injection of dexmedetomidine was designated as time 0.
Saline (0.9% NaCl) solution, IM.
Within a column, values with different superscript letters differ significantly (P < 0.05).
Within a column, values with different superscript letters differ significantly (P < 0.001).
Cardiorespiratory functions and rectal temperature
Administration of dexmedetomidine (5 or 20 μg/kg) caused a significant decrease in heart rate at 15 or 20 minutes, compared with the heart rate at time 0; the lowest heart rate was reached at 45 or 60 minutes and differed significantly from the value at time 0. Heart rate then increased over time and at 1,440 minutes was no longer significantly different from the heart rate at time 0. In contrast, electroacupuncture alone did not cause significant changes in heart rate during the experiment. Heart rate in goats receiving electroacupuncture plus dexmedetomidine (5 μg/kg) was significantly higher at 30 to 60 minutes than that in goats receiving dexmedetomidine at 20 μg/kg, but was significantly lower at 10 to 60 minutes than that in goats receiving the control treatment or goats receiving electroacupuncture alone (Table 2).
Effects of electroacupuncture and dexmedetomidine on changes in heart rate (beats/min) in healthy adult female goats (n = 6 goats/group).
| Group | 0 minutes | 5 minutes | 10 minutes | 15 minutes | 20 minutes | 30 minutes | 45 minutes | 60 minutes | 1,440 minutes |
|---|---|---|---|---|---|---|---|---|---|
| Control treatment* | 80.50 ± 6.50 | 80.00 ± 6.03 | 81.17 ± 5.64a | 80.00 ± 5.73a | 80.00 ± 6.07a,A | 80.00 ± 5.51a,A,B | 79.67 ± 5.24a,A | 79.50 ± 5.65a,A | 80.33 ± 7.31 |
| Dexmedetomidine (5 µg/kg, IM) | 80.67 ± 3.56 | 70.67 ± 11.17 | 68.00 ± 9.72b | 66.33 ± 9.67b | 64.00 ± 8.60†b | 61.17 ± 6.65†b,c,B | 56.67 ± 8.04‡b,B | 57.02 ± 8.6I‡b,B,C | 80.00 ± 2.19 |
| Dexmedetomidine (20 μg/kg, IM) | 81.50 ± 6.35 | 68.5 ± 15.10 | 62.17 ± 14.43b | 59.67 ± I2.32†b,A | 57.50 ± I2.80†B | 51.50 ± 11.93†c,C | 52.17 ± I0.53‡b,B | B 50.75 ± 5.6I‡,C | 80.17 ± 3.49 |
| Electroacupuncture | 77.67 ± 4.97 | 79.5 ± 5.43 | 80.67 ± 5.39a | 82.00 ± 4.00a,B | 83.I7 ± 4.26a,A | 83.33 ± 2.88a,A | 82.17 ± 3.87a,A | 80.67 ± 3.78a,A | 78.33 ± 2.25 |
| Electroacupuncture plus dexmedetomidire (5 µg/kg, IM) | 81.17 ± 3.43 | 74.67 ± 4.55 | 69.17 ± 6.68b | 65.17 ± 11.53b | 66.00 ± 9.57b | 66.00 ± 10.49b | 67.00 ± 10.35c | 67.07 ± 9.35c,A,B | 80.17 ± 3.43 |
Within a row, value differs significantly (P < 0.05) from the value at time 0.
Within a row, value differs significantly (p < 0.001) from the value at time 0.
Within a column, values with different superscript letters differ significantly (P < 0.05).
Within a column, values with different superscript letters differ significantly (P < 0.001).
See Table 1 for remainder of key.
Dexmedetomidine administration and electroacupuncture caused the respiratory rate to change in a pattern that was similar to that of the heart rate. The respiratory rate in goats receiving dexmedetomidine at 5 or 20 μg/kg decreased significantly (P < 0.001) at 5 minutes and reached the lowest value at 30 or 60 minutes, compared with the value at time 0. The respiratory rate then increased over time and at 1,440 minutes was no longer significantly different from the respiratory rate at time 0. Electroacupuncture alone did not cause significant changes in respiratory rate during the experiment. The respiratory rate for goats receiving electroacupuncture plus dexmedetomidine at 5 µg/kg was significantly higher than that for goats receiving dexmedetomidine at 20 μg/kg at 5 to 60 minutes. Respiratory rate of goats receiving electroacupuncture plus dexmedetomidine at 5 μg/kg was significantly lower at 20 to 60 minutes than that of goats receiving electroacupuncture alone (Table 3).
Effects of electroacupuncture and dexmedetomidine on changes in respiratory rate (breaths/min) in healthy adult female goats (n = 6 goats/group).
| Group | 0 minutes | 5 minutes | 10 minutes | 15 minutes | 20 minutes | 30 minutes | 45 minutes | 60 minutes | 1,440 minutes |
|---|---|---|---|---|---|---|---|---|---|
| Control treatment* | 19.03 ± 1.33 | 19.17 ± 2.23a | 19.00 ± 2.37a | 18.13 ± 2.32a,A,B | 18.23 ± 1.94a,b | 18.30 ± 2.35ba,b | 18.33 ± 2.14a,b,A,B | 18.33 ± 2.13a,b,A,B | 20.33 ± 2.3l |
| Dexmedetomidine (5 μg/kg, IM) | 22.00 ± 0.63 | l7.50 ± 1.38‡ | 15.17 ± 1.47‡b,A | 14.17 ± 1.33‡b,c,B,C | 13.33 ± 1.97‡c,d,A | 12.67 ± 1.37‡c,d,A | 13.00 ± 2.10‡c,d,B,C | 14.03 ± 0.89‡c,d,B,C | 21.00 ± 1.67 |
| Dexmedetomidine (20 Mg/kg, IM) | 21.17 ± 1.33 | l5.17 ± 1.60‡b | 14.50 ± 1.38‡b,A | 13.33 ± 1.37‡c,C | 12.33 ± 1.50‡d,A | 11.67 ± 1.63‡d,A | 11.17 ± 1.47‡d,C | 11.00 ± 1.55‡d,C | 20.83 ± 0.75 |
| Electroacupuncture | 20.13 ± 1.17 | 20.00 ± 1.41a | 20.17 ± 1.97B | 20.17 ± 2.48A | 20.80 ± 3.78a,B | 20.65 ± 4.18a,B | 20.13 ± 2.64a,A | 20.17 ± 2.48a,A | 20.17 ± 1.03 |
| Electroacupuncture plus dexmedetomidine (5 μg/kg, IM) | 21.67 ± 1.51 | l9.00 ± 1.90a | 17.83 ± 2.04 | 17.50 ± 1.87‡a,b | 16.83 ± 2.32‡b,c | 16.50 ± 1.87‡b,c | 15.17 ± 2.48‡b,c | 15.43 ± 2.48‡b,c | 21.17 ± 0.98 |
See Tables 1 and 2 for key.
Electroacupuncture plus dexmedetomidine at 5 μg/kg did not cause significant changes in rectal temperature during the experiment. Rectal temperature of goats decreased significantly at 60 minutes after administration of dexmedetomidine at 5 or 20 μg/kg, compared with the rectal temperature at time 0. Rectal temperature of goats receiving electroacupuncture plus dexmedetomidine (5 μg/kg) was significantly higher at 60 minutes, compared with that of goats receiving dexmedetomidine at 20 μg/kg, but was not significantly different throughout the experiment from that of goats administered dexmedetomidine at 5 μg/kg (Figure 1).
Effects of electroacupuncture (triangles), dexmedetomidine (5 μg/kg, IM [squares]; or 20 μg/kg, IM [circles]), electroacupuncture plus dexmedetomidine (5 μg/kg, IM [stars]), or saline (0.9% NaCl) solution (IM [control treatment; diamonds]) on mean ± SD rectal temperature in groups of healthy adult female goats (n = 6 goats/group). Start of administration of electroacupuncture or injection of dexmedetomidine was designated as time 0. *†Within a treatment, value differs significantly (*P < 0.05; †P < 0.001) from the value at time 0. a–dWithin a time point, values with different superscript letters differ significantly (P < 0.05). A,BWithin a time point, values with different superscript letters differ significantly (P < 0.001).
Citation: American Journal of Veterinary Research 77, 3; 10.2460/ajvr.77.3.252
Biochemical and hematologic variables
Serum glucose concentration increased significantly at 60 minutes for goats receiving dexmedetomidine at 5 μg/kg or at 30 and 60 minutes for goats receiving dexmedetomidine at 20 μg/kg or electroacupuncture plus dexmedetomidine (5 μg/kg), compared with the concentration at time 0. Electroacupuncture alone did not cause a significant change in the serum glucose concentration during the experiment. Compared with the concentration for goats receiving the control treatment, the serum glucose concentration increased significantly at 30 and 60 minutes for goats receiving dexmedetomidine at 20 μg/kg. The serum glucose concentration of goats receiving electroacupuncture plus dexmedetomidine (5 μg/kg) was significantly higher at 30 minutes than that of goats receiving electroacupuncture alone or dexmedetomidine at 5 μg/kg alone, but it did not differ significantly throughout the experiment from that of goats receiving dexmedetomidine at 20 μg/kg (Figure 2).
Effects of electroacupuncture and dexmedetomidine administration on mean ± SD serum glucose concentrations of healthy adult female goats. a–cWithin a time point, values with different superscript letters differ significantly (P < 0.05). A–CWithin a time point, values with different superscript letters differ significantly (P < 0.001). See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 77, 3; 10.2460/ajvr.77.3.252
Serum BUN and creatinine concentrations and ALT and AST activities of the goats did not change significantly, although they fluctuated during the experiment. The WBC count of goats receiving electroacupuncture alone increased significantly at 60 minutes, compared with the WBC count at time 0, but remained within the reference interval. There were no significant changes in other hematologic variables for any of the treated goats (data not shown).
Discussion
Acupuncture-induced antinociception is influenced by a variety of factors. Among them, acupuncture points and frequencies are the most important. Electroacupuncture with frequencies between 30 and 100 Hz provides effective antinociception for surgeries of the neck, chest, and abdomen of cattle.11 Investigators of 1 study19 used 36 Hz to stimulate the set of Bai hui, San tai, Erh gen, and San yan luo points in goats and obtained good antinociceptive effects. Investigators of another study23 used different frequencies to stimulate the same set of acupoints in goats and found that the pain threshold in goats stimulated by 60 Hz was greater than that obtained with other frequencies. In the present study, electroacupuncture at 60 Hz was used to stimulate a set of Bai hui, San tai, Erh gen, and San yan luo acupoints, which yielded an antinociceptive effect similar to that reported in another study.23
The degree of antinociception is commonly determined by scoring an animal's response to a pinprick in a particular region.24–26 This method is influenced by subjective factors. In 2 studies,27,28 investigators measured the pain threshold in sheep and goats with an algesimetry method based on a leg-lifting response to a subcutaneous electric stimulus. This method is not an involuntary reflex but instead represents a learned cognitive behavior. Additionally, this technique could not be used for restrained animals. Potassium iontophoresis is a convenient and reliable pain stimulus that can be provided rapidly and repeatedly with minimal loss in consistency of a subject's reported pain level.29 In 1973, the Research Group of Acupuncture Anesthesia of Peking Medical College30 first reported this quantitative method to measure pain thresholds in medical student volunteers for use in determining the efficacy of acupuncture-induced analgesia. Investigators of another study31 also used this method for the measurement of electroacupuncture-induced analgesia in humans. This method has been used to evaluate electroacupuncture-induced analgesia in cattle32 and goats.19 In the present study, potassium iontophoresis provided a tool for investigating changes in the pain threshold of treated goats. Electroacupuncture increased the pain threshold, which indicated that it provided good antinociception. The pain threshold induced by electroacupuncture increased and reached a maximal level at approximately 45 or 60 minutes after initiation of treatment, which is in accordance with results of another study19 of goats.
Antinociception induced by electroacupuncture is not sufficiently strong to completely block sharp, acute pain attributable to major surgery in some individuals.33 In other words, it is not reasonable to use electroacupuncture alone without analgesic supplementation to attain satisfactory antinociception. Therefore, attention has been paid to acupuncture-drug balanced antinociception.16,33 Electroacupuncture in combination with xylazine (an α2-adrenoceptor agonist) induced good antinociception in goats without some of the unwanted effects of α2-adrenoceptor agonists (eg, ruminal tympany, aspiration of refluxed material or saliva, bradycardia, decrease in respiratory rate and rectal temperature, and prolonged duration of recovery and recumbency).
In the present study, the high dose of dexmedetomidine (20 μg/kg) was selected on the basis of preliminary experiments in which it was found to cause deep sedation and antinociception. Electroacupuncture plus dexmedetomidine (5 μg/kg) provided an antinociceptive effect similar to that resulting from administration of dexmedetomidine at 20 μg/kg, but the adverse effects were less. To quantitatively estimate the degree of acupuncture-induced antinociception, some researchers have used an analgesic to ensure complete analgesia and have assessed the reduction of the amount of analgesic required in the electroacupuncture plus analgesic group, compared with the amount for the group receiving analgesic without acupuncture. The antinociceptive effect induced by electroacupuncture at 100 Hz for 30 minutes is approximately equivalent to the effect for 4 mg of morphine/kg in rats.18 Because the dose of morphine for a strong antinociceptive effect in rats is 10 mg/kg, the efficacy of electroacupuncture-induced antinociception is approximately half that resulting from a 10 mg/kg dose of morphine.18,34 A combination of electroacupuncture and epidural anesthesia for kidney transplants in humans resulted in a 48% reduction of epidural anesthetic.15 A combination of electroacupuncture and epidural anesthesia for surgery on the stomach in humans achieved a reduction in the dose of lidocaine by 40% to 46%, compared with the dose for a group administered lidocaine alone.17 In the study reported here, the combination of electroacupuncture and dexmedetomidine in goats provided a response similar to a reduction of the dexmedetomidine dose by 75%, compared with results for dexmedetomidine alone, which is consistent with the reduction of the dose for the combination of electroacupuncture plus xylazine in another study.19
Studies23,35 have revealed that differences in the frequency of electroacupuncture trigger the release of different opioid peptides in the CNS. Low-frequency (2 Hz) electroacupuncture exerts antinociceptive effects mainly by enhancing the release of enkephalin and β-endorphin, whereas high-frequency (100 Hz) electroacupuncture induces antinociceptive effects by facilitating the release of dynorphin in rats.35 Electroacupuncture at 60 Hz induces the simultaneous release of enkephalin, β-endorphin, and dynorphin in most of the antinociception-related nuclei in the CNS of goats.23 Additionally, antinociception attributable to acupuncture has been found to be facilitated by neurotransmitters such as catecholamines, including nor-adrenaline.36 Dexmedetomidine is highly selective for α2-adrenoceptors within the brain and spinal cord.37 Its presynaptic and postsynaptic inhibitory effects are responsible for antinociceptive actions.38 In the present study, the pain threshold of goats receiving electroacupuncture plus dexmedetomidine (5 μg/kg) was significantly higher, compared with that of goats receiving electroacupuncture alone or dexmedetomidine at 5 μg/kg alone, which indicated that a synergistic antinociceptive effect existed between electroacupuncture and dexmedetomidine. This synergism may have been caused, at least in part, by the coactivation of α-adrenoceptors or opioidergic-noradrenergic alterations.39–41 However, the related mechanism of synergism needs to be studied further.
In the present study, dexmedetomidine induced a profound decrease in the heart rate of goats, which is consistent with results of previous studies of goats3,6,42 and sheep.42 The reduction in heart rate may have been attributable to a decrease in sympathetic tone.7 The heart rate decreased in goats receiving the combination of electroacupuncture plus dexmedetomidine (5 μg/kg), compared with the heart rate in goats receiving dexmedetomidine (5 μg/kg) alone, which indicated that electroacupuncture attenuated the effect of dexmedetomidine on heart rate. Regulation of bradycardia by electroacupuncture may be related to excitation of sympathetic nerves and the resulting increase in serum concentrations of calcium, renin, angiotensin, and catecholamines.43,44
Almost all α2-adrenoceptor agonists reportedly cause some degree of respiratory depression.45,46 A decrease in the respiratory rate caused by dexmedetomidine has been reported for goats3 and buffalo calves.47 Similar findings were observed in the present study after administration of dexmedetomidine at doses of 5 or 20 μg/kg. However, electroacupuncture plus dexmedetomidine at 5 μg/kg induced less effect on respiratory rate, compared with the effect for dexmedetomidine alone at 5 or 20 μg/kg.
All α2-adrenoceptor agonists depress hypothalamic α2-adrenoceptors and cause hypothermia.48,49 A decrease in rectal temperature has been reported after dexmedetomidine administration to goats3 and dogs.50 In the study reported here, a decrease in rectal temperature was detected 60 minutes after administration of dexmedetomidine at 20 μg/kg. This might have been attributable to a decrease in skeletal muscle tone, a decrease in metabolic rate, or muscle relaxation along with the depression of thermoregulatory centers.25,48
On the basis of results of hematologic evaluations for the present study, there were no changes in RBC count, hemoglobin concentration, Hct, mean corpuscular volume, and mean corpuscular hemoglobin for treated goats. The WBC counts for goats receiving electroacupuncture increased at 60 minutes but remained within the reference interval. Numerous studies have indicated that electroacupuncture can be used to maintain body homeostasis. Acupuncture can elevate or reduce abnormal WBC counts into the reference range by regulating function of the bone marrow or constriction of the splenic sinusoid basal lamina micropores.51–53 Electroacupuncture also can suppress the production of adrenocortical hormone in response to stress.54,55 Electroacupuncture-induced transient changes in WBC count in the present study may have been associated with constriction of the splenic sinuses. An increase in serum glucose concentration has been reported in sheep56 and water buffalo57 after administration of medetomidine or dexmedetomidine. An increase in serum glucose concentration was also detected in the present study. This elevation in glucose concentration might have been attributable to α2-adrenergic inhibition of insulin release, stimulation of glucagon release, or both, from α and β cells of the pancreas, respectively, as well as an increase in glucose production by the liver.56,58 Relaxation of all body muscles during anesthesia may also lower the use of glucose at the tissue level, which can lead to hyperglycemia.57
In the present study, results indicated that electroacupuncture in combination with a low dose of dexmedetomidine (5 μg/kg, IM) provided antinociception similar to that for a high dose of dexmedetomidine (20 μg/kg, IM) without obvious effects on physiologic and biochemical variables of goats. Although variability of some variables, especially pain threshold, was great, which may have been caused by the genetic heterogeneity of the goats, there were significant treatment effects in the experiment. Therefore, electroacupuncture plus dexmedetomidine (5 μg/kg, IM) may be used for physical examination, diagnostic procedures, biopsy, application of plaster casts, application of surface medication, and minor surgeries in goats. However, whether it can be used for major surgeries in goats requires further confirmation.
Acknowledgments
Supported by the National Natural Science Foundation of China (Fund Nos. 31072177 and 31272619).
The authors declare that there were no conflicts of interest.
ABBREVIATIONS
| ALT | Alanine aminotransferase |
| AST | Aspartate aminotransferase |
Footnotes
Dexdomitor, Orion Pharma, Orion Corp, Espoo, Finland.
Multifunctional electrical pulse generator (G6805-3), Hua Yi Medical Instrument Factory, Shanghai, China.
Multiparameter monitor, Shenzhen (PM-9000), Mindray Biomedical & Electronics Co Ltd, Shenzhen, China.
Antisedan, Orion Pharma, Orion Corp, Espoo, Finland.
Galvanofaradism apparatus (DL-ZII), Shantou Medical Equipment Factory Co Ltd, Shantou, China.
PocH-100iV, Sysmex Corp, Kobe, Japan.
SPOTCHEM EZ sp-4430, Arkray Inc, Kyoto, Japan.
SPSS, version 18, SPSS Inc, Chicago, Ill.
References
1. Kastner SBR, von Rechenberg B, Keller K, et al. Comparison of medetomidine and dexmedetomidine as premedication in isoflurane anesthesia for orthopaedic surgery in domestic sheep. J Vet Med A Physiol Pathol Clin Med 2001; 48: 231–241.
2. Hunt JR, Grint NJ, Taylor PM, et al. Sedative and analgesic effects of buprenorphine, combined with either acepromazine or dexmedetomidine, for premedication prior to elective surgery in cats and dogs. Vet Anaesth Analg 2013; 40: 297–307.
3. Kumar R, Kinjavdekar P, Amarpal, et al. Clinicophysiological, haematobiochemical and haemodynamic effect of propofol and ketamine with dexmedetomidine in urolithic goats. Vet World 2014; 7: 566–573.
4. Unnerstall JR, Kopajtic TA, Kuhar MJ. Distribution of alpha 2 agonist binding sites in the rat and human central nervous system: analysis of some functional, anatomic correlates of the pharmacologic effects of clonidine and related adrenergic agents. Brain Res 1984; 319: 69–101.
5. Savola JM, Ruskoaho H, Puurunen J. Evidence for medetomidine as a selective and potent agonist at α2-adrenoreceptors. J Auton Pharmacol 1986; 6: 275–284.
6. Lawrence CJ, Prinzen FW, de Lang S. Hemodynamic and coronary vascular effects of dexmedetomidine in the anesthetized goat. Acta Anaesthesiol Scand 1997; 41: 830–836.
7. Kastner SBR, Boller J, Kutter APN, et al. Comparison of cardiopulmonary effects of dexmedetomidine administered as a constant rate infusion without loading dose in sheep and goats anaesthetised with sevoflurane. Small Rumin Res 2007; 71: 75–82.
8. Eze CA, Nweke RI, Nwangwu NC. Comparison of physiologic and analgesic effects of xylazine/ketamine, xylazine/lignocaine, and lignocaine anaesthesia in West-African Dwarf Goat. Niger Vet J 2004; 25: 39–47.
9. Rings DM, Muir WW. Cardiopulmonary effects of intramuscular xylazine-ketamine in calves. Can J Comp Med 1982; 46: 386–389.
10. Afshar FS, Baniadam A, Marashipour SP. Effect of xylazine-ketamine on arterial blood pressure, arterial blood pH, blood gases, rectal temperature, heart and respiratory rates in goats. Bull Vet Inst Pulawy 2005; 49: 481–484.
11. Wang DW, Jin YH. Present status of cesarean section under acupuncture anesthesia in China. Fukushima J Med Sci 1989; 35: 45–52.
12. Chen CL. Acupuncture anesthesia. In: Yu C, ed. Traditional Chinese veterinary acupuncture and moxibustion. Beijing: Chinese Agriculture Press, 1984;332–365.
13. Parmen V. Electroacupuncture analgesia in a rabbit ovariohysterectomy. J Acupunct Meridian Stud 2014; 7: 15–24.
14. Wang BG, Wang EZ, Chen XZ, et al. Transcutaneous electrical acupoint-stimulation potentiates the anesthetic effect of enflurane in humans. J Anesth 1995; 9: 40–43.
15. Qu GL, Zhuang XL, Xu GH, et al. Clinical observation on combined anesthetics—acupuncture anesthesia in 50 patients undergoing renal transplantation [in Chinese]. Chin J Pain Med 1996; 2: 72–77.
16. Dong QL, Wang GN. Effect of general anesthesia with combination of acupuncture and enflurane applied in radical operation of laryngocarcinoma. Chin J Integr Med 2006; 12: 306–309.
17. Qin BG, Lin YT, Cheng XX, et al. Electroacupuncture combined with low dose epidural anesthesia for subtotal gastrectomy. Chin J Pain Med 1996; 2: 135–143.
18. Tang NM, Dong HW, Wang XM, et al. Cholecystokinin antisense RNA increases the analgesic effect induced by electroacupuncture or low dose morphine: conversion of low responder rats into high responders. Pain 1997; 71: 71–80.
19. Liu DM, Zhou ZY, Ding Y, et al. Physiologic effects of electroacupuncture combined with intramuscular administration of xylazine to provide analgesia in goats. Am J Vet Res 2009; 70: 1326–1332.
20. Xu SF, Cao XD, Mo WY, et al. Effect of combination of drugs with acupuncture on analgesic efficacy. Acupunct Electrother Res 1989; 14: 103–113.
21. Xu W, Yan YS, Chen ZQ. Effect of ketamine on acupuncture analgesia [in Chinese]. Acupunct Res 1989; 14: 428–430.
22. Klide AM, Kung SH. Animal acupuncture points. In: Klide AM, Kung SH, eds. Veterinary acupuncture. 2nd ed. Philadelphia: University of Pennsylvania Press, 1982; 67–201.
23. Cheng LL, Ding MX, Xiong C, et al. Effects of electroacupuncture of different frequencies on the release profile of endogenous opioid peptides in the central nerve system of goats. Evid Based Complement Alternat Med 2012; 2012: 476457.
24. Kinjavdekar P, Singh Amarpal GR, Aithal HP, et al. Physiologic and biochemical effects of subarachnoidally administered xylazine and medetomidine in goats. Small Rumin Res 2000; 38: 217–228.
25. DeRossi R, Gaspar EB, Junqueira AL, et al. A comparison of two subarachnoid α2-agonists, xylazine and clonidine, with respect to duration of antinociception, and hemodynamic effects in goats. Small Rumin Res 2003; 47: 103–111.
26. Shah Z, Kalhore AB, Kachiwal AB, et al. Comparative studies on sedative and analgesic effects of xylazine and detomidine in goats. J Anim Plant Sci 2013; 23: 39–42.
27. Ludbrook G, Grant C, Upton R, et al. A method for frequent measurement of sedation and analgesia in sheep using the response to a ramped electrical stimulus. J Pharmacol Toxicol Methods 1995; 33: 17–22.
28. Grant C, Upton RN. The anti-nociceptive efficacy of low dose intramuscular xylazine in lambs. Res Vet Sci 2001; 70: 47–50.
29. Humphries SA, Long NR, Johnson MH. Iontophoretically applied potassium ions as an experimental pain stimulus for investigating pain mechanisms. Percept Psychophys 1994; 56: 637–648.
30. Research Group of Acupuncture Anesthesia of Peking Medical College. The effect of acupuncture on the human skin pain threshold. Chin Med J (Engl) 1973; 3: 151–157.
31. Ulett GA, Han S, Han JS. Electroacupuncture: mechanisms and clinical application. Biol Psychiatry 1998; 44: 129–138.
32. Peng H, Sun Y, Zhou W, et al. Effects of electroacupuncture on the pain threshold and the concentration of acetylcholine and the activity of acetylcholinesterase in the cerebrospinal fluid in cattle. J Huazhong Agric Univ 1982; 1: 61–63.
33. Han JS. Acupuncture anesthesia versus acupuncture-assisted anesthesia. In: Han JS, ed. The neurochemical basis of pain relief by acupuncture. Beijing: Peking University Medical Press, 2008;6–7.
34. Gades NM, Danneman PJ, Wixson SK, et al. The magnitude and duration of the analgesic effect of morphine, butorphanol, and buprenorphine in rats and mice. Contemp Top Lab Anim Sci 2000; 39: 8–13.
35. Han JS. Acupuncture: neuropeptide release produced by electrical stimulation of different frequencies. Trends Neurosci 2003; 26: 17–22.
36. Han JS, Tang J, Ren MF, et al. Central neurotransmitters and acupuncture analgesia. Am J Chin Med 1980; 8: 331–348.
37. Stenberg D. Physiological role of alpha 2-adrenoreceptors in the regulation of vigilance and pain. Acta Vet Scand Suppl 1989; 85: 21–28.
38. Yaksh TL. Pharmacology of spinal adrenergic systems which modulate spinal nociceptive processing. Pharmacol Biochem Behav 1985; 22: 845–858.
39. Shankar N, Varshney A, Bhattacharya A, et al. Electroacupuncture, morphine and clonidine: a comparative study of analgesic effects. Indian J Physiol Pharmacol 1996; 40: 225–230.
40. Herradon G, Ezquerra L, Nguyen T, et al. Noradrenergic and opioidergic alterations in neuropathy in different rat strains. Neurosci Lett 2008; 438: 186–189.
41. Kabalak A, Ekmekcioglu E, Ceylan A, et al. The synergistic antinociceptive interactions of morphine and dexmedetomidine in rats with nerve-ligation injury. Hippokratia 2013; 17: 326–331.
42. Kutter AP, Kastner SB, Bettschart-Wolfensberger R, et al. Cardiopulmonary effects of dexmedetomidine in goats and sheep anaesthetised with sevoflurane. Vet Rec 2006; 159: 624–629.
43. Hu J, Xie JM, Gao XQ, et al. Effects of acupuncture on intracellular free calcium and magnesium concentrations in cardiac myocytes of hemorrhagic hypotension rabbits [in Chinese]. Acupunct Res 1999; 4: 38–42.
44. Hsu CC, Weng CS, Sun MF, et al. Evaluation of scalp and auricular acupuncture on EEG, HRV and PRV. Am J Chin Med 2007; 35: 219–230.
45. Hammond RA, England GCW. The effect of medetomidine premedication upon propofol induction and infusion anesthesia in the dog. Vet Anaesth Analg 1994; 21: 24–28.
46. Shah Z, Ding MX, Hu ML. A review on the current use of alpha2 agonists in small ruminants. Kafkas Univ Vet Fak Derg 2014; 20: 633–639.
47. Khattri S, Kinjavdekar P, Amarpal, et al. Dexmedetomidine with butorphanol and propofol for total intravenous anesthesia in uraemic buffalo calves. Adv Anim Vet Sci 2013; 1: 15–23.
48. Ponder SW, Clarke WG. Prolonged depression of thermoregulation after xylazine administration to cats. J Vet Pharmacol Ther 1980; 3: 203–207.
49. MacDonald E, Scheinin H, Schienin M. Behavioural and neurological effects of medetomidine, a novel veterinary sedative. Eur J Pharmacol 1988; 158: 119–127.
50. Ahmad RA, Amarpal, Kinjavdekar HP, et al. Effects of midazolam or midazolam-fentanyl on sedation and analgesia produced by intramuscular dexmedetomidine in dogs. Asia J Anim Sci 2011; 5: 302–316.
51. Hau DM. Effects of electroacupuncture on leukocytes and plasma protein in the X-irradiated rats. Am J Chin Med 1984; 12: 106–114.
52. Mao HJ, Wu HH, Bu LL, et al. Relationship between electroacupuncture-induced regulatory effect on leukocytes and the caliber of splenic sinusoid basal lamina eyehole on rabbits [in Chinese]. Acupunct Res 2008; 33: 291–295.
53. Luo YH, Zhong GW, Zhao SP, et al. Efficacy observation of electroacupuncture intervention on severe acute pancreatitis at early stage complicated with intestinal paralysis. Chin Acupunct Moxibustion 2011; 31: 105–109.
54. Liao YY, Seto K, Saito H, et al. Effects of acupuncture on adrenocortical hormone production. (II) Effect of acupuncture on the response of adrenocortical hormone production to stress. Am J Chin Med 1980; 8: 160–166.
55. Han SHI, Yoon SH, Cho YW, et al. Inhibitory effects of electroacupuncture on stress responses evoked by tooth-pulp stimulation in rats. Physiol Behav 1999; 66: 217–222.
56. Brockman RP. Effect of xylazine on plasma glucose, glucagon and insulin concentration in sheep. Res Vet Sci 1981; 30: 383–384.
57. Singh GD, Kinjavdekar P, Amarpal, et al. Clinicophysiological and haemodynamic effects of fentanyl with xylazine, medetomidine and dexmedetomidine in isoflurane-anesthetised in water buffaloes (Bubalus bubalis). J S Afr Vet Assoc 2013; 84: 1–11.
58. Gasthuys F, Terpstra P, van de Hende C, et al. Hyperglycemia and diuresis during sedation with detomidine in the horse. Zentralbl Veterinarmed A 1987; 34: 641–648.
