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Canadian Journal of Anesthesia 53:1180-1185 (2006)
© Canadian Anesthesiologists' Society, 2006
Regional Anesthesia and Pain

Protective effect of prior administration of magnesium on delayed hyperalgesia induced by fentanyl in rats

[L’effet protecteur de l’administration préalable de magnésium sur l’hyperalgésie secondaire produite par le fentanyl chez le rat]

Alain C. Van Elstraete, MD, Philippe Sitbon, MD, Jean-Xavier Mazoit, MD PhD, Marc Conti, PharmD PhD and Dan Benhamou, MD

From the Department of Anesthesiology and Biochemistry Laboratory, Hôpital de Bicêtre, Assistance Publique-Hôpitaux de Paris, and the Anesthesia Laboratory UPRES-EA3540, Faculté de Médecine du Kremlin-Bicêtre Université Paris-Sud, Le Kremlin-Bicêtre, France.

Address correspondence to: Dr. Van Elstraete, Service d’Anesthésie-Réanimation, Hôpital de Bicêtre, 94275 Le Kremlin-Bicêtre, France. Phone: +(33) 145213441; Fax: +(33) 145212875; E-mail: alainvanel{at}hotmail.com


   Abstract
TOP
 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
Purpose: Magnesium exerts a physiological block of the ion channel on the N-methyl-D-aspartate receptor, and may therefore prevent the induction of central sensitization. The purpose of this study was to assess whether systemic magnesium can prevent long-lasting hyperalgesia induced by sc fentanyl administration in uninjured rats.

Methods: Long-lasting hyperalgesia was induced in male Sprague Dawley rats with sc fentanyl (four injections, 60 µg·kg–1 per injection at 15-min intervals). Magnesium sulphate (100 mg·kg–1) was injected ip 30 min prior to the first sc fentanyl injection. Sensitivity to nociceptive stimuli (paw-pressure test) was assessed for several days after injections.

Results: Subcutaneous fentanyl led to delayed hyperalgesia associated with a decrease in the nociceptive threshold lasting two days (35% decrease for the maximum effect). Intraperitoneal magnesium sulphate partially but significantly (P < 0.05) prevented the delayed decrease in the nociceptive threshold following sc administration of fentanyl.

Conclusions: This study shows that magnesium may prevent the delayed and prolonged hyperalgesia following fentanyl administration in rats.


   Introduction
TOP
 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
A growing body of evidence suggests that an active pronociceptive process is initiated by opioid administration.1 Recent preclinical studies have shown that systemic opioid administration in rats can lead to a long-lasting reduction of nociceptive threshold, a sign indicating central sensitization.2–5 Decreased analgesia and abnormal pain (thermal hyperalgesia and tactile allodynia) after administration of opioids suggest that neuropathic pain and opioid induced abnormal pain sensitivity share common pathophysiologic mechanisms.6,7 Among these neural mechanisms the N-methyl-Daspartate (NMDA) receptor has been shown to play a critical role.8–10

Magnesium exerts a physiological block of the ion channel on the NMDA receptor and is considered as a natural NMDA receptor antagonist.11 Such NMDA antagonism may therefore prevent the induction of central sensitization,12 and, thus, is likely to prevent opioid-induced pain sensitivity. The magnesium block is removed as part of the molecular sensitization process and we hypothesized that systemically administered magnesium could reduce sensitization following opioid-induced pain sensitivity by maintaining channel block at the NMDA receptor.

The purpose of this study was to investigate whether systemic magnesium might prevent long-lasting hyperalgesia induced by sc fentanyl administration in uninjured rats.


   Methods
TOP
 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
Animals
Experiments were performed on adult male Sprague- Dawley rats (CD1 Charles River; IFFA-CREDO, L’Arbresle, France; weight, 250–275 g at the beginning of the experiment) housed in individual standard cages under a 12-hr light 12-hr dark cycle (lights on at 8.00 AM) at a constant room temperature of 22 ± 2°C one week before experiments. Animals had access to food (Harland Teklod, Blackthorn, Bicester, Oxon, England) and water ad libitum. Experiments were approved by the Institution’s Animal Care and Use Committee and were carried out in accordance with guidelines from the International Association for the Study of Pain Committee for Research and Ethical Issues.13

Drugs
The following drugs were used: magnesium (magnesium sulphate; Sigma-Aldrich Co., Saint Quentin Fallavier, France) and fentanyl (fentanyl; Sigma-Aldrich Co., Saint Quentin Fallavier, France). All drugs were diluted in physiologic saline (0.9%). Fentanyl was injected subcutaneously (100 µL·100 g–1 body weight). Subcutaneous injections were performed on the back of unanesthetized rats with a 25-G needle. Magnesium was injected ip (2 mL·kg–1). Control animals received an equal volume of saline.

Measurement of nociceptive threshold
The threshold of response to increasing pressure was measured by a modification of the Randall–Selitto method,14 the paw-pressure vocalization test, with the use of an Analgesy Meter (Ugo Basile, Biosed, Camerio, Milan, Italy). The right hindpaw was positioned under a pressure pad, the probe tip (diameter 1 mm) being applied at the metacarpal level between the third and the fourth finger. A constantly increasing pressure was applied until the rat squeaked. A 600-g cutoff value was used to prevent tissue damage.4,15 The experiments were performed in a quiet room by the same investigator blinded to the treatment used.

General procedure
After arrival in the laboratory, animals were allowed five days to become accustomed to the colony room, gently handled daily for five minutes, and left in the test room for two hours (from 11:00 AM to 1:00 PM). All experiments began at 11.00 AM and were performed during the light part of the cycle. As previously described,4 to ensure nociceptive threshold stability, the basal nociceptive threshold was measured twice (with 30 min between the measurements) on the two days preceding the planned experimental day (D–2 and D–1). On the experimental day (D0), the basal nociceptive threshold was also determined twice before drug injections (30 min between measurements). Experiments with fentanyl were initiated only if no statistical changes were observed in basal nociceptive thresholds when estimated on days D–2, D–1 1, and D0. The rats were assigned randomly to the different experimental groups, and the investigator was unaware of the treatment used.

Experimental protocol
The study was performed in two phases. First, a study was performed to assess the action of systemic magnesium on fentanyl-induced hyperalgesia. Second, serum magnesium concentration, red cell magnesium concentration, and cerebrospinal fluid (CSF) magnesium concentration were measured in the fentanyl-induced hyperalgesic phase in naïve and magnesium-treated rats.

In phase I, there were four groups of animals. There were eight animals per group. According to the study of Célèrier et al.,4 and in order to induce a long-lasting hyperalgesia, fentanyl was injected four times (60 µg·kg–1 per injection) at 15-min intervals resulting in a total dose of 240 µg·kg–1 (groups A and B). Supplemental O2 3–4 L·min–1 was administered via a facemask throughout the procedure. Magnesium sulphate (100 mg·kg–1) was injected ip 30 min prior to the first sc fentanyl injection in group A whereas ip saline was injected in group B. As described previously ip magnesium sulphate 100 mg·kg–1 was unlikely to induce signs of toxicity.16 Control groups received sc saline with ip magnesium sulphate (group C) or sc saline with ip saline (group D). On D0, the nociceptive threshold was estimated every 30 min for a period of 240–360 min after the last fentanyl injection. Subsequent to D0, the nociceptive threshold was measured twice daily (30 min between both measurements) for five days (D+1–D+5).4

In phase II, there were two groups of animals. There were eight animals per group. According to the same protocol as in phase I, delayed hyperalgesia was induced in both groups with fentanyl. One group received ip magnesium, whereas the control group received ip saline. Twenty-four hours after ip injections, a lethal dose of ip pentothal was administered, and blood samples as well as CSF samples were collected from the rat’s heart and at the level of the cisterna magna, respectively.

Data and statistical analysis
The mean of the two measurements performed daily on days D–2, D–1, and D0 were compared [one-way analysis of variance (ANOVA) for repeated measures]. The basal reference value of the nociceptive threshold was chosen as the first measurement of the nociceptive threshold performed on day D0. Normal distribution was verified with the Kolsmogorov-Smirnov test. The nociceptive threshold was compared between groups and between days (D0, D+1 to D+5) using ANOVA (two-way, for repeated measures) followed by a Neuman-Keuls test as appropriate and unpaired Student’s t tests were used to assess comparisons between serum, red cells, and CSF magnesium concentrations. Data are expressed as the mean ± SD, and P < 0.05 was considered statistically significant.


   Results
TOP
 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
No statistically significant differences were found among the basal nociceptive thresholds of each experimental group: 340 ± 40 g (n = 8), 350 ± 40 g (n = 8), 340 ± 30 g (n = 8), 340 ± 10 g (n = 8) for groups A, B, C, and D respectively (one-way ANOVA, P > 0.05). The mean baseline nociceptive threshold value was 340 ± 30 g (n = 32).

Effects of sc fentanyl on the nociceptive threshold
Subcutaneous fentanyl (4 x 60 µg·kg–1) first caused a statistically significant short-lasting increase in nociceptive thresholds (P < 0.05; Figure 1AGo), and induced a statistically significant decrease in nociceptive thresholds on D+1 and D+2 (P < 0.05; Figure 1BGo). In contrast, sc saline did not alter the nociceptive threshold throughout the experiment (P > 0.05; Figures 1A and 1BGo).


Figure 1
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  		FIGURE 1 Short-lasting effect (A) and long-lasting effect (B) induced by sc fentanyl 60 µg·kg–1 x 4 compared with that of sc saline as measured by the paw-pressure vocalization test (n = 8 for each group). Mean nociceptive thresholds (± SD) are expressed in grams. *P < 0.05 (one-way ANOVA) compared with the basal nociceptive threshold value. Fentanyl or saline were injected four times at 15-min inter vals. Intraperitoneal saline was injected 30 min prior to the first sc fentanyl or saline injection.

 
Effects of ip magnesium pretreatment on the sc fentanyl induced changes in nociceptive thresholds

Intraperitoneal magnesium 100 mg·kg–1 did not modify the short-lasting effect (P > 0.05; Figure 2AGo), but significantly reduced the long-lasting decrease in nociceptive thresholds of sc fentanyl on D+1 and D+2 (P < 0.05; Figure 2BGo).


Figure 2
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  		FIGURE 2 Effects of ip magnesium pretreatment vs ip saline pretreatment on the short-lasting effect (A) and on the long-lasting effect (B) induced by sc fentanyl 60 µg·kg–1 x 4 as measured by the paw-pressure vocalization test (n = 8 for each group). Mean nociceptive thresholds (± SD) are expressed in grams. *P < 0.05 (one-way ANOVA) compared with the basal nociceptive threshold value for the magnesium group. #P < 0.05 (one-way ANOVA): longlasting hyperalgesia induced by sc fentanyl 60 µg·kg–1 x 4 after ip saline pretreatment vs after ip magnesium pretreatment. Fentanyl was injected four times at 15-min inter vals. Intraperitoneal saline or magnesium were injected 30 min prior to the first sc fentanyl injection.

 
Effects of ip magnesium alone or ip saline alone on nociceptive thresholds in naïve rats
Neither ip magnesium 100 mg·kg–1 nor ip saline altered the nociceptive threshold from D0 to D+5 (P > 0.05; Figure 3Go).


Figure 3
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  		FIGURE 3 Effects of ip magnesium vs ip saline pretreatment on the nociceptive threshold for days in opioid-naïve rats as measured by the paw-pressure vocalization test (n = 8 for each group). Mean nociceptive thresholds (± SD) were expressed in grams. There were no statistical differences between groups. Saline was injected four times at 15-min inter vals. Intraperitoneal saline or magnesium were injected 30 min prior to the first sc saline injection.

 
Magnesium concentrations
Serum magnesium concentration, red cell magnesium concentration, and CSF magnesium concentration were similar in both groups (TableGo).


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  		TABLE Magnesium concentrations (mmol·L–1) in serum, red cell, and CSF
 

   Discussion
TOP
 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
The main finding of this study is that systemic magnesium sulphate partially prevented the delayed hyperalgesia initiated by systemic fentanyl in uninjured rats.

Célèrier et al. have demonstrated that systemic administration of fentanyl in uninjured rats induced delayed hyperalgesia, a sign indicating central sensitization, by activating NMDA pain facilitatory processes. 4 Likewise, a growing body of evidence indicates that pronociceptive processes associated with central sensitization are associated primarily with amino acid activity at the NMDA receptor level,8–10 and studies have shown that opioid induced hyperalgesia is prevented by the NMDA receptor antagonists ketamine and MK-801.4,17,18 This is in accordance with previous studies which demonstrate that opioid-induced central sensitization and neuropathic pain share common pathophysiologic mechanisms.6,7 On the other hand, Begon et al. have shown in a preclinical study in rats that systemic magnesium and systemic MK-801 similarly reverse mechanical hyperalgesia in diabetic and mono-neuropathic rats.19 In agreement with these data, the present study therefore suggests that magnesium may prevent opioid-induced central sensitization through physiological block of the NMDA receptor.

Our study is also in accordance with preclinical studies, which report that intrathecal magnesium suppresses neuropathic pain responses in different rat models,20–22 and delays the development of tolerance when co-administered with opioids.23 However, concern may arise as to the actual effect of systemically administered magnesium at the spinal level. Magnesium crosses the blood-brain barrier by active transport.24 Even when iv magnesium is given in large doses no significant amount crosses the blood-brain barrier.25

The phase II of our study failed to demonstrate any significant difference in serum, red cell, and CSF concentrations of magnesium when measured 24 hr after ip injections of magnesium or saline after fentanyl-induced hyperalgesia in uninjured rats. We chose to measure magnesium concentrations at that time because the maximum decrease in nociceptive threshold has been shown to occur on days D+1 in this model of opioid-induced delayed hyperalgesia.4 This is in accordance with the results of Ko et al. who recently measured CSF magnesium concentration and serum magnesium concentration after perioperative iv magnesium sulphate infusion or placebo in patients undergoing abdominal hysterectomy.26 Although the serum magnesium concentration was significantly reduced in the control group, and whereas the serum magnesium concentration of the magnesium group exceeded twice the serum concentration observed in the control group, the CSF magnesium concentrations were similar in the two groups. However, a limitation of the study of Ko et al. and of our results is that magnesium concentrations in the CSF were measured only once. Therefore, CSF magnesium concentration was not compared in dependent samples in each group, and further studies evaluating the long-term dynamic relationship between CSF and serum magnesium concentrations are warranted. Furthermore, previous clinical studies have shown that systematically administered magnesium is effective in the management of neuropathic pain, and is therefore likely to act at the spinal level.27,28

Despite these observations, even if a spinal action of systemic magnesium on opioid-induced hyperalgesia exists, other mechanisms cannot be excluded. Magnesium is involved in several processes including gating of calcium channels.11 Conversely, impairment of motor function might have affected the results of the Randall-Selitto test. However, when systemic magnesium was administered alone there was no effect on the nociceptive threshold, and no motor impairment modified the Randall-Selitto test compared with saline (Figure 3Go). Cognitive impairment and impairment of vigilance have not been assessed in the study. A possible role of cognitive or vigilance impairment cannot therefore be excluded. On the other hand, hypercapnia subsequent to fentanyl administration was not assessed during the phase of increase in nociceptive threshold on D0. Potential prolonged neurological side-effects of hypercapnia interfering with nociceptive threshold assessment on days D+1 to D+5 cannot be ruled out.

In conclusion, our study shows that systemic magnesium administration confers a partial but significant prevention of opioid induced secondary hyperalgesia following systemic fentanyl in uninjured rats. Although these findings are encouraging, mechanistic clarifications are needed, and further evaluation of side effects and dose range studies are warranted before clinical applications can be considered.


   Footnotes
 
Accepted for publication May 29, 2006. Revision accepted September 18, 2006.

Competing interests: None declared.


   References
TOP
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
1 Mao J. Opioid-induced abnormal pain sensitivity: implications in clinical opioid therapy. Pain 2002; 100: 213–7.[Medline]

2 Laulin JP, Larcher A, Celerier E, Le Moal M, Simonnet G. Long-lasting increased pain sensitivity in rat following exposure to heroin for the first time. Eur J Neurosci 1998; 10: 782–5.[Medline]

3 Laulin JP, Celerier E, Larcher A, Le Moal M, Simonnet G. Opiate tolerance to daily heroin administration: an apparent phenomenon associated with enhanced pain sensitivity. Neuroscience 1999; 89: 631–6.[Medline]

4 Celerier E, Rivat C, Jun Y, et al. Long-lasting hyperalgesia induced by fentanyl in rats: preventive effect of ketamine. Anesthesiology 2000; 92: 465–72.[Medline]

5 Celerier E, Laulin JP, Corcuff JB, Le Moal M, Simonnet G. Progressive enhancement of delayed hyperalgesia induced by repeated heroin administration: a sensitization process. J Neurosci 2001; 21: 4074–80.[Abstract/Free Full Text]

6 Mao J, Price DD, Mayer DJ. Mechanisms of hyperalgesia and morphine tolerance: a current view of their possible interactions. Pain 1995; 62: 259–74.[Medline]

7 Mayer DJ, Mao J, Holt J, Price DD. Cellular mechanisms of neuropathic pain, morphine tolerance, and their interactions. Proc Natl Acad Sci USA 1999; 96: 7731–6.[Abstract/Free Full Text]

8 Chen L, Huang LY. Sustained potentiation of NMDA receptor-mediated glutamate responses through activation of protein kinase C by a mu opioids. Neuron 1991; 7: 319–26.[Medline]

9 Chen L, Huang LY. Protein kinase C reduces Mg2+ block of NMDA-receptor channels as a mechanism of modulation. Nature 1992; 356: 521–3.[Medline]

10 Mayer DJ, Mao J, Price DD. The development of morphine tolerance and dependence is associated with translocation of protein kinase C. Pain 1995; 61: 365– 74.[Medline]

11 Fawcett WJ, Haxby EJ, Male DA. Magnesium: physiology and pharmacology. Br J Anaesth 1999; 83: 302– 20.[Abstract/Free Full Text]

12 Woolf CJ, Thomson SW. The induction and maintenance of central sensitization is dependent on N-methyl- D-aspartic acid receptor activation; implications for the treatment of post-injury pain and hypersensitivity states. Pain 1991; 44: 293–9.[Medline]

13 Zimmermann M. Ethical guidelines for investigations of experimental pain in conscious animals. Pain 1983; 16: 109–10.[Medline]

14 Randall LO, Selitto JJ. A method for measurement of analgesic activity on inflamed tissue. Arch Int Pharmacodyn Ther 1957; 111: 409–19.[Medline]

15 Gentili ME, Mazoit JX, Samii KK, Fletcher D. The effects of a sciatic nerve block on the development of inflammation in carrageenan injected rats. Anesth Analg 1999; 89: 979–84.[Abstract/Free Full Text]

16 Mochizuki M, Akagi K, Inoue K, Shimamura K. A single dose toxicity study of magnesium sulfate in rats and dogs (Japanese). J Toxicol Sci 1998; 23(Suppl 1): 31–5.

17 Laulin JP, Maurette P, Corcuff JB, Rivat C, Chauvin M, Simonnet G. The role of ketamine in preventing fentanyl-induced hyperalgesia and subsequent acute morphine tolerance. Anesth Analg 2002; 94: 1263–9.[Abstract/Free Full Text]

18 Ben-Eliyahu S, Marek P, Vaccarino AL, Mogil JS, Sternberg WF, Liebeskind JC. The NMDA receptor antagonist MK-801 prevents long-lasting non-associative morphine tolerance in the rat. Brain Res 1992; 20: 304–8.

19 Begon S, Pickering G, Eschalier A, Dubray C. Magnesium and MK-801 have a similar effect in two experimental models of neuropathic pain. Brain Res 2000; 887: 436–9.[Medline]

20 Karasawa S, Ishizaki K, Goto F. The effect of intrathecal administration of magnesium sulphate in rats. Anaesthesia 1998; 53: 879–86.[Medline]

21 Takano Y, Sato E, Kaneko T, Sato I. Antihyperalgesic effects of intrathecally administered magnesium sulfate in rats. Pain 2000; 84: 175–9.[Medline]

22 Xiao WH, Bennett GJ. Magnesium suppresses neuropathic pain responses in rats via a spinal site of action. Brain Res 1994; 666: 168–72.[Medline]

23 McCarthy RJ, Kroin JS, Tuman KJ, Penn RD, Ivankovich AD. Antinociceptive potentiation and attenuation of tolerance by intrathecal co-infusion of magnesium sulfate and morphine in rats. Anesth Analg 1998; 86: 830–6.[Abstract]

24 Oppelt WW, MacIntyre I, Rall DP. Magnesium exchange between blood and cerebrospinal fluid. Am J Physiol 1963; 205: 959–62.[Abstract/Free Full Text]

25 Thurnau GR, Kemp DB, Jarvis A. Cerebrospinal fluid levels of magnesium in patients with preeclampsia after treatment with intravenous magnesium sulfate: a preliminary report. Am J Obstet Gynecol 1987; 157: 1435–8.[Medline]

26 Ko SH, Lim HR, Kim DC, Han YJ, Choe H, Song HS. Magnesium sulfate does not reduce postoperative analgesic requirements. Anesthesiology 2001; 95: 640–6.[Medline]

27 Brill S, Sedgwick PM, Hamann W, Di Vadi PP. Efficacy of intravenous magnesium in neuropathic pain. Br J Anaesth 2002; 89: 711–4.[Abstract/Free Full Text]

28 Crosby V, Wilcock A, Corcoran R. The safety and efficacy of a single dose (500 mg or 1 g) of intravenous magnesium sulfate in neuropathic pain poorly responsive to strong opioid analgesics in patients with cancer. J Pain Symptom Manage 2000; 19: 35–9.[Medline]





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