Center for Laboratory Animal Science, Tohoku Pharmaceutical University, 4-4-1 Komatsushima, Aoba-ku 981-8558, Sendai, Japan
* Corresponding author. E-mail: rando{at}tohoku-pharm.ac.jp
Accepted for publication April 29, 2005.
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Abstract |
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Methods. Experiments were performed on 133 male SpragueDawley rats weighing 280340 g. The animals were anaesthetized with urethane (1.3 g kg1, i.p.), and an arterial cannula was inserted to the level of the bifurcation of the femoral artery. The magnitude of the flexor reflex was examined by recording the electromyogram from the posterior biceps femoris/semitendinosus muscles.
Results. Our data show that the flexor reflexes evoked by intra-arterial (i.a.) injection of propofol (1%, 25100 µl) and capsaicin (0.050.2 µg) were dose dependent. An initial i.a. injection of procaine (2%, 200 µl) blocked both responses. Furthermore, the flexor reflex induced by these chemical stimuli were inhibited by morphine (5 mg kg1, s.c.) and restored with naloxone (1.5 mg kg1, s.c.). Pre-treatment with capsazepine (20 µg, i.a.), a selective VR1 antagonist, inhibited the capsaicin-evoked response, but not that of propofol. Indomethacin (10 mg kg1, i.p.), a non-selective cyclo-oxygenase inhibitor, inhibited only the propofol-evoked response and this recovered with arterial PGE2 (5 µg).
Conclusions. Collectively our data suggest that propofol-evoked vascular pain is mainly initiated by prostanoids.
Keywords: anaesthetics i.v., propofol ; analgesics non-opioid, indomethacin ; biotransformation (drug) ; capsaicin ; capsazepine ; reflexes, flexor
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Introduction |
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This study investigated the characteristics of propofol-evoked vascular pain by comparison with capsaicin, a potent algesic, using a vascular pain-evoked flexor reflex model8 in anaesthetized rats.
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Materials and methods |
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Dose and route of administration
Propofol (25, 50, and 100 µl), capsaicin (0.05, 0.1, and 0.2 µg), procaine (200 µl), prostaglandin E2 (5 µg), capsazepine (20 µg) and its vehicle were injected into the artery at a constant rate (0.8 ml min1) in Ringer's solution. Lidocaine (500 µg 10 µl1) was given by intrathecal (i.t.) injection with artificial cerebrospinal fluid (CSF; 126.7 mM NaCl, 2.5 mM KCl, 2.0 mM MgCl2, and 1.3 mM CaCl2, 20 µl min1). Morphine hydrochloride (5 mg kg1), naloxone hydrochloride (1.5 mg kg1) and its vehicle were injected subcutaneously. Urethane (1.3 g kg1), indomethacin (10 mg kg1) and its vehicle were administered intraperitoneally.
Animal preparation
The studies were approved by the Committee on Animal Experiments of Tohoku Pharmaceutical University. All experiments were performed on male SpragueDawley rats (n=133, Japan SLC), weighing 280340 g, which were housed in standard stainless steel cages (30.0x40.0x20.0 cm, widthxdepthxheight) at a constant temperature [23 (1)°C] and relative humidity [53 (2)%] under a 12-h lightdark cycle, with food (CE-2, CLEA Japan, Inc.) and water ad libitum. Arterial and i.t. cannulae were made of silicon-coated polyethylene tubing (PE-10) tapered to an appropriate size by heating. The arterial and i.t. cannulations were performed simultaneously under urethane anaesthesia. To reduce spinal cord stimulation, before making the incision for cannula insertion, the skin was anaesthetized with lidocaine. The arterial cannula was inserted about 1 cm into the left superficial caudal epigastric artery, so that the tip of the cannula reached the bifurcation of the femoral and superficial caudal epigastric arteries. The spinal cord was exposed via a laminectomy at the L34 level. An i.t. cannula filled with artificial CSF was inserted caudally through an opening in the dura, and its tip was carefully placed in the subarachnoid space at L56. One hour after surgery, the animal was used for the experiment.
Measuring the flexor reflex
The magnitudes of the flexor reflexes in response to arterial propofol, capsaicin, and a pinching stimulus of the skin on the hind limb were measured using an EMG of the left posterior biceps femoris/semitendinosus muscle (Fig. 1). EMG activity was recorded using concentric needle electrodes (26-gauge, Medtronic Inc.) inserted into the muscles and a DAT data recorder (RD-135T, TEAC Co.) after amplification with a polygraph (System 360, NEC Co., Japan). Each EMG was analysed with a signal processor (DP1100, NEC Co.), which summed the amplitudes (mV) of the collected action potentials every 50 µs and displayed the result in rectified form. For quantitative analysis, the area of the rectified form within the EMG was integrated (mV s2) and used as the EMG response. In addition, the latency and duration of the EMG responses were measured for propofol and capsaicin stimuli. During the experiments, the rats were maintained at 37 (1)°C with a heating sheet. All animals were only used once.
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Main experimental protocol
The effects of local anaesthetics
The effects of i.a. injection of procaine (200 µl) on propofol- and capsaicin-evoked EMG responses were examined in two groups of six rats (a total of 12 rats). Propofol or capsaicin were injected at 3, 60, and 120 min after the initial procaine injection. The effect of i.t. injection of lidocaine (500 µg 10 µl1) was performed using a similar protocol (a total of 12 rats). Propofol or capsaicin were injected at 5, 60, and 120 min after the initial lidocaine injection.
Desensitization
The potential for desensitization was evaluated with the administration of three repeated injections of propofol followed by one of capsaicin; or three repeated injections of capsaicin followed by one of propofol, within a short time interval (2 min) in six rats in each group (a total of 12 rats).
The effects of opioids
Rats were pre-treated with either morphine (5 mg kg1, s.c.) and naloxone (1.5 mg kg1, s.c.), morphine alone (5 mg kg1, s.c.) or saline (1 ml kg1, s.c.) (total 36 rats). Propofol or capsaicin were then injected at 30, 90, 150, and 210 min after pre-treatment.
The effect of capsazepine
In the experiments that used capsazepine (20 µg, i.a.), measurements of the propofol- and capsaicin-evoked flexor reflex were carried out at 1 and 60 min after arterial infusions of capsazepine or its vehicle (500 µl, i.a.) in five rats per group (a total of 20 rats).
The effect of indomethacin
Five rats were pre-treated with either indomethacin (10 mg kg1, i.p.) alone or, indomethacin (10 mg kg1) and prostaglandin E2 (5 µg, i.a.) (injected 55 min after the indomethacin) (20 rats). Propofol or capsaicin was injected at 60 and 120 min after pre-treatment with indomethacin. In addition, propofol was injected at 60 and 120 min after a further five rats pre-treated with TWEEN 80 (0.5%, 1 ml kg1, i.p.).
The effect of prostaglandin E2
The effects of prostaglandin E2 (5 µg) on the propofol- or capsaicin-evoked flexor reflex were performed 5 min after pre-treatment in five rats in each group (10 rats).
Statistical analysis
All data were expressed as the mean (SD). Unless mentioned specifically in the text, the data were subjected to one-way or repeated-measures ANOVA. When appropriate, the analysis included Fisher's Protected LSD post-hoc test. A significance level of P<0.05 was applied to all data.
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Results |
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Initial doseresponse studies
On the basis of the EMG value, latency and duration (Fig. 2), we decided to perform the subsequent experiments using propofol (50 µl) and capsaicin (0.1 µg).
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Discussion |
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In clinical studies, i.v. pre-treatment with the opioid alfentanil reduced the pain that occurred after an injection of propofol.5 In this study, arterial propofol and capsaicin had similar sensitivities to opiate receptors, as s.c. morphine markedly inhibited the flexor reflexes evoked by both i.a. propofol and capsaicin, and the antagonist naloxone restored these depressed responses. The same inhibitory effects of morphine on arterial bradykinin-evoked flexor reflexes have been reported in unanaesthetized rats.13 We have also reported similar results in another animal model of vascular pain.14 Ours and other studies indicate that vascular chemonociceptors are generally sensitive to opioids.
The vanilloid receptor (VR1) is located throughout the central and peripheral sensory nervous systems, mainly on C-fibres,15 16 and is sensitive to protons, high temperatures, and capsaicin in vitro.17 Moreover, capsaicin sensitivity is related to the expression of VR1 mRNA in the sensory ganglia of rats.18 This evidence indicates that many effects of capsaicin on the sensory system are exerted via VR1. Furthermore, capsazepine, a competitive VR1 antagonist,19 depressed various actions of capsaicin on sensory neurons either in vivo20 or in vitro.21 In this study, i.a. pre-treatment with capsazepine markedly depressed the capsaicin-evoked nociceptive reflex and shortened its latency and duration. However, it did not entirely depress that of propofol. Another in vitro study found that propofol did not influence the function of recombinant rat VR1 receptors.22 Considering these results and the properties of capsaicin, the vascular pain related to capsaicin may result from the activation of intra- or peri-vascular VR1 receptors on C-fibres, while that of propofol may arise from other receptors or mechanisms.
In contrast to the effects of capsazepine on the propofol- and capsaicin-evoked flexor reflex responses, we observed that indomethacin, a non-steroid anti-inflammatory drug (NSAID), strongly depressed propofol-evoked responses. In contrast, indomethacin had little effect on the capsaicin-evoked flexor responses. This is supported by the observation that indomethacin failed to affect the capsaicin-induced nociceptive cardiac reflexes of dogs.23 We have also already reported that, aspirin, did not inhibit i.a. capsaicin-induced aversive behaviour in guinea pigs.14 Another clinical study found that i.v. pre-treatment with aspirin alleviated the pain caused by propofol.24 NSAIDs exert their effects by inhibiting cyclo-oxygenase (COX) and consequently prostaglandin production.25 COX exists as two isomers, COX-1 and COX-2.26 In general, analgesic effects of these drugs are attributed to their inhibition of COX-2.27 Nakane and Iwama documented that propofol activated the plasma kallikreinkinin system, which resulted in the formation of bradykinin, a potent endogenous algesic, and caused pain.7 Other studies have demonstrated that NSAIDs block bradykinin-release of prostaglandin Es, which are involved in bradykinin-induced pain.28 We have also reported that arterial bradykinin excites thalamic nociceptive neurons, which are inhibited by NSAIDs and restored by arterial infusion of prostaglandin E2.29 Therefore, our data suggest that the depressive effects of indomethacin on propofol-evoked flexor reflexes resulted from inhibition of the activity of COX-2. In support of this hypothesis, the attenuated propofol responses were restored to control levels by i.a. infusion of prostaglandin E2, which is synthesized from the arachidonate cascade by COX.25 Moreover, arterial prostaglandin E2 alone augmented the propofol response accompanying a shortened latency greater than that of capsaicin.
In summary, our study revealed several characteristics of i.a. propofol-evoked pain using a flexor reflex model. The propofol response was compared with that of capsaicin. Propofol and capsaicin both evoked the flexor reflex in a dose-dependent, opioid-sensitive manner, although cross-desensitization was not observed between propofol and capsaicin. The VR1 antagonist capsazepine depressed only the capsaicin-evoked responses and not the propofol-evoked responses. The opposite results were seen in indomethacin-treated animals. Furthermore, arterial pre-infusion of prostaglandin E2 potentiated the propofol-evoked responses more strongly than those evoked by capsaicin. These results suggest that propofol characteristically causes vascular pain that occurs in response to prostanoids, particularly prostaglandin E2.
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References |
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2 Adam HK, Kay B, Douglas EJ. Blood disoprofol levels in anesthetised patients. Correlation of concentrations after single or repeated doses with hypnotic activity. Anaesthesia 1982; 37: 53640[ISI][Medline]
3 Ting CH, Arnott RH, Linkens DA, Angel A. Migrating from target-controlled infusion to closed-loop control in general anaesthesia. Comput Methods Programs Biomed 2004; 75: 12739[CrossRef][ISI][Medline]
4 McCulloch MJ, Lees NW. Assessment and modification of pain on induction with propofol (Diprivan). Anaesthesia 1985; 40: 111720[ISI][Medline]
5 Fletcher JE, Seavell CR, Bowen DJ. Pretreatment with alfentanil reduces pain caused by propofol. Br J Anaesth 1994; 72: 3424[Abstract]
6 Bachmann-Mennenga B, Ohlmer A, Heesen M. Incidence of pain after intravenous injection of a medium-/long-chain triglyceride emulsion of propofol. An observational study in 1375 patients. Arzneimittelforschung 2003; 53: 6216[ISI][Medline]
7 Nakane M, Iwama H. A potential mechanism of propofol-induced pain on injection based on studies using nafamostat mesilate. Br J Anaesth 1999; 83: 397404
8 Ando R, Yonezawa A, Watanabe C, Kawamura S. An assessment of vascular pain using the flexor reflex in anesthetized rats. Methods Find Exp Clin Pharmacol 2004; 26: 10915[CrossRef][ISI][Medline]
9 Beck PW, Handwerker HO. Bradykinin and serotonin effects on various types of cutaneous nerve fibers. Pflugers Arch 1974; 347: 20922[CrossRef][ISI][Medline]
10 Andoh R, Shima K, Miyagawa T, et al. Excitatory effects of dihydrocapsaicin on nociceptive neurons in the medial thalamus. Jpn J Pharmacol 1980; 30: 599605[ISI][Medline]
11 Szolcsanyi J, Anton F, Reeh PW, Handwerker HO. Selective excitation by capsaicin of mechano-heat sensitive nociceptors in rat skin. Brain Res 1988; 446: 2628[CrossRef][ISI][Medline]
12 Arndt JO, Klement W. Pain evoked by polymodal stimulation of hand veins in humans. J Physiol 1991; 440: 46778[Abstract]
13 Satoh M, Kawajiri S, Shishido K, Yamamoto M, Takagi H. Bradykinin-induced flexor reflex of rat hind-limb for evaluating various analgesic drugs. J Pharm Pharmacol 1979; 31: 1846[ISI][Medline]
14 Andoh R, Sakurada S, Kisara K, Takahashi M, Ohsawa K. Effects of intra-arterially administered capsaicinoids on vocalization in guinea pigs and medial thalamic neuronal activity in cats (abs. in English). Nippon Yakurigaku Zasshi 1982; 79: 27583[ISI][Medline]
15 Szallasi A, Conte B, Goso C, Blumberg PM, Manzini S. Vanilloid receptors in the urinary bladder: regional distribution, localization on sensory nerves, and species-related differences. Naunyn Schmiedebergs Arch Pharmacol 1993; 347: 6249[CrossRef][ISI][Medline]
16 Szallasi A, Nilsson S, Farkas-Szallasi T, Blumberg PM, Hokfelt T, Lundberg JM. Vanilloid (capsaicin) receptors in the rat: distribution in the brain, regional differences in the spinal cord, axonal transport to the periphery, and depletion by systemic vanilloid treatment. Brain Res 1995; 703: 17583[CrossRef][ISI][Medline]
17 Caterina MJ, Schumacher MA, Tominaga M, Rosen TA, Levine JD, Julius D. The capsaicin receptor: a heat-activated ion channel in the pain pathway. Nature 1997; 389: 81624[CrossRef][ISI][Medline]
18 Helliwell RJ, McLatchie LM, Clarke M, Winter J, Bevan S, McIntyre P. Capsaicin sensitivity is associated with the expression of the vanilloid (capsaicin) receptor (VR1) mRNA in adult rat sensory ganglia. Neurosci Lett 1998; 250: 17780[CrossRef][ISI][Medline]
19 Walpole CS, Bevan S, Bovermann G, et al. The discovery of capsazepine, the first competitive antagonist of the sensory neuron excitants capsaicin and resiniferatoxin. J Med Chem 1994; 37: 194254[CrossRef][ISI][Medline]
20 Dickenson AH, Dray A. Selective antagonism of capsaicin by capsazepine: evidence for a spinal receptor site in capsaicin-induced antinociception. Br J Pharmacol 1991; 104: 10459[ISI][Medline]
21 Bevan S, Hothi S, Hughes G, et al. Capsazepine: a competitive antagonist of the sensory neurone excitant capsaicin. Br J Pharmacol 1992; 107: 54452[ISI][Medline]
22 Hirota K, Smart D, Lambert DG. The effects of local and intravenous anesthetics on recombinant rat VR1 vanilloid receptors. Anesth Analg 2003; 96: 165660
23 Staszewska-Woolley J, Woolley G. Cardiac nociceptive reflexes: role of kinins, prostanoids and capsaicin-sensitive afferents. Pol J Pharmacol Pharm 1990; 42: 23747[ISI][Medline]
24 Bahar M, McAteer E, Dundee JW, Briggs LP. Aspirin in the prevention of painful intravenous injection of disoprofol (ICI35,868) and diazepam (Valium). Anaesthesia 1982; 37: 8478[ISI][Medline]
25 Vane JR, Botting RM. Anti-inflammatory drugs and their mechanism of action. Inflamm Res 1998; 47 (Suppl 2): S7887[CrossRef][ISI][Medline]
26 Vane JR. Inhibition of prostaglandin synthesis as a mechanism of action for aspirin-like drugs. Nat New Biol 1971; 231: 2325[ISI][Medline]
27 Hla T, Neilson K. Human cyclooxygenase-2 cDNA. Proc Natl Acad Sci USA 1992; 89: 73848
28 Lembeck F, Popper H, Juan H. Release of prostaglandins by bradykinin as an intrinsic mechanism of its algesic effect. Naunyn Schmiedebergs Arch Pharmacol 1976; 294: 6973[CrossRef][ISI][Medline]
29 Andoh R, Sakurada S, Sato T, Takahashi N, Kisara K. Potentiating effects of prostaglandin E2 on bradykinin and capsaicin responses in medial thalamic nociceptive neurons. Jpn J Pharmacol 1982; 32: 819[ISI][Medline]
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