The opioid agonist meperidine has actions, such as antishivering, that are more pronounced than those of other opioid agonists and that are not blocked with nonselective opioid antagonists. Agonists at the alpha(2) adrenoceptors, such as clonidine, are very effective antishivering drugs. Preliminary evidence also indicates that meperidine interacts with alpha(2) adrenoceptors. The authors therefore studied the ability of meperidine to bind and activate each of the alpha(2)-adrenoceptor subtypes in a transfected cell system.


The ability of meperidine to bind to and inhibit forskolin-stimulated cyclic adenosine monophosphate formation as mediated by the three alpha(2)-adrenoceptor subtypes transiently transfected into COS-7 cells has been tested. The ability of the opioid antagonist naloxone and the alpha(2)-adrenoceptor antagonists yohimbine and RX821002 to block the analgesic action of meperidine in the hot-plate test was also assessed. The ability of meperidine to fit into the alpha(2B) adrenoceptor was assessed using molecular modeling techniques.


Meperidine bound to all alpha2-adrenoceptor subtypes, with alpha(2B) having the highest affinity (alpha(2B), 8.6 +/- 0.3 microm; alpha(2C), 13.6 +/- 1.5 microm, P < 0.05; alpha(2A), 38.6 +/- 0.7 microm). Morphine was ineffective at binding to any of the receptor subtypes. Meperidine inhibited the production of forskolin-stimulated cyclic adenosine monophosphate mediated by all receptor subtypes but was most effective at the alpha(2B) adrenoceptor (alpha(2B), 0.6 microm; alpha(2A), 1.3 mm; alpha(2C), 0.3 mm), reaching the same level of inhibition (approximately 70%) as achieved with the alpha2-adrenoceptor agonist dexmedetomidine. The analgesic action of meperidine was blocked by naloxone but not by the alpha 2-adrenoceptor antagonists yohimbine and RX821002. The modeling studies demonstrated that meperidine can fit into the alpha(2B)-adrenoceptor subtype.


Meperidine is a potent agonist at the alpha2 adrenoceptors at its clinically relevant concentrations, especially at the alpha(2B)-adrenoceptor subtype. Activation of the alpha(2B) receptor does not contribute significantly to the analgesic action of meperidine. This raises the possibility that some of its actions, such as antishivering, are transduced by this mechanism.

MEPERIDINE is a potent opioid commonly used as an analgesic in postoperative settings. This compound is also frequently used to control shivering after general anesthesia. However, the mechanism for this therapeutic action of meperidine is not clear because other opioid narcotics such as sufentanil are much less effective for antishivering purposes. 1Further doubt about the role of opiate receptors for the antishivering effect of meperidine is raised by the finding that naloxone pretreatment does not inhibit the effects of meperidine on postanesthetic shivering. 2The administration of α2-adrenoceptor agonists, such as clonidine, are even more effective than meperidine at reducing postanesthetic shivering. 3,4Recently, we showed that meperidine is able to displace a radioalabeled α2-adrenoceptor ligand from its binding site in the central nervous system (unpublished observations). There are three α2-adrenoceptor subtypes (α2A, α2B, and α2C) that are ubiquitously distributed, and each may be uniquely responsible for some but not all of the actions of α2agonists. For example, the α2B-adrenoceptor subtype mediates the acute hypertensive response to α2agonists, 5whereas the α2Aadrenoceptor is responsible for the anesthetic and sympatholytic responses. 6In this study we investigated whether meperidine binds to cells containing the different α2-receptor subtypes and, if so, whether it functions as an agonist or antagonist. Because the α2adrenoceptors also transduce analgesic responses, we studied whether these adrenoceptors are required for the analgesic action of meperidine. Finally, we sought to model the binding of meperidine at the putative binding pocket of the α2B-adrenoceptor subtype.


All reagents were obtained from Sigma (St. Louis, MO) except bovine calf serum (Gemini Bio-Products, Calabasas, CA), gentamicin (Boehringer Mannheim, Indianapolis, IN), pCDNA-3 (Invitrogen, Carlsbad. CA), [3H]RX821002 (Amersham, Piscataway, NJ), RX821002 (RBI, Natick, MA), and meperidine (AstraZeneca, Wilmington, DE).

Transfection of Cells

Genes encoding human α2A(or C10, 7α2B[or C2]) 8and α2C(or C4) 9adrenoceptors were cloned into the multiple cloning site of pCDNA-3 vectors. Each adrenoceptor was expressed transiently in COS-7 cells using diethylaminoethyl-dextran–mediated transfection. 10COS-7 cells were maintained in Dulbecco modified Eagle medium supplemented with 10% bovine calf serum and 25 mg/l gentamicin.

Radiolabeled Ligand Binding of Transfected Cells

Cells were collected 3 days after transfection and rinsed twice with cold phosphate-buffered saline, and then 7 ml ice-cold lysis buffer (10 mm Tris-HCl, 1 mm EDTA, pH 7.4) was added. Cells were scraped off the flask and collected. The flask was rinsed with an additional 3 ml lysis buffer, and the washings were pooled. Cells were homogenized by four 8-s bursts at full speed using a Polytron homogenizer. The nuclei were pelleted by centrifugation at 220 g  for 5 min at 4°C, and the supernatant was centrifuged at 30,000 g  for 30 min at 4°C. The pelleted membranes were resuspended in an appropriate volume of binding buffer (75 mm Tris-HCl, 12.5 mm MgCl2, 1 mm EDTA, 0.01% CHAPS, pH 7.4). Binding experiments were performed in 500-μl volumes of buffer for 90 min at 25°C, using a nonselective α2ligand, [3H]RX821002 (1813 GBq). The bound radiolabeled ligand was separated from the free ligand by filtration through GF/C filters using a vacuum filtration manifold (Brandel Cell Harvester; Brandel, Gaithersburg, MD). Saturation binding isotherms were performed by incubating membranes with varying concentrations of the radioligand [3H]RX821002 (2.0, 13.0, and 3.2 nm for α2A, α2B, and α2Cadrenoceptors, respectively), and nonspecific binding was determined by adding 10 μm rauwolscine to radiolabeled binding studies. Competition experiments were conducted by incubating membranes with varying concentrations of competing ligand (meperidine and morphine) and a constant concentration of [3H]RX821002, and nonspecific binding was determined in the presence of 10 μm rauwolscine. Equilibrium dissociation constants (K  dand K  ivalues) and EC50values were determined from saturation isotherms and competition curves. Saturation isotherm data were analyzed by a nonlinear least squares curve-fitting technique, and the competition data were analyzed according to the Cheng-Prusoff equation using GraphPAD Prism (GraphPAD Software Inc., San Diego, CA).

Inhibition of Forskolin-stimulated Adenylyl Cyclase

Cells were collected as for radiolabeled ligand binding of transfected cells. Membranes from cells (at least 1.5 × 106for each 24-well assay) were prepared fresh just before use by homogenizing in 600 μl of ice-cold assay buffer (75 mm Tris, 25 mm MgCl2, 2 mm EDTA, pH 7.4) with 15 up–down strokes in a 2-ml glass homogenizer. Membrane preparation (20 μl) was added to 20 μl of “cyclase mixture” (2.7 mm mono{cyclohexylammonium} phosphoenolpyruvate, 53 μm GTP3Na.3 H2O, 0.2 IU pyruvate kinase, 1.0 IU myokinase, 125 μm adenosine triphosphate) and 10 μl of “reaction mixture.” To determine the inhibition of forskolin-stimulated adenylyl cyclase activity by meperidine and dexmedetomidine, the reaction mixture was composed of 100 μm forskolin and varying concentrations of meperidine or dexmedetomidine. Furthermore, to investigate the effect of rauwolscine on the inhibition of forskolin-stimulated adenylyl cyclase activity by meperidine, the reaction mixture was composed of 100 μm forskolin, 0.5 μm meperidine, and 20 μm rauwolscine. After addition of the membrane preparation, the cells were shaken (220 rpm) at 37°C for 10 min. The reaction was terminated by adding 10 μl ice-cold 0.8 m perchloric acid. The samples were left at room temperature for 20 min, after which 15 μl of 2N KOH in 25 mm HEPES was added. Tubes were centrifuged for 5 min in a microcentrifuge, and the supernatant was removed and assayed for cyclic adenosine monophosphate (cAMP) by the scintillation proximity assay kit (Amersham Pharmacia Biotech, Piscataway, NJ). Reaction mixture–inhibited cAMP accumulation was expressed as a percent of forskolin-alone stimulation; these data were analyzed by a nonlinear least squares curve-fitting technique, and EC50values were determined using GraphPAD Prism (Graph-Pad Software Inc.).

Analgesic Effects of Opioids

Experimental Animals.

All experimental protocols were reviewed and approved by the Subcommittee for Animal Studies (Veterans Affairs Palo Alto Health Care System, Palo Alto, CA) before the initiation of work. All protocols conform to the guidelines for the study of pain in awake animals as established by the International Association for the Study of Pain. Every effort was made to minimize animal suffering and to use only the number of animals necessary to produce reliable scientific data. In all studies presented, male C57BL/6 mice aged 12–16 weeks were used (Jackson Labs, Bar Harbor, ME). These mice were kept in cages (4–6 mice per cage) with a light–dark cycle of 12 h–12 h. Food and water were provided ad libitum . Animals were weighed on the day of experimentation for the calculation of drug dosages.

Drug Administration.

Drugs were injected alone or in combination subcutaneously in a total volume of approximately 50 μl. The animals were returned to their cages for 25 min after the injection of drugs and before hot-plate assay.

Hot-plate Assay.

The hot-plate assay was performed as described by O'Callaghan and Holtzman, 11with equipment from IITC (Woodland Hills, CA). The hot plate was set thermostatically at 54 ± 0.1°C. Mice were placed in a rectangular clear enclosure on the hot plate, and the time to licking of a hind paw, the endpoint of the assay, was measured with a stopwatch. Animals were left on the hot plate no longer than 60 s to prevent injury.

Molecular Modeling

Initial transmembrane topology and secondary structure predictions were made by submitting the sequence of the human α2Badrenoceptor to the Predict Protein Server at Columbia University (New York, NY, on August 19, 2000). The PHDhtm algorithm was used to make the topology predictions. 12The secondary structure analysis of the rhodopsin template (chain A of protein ID 1F88 in the protein database of the Research Collaboratory for Structural Bioinformatics **), and the production of an annotated template file was performed using the Kabsch and Sander 13algorithm. The Seqfold algorithm, 14available through the InsightII 2000 Modeling Environment (Molecular Simulations, Inc., San Diego, CA), was then used to align the sequence of the α2Aadrenoceptor to that of bovine rhodopsin. This algorithm allows the alignment of a sequence of unknown 3-dimensional structure to a template of known 3-dimensional structure based on sequence similarity, as scored by the Gonnet matrix, 15as well as fold similarity. Further refinement of the sequence alignment was made by importing it into the SwissPDB Viewer 16and calculating the mean force potential of Sippl 17for several additional manual sequence threadings. Final alignment of the sequence of the α2Breceptor to the rhodopsin template was refined based on the experimental data derived in this laboratory. The coordinates of the atoms within the α2Breceptor were then assigned. Side chains were initially optimized using the rotamer refinement function of the SwissPDB Viewer. 16Energy optimization of the structure was performed using the Hyperchem 5.1 software package (Hypercube Inc., Gainesville, FL) with the Amber 3.0 all-atom forcefield. This was performed initially only on the side chains and then on the entire structure without restraints. Optimization was initially performed via  the steepest descents method followed by the method of Polak-Ribiere.

The initial meperidine molecule was constructed and optimized using the Builder module within InsightII 2000. A model of the α2Badrenoceptor was constructed based on homology modeling techniques. In an attempt to understand the selective binding of meperidine to the human α2B-adrenoceptor subtype, simulated docking experiments were performed using the Affinity module within the InsightII 2000 Modeling Environment (Molecular Simulations, Inc.).

Statistical and Data Analysis

Statistical significance was determined by using one-way analysis of variance followed by Bonferroni multiple comparison tests. The EC50of the cAMP inhibition curves were calculated by nonlinear regression fitting to a sigmoidal dose–response model with variable slope.


Analysis of the equilibrium dissociation constants (K  d) of [3H]RX821002 for human α2-adrenoceptor subtypes showed that the ligand has lowest affinity for the human α2B-adrenoceptor subtype (α2B, 13.1 ± 1.5 nm; α2A, 2.2 ± 0.3 nm; α2C, 6.2 ± 0.3 nm; mean ± SD, P < 0.01, n = 4.). Meperidine competes for the binding of [3H]RX821002 for each of the human α2-adrenoceptor subtypes (fig. 1); morphine, another opioid ligand, does not displace the radiolabeled ligand off any of the human α2-adrenoceptor subtypes (fig. 2). Analysis of the inhibitory constant of meperidine showed that it has highest affinity for the human α2B-adrenoceptor subtype (α2B, 8.6 ± 0.3 μm; α2C, 13.6 ± 1.5 μm, P < 0.05; α2A, 38.6 ± 0.7 μm, P < 0.001 from the α2B-receptor value; mean ± SD, n = 4).

Meperidine potently inhibits forskolin-stimulated adenylyl cyclase activities in cells transfected with the human α2B-adrenoceptor subtype over the same concentration range as its analgesic activity (0.63 μm). The inhibitory action of meperidine on forskolin-stimulated adenylyl cyclase activity at the α2Breceptor, as defined as the EC50that achieved half maximal inhibition, is approximately 1,000-fold less than is required to reach the same level of inhibition with the other receptor subtypes (α2A, 1.3 mm; α2C, 0.3 mm;fig. 3). In fact, meperidine is as efficacious as dexmedetomidine, the highly selective and potent α2agonist, at inhibiting forskolin-stimulated adenylyl cyclase activities in cells transfected with the α2B-adrenoceptor subtype (fig. 4). That meperidine exerts its inhibitory action through α2adrenoceptors itself is evident from the fact that the inhibitory action of meperidine (50 μm) on α2B-mediated inhibition of forskolin-stimulated cAMP production is blocked by the α2-receptor antagonist rauwolscine (20 μm) (meperidine, 73.8 ± 5.1%; meperidine plus rauwolscine, 101 ± 2.5% of control level; mean ± SD, P < 0.01, n = 4).

The data in figure 5demonstrate that mice treated with 50 mg/kg meperidine had prolonged latencies for hind-paw licking when compared with saline-injected animals. Preliminary experiments established that 50 mg/kg meperidine was an approximate ED50for meperidine in this assay. This antinociceptive effect was completely blocked by the coadministration of 1 mg/kg naloxone, an opioid receptor antagonist. However, neither of two α2-adrenoceptor antagonists, namely, the nonimidazoline yohimbine (1 mg/kg) or the imidazoline RX 821002 (2 mg/kg), significantly reduced the meperidine-mediated analgesia. These doses of α2-adrenoceptor antagonists were previously shown to antagonize the antinociceptive effects of clonidine in mice when using the hot-plate assay. 18 

Assuming that the amino acid residues that could be affecting binding are within 0.4 nm of the ligand, there is a potential binding pocket made up of transmembrane domains 3, 4, 5, 6, and 7 (fig. 6). Further examination within this 4-Å radius reveals the amino acids in the α2Badrenoceptor, which differ from their counterparts in the α2Aadrenoceptor. They are LEU 145, ILE 173, SER 177, and SER 390. The corresponding residues in the α2Aadrenoceptor are PHE 166, VAL 197, CYS 201, and THR 393, respectively, which will impose different constraints on the ability of the ligand to dock (fig. 6). The corresponding residues in the α2Cadrenoceptor are PHE 184, ILE 211, CYS 215, and ILE 400. Another possible residue that is in close proximity to the meperidine (but just outside of the arbitrary 4-Å limit) is GLY 394 on the α2Badrenoceptor; the corresponding residue on the other receptor subtypes is THR 397 in the α2Aadrenoceptor and TYR 404 in the α2Cadrenoceptor. Thus, there exist structural reasons why meperidine should have activity at one receptor subtype and not another.


The opiate receptor agonist meperidine competes directly with α2-adrenoceptor ligands for the human α2-adrenoceptor subtypes (fig. 1). Morphine, another μ-opiate receptor agonist, has no affinity for these sites at clinically relevant concentrations (fig. 2). Meperidine has highest affinity for the α2B-adrenoceptor subtype, where it exerts comparable agonist efficacy to that seen with the highly selective α2agonist dexmedetomidine (fig. 4). This agonist action is blocked by an α2antagonist. The analgesic action of meperidine is not blocked by α2antagonists but is blocked by an opiate antagonist.

The α2-adrenoceptor agonists are either imidazoline, guanidinium, or phenylethanolamine compounds and are structurally dissimilar from the phenylpiperidine meperidine. However, there are examples of other piperidine compounds that exert their pharmacologic activity at the α2adrenoceptor. 19Interestingly, another piperidine compound causes a diuretic action via  renal α2adrenoceptors 20and is considered to be mostly, if not exclusively, of the α2Bvariety. Furthermore, as is seen in the results of the molecular modeling, there appear to be structural differences that may grossly account for the differential, subtype-specific binding of meperidine. In particular, there are probably differences in the binding pocket size and relative affinity for meperidine in the α2Aadrenoceptor and the α2Cadrenoceptor because of the proximity of a phenylalanine in the binding pocket, where there is a much smaller ILE in the more favorable binding pocket of the α2Badrenoceptor. Likewise, there is a glycine in the α2Badrenoceptor, whereas there are the much larger and more polar THR in the α2Aadrenoceptor and the TYR in the α2Cadrenoceptor.

The fact that meperidine is a potent agonist at the α2adrenoceptors raises the possibility that some of its actions are transduced by this mechanism. In reviewing the pharmacologic actions of α2-adrenoceptor agonists and those of meperidine, there is correspondence for analgesia and antishivering actions. The free plasma concentration of meperidine corresponding to antishivering effect is approximately 1–3 μm. 21To reduce cAMP concentrations to 50% of maximal, a concentration of 1–3 μm meperidine is certainly sufficient. It is unknown what proportion of α2Badrenoceptors must be occupied by meperidine to achieve an antishivering effect, but because 1 μm meperidine has significant cyclase inhibitory power at the α2Breceptor, it is feasible that 1–3 μm would be sufficient. These clinically achieved meperidine concentrations would also be analgesic. 22We have effectively ruled out the participation of α2adrenoceptors in the analgesic action of meperidine because neither the imidazoline (RX821002) nor the nonimidazoline (yohimbine) α2-adrenoceptor antagonists attenuated its antinociceptive action. As expected, the analgesic action of meperidine was reversed by a nonselective opiate receptor antagonist.

Of the many responses transduced by α2adrenoceptors, few are transduced by the α2B-adrenoceptor subtype. 23Of the α2-adrenoceptor–mediated actions attributed to the α2Bsubtype, the most well substantiated is the direct vasoconstrictive response in the peripheral vasculature. 5Concerning the analgesic action of the α2agonists, earlier pharmacologic evidence suggested that only the α2Asubtype transduced the analgesic action 24,25; however, evidence is now accumulating for a role for the other two subtypes. Prazosin-sensitive α2-adrenoceptor subtypes (either the α2Bor α2C) were shown to inhibit release of substance P in a spinal cord preparation. 26In addition, ST-91, a non–α2Asubtype preferring α2agonist, was shown to induce antinociception in rats when it was administered intrathecally, an effect that was blocked by prazosin. 27–30We recently showed that the antinociceptive action of nitrous oxide was reduced by 65% in the hot-plate assay and totally absent in the tail-flick assay in mice lacking the α2B-adrenoceptor subtype. These data therefore suggested that the α2B-adrenoceptor subtype has a role to play in nociception. However, there are no direct data implicating one or other α2-adrenoceptor subtype for the antishivering action of α2agonists.

Postanesthetic shivering occurs through a disorder in thermoregulation partly caused by differential recovery of excitatory and inhibitory centers. Thermoregulation is composed of multiple feedback systems and neurotransmitters together with the integration of information at each of several levels, including afferent impulses, hypothalamic centers, and skeletal muscles. 31Based largely on responsiveness to pharmacologic probes, adrenergic, 32serotonergic, 3,33and cholinergic 34pathways have each been causally implicated. Neuroanatomic studies have demonstrated that noradrenergic nuclei in the locus coeruleus are interconnected with hypothalamic thermoregulatory centers 35–37; furthermore, there is evidence that α adrenoceptors mediate the decrease in temperature after central administration of norepinephrine. 38The distribution of the α2B-adrenoceptor subtype may shed light on whether meperidine transduces its antishivering action through the α2B-adrenoceptor subtype. In rat spinal cord and dorsal root ganglion, mRNA for the α2A-, α2B-, and α2C-adrenoceptor subtypes have been identified. Within the brain, the most prevalent sites for α2BmRNA are in the thalamus and the cerebellum. 39 

The antishivering action of meperidine has previously been attributed to its action on κ-opioid receptors. After administration of naloxone, an opioid receptor antagonist that blocks both μ receptors and κ receptors at high doses and only μ receptors when administered at low doses, a differential effect of meperidine was revealed. Only a high dose of naloxone was able to prevent the effect of meperidine on shivering; when administered in low doses, naloxone did not influence the action of meperidine, thus indicating that κ receptors and not μ receptors may mediate its antishivering action. 2However, other more κ-receptor–selective drugs, such as pentazocine, failed to inhibit postanesthetic shivering, thus suggesting that κ-opioid receptors are not implicated. 40In addition, the effect of meperidine on shivering is more effective than that of pure μ-opioid receptor agonists at equianalgesic doses. 1,41Thus, an α2-adrenoceptor–mediated mechanism of action of meperidine on postanesthetic shivering as suggested by the data presented here is conceivable. Clinically, α2-adrenoceptor agonists such as clonidine have been successfully used both for prevention and treatment of postanesthetic shivering, 3,42–45indicating that α2adrenoceptors mediate this action. Our current findings suggest that it is likely to be caused by the activation of the α2B-adrenoceptor subtype.

The authors thank the Medical Research Council (London, UK), National Institutes of Health (Bethesda, Maryland), and the Department of Veterans Affairs (Washington, DC).


Alfonsi P, Sessler DI, Du Manoir B, Levron JC, Le Moing JP, Chauvin M: The effects of meperidine and sufentanil on the postoperative patients. A nesthesiology 1998; 89: 43–8
Kurz M, Belani KG, Sessler DI, Kurz A, Larson MD, Schroeder M, Blanchard D: Naloxone, meperidine, and shivering. A nesthesiology 1993; 79: 1193–201
Joris J, Banache M, Bonnet F, Sessler DI, Lamy M: Clonidine and ketanserin both are effective treatment shivering. A nesthesiology 1993; 79: 532–9
Macintyre PE, Pavlin EG, Dwersteg JF: Effect of meperidine on oxygen consumption, carbon respiratory gas exchange in postanesthesia shivering. Anesth Analg 1987; 66: 751–5
Link RE, Desai K, Hein L, Stevens ME, Chruscinski A, Bernstein D, Barsh GS, Kobilka BK: Cardiovascular regulation in mice lacking subtypes b and c. Science 1996; 273: 803–5
Lakhlani PP, MacMillan LB, Guo TZ, McCool BA, Lovinger DM, Maze M, Limbird LE: Substitution of a mutant alpha2A-adrenergic receptor via “hit and run” gene targeting reveals the role of this subtype in sedative, analgesic, and anesthetic-sparing responses in vivo. Proc Natl Acad Sci U S A 1997; 94: 9950–5
Kobilka BK, Matsui H, Kobilka TS, Yang-Feng TL, Francke U, Caron MG, Lefkowitz RJ, Regan JW: Cloning, sequencing, and expression of the gene coding for the human platelet alpha 2-adrenergic receptor. Science 1987; 238: 650–6
Regan JW, Kobilka TS, Yang-Feng TL, Caron MG, Lefkowitz RJ, Kobilka BK: Cloning and expression of a human kidney cDNA for an alpha 2-adrenergic receptor subtype. Proc Natl Acad Sci U S A 1988; 85: 6301–5
Lomasney JW, Lorenz W, Allen LF, King K, Regan JW, Yang-Feng TL, Caron MG, Lefkowitz RJ: Expansion of the alpha 2-adrenergic receptor family: Cloning and characterization of a human alpha 2-adrenergic receptor subtype, the gene for which is located on chromosome 2. Proc Natl Acad Sci U S A 1990; 87: 5094–8
Kobilka BK, Kobilka TS, Daniel K, Regan JW, Caron MG, Lefkowitz RJ: Chimeric alpha 2-, beta 2-adrenergic receptors: Delineation of domains involved in effector coupling and ligand binding specificity. Science 1988; 240: 1310–6
O'Callaghan JP, Holtzman SG: Quantification of the analgesic activity of narcotic antagonist by a modified hot-plate procedure. J Pharmacol Exp Ther 1975; 192: 497–505
Rost B, Casadio R, Fariselli P, Sander C: Transmembrane helices predicted at 95% accuracy. Protein Sci 1995; 4: 521–33
Kabsch W, Sander C: Dictionary of protein secondary structure: pattern recognition of hydrogen-bonded and geometrical features. Biopolymers 1983; 22: 2577–637
Olszewski KA YL, Edwards D: SeqFold, fully automated fold recognition and modeling software, validation and application. Theor Chem Acc 1999; 101: 57–61
Gonnet GH, Cohen MA, Benner SA: Exhaustive matching of the entire protein sequence database. Science 1992; 256: 1443–5
Guex N, Peitsch MC: SWISS-MODEL and the Swiss-PDB Viewer: An environment for comparative protein modeling. Electrophoresis 1997; 18: 2714–23
Sippl MJ: Calculation of conformational ensembles from potentials of mean force: An approach to the knowledge-based prediction of local structures in globular proteins. J Mol Biol 1990; 213: 859–83
Oluyomi AO, Hart SL: Alpha-adrenoceptor involvement in swim stress-induced antinociception in the mouse. J Pharm Pharmacol 1990; 42: 778–84
Orito K, Imaizumi T, Yoshida K, Fujiki H, Kishi M, Teramoto S, Tanaka M, Shimizu H, Tominaga M, Kimura Y, Kambayashi J, Mori T: Mechanisms of action of OPC-28326, a selective hindlimb vasodilator. J Pharmacol Exp Ther 1999; 291: 604-11
Wang YX, Clarke GD, Sbacchi M, Petrone G, Brooks DP: Contribution of alpha-2 adrenoceptors to kappa opioid agonist-induced water diuresis in the rat. J Pharmacol Exp Ther 1994; 270: 244–9
Kurz A, Ikeda T, Sessler DI, Larson MD, Bjorksten AR, Dechert M, Christensen R: Meperidine decreases the shivering threshold twice as much as the vasoconstriction threshold. A nesthesiology 1997; 86: 1046–54
Blake DW, Stainsby GV, Bjorksten AR, Dawson PJ: Patient-controlled epidural versus intravenous pethidine to supplement epidural bupivacaine after abdominal aortic surgery. Anaesth Intensive Care 1998; 26: 630–5
Kable JW, Murrin LC, Bylund DB: In vivo gene modification elucidates subtype-specific functions of alpha(2)-adrenergic receptors. J Pharmacol Exp Ther 2000; 293: 1–7
Millan MJ: Evidence that an alpha 2A-adrenoceptor subtype mediates antinociception in mice. Eur J Pharmacol 1992; 215: 355–6
Millan MJ, Bervoets K, Rivet JM, Widdowson P, Renouard A, Le Marouille-Girardon S, Gobert A: Multiple alpha-2 adrenergic receptor subtypes: II. Evidence for a role of rat R alpha-2A adrenergic receptors in the control of nociception, motor behavior and hippocampal synthesis of noradrenaline. J Pharmacol Exp Ther 1994; 270: 958–72
Ono H, Mishima A, Ono S, Fukuda H, Vasko MR: Inhibitory effects of clonidine and tizanidine on release of substance P from slices of rat spinal cord and antagonism by alpha-adrenergic receptor antagonists. Neuropharmacology 1991; 30: 585–9
Graham BA, Hammond DL, Proudfit HK: Differences in the antinociceptive effects of alpha-2 adrenoceptor agonists in two substrains of Sprague-Dawley rats. J Pharmacol Exp Ther 1997; 283: 511–9
Graham BA, Hammond DL, Proudfit HK: Synergistic interactions between two alpha(2)-adrenoceptor agonists, dexmedetomidine and ST-91, in two substrains of Sprague-Dawley rats. Pain 2000; 85: 135–43
Takano Y, Takano M, Yaksh TL: The effect of intrathecally administered imiloxan and WB4101: Possible role of alpha 2-adrenoceptor subtypes in the spinal cord. Eur J Pharmacol 1992; 219: 465–8
Takano Y, Yaksh TL: Characterization of the pharmacology of intrathecally agonists and antagonists in rats. J Pharmacol Exp Ther 1992; 261: 764–72
Farber NE, Poterack KA, Kampine JP, Schmeling WT: The effects of halothane, isoflurane, and enflurane on responses in the neuraxis of cats. A nesthesiology 1994; 80: 879–91
Brichard G, Johnstone M: The effect of methylphenidate (Ritalin) on post-halothane muscular spasticity. Br J Anaesth 1970; 42: 718–22
Powell RM, Buggy DJ: Ondansetron given before induction of anesthesia reduces shivering after general anesthesia. Anesth Analg 2000; 90: 1423–7
Horn EP, Standl T, Sessler DI, von Knobelsdorff G, Buchs C, Schulte am Esch J: Physostigmine prevents postanesthetic shivering as does meperidine or clonidine. A nesthesiology 1998; 88: 108–13
Swanson LW: An autoradiographic study of the efferent connections of the preoptic region in the rat. J Comp Neurol 1976; 167: 227–56
Parent A, Steriade M: Afferents from the periaqueductal gray, medial hypothalamus and medial thalamus to the midbrain reticular core. Brain Res Bull 1981; 7: 411–8
Unnerstall JR, Kopajtic TA, Kuhar MJ: Distribution of alpha-2 agonist binding sites in the rat and human nervous system: Analysis of some functional, anatomic pharmacologic effects of clonidine and related adrenergic agents. Brain Res 1984; 319: 69–101
Mora F, Lee TF, Myers RD: Involvement of alpha- and beta-adrenoreceptors in the central action of norepinephrine on temperature, metabolism, heart and respiratory rates of the conscious primate. Brain Res Bull 1983; 11: 613–6
Renouard A, Widdowson PS, Millan MJ: Multiple alpha 2 adrenergic receptor subtypes: I. Comparison of [3H]RX821002-labeled rat R alpha-2A adrenergic receptors in cerebral cortex to human H alpha-2A adrenergic receptor and other populations of alpha-2 adrenergic subtypes. J Pharmacol Exp Ther 1994; 270: 946–57
Terasako K, Yamamoto M: Comparison between pentazocine, pethidine and placebo in he treatment of post-anesthetic shivering. Acta Anaesthesiol Scand 2000; 44: 311–2
Pauca AL, Savage RT, Simpson S, Roy RC, Miyakawa H, Matsumoto K, Matsumoto S, Mori M, Yoshitake S, Noguchi T, Taniguchi K, Honda N: Effect of pethidine, fentanyl and morphine on post-operative shivering in man. Acta Anaesthesiol Scand 1984; 28: 138–43
Horn EP, Werner C, Sessler DI, Steinfath M Schulte am Esch J: Late intraoperative clonidine administration prevents shivering after total intravenous or volatile anesthesia. Anesth Analg 1997; 84: 613–7
Erkola O, Korttila K, Aho M, Haasio J, Aantaa R, Kallio A: Comparison of intramuscular dexmedetomidine and for elective abdominal hysterectomy. Anesth Analg 1994; 79: 646–53
Jalonen J, Hynynen M, Kuitunen A, Heikkila H, Perttila J, Salmenpera M, Valtonen M, Aantaa R, Kallio A: Dexmedetomidine as an anesthetic adjunct in coronary artery bypass grafting. A nesthesiology 1997; 86: 331–45
Talke P, Tayefeh F, Sessler DI, Jeffrey R, Noursalehi M, Richardson C: Dexmedetomidine does not alter the sweating threshold, but comparably and linearly decreases the vasoconstriction and shivering thresholds. A nesthesiology 1997; 87: 835–41