JOURNAL HOME CME HOME THIS MONTH PAST ISSUES ETOC COLLECTIONS AUTHORS REVIEWERS EDITORIAL BOARD FEEDBACK RSS HELP
		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (6) Citing Articles via Google Scholar Google Scholar Articles by Chen, Y. Articles by Hertz, L. Search for Related Content PubMed PubMed Citation Articles by Chen, Y. Articles by Hertz, L.

---

NEUROSURGICAL ANESTHESIA

A Correlation Between Dexmedetomidine-Induced Biphasic Increases in Free Cytosolic Calcium Concentration and Energy Metabolism in Astrocytes

Departments of Pharmacology and Anesthesia, University of Saskatchewan, Saskatoon, Saskatchewan, Canada

Address correspondence to Ye Chen, MD, PhD, Stroke Branch, NINDS/NIH, 36 Convent Dr., MSC 4128, Bethesda, MD 20892-4128. Address e-mail to chenye{at}codon.nih.gov

	Abstract

Top Abstract Introduction Methods Results Discussion References

 
The ₂-adrenergic agonist, dexmedetomidine, increases free cytosolic calcium concentration ([Ca²⁺]_i) in astrocytes, but not in neurons. The present study was performed to characterize the origin of the increased Ca²⁺ in mouse astrocytes cultured from the cerebral cortex, the dose dependence of the effect, and its functional consequences. The increase in [Ca²⁺]_i was independent of extracellular Ca²⁺, but was inhibited by dantrolene, showing that it is derived from intracellular stores; two peaks in [Ca²⁺]_i were demonstrated—one around 100 nM dexmedetomidine and the other in the low micromolar range. A similar dose dependence was found for pyruvate dehydrogenation, the initial metabolic reaction of oxidative degradation of pyruvate, suggesting that the these events are interrelated. The ₂-adrenergic antagonist, yohimbine, abolished the metabolic stimulation at both peaks. However, whereas the increase in [Ca²⁺] _i at 100 nM is abolished by yohimbine, increase in the micromolar range was partly inhibited by yohimbine and partly by idazoxan, an inhibitor at the imidazoline-preferring site. The stimulation of energy metabolism in cerebrocortical astrocytes may explain the repeated finding that dexmedetomidine does not decrease oxidative metabolism in the brain in vivo. The functional importance of the additional imidazoline receptor-mediated increase in [Ca²⁺]_i at large dexmedetomidine concentrations is unknown.

Implications: Cytosolic calcium concentration and metabolism were measured in cultured astrocytes, the predominant glial cells. The results suggest that dexmedetomidine may owe its anesthetic effects to a Ca²⁺-dependent increase in astrocytic energy metabolism, allowing these cells to more effectively remove extracellular glutamate and potassium ions, and thus, decreasing neuronal excitability.

	Introduction

Top Abstract Introduction Methods Results Discussion References

 
Dexmedetomidine is a potent and highly specific ₂-adrenergic agonist which, in receptor binding experiments, has an ₂/₁ selectivity ratio of 1600, or several times higher than clonidine (1). It potently reduces the amount of volatile anesthetics and fentanyl-like opioids required for anesthesia, and induces, on its own, hypnosis at doses >100 µg (0.5 µmol) per kg and increases sleep time dose-dependently up to 1000 µg (5.4 µmol) per kg after intraperitoneal injection in rats (2). Its wide therapeutic window is reflected by a more than 20-fold difference between 50% effective plasma concentration required for loss of the whisker reflex (5.4 nM) and loss of the cornea reflex (132 nM) in the rat (3). In addition to stimulating ₂-adrenergic receptors, dexmedetomidine also activates an imidazoline-preferring site (4–5).

It was originally assumed that all ₂-adrenergic receptors are located presynaptically and inhibit noradrenaline release. Although ₂-adrenergic agonists undoubtedly have such an effect, compelling evidence for an additional localization on postjunctional target cells has appeared. The target cells in the central nervous system displaying ₂-adrenergic receptors are not only neurons, but include astrocytes (6), the predominant glial cells, which in the human brain outnumber neurons. Stimulation of postjunctional ₂-adrenergic receptors activates the phosphatidylinositol second messenger system, as seen from the observation that the prototypical ₂-adrenergic agonist clonidine causes an increase in free cytosolic calcium concentration ([Ca²⁺]_i) in cultured astrocytes (7–9). This increase stimulates entry of pyruvate into the tricarboxylic acid cycle by activation of the pyruvate dehydrogenase complex, secondary to an increase in intramitochondrial Ca²⁺, which in astrocytes, exerts a stimulatory effect on key metabolic enzymes, including the pyruvate dehydrogenase complex (8–9).

We have shown that dexmedetomidine potently causes a rise in [Ca²⁺]_i in astrocytes, but not in the neurons we studied (10). This stimulation has been confirmed by Enkvist et al. (11). In the present study, we extended our investigation to measuring dexmedetomidine effects on [Ca²⁺]_i in astrocytes over a wider concentration range, revealing a biphasic effect and showing that the increase in [Ca²⁺]_i is independent of extracellular Ca²⁺ but dependent on intracellular Ca²⁺ stores. Moreover, the dose dependency and pharmacological characteristics were compared with the effects of dexmedetomidine on pyruvate dehydrogenation. Based on this comparison, it was concluded that there appears to be a causal correlation, i.e., that the increase in [Ca²⁺]_i leads to a stimulation of the pyruvate dehydrogenase complex. A stimulation of energy metabolism in astrocytes contrasts the effect of barbiturate anesthetics in astrocytes (12) and in the brain (13), but is consistent with a well-maintained rate of cerebral oxidative metabolism during the administration of dexmedetomidine, despite a marked reduction in cerebral blood flow (14–16).

	Methods

Top Abstract Introduction Methods Results Discussion References

 
This study was approved by our institution’s animal care and use committee. All chemicals for preparation of tissue culture medium and most other nonradiolabeled chemicals, except dexmedetomidine and idazoxan, were purchased from Sigma Chemical, St. Louis, MO; dexmedetomidine was donated by Orion Corporation Farmos, Turku, Finland, and idazoxan was bought from Research Biochemicals, Natick, MA. [1-¹⁴C]pyruvate was from NEN, DuPont Canada, Mississauga, Ontario, Canada.

Cultures of astrocytes were prepared as previously described (17–18). The neopallia, i.e., the parts of the cerebral hemispheres above the lateral ventricles, were dissected out of the brains from newborn Swiss mice and mechanically dissociated. The resulting cell suspension, in tissue culture medium (a slightly modified Dulbecco’s medium (17) with horse serum), was seeded in Falcon Primaria culture dishes or on thoroughly rinsed coverslips (8) placed in the culture dishes, and grown under a CO₂/air (5%:95%) atmosphere at 37°C. After the first 2 wk culturing was continued in the presence of 0.25 mM dibutyryl cyclic adenosine monophosphate, a procedure known to promote morphological and functional differentiation of the cells (17–18), including an enhancement of the expression of ₂ receptors (11). The cells were used after 3–6 wk in culture. Astrocytes were >95% of the cell population, and neurons were absent (18). Such cultures constitute an excellent model for many functional characteristics of astrocytes in situ.

Production of labeled CO₂ from [1-¹⁴C]pyruvate was measured during incubation of individual cultures in an air-tight chamber to specifically determine the rate of pyruvate dehydrogenation (8). This was done in a glucose-free medium, so that unlabeled pyruvate formed from glucose would not compete with labeled pyruvate for dehydrogenation. At the end of the 30-min experimental period, the medium was acidified (and the experiment terminated) by injection of acetic acid into the medium, converting bicarbonate to CO₂. During subsequent incubation for 60 min on a hot plate (60°C) to create air currents within the chamber, all CO₂ was quantitatively trapped into 10% tetramethylammonium hydroxide, injected at the beginning of this period into a presuspended beaker. The beaker with its content of tetramethylammonium hydroxide and trapped CO₂ was transferred into a counting vial, and radioactivity was determined by using a Rack Beta liquid scintillation counter (LKB-Wallac 1217–001). Cell protein was determined by the aid of the conventional Lowry technique as previously described (8), and rates of pyruvate dehydrogenation were calculated per mg protein on the basis of the specific activity of the medium.

[Ca²⁺]_i was determined by the aid of the fluorescent probe, Indo-1 (8). Cultures on glass coverslips were incubated with 4 µM Indo-1/AM (Molecular Probes, Eugene, OR) for 30 min at 37°C. After dye loading, a coverslip was placed in a flow-through chamber and continuously superfused at 37°C with saline (116 mM NaCl, 5.4 mM KCl, 1.8 mM CaCl₂, 0.8 mM MgSO₄, 1.0 mM NaH₂PO₄, 26.2 mM NaHCO₃, and 7.5 mM glucose), aerated with a 5% CO₂/95% air gas mixture. The cells were illuminated from a 355 nm excitation source, the fluorescent light from an area comprising approximately 30 individual cells were collected and measured at wavelengths of 410 and 480 nm, and the ratio between the light emitted at each of the two wavelengths was recorded. Unless several different experimental conditions were used in the same culture (requiring a long incubation time), the cells were permeabilized with 10 mM digitonin at the end of the experiment to calibrate the system and calculate actual values for [Ca²⁺]_i from the fluorescence ratios (8). In this procedure, EGTA in a solution containing no Ca²⁺ was added onto the coverslip until the minimum fluorescence intensity was reached, and the 410:480 nm fluorescence ratio was recorded; subsequently a saline solution containing 1.5 mM Ca²⁺ (and 10 mM digitonin) was superfused and the corresponding fluorescence ratio determined. From the ratios at, respectively, zero and 1.5 mM Ca²⁺, concentrations of Ca²⁺ corresponding to the ratios recorded during the experiments were calculated (8). Effects on [Ca²⁺]_i by exposure to drugs or combinations of drugs were accomplished by change of perfusion medium to a similar medium supplemented with the drug(s) in question. With the equipment used and the drugs administered, responses to medium change occurred after a latency phase of approximately 30 s, reflecting the time required for the fluid to flow through the dead space of the perfusion system. The source of the increased [Ca²⁺]_i was studied by testing the effect of Ca²⁺ deletion in the medium and of the drug dantrolene, known to inhibit Ca²⁺ release from intracellular stores (19).

Statistical analysis was performed by using the computer software package StatView SE + Graphics^TM version 1.03 (from Abacus Concepts, Berkeley, CA). One-factor analysis of variance followed by Fisher’s protected least significant difference test was used for analysis of variance parameters at a multicomparison significance level of 95.

	Results

Top Abstract Introduction Methods Results Discussion References

 
Dexmedetomidine caused a biphasic increase in [Ca²⁺]_i with one peak (an increase of approximately 300 nM) around 100 nM, a reduction, but no abolishment, of the stimulation at 300 nM to 1 µM and a second peak in the micromolar range (Fig. 1). The increase in [Ca²⁺]_i was independent of extracellular Ca²⁺ (Fig. 2A), but abolished by pretreatment for 4 h with dantrolene, which impairs release of Ca²⁺ from intracellular stores (see Methods section) without destroying the cells, as can be seen from a maintained increase in [Ca²⁺]_i during exposure to an increased concentration of K⁺ (Fig. 2B). These observations indicate that dexmedetomidine causes a release of intracellularly bound Ca²⁺. In contrast to the peak at 100 nM, which is abolished in the presence the ₂-adrenergic antagonist, yohimbine (10), that in the micromolar range was only partly inhibited by yohimbine (Fig. 2C) and partly inhibited by idazoxan (Fig. 2D), an inhibitor of the imidazoline-preferring site (4).

View larger version (17K): [in this window] [in a new window]   Figure 1. Concentration-response relationship for dexmedetomidine’s effect on free cytosolic Ca2+ concentration ([Ca2+]i) in primary cultures of mouse astrocytes. Results are averages ± SEM of 3–18 individual experiments, using cultures from at least two different batches. *Significantly different (P < 0.05) from control.

View larger version (21K): [in this window] [in a new window]   Figure 2. Tracings of free cytosolic Ca2+ concentration ([Ca2+]i), A, expressed as nM or B, C, fluorescence ratios, in individual primary cultures of mouse astrocytes. A, Increase in [Ca2+]i by 100 nM dexmedetomidine (Dex) in the absence of extracellular Ca2+. B, Abolishment of increase in [Ca2+]i evoked by 100 nM dexmedetomidine, but preservation of [Ca2+]i response to 40 mM K+, in culture treated with 10 mM dantrolene for 4 h. C, Effect of 25 µM dexmedetomidine alone and in the presence of 100 µM yohimbine (yoh). D, Effect of 25 µM dexmedetomidine alone and in the presence of 100 µM idazoxan (Ida).

View larger version (16K): [in this window] [in a new window]   Figure 3. Concentration-response relationship for dexmedetomidine’s effect on CO2 production from 1-[14C]pyruvate, a measurement of rate of pyruvate dehydrogenation, in primary cultures of mouse astrocytes. Results are averages ± SEM of 4–10 individual experiments, using cultures from at least two different batches. *Significantly different (P < 0.05) from control.

View larger version (25K): [in this window] [in a new window]   Figure 4. Stimulatory effect of 10 µM dexmedetomidine () and its inhibition by 100 µM yohimbine () or 100 µM idazoxan (]) on CO2 production in primary cultures of mouse astrocytes. Values are expressed as percentage of control (, without dexmedetomidine). Results are averages ± SEM of six individual experiments, using cultures from at least two different batches. *Significantly different (P < 0.05) from control. Significantly different (P < 0.05) from the effect of dexmedetomidine alone.

	Discussion

Top Abstract Introduction Methods Results Discussion References

The present experiments confirm previous observations by ourselves (10) and others (11) that at least one of dexmedetomidine’s actions is exerted on [Ca²⁺]_i in astrocytes. In vivo, astrocytes are targets for noradrenergic fibers extending from locus ceruleus. They express ₂-adrenergic receptors (5–6) and react to the ₂-adrenergic agonist clonidine with increases in [Ca²⁺]_i and in rate of energy metabolism, including pyruvate dehydrogenation (7–9). The present results do not exclude that similar or different effects might occur in neurons, which also possess ₂-adrenergic receptors (5–6). However, we previously observed that dexmedetomidine does not increase [Ca²⁺]_i in corresponding neuronal cultures (10), and that noradrenaline does not stimulate oxidative metabolism in neurons (9). Moreover, Savola et al. (22) observed very little direct effect of dexmedetomidine on firing of hippocampal CA₁ neurons in the brain slices, and increased K⁺ concentrations, which stimulate pyruvate dehydrogenase activity in synaptosomes (23), do not enhance pyruvate oxidation in astrocytes (Y. Chen and L. Hertz, unpublished observations), although they do increase [Ca²⁺]_i (9).

The observation that dexmedetomidine increases [Ca²⁺]_i by promoting Ca²⁺ release from intracellular stores is consistent with a similar finding by Enkvist et al. (11). Moreover, rilmenidine, another drug stimulating both ₂-adrenergic and imidazoline-preferring receptors, causes a [Ca²⁺]_i surge which is prevented by thapsigargin, an inhibitor of endoplasmic reticulum Ca²⁺-ATPase (24). The identical concentration dependence of the dexmedetomidine effect on pyruvate dehydrogenation and on the peaks in [Ca²⁺]_i strongly suggest that these two phenomena are interrelated, probably by a Ca²⁺-mediated activation of the pyruvate dehydrogenase complex. This conclusion is strengthened by the demonstration that ₂-adrenergic stimulation of pyruvate dehydrogenation by noradrenaline is abolished by prolonged Ca²⁺ depletion, combined with elevation of the magnesium concentration, a procedure known to inhibit mitochondrial Ca²⁺ increase following elevation of [Ca²⁺]_i (8–9). However, in contrast to the lack of effect on pyruvate oxidation between the two peaks, a residual increase in [Ca²⁺]_i remained. Moreover, at 25 µM dexmedetomidine, the increase in [Ca²⁺]_i was partly inhibited by yohimbine and partly by idazoxan. These findings suggest that dexmedetomidine in the low micromolar range causes not only a Ca²⁺-mediated stimulation of pyruvate dehydrogenase activity, but also an increase in [Ca²⁺]_i, which has no effect on pyruvate metabolism and is caused by stimulation of the imidazoline preferring site. This conclusion is supported by the ability of a supposedly more specific ligand for the imidazoline binding site, cirazoline, to increase [Ca²⁺]_i in astrocytes (24). There is precedence for the existence of functionally different pools of intracellular Ca²⁺ in astrocytes, because noradrenaline increases [Ca²⁺]_i in at least two functionally separate compartments, whereas clonidine, even at large concentrations, appears only to increase the Ca²⁺ pool that is correlated with stimulation of pyruvate dehydrogenation (8). This difference between clonidine and dexmedetomidine may contribute to their different pharmacological profile.

The demonstration of two peaks in both [Ca²⁺]_i and rate of pyruvate dehydrogenation, one around 100 nM dexmedetomidine and the second at concentrations >1 µM, is consistent with the wide therapeutic window of the drug (2–3). The plasma concentrations associated with many of dexmedetomidine’s effects in vivo (3) are similar to the peak around 100 nM; however, maximum effects may require concentrations corresponding to the second peak. The observation that the astrocytic response to 100 nM dexmedetomidine exclusively reflects stimulation of ₂-adrenergic receptors, whereas there is an additional effect on the imidazoline-preferring site in the micromolar range, is consistent with other evidence that several pharmacologic actions of ₂-adrenergic agonists are mediated by simultaneous activation of imidazoline receptors (5). Such a mechanism of action opens the possibility for not only quantitative but also qualitative differences between the effects of dexmedetomidine at small and large concentrations (e.g., anesthetic-sparing versus hypnotic effects). However, the functional consequences of an imidazoline receptor-mediated increase in [Ca²⁺]_i in astrocytes is unknown.

There may be a correlation between the ability of dexmedetomidine at both small and large concentrations to increase rate of oxidative metabolism in astrocytes, which accounts for a sizable fraction of cerebral energy metabolism (18), and the repeated observation that this anesthetic does not decrease oxidative metabolism in the brain (14–16). This is a clear-cut difference from many other anesthetics or anesthetic adjuvants, e.g., barbiturates, which strongly inhibit oxidative metabolism in the brain (13) and in cultured neural cells (12). One can only speculate how an increase in astrocytic energy metabolism can enhance anesthesia; however, it should be kept in mind that astrocytes regulate the extracellular surroundings of neurons by accumulating neuroactive compounds like K⁺ and glutamate by energy-demanding uptake processes (9). This is consistent with the concept that enhancement of glutamate uptake can induce anesthesia and that halothane at pharmacologically relevant concentrations enhances glutamate uptake, especially in astrocytes (25). This might represent a novel mechanism of action for general anesthetics.

	References

Top Abstract Introduction Methods Results Discussion References

 

1. Virtanen R. Pharmacological profiles of medetomidine and its antagonist, atipamezole. Acta Vet Scand 1989; (Suppl 85):29–37.
2. Doze V, Chen BX, Li Z, Maze M. Pharmacologic characterization of the receptor mediating the hypnotic action of dexmedetomidine. Acta Vet Scand 1989; (Suppl 85):61–4.
3. Bol CJ, Vogelaar JP, Mandema JW. Anesthetic profile of dexmedetomidine identified by stimulus-response and continuous measurements in rats. J Pharmacol Exp Ther 1999;291:153–60.[Abstract/Free Full Text]
4. Khan ZP, Ferguson CN, Jones RM. Alpha₂ and imidazoline receptor agonists. Their pharmacology and therapeutic role. Anaesthesia 1999;54:146–65.[ISI][Medline]
5. Kagawa K, Mammoto T, Hayashi Y, et al. The effect of imidazoline receptors and ₂-adrenoceptors on the anesthetic requirement (MCA) for halothane in rats. Anesthesiology 1997;87:963–7.[Medline]
6. Lee A, Rosin DL, Van Bockstaele EJ. Alpha_2A-adrenergic receptors in the rat nucleus locus ceruleus: Subcellular localization in catecholaminergic dendrites, astrocytes, and presynaptic axon terminals. Brain Res 1998;795:157–69.[Medline]
7. McCarthy KD, Salm AK. Pharmacologically distinct subsets of astroglia can be identified by their calcium response to neuroligands. Neurosci 1991;41:325–33.[ISI][Medline]
8. Chen Y, Hertz L. Noradrenaline effects on pyruvate decarboxylation: Correlation with calcium signaling. J Neurosci Res 1999;58:599–606.[Medline]
9. Hertz L, Peng L. Effects of monoamine transmitters on neurons and astrocytes: Correlation between energy metabolism and intracellular messengers. Prog Brain Res 1992;94:283–301.[Medline]
10. Zhao Z, Code WE, Hertz L. Dexmedetomidine, a potent and highly specific ₂ agonist, evokes cytosolic calcium surge in astrocytes but not in neurons. Neuropharmacology 1992;31:1077–9.[ISI][Medline]
11. Enkvist MO, Hamalainen H, Jansson CC, et al. Coupling of astroglial ₂-adrenoreceptors to second messenger pathways. J Neurochem 1996;66:2394–401.[ISI][Medline]
12. Hertz E, Shargool M, Hertz L. Effects of barbiturates on energy metabolism by cultured astrocytes and neurons in the presence of normal and elevated potassium concentrations. Neuropharmacology 1986;25:533–9.[Medline]
13. Nemoto EM, Klementavicius R, Melick JA, Yonas H. Suppression of cerebral metabolic rate for oxygen (CMRO₂) by mild hypothermia compared with thiopental. J Neurosurg Anesthesiol 1996;8:52–9.[ISI][Medline]
14. Zornow MH, Fleischer JE, Scheller MS, et al. Dexmedetomidine, an ₂-adrenergic agonist, decreases cerebral blood flow in the isoflurane-anesthetized dog. Anesth Analg 1990;:70624–30.
15. Karlsson BR, Forsman M, Roald OK, et al. Effect of dexmedetomidine, a selective and potent ₂-agonist, on cerebral blood flow and oxygen consumption during halothane anesthesia in dogs. Anesth Analg 1990;71:125–9.[Abstract/Free Full Text]
16. McPherson RW, Koehler RC, Kirsch JR, Traystman RJ. Intraventricular dexmedetomidine decreases cerebral blood flow during normoxia and hypoxia in dogs. Anesth Analg 1997;84:139–47.[Abstract]
17. Juurlink BHJ, Hertz L. Astrocytes. In: Boulton AA, Baker GB, Walz W, eds. Neuromethods. New York:Humana Clifton, 1992:269–321.
18. Hertz L, Peng L, Lai JCK. Functional studies in cultured astrocytes: Methods 1998;16:293–310.[Medline]
19. Schousboe A, Frandsen A, Krogsgaard-Larsen P. Pharmacological and functional characterization of excitatory amino acid mediated cytotoxicity in cerebral cortical neurons. Cell Biol Toxicol 1992;8:93–100.[Medline]
20. Segal IS, Vickery RG, Walton JK, et al. Dexmedetomidine diminishes halothane anesthetic requirements in rats through a postsynaptic ₂ adrenergic receptor. Anesthesiology 1988;69:818–23.[ISI][Medline]
21. Guo TZ, Reid K, Davies MF, et al. Chronic desipramine treatment desensitizes the rat to anesthetic and antinociceptive effects of the ₂-adrenergic agonist dexmedetomidine. Anesthesiology 1998;88:1634–42.[Medline]
22. Savola MK, MacIver MB, Doze VA, et al. The ₂-adrenoceptor agonist dexmedetomidine increases the apparent potency of the volatile anesthetic isoflurane in rats in vivo and in hippocampal slice in vitro. Brain Res 1991;548:23–8.[ISI][Medline]
23. Huang HM, Toral-Barza L, Sheu KF, Gibson GE. The role of cytosolic free calcium in the regulation of pyruvate dehydrogenase in synaptosomes. Neurochem Res 1994;19:89–95.[Medline]
24. Ozog MA, Wilson JX, Dixon SJ, Cechetto DF. Rilmenidine elevates cytosolic free calcium concentration in suspended cerebral astrocytes. J Neurochem 1998;71:1429–35.[Medline]
25. Miyazaki H, Nakamura Y, Arai T, Kataoka K. Increase of glutamate uptake in astrocytes: A possible mechanism of action of volatile anesthetics. Anesthesiology 1997;86:1359–66.[ISI][Medline]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (6) Citing Articles via Google Scholar Google Scholar Articles by Chen, Y. Articles by Hertz, L. Search for Related Content PubMed PubMed Citation Articles by Chen, Y. Articles by Hertz, L.

Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999