| JOURNAL HOME | CME HOME | THIS MONTH | PAST ISSUES | ETOC | COLLECTIONS |
| AUTHORS | REVIEWERS | EDITORIAL BOARD | FEEDBACK | RSS | HELP |
| ||||||||||||||
| ||||||||||||||
|
|
|
|
||||||||||||
|
||||||||||||||
*Department of Anaesthesiology and Intensive Care Medicine,
Institute of Medical Informatics, and
Rudolf-Buchheim-Institute for Pharmacology, Justus-Liebig-University, Giessen, Germany
Address correspondence and reprint requests to Dr. med. Dr. rer. nat. Reginald Matejec, Department of Anaesthesiology and Intensive Care Medicine, Rudolf-Buchheim-Str. 7, D-35392 Giessen, Germany. Address e-mail to reginald.matejec{at}chiru.med.uni-giessen.de
 |
Abstract |
|---|
 Top Abstract IntroductionMethodsResultsDiscussionReferences |
|---|
IMPLICATIONS: ß-Endorphin immunoreactive material has been determined in plasma and cerebrospinal fluid under perioperative conditions. Its release into the cardiovascular compartment is related to postoperative pain severity, although its analgesic significance remains to be elucidated.
|
Introduction |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
In view of the opioid properties of ß-endorphin, an analgesic function of ß-endorphin IRM released under perioperative conditions into blood has been frequently considered (2,5,10,11). However, reports presenting evidence for this by referring to correlations of perioperative ß-endorphin IRM plasma levels with severity of pre-, intra-, or postoperative pain are inconsistent (10,12,13).
There have been only sporadic and contradictory findings in humans on ß-endorphin IRM levels in the cerebrospinal fluid (CSF) before, during or after surgery; CSF levels ranged from approximately 5 to 100 pmol/L and showed moderate to negligible alterations in response to surgical stress or postoperative pain (7,8,11,14). A negative correlation between ß-endorphin IRM levels in CSF before surgery and the postoperative morphine requirement was reported in one study on patients undergoing transurethral prostate resection (15).
In this study, we determined ß-endorphin IRM in plasma and CSF of 17 patients undergoing hip or knee arthroplasty, before surgery (tA); after termination of surgery and propofol anesthesia, but still under spinal anesthesia with bupivacaine (tB); with postoperative pain (tC); and 1 day after surgery (tD). Pain severity was rated at all four times by the patients’ using a visual analog scale (VAS). This experimental design allowed us to search for correlations between plasma or CSF ß-endorphin IRM levels measured at times tA, tB, tC, and tD and to determine the severity of pain whenever it was observed at these times.
|
Methods |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Pain severity assessment was quantified by the subjects themselves with use of a 10-point VAS on which 0 represented "no pain" and 10 represented "pain as bad as it could be." The patients were familiarized with the use of the VAS before surgery and were asked to evaluate the intensity of their pain at four times: just before the induction of spinal anesthesia (tA); 10 min after termination of propofol anesthesia, i.e., after termination of surgery, but with spinal anesthesia still effective (tB); with postoperative pain on the day of surgery before spinal administration of morphine as an analgesic (tC); and 1 day after surgery (tD). Only 2 of 17 patients still received analgesic medication. At these four times, blood and CSF were withdrawn as well.
All patients had been hospitalized the day before surgery. They were premedicated with midazolam 7.5 mg per os, 30 min before the induction of anesthesia. During anesthesia, routine monitoring was used. After the administration of 500 mL of lactated Ringer’s solution into a forearm or dorsal hand vein, a central venous catheter (Cavafix, Certo-375, 16 gauge; B. Braun, Melsungen, Germany) was inserted into the vena basilica or vena cephalica, and the tip was positioned just outside the atrium dextrum cordis (supervised by electrocardiogram). After intradermal application of prilocaine 1% for local anesthesia, a 22-gauge spinal catheter over a 27-gauge needle (Spinocath; B. Braun) was inserted at the L3-4 intervertebral space and advanced 4 cm into the subarachnoid space.
Thereafter, blood (from the central venous catheter) and CSF (from the spinal catheter) were drawn (tA). Then, hyperbaric bupivacaine 0.5% (1.5–3.5 mL) was injected into the subarachnoid space. The level of sensory block, usually up to T10, was examined with the pinprick technique. In addition to spinal anesthesia, the patients received propofol (2,6-di-isopropylphenol; 1.31–10.42 mgpropofol · kg-1body weight · h-1) as an anesthetic, which allowed spontaneous respiration during the operation. After completion of surgery, the infusion of propofol was stopped, approximately 10 min later the patients woke up, and five more minutes later, the patients graded their pain intensity via VAS; at this time, blood and CSF were withdrawn again (tB). Postoperative pain (VAS) was recorded once per hour within the first 10 h after surgery. On occurrence of postoperative pain, patients graded their pain intensity (VAS) by themselves. Blood and CSF were taken at this time (tC), and then patients received morphine (0.3–0.5 mg) and dehydrobenzperidol (0.5–0.7 mg) through the spinal catheter. One day after surgery (tD), pain was quantified again, and blood and CSF were taken before removal of the spinal catheter.
Blood and CSF samples were collected at four times—tA, tB, tC, and tD—as described previously. Blood (10 mL) was taken from the central venous catheter, mixed with 125 µL of EDTA (0.08 g/mL), placed immediately on ice, and centrifuged at 1000g for 15 min at 4°C. Plasma 5 mL was acidified with 0.5 mL of HCl (1 mol/L). CSF 5 mL (free of blood) was withdrawn from the spinal catheter and immediately placed on ice. Five milliliters of the CSF was also acidified with 0.5 mL of HCl (1 mol/L). Acidified samples were frozen and stored at -20°C until extraction.
Synthetic human ß-endorphin(1-31) was obtained from Bachem (Heidelberg, Germany). All other reagents were analytical-reagent grade (p.A.) from Merck, Darmstadt, Germany.
For standardization, plasma samples were obtained from healthy volunteers, and CSF samples were obtained from patients who had been admitted to the neurosurgical department of the University of Giessen for increased intracranial pressure due to an accident. None of the healthy volunteers or the neurosurgical patients had a history of seizures, cerebrovascular disease, or degenerative neurologic disease. Plasma or CSF samples were passed through activated Sep-Pak C18 cartridges (Waters, Milford, MA) at neutral pH. The ß-endorphin was retained on the cartridges after this neutral extraction procedure, and plasma and CSF from the volunteers and neurosurgical patients, respectively, contained only minor concentrations of ß-endorphin IRM. Defined amounts of ß-endorphin(1-31) were added to the eluate. These standard samples were essentially treated like the samples obtained from the patients; i.e., they were acidified and stored at -20°C until further processing.
The extraction was conducted as described previously (16). In brief, the samples were thawed at 4°C, and 5-mL aliquots of acidified plasma or CSF were passed at 4°C through Sep-Pak C18 cartridges that had been activated previously with 5 mL of methanol followed by 5 mL of urea (8 mol/L) and 10 mL of water at 4°C. Then the cartridges were washed with 10 mL of acetic acid (4% in water) and 10 mL of water. Elution of ß-endorphin IRM from the cartridges was achieved with 10 mL of 1-propanol/acetic acid (96:4 vol/vol). The eluate was dried at room temperature by using a Speed Vac Concentrator (Savant Instruments, Holbrook, NY). The remaining aqueous phase was lyophilized, the residue was reconstituted on ice in 0.5 mL of buffer 1 (0.02 M sodium phosphate [pH 7.50], containing 0.15 M sodium chloride, 0.1% [wt/vol] gelatin, 0.01% [wt/vol] bovine serum albumin, and 0.01% [wt/vol] thimerosal) (16), and 100-µL aliquots were frozen and stored at -20°C until analysis of the extracts in a RIA.
ß-Endorphin(17-26) IRM in the plasma and CSF extracts was determined in a one-site fluid-phase RIA as in principle described (16) and recently characterized (17). In brief, residues from lyophilization were reconstituted in buffer 1 on ice, and aliquots were incubated together with an antiserum (code 84E) against the (17-26) fragment of human ß-endorphin (diluted 1:10,000 with buffer 1) and with 125Jod-labeled ß-endorphin(1-31) in buffer 2 (buffer 1 containing 0.1% [vol/vol] Triton X-100) at 4°C for 24 h. Then the samples were incubated together with charcoal for adsorption of free labeled peptide and were subsequently centrifuged. The supernatants were analyzed for radioactivity in a gamma counter for determination of antibody-bound labeled peptide.
Because this study was an exploratory trial, statistical analysis had to be performed in an exploratory manner. This objective could not be met by simple tests of predefined hypotheses. However, although data analysis was performed in a descriptive manner and entailed data exploration, P values were calculated. According to the ICH E 9 Guideline on Statistical Principles for Clinical Trials, the analyzed hypotheses were chosen data dependent. ß-Endorphin IRM concentrations were given as first, second (median), and third quartiles of the values obtained for times tA, tB, tC, and tD. To analyze differences between ß-endorphin IRM concentrations at times tA, tB, tC, and tD, Wilcoxon’s signed rank test, the associated Hodges-Lehmann estimator (
), and the 95% distribution-free confidence interval based on this test were used (18). Analysis of correlations between the concentration of ß-endorphin IRM and the intensity of pain (VAS) was done by the use of Spearman’s rank correlation coefficient (rs).
|
Results |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Concentrations of ß-endorphin IRM determined in venous blood plasma before surgery (tA); after termination of propofol anesthesia, but with spinal anesthesia still effective (tB); on occurrence of postoperative pain (tC); and 1 day after surgery (tD) have been condensed to box and whisker plots of minimum and maximum values as well as first, second (medians), and third quartiles of the concentrations (Fig. 1A). To estimate differences between these concentrations, Hodges-Lehmann estimators, B-A, C-B, and D-C (Fig. 1A), as well as A-D or B-D (see legend to Fig. 1), have been determined. Concentration differences significantly different from zero are indicated by a 95% confidence interval limited by two negative or two positive values, with one of the two values also allowed to be zero. In addition, the significance of the concentration differences was also tested with Wilcoxon’s matched-pairs signed rank test (Fig. 1).
|
|
B-A, C-B, D-C), with upper and lower limits of their 95% confidence intervals, are presented as a box and whisker plot in Fig. 1B. In CSF, in contrast to plasma, the ß-endorphin IRM level after surgery under spinal anesthesia (tB) was moderately, but significantly, increased as compared with times tA and tC (Fig. 1B). Also in contrast to plasma, an increase of ß-endorphin IRM in CSF with postoperative pain (tC) in comparison with times tB and tD was not observed. Correlations between postoperative pain severity (tC) and ß-endorphin IRM concentrations in CSF at times tC or tA were not significant
|
|
|
Discussion |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
The ß-endorphin IRM concentrations in plasma under perioperative conditions have been frequently determined (1–8,10–12), and an analgesic function of this material has often been considered (2,5,10,11,15) or tacitly assumed in view of the opioid properties of ß-endorphin(1-31). However, evidence should be presented for this (whereby studies using opioid antagonists, and so on, are difficult to conduct in humans, for ethical reasons), at least on the basis of interrelationships between ß-endorphin IRM concentrations in plasma and postoperative pain severity as a measure for an analgesic ß-endorphin effect.
There are very few studies on this kind of interrelationship under perioperative conditions. Cohen et al. (12) reported a negative correlation of intraoperative ß-endorphin IRM plasma levels with postoperative morphine requirements. Further, a negative correlation was found (10) of intraoperative ß-endorphin IRM plasma concentrations in the percentage of preoperative levels with intraoperative pain severity (based on third-molar extraction under local anesthesia). Moreover (13), a negative correlation of a data pool of pre-, intra-, and postoperative ß-endorphin IRM plasma levels with a data pool of pre-, intra-, and postoperative pain severity measurements (based on data obtained under continuous postoperative morphine analgesia) was reported.
From the last two studies (10,13), clear-cut information is difficult to derive concerning an interrelationship between ß-endorphin IRM plasma levels and postoperative pain severity under the aspect of a functional significance of ß-endorphin IRM. The study of Cohen et al. (12) provides for the prediction of postoperative pain severity on the basis of intraoperative ß-endorphin plasma levels. We tried to add to the available information by concentrating on the simultaneous determination of plasma ß-endorphin IRM concentrations and pain severity under perioperative conditions, i.e., before surgery (tA), after surgery but still under spinal anesthesia (tB), on postoperative pain (tC), and one day after surgery (tD).
Thus, looking simultaneously at either variable, we found a highly significant positive correlation for the severity of postoperative pain (tC) and ß-endorphin IRM plasma levels with postoperative pain (tC); the results of several studies are just compatible with this finding (2,5–7). From this correlation, however, it was not possible to derive which of the two variables was independent and which was dependent (i.e., whether pain severity was responsible for the ß-endorphin IRM concentration in the plasma or vice versa). A further result appeared to clarify this question: although less pronounced, a clearly significant positive correlation was also observed for postoperative pain severity (tC) and preoperative plasma ß-endorphin IRM levels (tA). Thus, the ß-endorphin IRM plasma concentration appeared to be the independent variable.
A direct pain-enhancing effect of the material appears to be unlikely, and a direct pain-inhibiting effect under postoperative conditions has never been proven. Findings raised under conditions different from the perioperative situation do not speak in favor of an analgesic effect of ß-endorphin IRM under perioperative conditions (20–24). However, preoperative and postoperative ß-endorphin IRM concentrations in plasma, because they are positively correlated with pain severity, might be the indicator of a system located upstream of the pituitary level in the central nervous system, which possibly participates in discriminative or emotional pain control. A predictive value of the preoperative ß-endorphin IRM plasma level with regard to postoperative pain severity remains to be elucidated.
The functional significance of ß-endorphin IRM released under perioperative conditions into the cardiovascular compartment is not clear as yet (25); an immunological significance appears to be likely in view of a variety of ß-endorphin effects on immune cells (19), but this is not proven (26). However, the release of ß-endorphin IRM into the cardiovascular compartment cannot be excluded as a stress adaptation process of functional significance; from this point of view, its suppression by various anesthetic techniques might not be merely advantageous. This might also be true for the rest of the proopiomelanocortin fragments, some of which have been shown in another part of this study to be released into blood or CSF in parallel to ß-endorphin IRM (Matejec et al., unpublished data).
There are almost no studies wherein ß-endorphin IRM has been determined simultaneously in plasma and CSF under perioperative conditions. However, the results of a number of studies conducted under different conditions make it very clear that the release of ß-endorphin IRM into the cardiovascular compartment and into the CSF compartment is regulated separately (7,8,14,23,24). In fact, in contrast to suppression of ß-endorphin IRM release from the pituitary into blood, postoperative spinal anesthesia provoked a slight increase of ß-endorphin IRM concentration in CSF. Although an increase under the conditions of our study has not been reported, findings such as an increase of CSF ß-endorphin IRM under thiopental anesthesia (14) or under the influence of morphine (7) are compatible. Further, although not significant, the negative correlation of postoperative pain severity VAS (tC) with preoperative (tA) and postoperative (tC) ß-endorphin IRM CSF levels is compatible with a negative correlation of preoperative ß-endorphin IRM CSF levels with the postoperative requirements for analgesic medication reported previously (15).
The functional significance of this phenomenon is not clear. However, the activation of the hypophyseal proopiomelanocortin system, including the release of ß-endorphin IRM into the blood, is believed to be a response of the organism to a peripheral attack, such as surgical tissue destruction. Therefore, an activation of the central proopiomelanocortin system leading to ß-endorphin IRM release into CSF might be explained by the response to an attack against the central nervous system induced by spinal anesthesia, leading to a suppression of afferent neuronal input.
|
Acknowledgments |
|---|
The authors wish to express their gratitude to Beate Dickopf for expert technical assistance. The study was supported by the Anaesthesiology Research Support Program of the Medical School of the University of Giessen.
|
References |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
This article has been cited by other articles:
|
|
 |
|
  B. F. Degenhardt, N. A. Darmani, J. C. Johnson, L. C. Towns, D. C. J. Rhodes, C. Trinh, B. McClanahan, and V. DiMarzo Role of Osteopathic Manipulative Treatment in Altering Pain Biomarkers: A Pilot Study J Am Osteopath Assoc, September 1, 2007; 107(9): 387 - 400. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. Taddio, V. Shah, P. Shah, and J. Katz {beta}-Endorphin Concentration After Administration of Sucrose in Preterm Infants Arch Pediatr Adolesc Med, November 1, 2003; 157(11): 1071 - 1074. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
c) between tA and tB, tB and tC, or tC and tD,, the Hodges-Lehmann estimators 
