The chronic use of morphine and other opioids is associated with opioid-induced hypersensitivity (OIH) and analgesic tolerance. Among the different forms of OIH and tolerance, the opioid receptors and cell types mediating opioid-induced mechanical allodynia and anti-allodynic tolerance remain unresolved. Here we demonstrated that the loss of peripheral μ-opioid receptors (MORs) or MOR-expressing neurons attenuated thermal tolerance, but did not affect the expression and maintenance of morphine-induced mechanical allodynia and anti-allodynic tolerance. To confirm this result, we made dorsal root ganglia-dorsal roots-sagittal spinal cord slice preparations and recorded low-threshold Aβ-fiber stimulation-evoked inputs and outputs in superficial dorsal horn neurons. Consistent with the behavioral results, peripheral MOR loss did not prevent the opening of Aβ mechanical allodynia pathways in the spinal dorsal horn. Therefore, the peripheral MOR signaling pathway may not be an optimal target for preventing mechanical OIH and analgesic tolerance. Future studies should focus more on central mechanisms.
Humans ; Morphine/pharmacology* ; Hyperalgesia/metabolism* ; Analgesics, Opioid/pharmacology* ; Neurons/metabolism* ; Signal Transduction

The use of opioid analgesics has a long history in clinical settings, although the functions of opioid receptors, especially their role in the brain, are not well understood yet. Recent studies have generated abundant new data on opioid receptor-mediated functions and the underlying mechanisms. The most exciting finding in the past decade is probably the neuroprotection against hypoxic/ischemic stress mediated by delta-opioid receptors (DOR). An up-regulation of DOR expression and the release of endogenous opioids may increase neuronal tolerance to hypoxic/ischemic stress. The DOR signal triggers, depending on stress duration and severity, different mechanisms at multiple levels to preserve neuronal survival, including the stabilization of ionic homeostasis, an increase in pro-survival signaling (e.g., PKC-ERK-Bcl 2) and the enhanced anti-oxidative capacity. Recent data on DOR-mediated neuroprotection provide us a new concept of neuroprotection against neurological disorders and have a potentially significant impact on the prevention and treatment of some serious neurological conditions, such as stroke.
Analgesics, Opioid ; pharmacology ; Humans ; Hypoxia ; metabolism ; Neurons ; metabolism ; Neuroprotective Agents ; pharmacology ; Receptors, Opioid, delta ; metabolism ; Signal Transduction

Radiant heart(RD) and Meperidine(MEP) have been used to suppress postanesthesia shivering. However their efficacies to date have only been assessed by observation of visible shivering. We measured the effects of RH and MEP on oxygen consumption (VO2), minute volume(VE) in sixteen otherwise healthy patients(two groups of eight each) shivering after general anesthesia. RH successfully supressed visible shivering in all patients and was associated with significant decrease in VO2(16% of baseline) and VE(13% of baseline, p<0.05). In the reshivering patients, the effect of RH on VO2 was less than initial RH therapy owing to sustained invisible shivering. MEP suppressed visible shivering in seven patients and was associated with 13% decrease in VO2. In conclusion, RH and MEP are effective methods of reducing the elevated oxygen consumption by shivering.
Analgesics ; Anesthesia, General ; Heart ; Hot Temperature* ; Humans ; Meperidine* ; Metabolism ; Oxygen Consumption* ; Oxygen* ; Shivering*

The present study investigated the effect of emodin on the serum metabolite profiles in the chronic constriction injury(CCI) model by non-target metabolomics and explored its analgesic mechanism. Twenty-four Sprague Dawley(SD) rats were randomly divided into a sham group(S), a CCI group(C), and an emodin group(E). The rats in the emodin group were taken emodin via gavage once a day for fifteen days(50 mg·kg~(-1)) on the first day after the CCI surgery. Mechanical withdrawal threshold(MWT) and thermal withdrawal threshold(TWL) in each group were performed before the CCI surgery and 3,7, 11, and 15 days after surgery. After 15 days, blood samples were collected from the abdominal aorta. The differential metabolites were screened out by non-target metabolomics and analyzed with Kyoto Encyclopedia of Genes and Genomes(KEGG) and ingenuity pathway analysis(IPA). From the third day after CCI surgery, the MWT and TWL values were reduced significantly in both CCI group and emodin group, compared with the sham group(P<0.01). At 15 days post-surgery, the MWT and TWL values in emodin group increased significantly compared with the CCI group(P<0.05). As revealed by non-target metabolomics, 72 differential serum metabolites were screened out from the C-S comparison, including 41 up-regulated and 31 down-regulated ones, while 26 differential serum metabolites from E-C comparison, including 10 up-regulated and 16 down-regulated ones. KEGG analysis showed that the differential metabolites in E-C comparison were enriched in the signaling pathways, such as sphingolipid metabolism, arginine biosynthesis, glycerophospholipid metabolism, and tryptophan metabolism. IPA showed that the differential metabolites were mainly involved in the lipid metabolism-molecular transport-small molecule biochemistry network. In conclusion, emodin can exert an analgesic role via regulating sphingolipid metabolism and arginine biosynthesis.
Analgesics/pharmacology* ; Animals ; Arginine ; Emodin/pharmacology* ; Neuralgia/metabolism* ; Rats ; Rats, Sprague-Dawley ; Sphingolipids

AIMTo investigate the stereoselectivity in absorption of trans tramadol (trans T) in rat intestine.

METHODSThe duodenum, jejunum and ileum were separately perfusated in situ with trans T dissolved in Krebs-Ringer buffer. Trans T enantiomers in the perfusate were analyzed with a high performance capillary electrophoresis (HPCE) method.

RESULTSThe absorbed fractions of trans T enantiomers were similar among the different segments of the rat intestine. The absorbed fraction of (+)-trans T was lower than that of (-)-trans T when the concentration of trans T was not higher than 40 mumol.L-1. As the concentration of trans T increased, the absorbed fractions of trans T enantiomers were reduced and the difference in absorbed fractions between trans T enantiomers became not significant.

CONCLUSIONTrans T enantiomers can be absorbed in different parts of the rat intestine. The intestinal absorption of trans T was stereoselective, (-)-trans T being preferentially absorbed.

Analgesics, Opioid ; pharmacokinetics ; Animals ; Duodenum ; metabolism ; Female ; Ileum ; metabolism ; Intestinal Absorption ; Intestine, Small ; metabolism ; Jejunum ; metabolism ; Male ; Rats ; Rats, Sprague-Dawley ; Stereoisomerism ; Tramadol ; pharmacokinetics

AIMTo investigate the gender-related differences in the metabolism of trans tramadol (trans T) enantiomers and the glucuronidation of trans O-demethyltramadol (M1) enantiomers.

METHODSIn vitro, trans T or M1 were separately incubated with liver microsomes of male or female rats. The concentrations of the enantiomers of trans T and M1 were determined by an HPCE method.

RESULTSCompared with (+)-enantiomers, (-)-trans T was preferentially metabolized, and (-)-M1 was produced faster in rat liver microsomes. (+)-M1 and (-)-M1 were preferentially glucuronidated in the liver microsomes of male and female rats, respectively. Compared with those in male rat liver microsomes, the enantiomeric ratios of CLint for M1 formation and M1 glucuronidation were more deviated from 1 in female rat liver microsomes.

CONCLUSIONIn vitro, trans T metabolism, M1 formation and M1 glucuronidation were found to be stereoselective in rat liver microsomes. There were gender-related differences in the stereoselectivity in M1 formation and M1 glucuronidation, with a larger extent in female rat liver microsomes.

Analgesics, Opioid ; metabolism ; Animals ; Female ; Glucuronic Acid ; metabolism ; Male ; Microsomes, Liver ; metabolism ; Rats ; Rats, Sprague-Dawley ; Sex Factors ; Stereoisomerism ; Tramadol ; analogs & derivatives ; metabolism

Large doses of acetaminophen (APAP) could cause oxidative stress and tissue damage through production of reactive oxygen/nitrogen (ROS/RNS) species and quinone metabolites of APAP. Although ROS/RNS are known to modify DNA, the effect of APAP on DNA modifications has not been studied systematically. In this study, we investigate whether large doses of APAP can modify the nuclear DNA in C6 glioma cells used as a model system, because these cells contain cytochrome P450-related enzymes responsible for APAP metabolism and subsequent toxicity (Geng and Strobel, 1995). Our results revealed that APAP produced ROS and significantly elevated the 8-oxo- deoxyguanosine (8-oxodG) levels in the nucleus of C6 glioma cells in a time and concentration dependent manner. APAP significantly reduced the 8- oxodG incision activity in the nucleus by decreasing the activity and content of a DNA repair enzyme, Ogg1. These results indicate that APAP in large doses can increase the 8-oxodG level partly through significant reduction of Ogg1 DNA repair enzyme.
Acetaminophen/*metabolism ; Analgesics, Non-Narcotic/*metabolism ; Animals ; Cell Line, Tumor ; DNA/metabolism ; DNA Damage ; DNA Glycosylases/*metabolism ; DNA Repair ; Deoxyguanosine/chemistry/*metabolism ; Glioma/*metabolism ; Glutathione/metabolism ; Humans ; Rats ; Reactive Nitrogen Species/metabolism ; Reactive Oxygen Species/metabolism

Spinal gabapentin has been known to show the antinociceptive effect. Although several assumptions have been suggested, mechanisms of action of gabapentin have not been clearly established. The present study was undertaken to examine the action mechanisms of gabapentin at the spinal level. Male SD rats were prepared for intrathecal catheterization. The effect of gabapentin was assessed in the formalin test. After pretreatment with many classes of drugs, changes of effect of gabapentin were examined. General behaviors were also observed. Intrathecal gabapentin produced a suppression of the phase 2 flinching, but not phase 1 in the formalin test. The antinociceptive action of intrathecal gabapentin was reversed by intrathecal NMDA, AMPA, D-serine, CGS 15943, atropine, and naloxone. No antagonism was seen following administration of bicuculline, saclofen, prazosin, yohimbine, mecamylamine, L-leucine, dihydroergocristine, or thapsigargin. Taken together, intrathecal gabapentin attenuated only the facilitated state. At the spinal level, NMDA receptor, AMPA receptor, nonstrychnine site of NMDA receptor, adenosine receptor, muscarinic receptor, and opioid receptor may be involved in the antinociception of gabapentin, but GABA receptor, L-amino acid transporter, adrenergic receptor, nicotinic receptor, serotonin receptor, or calcium may not be involved.
Acetic Acids/administration & dosage ; Acetic Acids/metabolism ; Acetic Acids/pharmacology* ; Adrenergic Antagonists/metabolism ; Adrenergic alpha-Antagonists/metabolism ; Analgesics/administration & dosage ; Analgesics/metabolism ; Analgesics/pharmacology* ; Animals ; Atropine/metabolism ; Dihydroergocristine/metabolism ; Enzyme Inhibitors/metabolism ; Excitatory Amino Acid Agonists/metabolism ; GABA Antagonists/metabolism ; Injections, Spinal ; Leucine/metabolism ; Male ; Mecamylamine/metabolism ; Muscarinic Antagonists/metabolism ; N-Methylaspartate/metabolism ; Naloxone/metabolism ; Narcotic Antagonists/metabolism ; Nicotinic Antagonists/metabolism ; Pain Measurement ; Quinazolines/metabolism ; Rats ; Rats, Sprague-Dawley ; Serine/metabolism ; Spinal Cord/drug effects* ; Thapsigargin/metabolism ; Triazoles/metabolism ; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid/metabolism

OBJECTIVETo study transdermal absorption characteristics of eugenol in compound Nanxing pain-relieving cataplasm, and discuss the effect of gaultherolin on the transdermal absorption of the cataplasm.

METHODThe improved franz diffusing cell was adopted with hairless mice skins as transdermal carriers. The content of eugenol in receptor liquid, skins and cataplasm were analyzed by HPLC and compared with the cataplasm without gaultherolin.

RESULTThe penetration rates of eugenol of cataplasms with and without gaultherolin were 13.18 and 9.58 microg x cm(-2) x h(-1), with the retention amount in skins of (185.02 +/- 19.23) and (160.23 +/- 16.54) microg x g(-1) and the retention amount in cataplasms was (1.96 +/- 0.12) and (1.71 +/- 0.15) mg, respectively.

CONCLUSIONEugenol in compound Nanxing pain-relieving cataplasm has good pereutaoeous permeation. Gaultherolin in the cataplasm prescription can promote the absorption of eugenol.

Analgesics ; chemistry ; metabolism ; therapeutic use ; Animals ; Chemistry, Pharmaceutical ; methods ; Drugs, Chinese Herbal ; chemistry ; metabolism ; therapeutic use ; Mice ; Pain ; drug therapy ; Salicylates ; chemistry ; Skin ; metabolism ; Skin Absorption ; Time Factors

AIMTo study the stereoselectivity in O-demethylation of trans tramadol.

METHODSWith or without quinine and quinidine as inhibitors, rat liver microsomes were incubated in vitro with the enantiomers or the racemate of trans tramadol. The concentrations of the enantiomers of trans tramadol and O-demethyltramadol in the incubates were determined by high performance capillary electrophoresis. The O-demethylation processes were assayed by using the enzyme kinetic analysis method.

RESULTSAfter incubation, the concentrations of (-)-O-demethyltramadol were higher than those of (+)-enantiomer in all rat liver microsomal incubates. Enzyme kinetic analysis showed that the Km of the formation of the enantiomers of O-demethyltramadol were similar; The Vmax and Clint of the formation of (-)-O-demethyltramadol were significantly higher than those of the formation of (+)-enantiomer. When the racemate of trans tramadol was used as the substrate, there was interaction between the two enantiomers. The Km of the formation of the enantiomers of O-demethyltramadol increased, the Vmax of the formation of (+)-O-demethyltramadol decreased, the Vmax of the formation of (-)-O-demethyltramadol increased slightly. The O-demethylation of the enantiomers of trans tramadol was shown to be inhibited competitively by quinine and quinidine. The Ki of quinine and quinidine were 1.6 and 10.8 mumol.L-1 to the formation of (-)-O-demethyltramadol, 0.8 and 3.4 mumol.L-1 to the formation of (+)-O-demethyltramadol, respectively. Furthermore, quinine and quinidine were found to have stereoselective inhibition on the formation of O-demethyltramadol, both mainly inhibited the formation of (+)-O-demethyltramadol.

CONCLUSIONThe O-demethylation of trans tramadol was found to be stereoselective in rat liver microsomes in vitro, preferentially metabolized (-)-enantiomer. The stereoselectivity could be influenced by the interaction between the two enantiomers and the enzyme selective inhibitors.

Analgesics, Opioid ; metabolism ; Animals ; Cell Separation ; Male ; Microsomes, Liver ; metabolism ; Quinidine ; pharmacology ; Quinine ; pharmacology ; Rats ; Rats, Sprague-Dawley ; Stereoisomerism ; Tramadol ; analogs & derivatives ; metabolism