Synergistic interaction between alpha 2-adrenergic agonists and benzodiazepines in rats.

Both alpha 2-adrenergic agonists and benzodiazepines exert anxiolytic and sedative effects when administered as preoperative medications. Clinical effects achieved with a combination of drugs, representative of these classes of compounds, is greater than that which could be expected from a simple additive response. Therefore, we investigated the nature of the interaction between dexmedetomidine, the highly-selective alpha 2-adrenergic agonist, and midazolam in a series of in vivo and in vitro studies in rats. Rats were administered midazolam, dexmedetomidine, or a combination of midazolam and dexmedetomidine intravenously to derive three dose-response curves for loss of righting reflex (LRR). LRR was determined in rats in a rotating cage (4 rotations/min) by observing whether the rat failed to maintain its upright posture for greater than or equal to 15 s exactly 2.5 min after drug administration. The effect of either flumazenil (benzodiazepine receptor antagonist) or atipamezole (the alpha 2-adrenergic antagonist) on the LRR was also determined. A probit analysis was performed and an isobologram for the ED50 was derived to assess the nature of the interaction. Rat brain membranes were prepared for receptor binding assays using [3H]-flumazenil and [3H]-rauwolscine to characterize the benzodiazepine and alpha 2-adrenergic receptors, respectively. The ability of either midazolam or dexmedetomidine to displace the radiolabeled ligand from the alternative receptor was assessed. To detect a possible kinetic interaction between the two drugs, separate cohorts of rats were administered the two drugs individually or in combination at the combination ED50 doses.(ABSTRACT TRUNCATED AT 250 WORDS)     

The interaction between intrathecal neostigmine and GABA receptor agonists in rats with nerve ligation Injury

Nerve ligation injury may produce a pain syndrome that includes tactile allodynia. Reversal effects on tactile allodynia have been demonstrated after the intrathecal administration of gamma-aminobutyric acid (GABA) receptor agonists or cholinesterase inhibitors in rats. We examined the drug interactions between neostigmine and muscimol or baclofen in a rat model of nerve ligation injury. Rats were prepared with tight ligation of the left L5-6 spinal nerves and chronic intrathecal catheter implantation. Tactile allodynia was measured by applying von Frey filaments ipsilateral to the lesioned hindpaw. Thresholds for paw withdrawal were assessed. Neostigmine (0.3-10 microg), muscimol (0.1-10 microg), and baclofen (0.1-3.0 microg) were administered to obtain the dose-response curve and the 50% effective dose (ED(50)). Fractions of ED(50) values were administered intrathecally to establish the ED(50)s of drug combinations (neostigmine-muscimol and neostigmine-baclofen). The drug interactions were performed. Intrathecal neostigmine, muscimol, baclofen, and their combinations produced a dose-dependent increase in withdrawal threshold of the lesioned hindpaw. Both analyses revealed a synergistic interaction for the neostigmine-muscimol combination, whereas the effect of the neostigmine-baclofen combination was additive. These results suggest that the activation of both muscarinic and GABA(A) receptors is required for synergistic interaction. IMPLICATIONS: This study indicates that drug interaction is synergistic for the neostigmine-muscimol combination, whereas the effect of the neostigmine-baclofen combination is additive. In a rat model of nerve ligation injury, neostigmine, muscimol, baclofen, and their combinations provide an antagonism on touch-evoked allodynia at the spinal level.     

Comparative somatic and visceral antinociception and neurotoxicity of intrathecal bupivacaine, levobupivacaine, and dextrobupivacaine in rats

BACKGROUND: The current study investigated whether racemic bupivacaine and its S(-)- and R(+)-enantiomers, levobupivacaine and dextrobupivacaine, differ in somatic and visceral antinociception and neurotoxicity when administered intrathecally in rats. METHODS: In experiment 1, rats intrathecally received 15 microl saline or 0.125, 0.25, 0.5, or 1% bupivacaine, levobupivacaine, or dextrobupivacaine. The tail-flick and colorectal distension tests were performed to assess somatic and visceral antinociceptive effects, respectively, for 180 min after injection. In experiment 2, rats given 0.25% anesthetic solutions were evaluated with colorectal distension-induced response in blood pressure and heart rate. In experiment 3, four groups of rats received a 1-h infusion of saline or 2.5% bupivacaine, levobupivacaine, or dextrobupivacaine. Additional rats received either 1.25% bupivacaine or levobupivacaine for 1 h. Four days after infusion, animals were assessed for persistent sensory impairment using the tail-flick test. Spinal cords and nerve roots were obtained for histologic analysis. RESULTS: In experiment 1, the three drugs produced similar time course effects and dose-effect relations in tail-flick latency. Colorectal distension thresholds and motor paralysis were slightly lower and less apparent, respectively, at some concentrations in rats given levobupivacaine than in those given the other agents. In experiment 2, colorectal distension-induced response in heart rate was less depressed in rats given levobupivacaine than in those given the other anesthetics. In experiment 3, three groups of rats given 2.5% anesthetic solutions developed similar significant increases in tail-flick latency and incurred similar morphologic damage. Two groups of rats receiving 1.25% anesthetic solutions were similar in functional impairment and nerve injury scores. CONCLUSIONS: The results suggest that, when administered intrathecally in rats, bupivacaine and its R(+)- and S(-)-enantiomers are similar for somatic antinociception and neurotoxicity but slightly different in visceral antinociception and motor paralysis, in which levobupivacaine is less potent than the others.     

Interaction between midazolam and epibatidine in spinally mediated antinociception in rats

Purpose  Both γ-aminobutyric acid (GABA)_A receptors and nicotinic cholinergic receptors have important roles in antinociception in the spinal cord. The antinociceptive effects of midazolam (a GABA_A agonist) and epibatidine (a nicotinic cholinergic agonist) in the spinal cord have been reported. The present study was performed to investigate the interaction between intrathecal midazolam and epibatidine. Methods  Sprague-Dawley rats with lumbar intrathecal catheters were tested for their tail withdrawal response to thermal stimulation (tail-flick test) or for their paw flinches in response to formalin injection (formalin test) after the intrathecal administration of epibatidine or a combination of midazolam and epibatidine. The combination doses were 1/16, 1/8, 1/4, 1/2, 1, 2, and 4 times the 50% effective dose (ED50) of each agent in each test. The interaction of midazolam and epibatidine was investigated by isobolographic analysis. Behavioral side effects were also investigated. Results  In the tail-flick test, the ED50 values of the combination were significantly higher than the theoretical additive values. In the formalin test, the ED50 values of the combination were significantly lower than the theoretical additive values in phase 1, but were not different from the theoretical additive values in phase 2. Conclusion  The intrathecal combination of midazolam and epibatidine had antagonistic effects on thermal acute nociception, while the combination had synergistic effects on acute inflammatory nociception, with only additive effects on inflammatory-facilitated nociceptive responses. This work was done at the Department of Anesthesiology, The University of Tokyo.     

Interaction between midazolam and serotonin in spinally mediated antinociception in rats

Purpose  Intrathecal administration of serotonin (5-HT) is antinociceptive through the involvement of spinal cord γ-aminobutyric acid (GABA) receptors. Therefore, 5-HT would interact with the GABA agonist, midazolam, which is well known to exert spinally mediated antinociception in the spinal cord. The present study investigated the antinociceptive interaction between spinally administered 5-HT and midazolam, using two different rat nociceptive models. Methods  Sprague-Dawley rats with lumbar intrathecal catheters were tested for their thermal tail withdrawal response and paw flinches induced by formalin injection after the intrathecal administration of midazolam or 5-HT, or the midazolam/ HT combination. The effects of the combination were tested by isobolographic analysis, using the combination of each 1, 1/2, 1/4, 1/8, and 1/16 of the 50% effective dose (ED50). The total fractional dose was calculated. Behavioral side effects were also examined. Results  5-HT alone and midazolam alone both showed dose-dependent antinociception in both the tail flick test and the formalin test. The ED50 of the combination was not different from the calculated additive value either in the tail flick test or in phase 2 of the formalin test, but it was significantly smaller than the calculated additive value in phase 1 of the formalin test. The total fractional dose value was 0.90 in the tail flick test, 0.093 in phase 1 of the formalin test, and 1.38 in phase 2 of the formalin test. The agitation, allodynia, or motor disturbance observed with either agent alone was not seen with the combination treatment. Conclusion  The antinociceptive effects of intrathecal midazolam and 5-HT were additive on thermal acute and inflammatory facilitated stimuli, and synergistic on inflammatory acute stimulation.     

Effects of isoflurane on gamma-aminobutyric acid type A receptors activated by full and partial agonists

BACKGROUND: Volatile anesthetics prolong inhibitory postsynaptic potentials in central neurons an allosteric action on the gamma-aminobutyric acid type A (GABA(A)) receptor, an effect that may underlie the hypnotic actions of these agents. Inhaled anesthetics such as isoflurane act to enhance responses to submaximal concentrations of GABA, but it is not clear whether their effect is mediated by an increase in the binding of the agonist or by changes in receptor gating behavior. To address this question, the authors studied the effects of isoflurane on a mutant GABA(A) receptor with a gating defect that decreases receptor sensitivity by lowering agonist efficacy. They then compared the effects of clinically relevant concentrations of isoflurane on the actions of GABA and piperidine-4-sulfonic acid (P4S), a partial agonist at the GABA(A) receptor. METHODS: The authors created a mutant of the GABA receptor alpha subunit (L277A) by site-directed mutagenesis. The mutant subunit was coexpressed with beta(2) and gamma(2S) subunits in HEK293 cells, and responses to GABA and P4S were recorded using the whole-cell patch clamp technique. EC values were determined for the full agonist GABA and the partial agonist P4S. The authors also determined the relative efficacy (epsilon) of P4S. These measurements were then repeated in the presence of isoflurane. RESULTS: The concentration-response curve for GABA was shifted to the right (EC(50) = 278 microm) in the alpha(1)(L277A)beta(2)gamma(2S) mutant receptor, compared with the corresponding wild-type alpha(1)beta(2)gamma(2S) GABA(A) receptor (EC(50) = 16 microm). P4S is a partial agonist at both receptors, with a dramatically decreased relative efficacy at the mutant receptor (epsilon = 0.24). When the mutant receptor was studied in the presence of isoflurane, the concentration-response curves for both GABA and P4S were shifted to the left (EC(50) for GABA = 78 microm); the efficacy of P4S also increased significantly (epsilon = 0.40). CONCLUSION: By studying a mutant GABA receptor with impaired gating, the authors were able to demonstrate clearly that isoflurane can increase the efficacy of a partial agonist, as well as increase agonist potency. These data suggest that the volatile anesthetic isoflurane exerts at least some of its effects on the GABA(A) receptor via alterations in gating rather than simply changing binding or unbinding of the agonist.     

Attenuation of morphine-induced antinociception by L-glutamic acid at the spinal site in rats

The present experimental study was planned to evaluate the effect of intrathecal administration of L- glutamic acid upon antinociception produced by intrathecal morphine in a prospective- controlled manner in conscious freely mobile Sprague- Dawley albino rats. After chronic catheterization of the spinal subarachnoid space, rats were randomly allocated into 12 treatment groups of ten each and the same number of rats served as saline control for the comparison. L- glutamic acid (100 mmol), morphine (1.2 mmol), ketamine (50 mmol) and saline (150 mmol) were injected intrathecally in 5 μl volumes. Naloxone was injected in a dose of 1 mg · kg^{? 1} im. Immediately before and 15, 30 min, 1, 2 and 3 hr after injection, rats were subjected to a thermal noxious stimulus, using a tailflick technoanalgesiometer and tail- flick latencies (TFL) were recorded. Intrathecal administration of L- glutamic acid attenuated the antinociceptive effect of intrathecal morphine with a decrease in TFL (1.4 ± 0.3 sec; P < 0.0001) from 6.6 ± 0.3 sec. Ketamine led to abolition of this effect (P < 0.01). In rats, pretreated with naloxone, there was restoration as well as augmentation of morphine- induced antinociception in the presence of L- glutamic acid with an increase in TFL (9.0 ± 0.4 sec; P < 0.0001). We conclude that there is modulation of opioid receptors by L- glutamic acid at the spinal site in rats.     

Intracerebroventricular morphine produces antinociception by evoking gamma-aminobutyric acid release through activation of 5-hydroxytryptamine 3 receptors in the spinal cord

BACKGROUND: It has been generally considered that supraspinal morphine activates the serotonergic descending inhibitory system and releases serotonin (5-hydroxytryptamine [5-HT]) in the spinal cord, producing antinociception through activation of 5-HT receptors. The involvement of a spinal gamma-aminobutyric acid-mediated (GABAergic) system is also suggested in supraspinal morphine antinociception. It has been reported that spinal GABAergic system contributes to 5-HT3 receptor-mediated antinociception. In this study, the authors investigated the contribution of spinal 5-HT3 receptor and the GABAergic system in the intracerebroventricular morphine-induced antinociception. METHODS: Male Sprague-Dawley rats were used. Using the spinal microdialysis method, concentrations of 5-HT and GABA were measured after intracerebroventricular morphine administration. The effect of intracerebroventricular naloxone or spinal perfusion of a selective 5-HT3 receptor antagonist 3-tropanyl-indole-3-carboxylate methiodide on the spinal release of GABA after intracerebroventricular morphine administration was also examined. In the behavioral study, involvement of 5-HT3 receptors or GABAA receptors in the intracerebroventricular morphine-induced antinociceptive effect was investigated using the tail-flick test. RESULTS: Intracerebroventricular morphine (40 nmol) significantly increased spinal GABA and 5-HT release. Evoked spinal GABA release was reversed by intracerebroventricular naloxone (40 nmol) or spinal perfusion of 3-tropanyl-indole-3-carboxylate methiodide (1 mm). In the behavioral study, intracerebroventricular morphine produced significant antinociception. Intrathecal administration of either GABAA receptor antagonist bicuculine or 3-tropanyl-indole-3-carboxylate methiodide but not vehicle reversed the morphine-induced antinociceptive effect. CONCLUSION: Intracerebroventricular morphine evokes spinal GABA release via the activation of 5-HT3 receptors in the spinal cord, resulting in antinociceptive effect.     

γ-氨基丁酸转运体-1在大鼠神经病理性痛形成中的作用

目的 探讨大鼠腰段脊髓γ-氨基丁酸(GABA)转运体-1(GAT-1)在神经病理性痛形成中的作用.方法 SD大鼠112只,随机分为2组(n=56):假手术组(s组)和慢性坐骨神经结扎损伤组(CCI组).结扎大鼠左侧坐骨神经建立CCI模型.于CCI前、CCI后1、3、5、7、10、14 d随机取8只大鼠,测定机械刺激缩足反应阈值(MWT)和热刺激缩足反应潜伏期(TWL).于CCI前、CCI后l、3、7、14d随机取6只大鼠,取腰段脊髓,采用免疫组织化学法检测大鼠脊髓背角GAT-1蛋白的表达.结果 与CCI前比较,2组CCI后各时点MWT和TWL均降低(P＜0.05);与S组比较,CCI组CCI后各时点MWT和TWL均降低,CCI后1、3 d GAT-1表达升高(P＜0.05或0.01).结论 大鼠神经病理性痛的形成与GAT-1表达增多有关.     

Cilostazol and diltiazem attenuate cyclosporine-induced nephrotoxicity in rats

Aim

Cyclosporine (CsA), an important agent used in organ transplantation to prevent rejection, displays nephrotoxicity as the most important side effect limiting usage. In this study, we sought to evaluate the effects of cilostazol and diltiazem to counter the nephrotoxicity induced by the calcineurin inhibitor CsA.

Materials and methods

Animals were randomly divided into seven groups, each consisting of eight animals: sham, controls, cilostazol, diltiazem, CsA, CsA plus diltiazem, and CsA plus cilostazol treatment. At the end of a 60-minute ischemic period, we administered the drugs after reperfusion for 7 days thereafter. CsA (10 mg/kg/d) was intraperitoneally for 7 days; cilostazol (10 mg/kg/d) orally by catheter for 7 days; diltiazem (5 mg/kg/d) intraperitoneally for 7 days. At the end of the 7-day treatment period, blood and tissue samples were harvested for biochemical, and serological evaluation.

Results

Ischemia-reperfusion injury significantly increased malondialdehyde (MDA) levels as well as decreased catalase (CAT) activities and superoxide dysmutase (SOD) content. The lowest MDA mean level was observed in the diltiazem and, the highest in the control group. The lowest CAT mean levels were noted in the CsA and diltiazem groups with highest CAT content was in the CsA and cilostazol groups. The lowest SOD mean level occurred in the sham group; the highest, in the CsA group.

Conclusion

Cilostazol and especially diltiazem were effective to mitigate renal ischemia-reperfusion injury.     

Interaction between sufentanil and U-50488H with respect to antinociception and respiratory depression in rats

Background: Opiate receptors have been argued to differentially regulate analgesia and respiratory depression. In order to validate possible interactions between the opiate mu- and kappa-receptors, interactions between sufentanil and U-50488H were studied in rats.
Methods: Rats equipped with an arterial catheter were tested in the tail flick latency (TFL) test after intravenous treatment with sufentanil (a mu-agonist), U-50488H a kappa-agonist) or fixed ratio combinations of both drugs. Simultaneously, respiratory changes were monitored by blood gas analysis.
Results: The ED₅₀s of sufentanil for a TFL >6.0 and <10.0 s were 0.0002 and 0.00059 mg/kg. For U-50488H the corresponding values were 1.53 and 8.11 mg/kg. Using a fixed dose ratio of 1/10000, an additivity was demonstrated between sufentanil and U-50488H in terms of antinociception. With regard to respiratory parameters, PaCO₂ significantly increased after all doses of sufentanil early after treatment. At the higher doses tested, there was also a decrease in PaO₂ and O₂ saturation. For U-50488H only the highest doses resulted in an early and small shift in PaCO₂. The combination of sufentanil/U-50488H resulted in only a small increase in PaCO₂ at the highest dose regimen tested.
Conclusion: The results presented here demonstrate that drug mixtures of sufentanil and U-50488H can be additive with respect to antinociception with additionally less risk for respiratory side-effects, as compared with sufentanil alone. Therefore, a combination of mu- and kappa-opiate receptor agonists might be more beneficial than each agent alone.     

不同剂量咪达唑仑与乳化异氟醚对大鼠催眠效应的相互作用

目的 评价不同剂量咪达唑仑与乳化异氟醚对大鼠催眠效应的相互作用.方法 成年雄性SD大鼠125只,体重240～300 g,随机分为5组(n=25),采用改良序贯法进行实验,M组和I组分别经尾静脉注射咪达唑仑、乳化异氟醚,首剂量分别为17.3 mg/kg、0.55 ml/kg;MI1组、MI2组和MI3组分别经尾静脉注射1/4、1/2、3/4咪达唑仑催眠效应半数有效剂量(ED50)+乳化异氟醚(首剂量分别为0.22、0.19、0.12 ml/kg),各组相邻剂量比值均为0.85,采用改良序贯法计算各组咪达唑仑、乳化异氟醚催眠效应的ED50,及其95%可信区间(95%CI).催眠有效的标准:前爪翻正反射消失.采用等辐射分析法判断不同剂量咪达唑仑与乳化异氟醚催眠效应的相互作用.结果 M组咪达唑仑催眠效应的ED50及其95%CI为26(22～30)mg/kg;I组、MI1组、MI2组及MI3组乳化异氟醚催眠效应的ED50及其95%CI分别为0.67(0.61～0.73)、0.30(0.28～0.33)、0.22(0.18～0.26)、0.18(0.16～0.20)ml/kg.MI1,组、MI1组、MI3组两药相互作用系数分别为1.51(P<0.01)、1.21(P<0.05)、0.98(P0.05).结论 咪达唑仑6.5、13 mg/kg复合乳化异氟醚时两药的催眠效应为协同作用,咪达唑仑19.5 mg/kg复合乳化异氟醚时两药的催眠效应为相加作用.     

Synergistic antinociception between zaprinast and morphine in the spinal cord of rats on the formalin test

BACKGROUND AND OBJECTIVE: The cyclic guanosine monophosphate level, which causes an antinociception, is increased in cells as a direct result of phosphodiesterase inhibition. This study used a nociceptive test to examine the nature of the pharmacological interaction between intrathecal zaprinast, a phosphodiesterase inhibitor, and morphine. METHODS: Catheters were inserted into the intrathecal space through an incision in the atlantooccipital membrane of male Sprague-Dawley rats. As a nociceptive model, 50 microL of a 5% formalin solution was injected into the hind paw. After observing the effect of zaprinast (37, 111, 369 nmol) and morphine (1, 4, 10, 40 nmol) alone, the interactions of their combination were examined by an isobolographic analysis. RESULTS: Intrathecal zaprinast (P < 0.05) and morphine (P < 0.05) dose-dependently suppressed the flinching observed during phase 1 and phase 2 in the formalin test. The ED50 values (95% confidence intervals) of zaprinast and morphine in phase 1 were 161.9 (87.9-298.3) and 11.6 nmol (4.8-27.9 nmol), respectively. The phase 2 ED50 values (95% confidence intervals) of zaprinast and morphine were 229.9 (142.5-370.9) and 3.9 nmol (1.9-7.6 nmol), respectively. Isobolographic analysis revealed a synergistic interaction after intrathecal delivery a zaprinast-morphine mixture in both phases. The ED50 values of (95% confidence intervals) zaprinast in the combination of zaprinast with morphine in phase 1 and phase 2 were 14.2 (4.9-40.6) and 10.4 nmol (3-35.9 nmol), respectively. CONCLUSIONS: Intrathecal zaprinast and morphine are effective against acute pain and facilitated pain state. Zaprinast interacts synergistically with morphine.     

肺组织γ-氨基丁酸A型受体在大鼠内毒素诱发急性肺损伤中的作用

目的 探讨肺组织γ-氨基丁酸A型受体(GABAAR)在大鼠内毒素诱发急性肺损伤中的作用.方法 成年健康雄性Wistar大鼠32只,8周龄,体重200 ～ 230 g,采用随机数字表法,将其随机分为4组(n=8)∶正常对照组(C组)、内毒素组(LPS组)、γ-氨基丁酸预先给药+内毒素组(GABA组)和GABAAR拮抗剂荷包牡丹碱预先给药+内毒素组(BIC组).LPS组、GABA组和BIC组尾静脉注射LPS 5 mg/kg,C组给予等容量生理盐水;GABA组和BIC组分别于给予LPS前30 min时腹腔注射γ-氨基丁酸50 mg/kg和荷包牡丹碱10 μmol/kg.于给予LPS后6h时,采集动脉血样,测定PaO2,然后取肺组织,测定肺湿/干重比(W/D)、GABAAR表达、IL-6、TNF-α、MDA的含量和SOD活性,光镜下观察肺组织病理学结果.结果 与C组比较,LPS组、GABA组和BIC组PaO2降低,LPS组和GABA组肺组织W/D、TNF-α、IL-6和MDA的含量升高,肺组织GABAAR表达上调,肺组织SOD活性降低(P＜0.05);与LPS组比较,GABA组肺组织W/D、TNF-α、IL-6和MDA的含量升高,肺组织GABAAR表达上调,肺组织SOD活性降低(P＜0.05),而BIC组上述指标差异无统计学意义,GABA组和BIC组PaO2差异无统计学意义(P＞0.05).结论 肺组织GABAAR参与了大鼠内毒素诱发急性肺损伤的发展.     

Oxidative stress affects synaptosomal gamma-aminobutyric acid and glutamate transport in diabetic rats: the role of insulin

Evidence suggests that oxidative stress is involved in the pathophysiology of diabetic complications and that insulin has a neuroprotective role in oxidative stress conditions. In this study, we evaluated the in vitro effect of insulin in the susceptibility to oxidative stress and in the transport of the amino acid neurotransmitters gamma-aminobutyric acid (GABA) and glutamate in a synaptosomal fraction isolated from male type 2 diabetic Goto-Kakizaki (GK) rat brain cortex. The ascorbate/Fe(2+)-induced increase in thiobarbituric acid reactive substances (TBARSs) was similar in Wistar and GK rats and was not reverted by insulin (1 micromol/l), suggesting that other mechanisms, rather than a direct effect in membrane lipid peroxidation, may mediate insulin neuroprotection. Diabetes did not affect GABA and glutamate transport, despite the significant decrease in membrane potential and ATP/ADP ratio, and insulin increased the uptake of both GABA and glutamate in GK rats. Upon oxidation, there was a decrease in the uptake of both neurotransmitters and an increase in extrasynaptosomal glutamate levels and in ATP/ADP ratio in GK rats. Insulin treatment reverted the ascorbate/Fe(2+)-induced decrease in GABA accumulation, with a decrease in extrasynaptosomal GABA. These results suggest that insulin modulates synaptosomal GABA and/or glutamate transport, thus having a neuroprotective role under oxidizing and/or diabetic conditions.     

cPKCs在大鼠内脏炎性痛形成中的作用

目的 探讨cPKCs在大鼠内脏炎性痛形成中的作用.方法 成年Wistar大鼠96只,体重200～250 g,雌雄不拘.随机分为4组(n=24):对照组(C组)、生理盐水组(NS组)、PMA组和H-7组.大鼠蛛网膜下腔置管后,采用直肠粘膜下注射福尔马林的方法,制备大鼠内脏炎性痛模型.C组不给予任何处理,NS组、PMA组、H-7组分别于给予福尔马林前30 min经PE-10管注射0.9%生理盐水20 μl、cPKCs和nPKCs激动剂PMA 100 ng(生理盐水稀释至20 μl)、PKC抑制剂H-7 200 μg(生理盐水稀释至20 μl),然后分别注入0.9%生理盐水10 μl冲洗PE-10管.各组于给予福尔马林后30、60、120 min时取8只大鼠,测定内脏痛评分,然后取脊髓,测定cPKCs膜转位水平.结果 与NS组比较,给予福尔马林后30、60 min时PMA组内脏痛评分升高,H-7组内脏痛评分降低(P＜0.05或0.01).与C组比较,NS组给予福尔马林后30 min时PKCγ膜转位水平升高,PMA组给予福尔马林后30、60 min时PKCγ膜转位水平升高(P＜0.01).与Ns组比较,给予福尔马林后30、60 min时PMA组PKCγ膜转位水平升高,H-7组PKCγ膜转位水平降低(P＜0.05).结论 cPKCs型的PKCγ亚型参与了大鼠内脏炎性痛的形成.     

Dextromethorphan potentiates morphine antinociception at the spinal level in rats

PURPOSE: Morphine is an effective analgesic, but adverse effects limit its clinical use in higher doses. The non-opioid antitussive, dextromethorphan (DM), can potentiate the analgesic effect of morphine and decrease the dose of morphine in acute postoperative pain, but the underlying mechanism remains unclear. We previously observed that DM increases the serum concentration of morphine in rats. Therefore, we investigated the effects of drugs administered at the spinal level to exclude possible pharmacokinetic interactions. As DM has widespread binding sites in the central nervous system [such as N-methyl-D-aspartate (NMDA) receptors, sigma receptors and alpha(3)ss(4) nicotinic receptors], we investigated whether the potentiation of morphine antinociception by DM at the spinal level is related to NMDA receptors. METHODS: We used MK-801 as a tool to block the NMDA channel first, and then studied the interaction between intrathecal (i.t.) morphine and DM. The tail-flick test was used to examine the antinociceptive effects of different combinations of morphine and other drugs in rats. RESULTS: DM (2-20 microg) or MK-801 (5-15 microg) showed no significant antinociceptive effect by themselves. The antinociceptive effect of morphine (0.5 microg, i.t.) was significantly enhanced by DM and reached the maximal potentiation (43.7%-50.4%) at doses of 2 to 10 microg. Pretreatment with MK-801 (5 or 10 microg, i.t.) significantly potentiated morphine antinociception by 49.9% or 38.7%, respectively. When rats were pretreated with MK-801, DM could not further enhance morphine antinociception (45.7% vs 50.5% and 43.3%). CONCLUSION: Our results suggest that spinal NMDA receptors play an important role in the effect of DM to potentiate morphine antinociception.