| Remifentanil, as a potent short-acting μ-opioid receptor agonist, remains first-line analgesic available for analgesia in general anesthesia, however, numerous experimental and clinical researches demonstrated that remifentanil medication might result in remifentanil-induced hyperalgesia(RIH), likely due to its rapid-onset and short duration. Numerous clinical articles have manifested that remifentanil, at clinically relevant dose(0.1-0.5μg·kg-1·min-1) as an intraoperative analgesic could cause pain hypersensitivity and enhance postoperative analgesics consumption, which may limit its use. So some effective preventive measures should be explored.Our previous studies have identified that NR2B-containing NMDA receptor membrane trafficking in the spinal cord dorsal horn might be involved in development and maintenance of RIH. It is well known that NMDAR activation releases superoxide and NO which may produce peroxynitrite(PN) to cause manganese superoxide dismutase(Mn SOD) nitration and inactivation, thus inducing hyperalgesia. Hydrogen, one of the ROS scavengers, could selectively reduce hydroxyl radicals and peroxynitrite anion and enhance Mn SOD activity to exert therapeutic antioxidant function. However, whether hydrogen could abolish hyperalgesia via mitigating peroxidation and Mn SOD nitration has not been reported yet. This study was conducted to test the hypothesis that hydrogen-rich saline(HRS) would attenuate hyperalgesia induced by remifentanil by regulation of Mn SOD activity and NR2B-containing NMDA receptor expression and trafficking in the spinal cord in a rat model of remifentanil infusion.Objective To investigate antihypernociceptive effect of intraperitoneal administration of HRS with different doses in RIH and select the most optional preventive dose; To valuate changes of NMDA receptor trafficking and Mn SOD nitration in incisional pain-remifentanil-induced hyperalgesia after intraperitoneal administration of HRS with the most optional preventive dose; To discuss whether NR2B-containing NMDA receptor was involved in antihyperalgesion of HRS via inhibition of Mn SOD nitration by intrathecal injection of selective NR2 B antagonist Ro25-6981.MethodsⅠ 80 SD male rats(240~260 g) were randomly divided into 8 groups(n=10 each): group C(normal saline infusion); group C+ H1, C+ H2, C+ H3(intraperitoneal injection of HRS 2.5ml/kg, 5ml/kg, 10ml/kg at the end of NS infusion); group R(remifentanil 1μg·kg-1·min-1for 1h, iv); group H1, H2, H3(intraperitoneal injection of hydrogen-rich saline 2.5ml/kg, 5ml/kg, 10ml/kg at the end of remifentanil infusion). We examined hydrogen concentration in arterial and venous blood at 5min before and 5, 10, 15, 20, 30, 45 and 60 min after HRS administration. Arterial blood gas analysis was measured and recorded at 5min before and 15 and 45 min after administration of HRS. Paw withdrawal mechanical threshold(PWT) and paw withdrawal thermal latency(PWL) were measured at 24 h before and 2, 6, 24 and 48 h after remifentanil or NS administration.Ⅱ 80 SD male rats(240~260 g) were randomly divided into 8 groups(n=10 each): C group(a sham operation, NS iv); I group(NS iv); G group(glycine 15μg·kg-1·min-1for 60 min, iv); R group(remifentanil iv); H+C group(HRS ip, a sham operation, NS iv); H+I group(HRS ip, NS iv); H+G group(HRS ip, glycine iv); H+R group(HRS ip, remifentanil iv). HRS(10ml/kg) was injected after NS, glycine and remifentanil infusion. A surgical incision was prepared in all groups except group C and H+C. PWT and PWL were measured at 1d before and 1, 2, 3, 5, 7d after operation. The L4-L6 segments of dorsal horn were collected after the last behavioral testing for determining the expression and nitration of Mn SOD, and the expression of the total and membrane NMDAR(NR2A and NR2B).Ⅲ 80 SD male rats(240~260 g) were randomly divided into 8 groups(n=10 each): group C(NS iv); group C+ Ro 3(Ro 25-6981 50 μg); group R; group Ro 1, Ro 2, Ro 3(Ro 25-6981 5 μg, 10 μg, 50 μg); group H; group Ro 1+ H. A surgical incision was prepared in all groups except group C and C+ Ro 3. Ro25-6981 was given intrathecally 10 min before after NS or remifentanil infusion. HRS(2.5 ml/kg) was injected intraperitoneally after remifentanil infusion. PWT and PWL were measured at 1d before and 1, 2, 3, 5, 7d after operation. The L4-L6 segments of dorsal horn were collected after completing behavioral tests for determining Mn SOD expression and nitration.ResultsⅠ Hydrogen concentration dose-independently increased 5min, peaked 15 min, and returned to basal level 45 min after HRS administration(P<0.01); Compared with group C, rats treated with remifentanil and hydrogen-rich saline showed a significant decrease in PWT and PWL(P < 0.01), while compared with group R, group H2 and H3 dose-dependently induced a remarkable increase in PWT and PWL(P < 0.01), 10ml/kg HRS exerts a best effect and minimal effective concentration was observed to be higher than 10 μmol/L; no significant differences in p H, Pa O2, Pa CO2, and Sa O2 were observed among all groups after administration of HRS(P >0.05).Ⅱ We found that the analgesic effect of remifentanil was followed by long-term hyperalgesia lasting at least postoperative 7 days, which was accompanied with increase in NR2 B expression and trafficking from cytoplasm to surface and Mn SOD nitration in dorsal horn(P<0.01). Pretreatment with HRS(10ml/kg) significantly attenuated mechanical and thermal hyperalgesia, blocked NR2 B trafficking and Mn SOD nitration in dorsal horn after remifentanil infusion(P<0.01). There are no significant changes in the levels of NR2 A and Mn SOD in all groups(P >0.05).Ⅲ Ro25-6981 not 5 μg but 10 and 50 μg dosage-dependently attenuated hyperalgesia, and inhibited Mn SOD nitration(P<0.01). Hyperalgesia and Mn SOD nitration were attenuated after the combination of HRS(2.5ml/kg) and Ro25-6981(5μg)(P<0.01).Conclusion Hydrogen-rich saline dose-dependently plays a preventive role in remifentanil-induced hyperalgesia, furthermore, the dose of 10ml/kg exerts a best result; Remifentanil may cause postoperative hypernociception lasting at least 7days, and HRS(10ml/kg) might reverse remifentanil-induced hyperalgesia, modulate NR2 B trafficking and control Mn SOD nitration; Ro25-6981 dose-dependently plays a preventive role in RIH, furthermore, the dose of 50μg exerts a best result. HRS might reverse remifentanil-induced hyperalgesia, through regulating NR2B-containing NMDAR trafficking to control Mn SOD nitration. |
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