Objective To evaluate the role of autophagy in remifentanil-induced hyperalgesia in the rats with incisional pain.Methods Forty pathogen-free healthy male Sprague-Dawley rats,aged 2-3 months,weighing 250-280 g,were divided into 5 groups (n =8 each) using a random number table:control group (group C),remifentanil group (group R),incisional pain group (group Ⅰ),incisional pain plus remifentanil group (group IR) and incisional pain plus remifentanil plus autophagy inhibitor 3-methyladenine (3-MA) group (group MA).In group R,remifentanil was infused for 60 min at a rate of 1 μg · kg-1 · min-1 through the caudal vein.In group IR,a 1-cm longitudinal incision was made through skin,fascia and muscle of the plantar aspect of both hindpaws in anesthetized rats at 10 min of remifentanil infusion.In group MA,3-MA 15 mg/kg was injected intraperitoneally at 1 h before establishment of the model,and the other treatments were similar to those previously described in group IR,while the equal volume of normal saline was given in the other groups.The mechanical paw withdrawal threshold (MWT) and thermal paw withdrawal latency (TWL) were measured at 24 h before infusion and 2,6,24 and 48 h after infusion (T0-4).The rats were sacrificed after the last measurement of pain threshold at T4,and the L4-6 segments of the spinal cord were removed for determination of the expression of microtubule-associated protein 1 light chain 3 Ⅱ (LC3 Ⅱ),Beclin-1 and P62 by Western blot.Results Compared with group C,the MWT was significantly decreased and the TWL was shortened at T1-4 in R,Ⅰ,IR and MA groups,the expression of LC3 Ⅱ and Beclin-1 was up-regulated,and P62 expression was down-regulated in R and IR groups,the expression of LC3 Ⅱ was up-regulated at T4 in group Ⅰ,and the expression of LC3 Ⅱ and Beclin-1 was up-regulated at T4 in group MA (P＜0.0.5).Compared with group R,the MWT was significantly decreased and the TWL was shortened at T1-4,and the expression of LC3 Ⅱ was up-regulated at T4 in group IR (P＜0.05).Compared with group Ⅰ,the MWT was significantly decreased and the TWL was shortened at T1-4,and the expression of LC3 Ⅱ and Beclin-1 was up-regulated and P62 expression was down-regulated at T4 in group IR (P＜0.05).Compared with group IR,the MWT was significantly decreased and the TWL was shortened at T1-4,and the expression of LC3 Ⅱ and Beclin-1 was down-regulated and P62 expression was up-regulated at T4 in group MA (P＜0.05).Conclusion Autophagy is involved in the development and maintenance of remifentanil-induced hyperalgesia in the rats with incisional pain.

Objective:To evaluate the relationship between autophagy and oxidative stress during remifentanil-induced hyperalgesia in the rats with incisional pain.Methods:Thirty-two clean-grade healthy male Sprague-Dawley rats, weighing 230-250 g, aged 2-3 months, were divided into 4 groups ( n=8 each) using a random number table method: incisional pain group (I group), remifentanil + incisional pain group (RI group), autophagy inhibitor 3-methyladenine + remifentanil + incisional pain group (MRI group) and autophagy agonist rapamycin group + remifentanil + incisional pain group (RRI group). The model of incision pain was developed and the equal volume of normal saline was intravenously infused simultaneously for 60 min.In RI, MRI and RRI groups, the model of incision pain was developed and remifentanil 1 μg·kg -1·min -1 was simultaneously infused for 60 min.In MRI group, 3-methyladenine 15 mg/kg was intraperitoneally injected at 12 h before developing the model, and rapamycin 10 mg/kg was intraperitoneally injected at 12 h before developing the model in RRI group.Thermal paw withdrawal latency (TWL) and mechanical paw withdrawal threshold (MWT) were measured at 24 h before infusion of remifentanil or normal saline (T 0) and at 2, 6, 24 and 48 h after the end of infusion (T 1-4). The rats were sacrificed after the end of behavioral testing, and the lumbar enlargement segments of the spinal cord were harvested for determination of the expression of autophagy microtubule-associated protein 1 light chain 3Ⅱ (LC3Ⅱ), Beclin-1 and P62 (by Western blot), activity of superoxide dismutase (SOD) (by xanthine oxidase method) and content of malondialdehyde (MDA) (by thiobarbital method). Results:Compared with the baseline at T 0, PWT was significantly decreased and TWL was shortened at T 1-4 in the four groups ( P<0.05). Compared with I group, MWT was significantly decreased and TWL was shortened at T 1-4, the expression of LC3 Ⅱand Beclin-1 was up-regulated, the expression of P62 was down-regulated, SOD activity was decreased, and MDA content was increased in RI group ( P<0.05). Compared with RI group, MWT was significantly decreased and TWL was shortened at T 1-4, the expression of LC3 Ⅱand Beclin-1 was down-regulated, the expression of P62 was up-regulated, SOD activity was decreased, and MDA content was increased in MRI group ( P<0.05), and MWT was significantly increased and TWL was prolonged at T 1-4, the expression of LC3 Ⅱand Beclin-1 was up-regulated, the expression of P62 was down-regulated, SOD activity was increased, and MDA content was decreased in RRI group ( P<0.05). Conclusions:Autophagy is involved in the process of remifentanil-induced incisional hyperalgesia through regulating the level of oxidative stress in rats.