Long-term Effect Of Sciatic Nerve Block With Ropivacaine PEG-PLA Microparticles On Postoperative Pain In Rats

Objective:To investigate the efficacy of ropivacaine PEG-PLA microspheres for sciatic nerve block in rats; to explore the effect of sustain released ropivacaine microspheres on expression of c-fos in spinal cord of rats and the toxicity of the microspheres.Methods:Eighty Wistar rats were randomly divided into four groups (n=20, each) and were treated with0.2mL of0.9%saline (control group),10mg of PEG-PLA (PEG-PLA group),0.2mL of0.5%ropivacaine (ropivacaine group) and10mg of10%Rop-PEG-PLA microspheres (Rop-PEG-PLA group), respectively. The incision pain models were produced as described by Brennan. MWT and TWL were measured at24h before incisions and at2,4,8h, as well as1,2,3,5and7d after incision. Expression of c-fos in the spinal cord was determined by immunohistochemistry at2h and2d after incision. The ropivacaine concentration in plasma of ropivacaine group and Rop-PEG-PLA group was detected by HPLC analysis. Histopathological changes around sciatic nerve and in major organs were also evaluated.Results:Behavioral testing and c-fos expression in PEG-PLA group showed no significant difference compared with those in control group (P>0.05). The thresholds and latencies in ropivacaine group and Rop-PEG-PLA group were significantly higher than those in control group at2h after incision (P<0.05). Expression of Fos protein was suppressed in ropivacaine group and Rop-PEG-PLA group at2h after incision, compared with that of control group (P<0.05). The duration of anti-hyperalgesia effect (3d vs2h) and ropivacaine concentration in plasma (8h vs4h) in Rop-PEG-PLA group were longer than that in ropivacaine group, and c-fos expression in Rop-PEG-PLA group was lower than that in ropivacaine group (P<0.05). No significant histopathological changes were observed.Conclusion:Single administration of ropivacaine PEG-PLA microspheres for sciatic nerve block provides an effective analgesia of postoperative pain for3d. The analgesic action of sustain released ropivacaine microspheres is related to inhibition of c-fos expression. The toxicity of microspheres were not observed.