Abstract:

[Abstract]   Objective   To investigate effects of intrathecal injection of morphine and fentanyl combined with lowdose naloxone on the pain behavior and the expression of blood motilin (MTL) in the rat model of incisional pain． Methods   A total of 72 healthy male Sprague-Dawley rats (weight 180-220 g), successfully intrathecally catheterized, were randomly divided into 6 groups (n=12 ): normal saline group (NS group), incisional pain group (P group), morphine (5 μg/kg)+ fentanyl (0.25 μg/kg) group (MFP group), morphine+ fentanyl+ naloxone (0.2 ng/kg, 1 ng/kg, 5 ng/kg) group (MFPN1, MF?PN2 and MFPN3 groups). All groups except NS group were made the model of incisional pain on the right plantar surface. At 24-hours before intrathecal cathetherization (T0), 24-hours before modelling (T1), 1-hours (T2), 3-hours (T3) , 6-hours (T4), 24 -hours (T5) , 48-hours (T6) and 72-hours (T7) after modelling respectively, paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL) were detected in right hind paw in 6 rats of each group. The other 6 rats in each group were sacrificed 6-hour after operation. The plasma expression of motilin was detected by ELISA.   Results   Compared with NS group, the PWMT was not significantly different in all time points in MFPN2 group. The values of PWTL were significantly longer at T2 and T5 in MFPN2 group than those of NS group (P＜ 0.05)． The PWMT and the PWTL were significantly decreased at T2, T3 and T4 in P and MFPN3 groups than those of NS group (P＜ 0.05)． Compared with P group, the PWMT at T6, and PWTL at T3 and T4 were significantly decreased in MFPN3 group (P<0.05). The MTL at T6 was significantly decreased in P, MFP, MFPN1 and MFPN3 groups compared with that of NS group (P<0.05). There was no significant difference in MTL between MFPN2 group and NS group (P>0.05)． Conclusion   In the rat model of incisional pain, intrathecal injection of naloxone at 1 ng/kg can inhibit the down-regulation of blood motillin caused by morphine and fentanyl, and which can up-regulate the PWTL, enhancing the analgesic effects of opioids．

Key words: motilin, morphine, naloxone, fentanyl, incisional pain, gastrointestinal dynamics