ABSTRACT
Objective To evaluate the effects of intrathecal low-dose naloxone,morphine and fentanyl on the expression of motilin (MTL) in the spinal cord in rats with incisional pain.Methods Seventy-two healthy male Sprague-Dawley rats,weighing 180-220 g,in which intrathecal catheters were successfully implanted,were randomly divided into 6 groups (n =12 each) using a random number table:normal saline group (NS group),morphine + fentanyl group (MF group),incisional pain group (P group),naloxone + incisional pain group (NP group),morphine + fentanyl + incisional pain group (MFP group),and morphine + fentanyl + naloxone +incisional pain group (MFNP group).Incisional pain was induced by an incision made into the plantar surface of the right hindpaw.At 20 min before induction of incisional pain,the mixture of morphine 5 μg/kg and fentanyl 0.25 μg/kg was injected intrathecally in MF,MFP and MFNP groups,and naloxone 1 ng/kg was given in NP and MFNP groups.Six rats from each group were randomly chosen,and paw withdrawal threshold to mechanical stimulation (PWMT) and paw withdrawal latency to thermal stimuli (PWTL) were measured before intrathecal catheterization (T0,baseline),at 24 h before induction of incisional pain (T1),and at 1,3 and 6 h after induction of incisional pain (T2-4).The left 6 rats from each group were chosen and sacrificed and the spinal cord were removed at 6 h after operation for detection of MTL content in the spinal cord,body of the stomach and duodeum tissues (by ELISA).Results Compared with the baseline value at T0,PWMT was significantly increased at T3,and PWTL was prolonged at T2-4 in MF group,PWMT was decreased and PWTL was shortened at T2-4 in P group and at T3,4 in NP group,PWMT was increased at T2,3 in MFP group,and PWMT was increased and PWTL was prolonged at T2 in MFNP group (P ＜ 0.05).Compared with NS group,MTL contents in spinal cord and body of the stomach were significantly decreased in MF and NP groups,MTL cortent in duodeum was decreased in group MF,while increased in group NP and MTL content in spinal cord was increased,and MTL content in body of the stomach was decreased in P and MFP groups,MTL content in duodeum was increased in group P,while decreased in group MFP(P ＜ 0.05),however,no significant change was found in MTL content in MFNP group (P ＞ 0.05).Conclusion Intrathecal low-dose naloxone combined with morphine and fentanyl can inhibit up-regulation of the expression of MTL in the spinal cord in rats with incisional pain and is involved in the maintenance of stable gastrointestinal motility.