Effect of intrathecal morphine and fentanyl on level of natural killer cells in hippocampus of rats with incisional pain

Objective To evaluate the effect of intrathecal morphine and fentanyl on the level of natural killer(NK)cells in the hippocampus of rats with incisional pain. Methods Ninety-six healthy male Sprague-Dawley rats, weighing 180-220 g, aged 6-8 weeks, in which intrathecal catheters were successfully implanted, were divided into 4 groups(n=24 each)using a random number table: control group(C group), incisional pain group(P group), intrathecal morphine-fentanyl group(MF group)and intrathecal morphine-fentanyl plus incisional pain group(MFP group). A 1-cm longitudinal incision was made through skin, fascia and muscle of the plantar aspect of the right hindpaw in sevoflurane-anesthetized rats.At 20 min before establishment of the incisional pain model, the mixture of morphine 5 μg/kg and fentanyl 0.25 μg/kg was intrathecally injected in MFP group, while the equal volume of normal saline was given instead in NS and P groups.Six rats were selected at 24 h before establishment of the model(T0, baseline)and at 1, 6, 24, 48 and 72 h after establishment of the model(T1-5), and the mechanical paw withdrawal threshold(MWT)and thermal paw withdrawal latency(TWL)were measured.Six rats from each group were selected at T0, T2, T3 and T5, venous blood samples were taken from the peripheral vein, the animals were then sacrificed immediately, and the hippocampi and spleen were quickly harvested.The levels of NK cells in peripheral blood, hippocampi and spleen were measured. Results Compared with group C, the MWT was significantly decreased, the TWL was shortened, the levels of NK cells in hippocampi were increased at T2-5, the levels of NK cells in the spleen were increased at T2 and decreased at T3, 5, and the levels of NK cells in peripheral blood were decreased at T2, 3 in group P(P 0.05), the levels of NK cells in the spleen were increased at T2 and decreased at T5, the levels of NK cells in peripheral blood were decreased at T2, 5(P 0.05). Compared with group P, the MWT was significantly increased, the TWL was prolonged, the levels of NK cells in hippocampi were decreased at T2-5, and the levels of NK cells in the spleen and peripheral blood were decreased at T2-5 and increased at T3 in group MFP(P<0.05). Conclusion Intrathecal morphine and fentanyl can maintain the level of NK cells stable in the hippocampus, which may be helpful for maintenance of immune function of rats with incisional pain. Key words: Morphine; Piperidines; Pain, postoperative; Injections, spinal; Killer cells, natural; Hippocampus