Objective: To evaluate the immunological function in rats with formalin inflammatory pain through intrathecal pumping different dosages of morphine.
Methods: Thirty-two Sprague-Dawley rats were randomly divided into 4 groups (n = 8 in each group): saline group (NS) and morphine group included M1 group (10 microg/h) , M2 group (5 microg/h), and M3 group (2.5 microg/h). Chronic intrathecal catheterization was performed under anesthesia with 10% chloral hydrate (300-350) mg/kg according to M2 group (5 microg/h) and M3 group (2. 5 microg/h). Chronic intrathecal catheterization was modified Yaksh's. After 7 days, pain intensity scoring (PIS) was utilized to assess antinociceptive effect of morphine. And spleens were aseptically removed to obtain splenic cells. T lymphocyte function was evaluated based on Concanavalin-A induced splenocyte proliferation. A modified lactic acid dehydrogenase release assay was used to assess NK cell activity. Phenotypic expression of cell surface markers of T lymphocyte subsets (CD3+, CD3+ CD4+, CD3+ CD8+, and CD4+ / CD8+ ) and NK cell ( CD161+) in the spleen were analyzed by flow cytometry.
Results: Compared with the NS group, PIS of morphine group decreased obviously (P < 0.01) and was dose-dependent in the early and late phase of formalin pain, but there were no significant differences among morphine groups. Spleen index, splenocyte proliferation and NK cell activity were significantly suppressed by intrathecal pumping morphine. Phenotypic expression of T lymphocyte subsets and NK cell assessed by flow cytometry were different from the control group in all morphine groups.
Conclusion: There was significant antinociception of intrathecal pumping morphine. After intrathecal pumping different dosages of morphine (10 microg/h,5 microg/h, and 2.5 microg/h), the function of cellular immunity was suppressed and was dose-dependent.