Objective: To evaluate the effect of intrathecal pumping tramadol on cell-mediated immunity in rats with formalin inflammatory pain.
Methods: Thirty-two Sprague-Dawley adult male rats weighting 250 approximately 300 g were randomly divided into 4 groups (n=8 in each group):Saline group (NS) and 3 tramadol groups (T1,T2,and T3). The rats were anesthetized with intraperitoneal chloral hydrate (300 approximately 350)mg/kg. Microspinal catheter was inserted into the subarachnoid space at the lumber region according to modified Yaksh techniques. In the tramadol groups,after 5 days tramadol was continuously infused through the spinal catheter at 50 (T1),25 (T2), and 12.5 microg/h (T3) for 7 days. In the NS group normal saline was continuously infused instead of tramadol. On Day 7 formalin (5%, 50 microL) was injected into the plantar surface of the left hindpaw. The number of flinches, lickings and total time of licking was recorded for 60 min.Pain intensity scoring(PIS)(0 approximately 3;0= no pain, 3=severe pain) was used to assess the antinociceptive effect of intrathecal tramadol. The rats were killed after the evaluation of pain intensity. Body weight and spleen weight were measured and spleen index (spleen weight/body weight) was calculated. T-lymphocyte function was evaluated based on Concanavalin-A(ConA) induced splenocyte proliferation. A modified lactic acid dehydrogenase(LDH) release assay was done to assess the NK cell activity. Phenotypic expressions 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: The PIS scores were significantly lower in the T1,T2,and T3 groups than those in the NS group. The spleen index and splenocyte proliferation induced by ConA were significantly suppressed in the T1 group,and the phenotypes of T lymphocyte subsets were significantly changed,but no significant difference was found in the T2 and T3 groups compared with the NS group. There were no differences in NK cell activity in the 3 tramadol groups from the control group.
Conclusion: Intrathecal pumping tramadol has significantly antinociceptive effect. Intrathecal pumping higher dosage tramadol (50microg/h) suppresses T lymphocyte proliferation and alteres T lymphocyte subset phenotype but does not affect NK cell activity. General analgesic dosage tramadol (25 and 12.5 microg/h) has no effect on the immune function.