Effects of intrathecally coadministered dexamethasone and spironolactone on pain behaviors in a rat model of radicular pain

Objective To investigate the effects of intrathecally coadministered dexamethasone and spironolactone in trathecally on radicular pain behaviors.Methods Using rat model of radicular pain induced by chronic compression of dorsal root ganglion (CCD) ,48 male SD rats successfully received intrathecal catheter implantation and without motor dysfunction were randomly divided into Sham-operation group (Sham group, n= 12),Control group ( C group, n = 12 ), Dexamethasone group ( D group, n = 8 ), Spironolactone group ( S group, n = 8 )and Dexamethasone plus spironolactone group (DS group, n=8).Rats in D group,S group or DS group were intrathecally treated with dexamethasone 4 μg, spironolactone 3 μg or dexamethasone 4 μg plus spironolactone 3 μg twice daily on day 2 ～4 after CCD respectively,while rats in C and Sham group received 10μl 10% alcohol.Paw withdrawal mechanical threshold(PWMT) and paw withdrawal thermal latency (PWTL) were tested on day 1 before CCD and day 1,4,7,10,14,17 and 21 after CCD.Results Compared with Sham group, both PWMT and PWTL were significantly decreased after CCD surgery on the ipsilateral side(P＜0.01 ＝.Intrathecally administrated with dexamethasone significantly improved pain behaviors (P＜0.01 ＝ and these therapeutic effects lasted up to 10 days after CCD surgery.As with dexamethasone,intrathecal spironolactone also significantly attenuated PWMT (P＜0.01 ＝ and PWTL (P＜0.01 ＝ and the change lasted up to 7 days after CCD surgery.Coadministration spironolactone and dexamethasone exhibited significant synergies( PWMT: ( 13.52 ± 0.72) g vs ( 11.58 ± 1.38 ) g, P ＜0.01; PWTL: ( 19.63 ± 1.68) s vs ( 14.14 ± 1.52) s, P ＜ 0.01 ＝.These effects lasted up to at least 10 days.Conclusion Both dexamethasone and spironolactone intrathecally have therapeutic effects on radicular pain behaviors, combination injection of these two drugs could generate significant synergies. Key words: Neuropathic pain;  Dexamethasone;  Spironolactone;  Pro-inflammatory cytokine