The Mechanisms Of Intrathecal Propentofylline Attenuate Rat Inflammation Thermal Hyperalgesia

Objective To investigate whether activation of astrocytes is involved in the induction and maintenance of Complete Freund's Adjuvant (CFA)-induced inflammatory pain, observe whether Intrathecal injection propentofylline (PPF) reduces the expression of glial fibrillary acidic protein (GFAP) in the spinal cord of the inflammatory rat, and have anti-hyperalgesic effect. Methods Seventy-eight male adult Holzman Sprague-Dawley rats (180-220g) were used. In a rat model of arthritic pain model induced by inject CFA 50μl into right hind paw of ankle mortise lateral subcutaneouly. Part one: forty-eight rats were randomly divided into 6 groups (n=8 each). Normal saline (NS) group: normal rats received normal saline (NS) both intrathecal injection (i.t.) and subcutaneously (sc). Model group: normal rats were received 50μl CFA in right hind paw of ankle mortise subcutaneouly. PPF single group: normal rats received PPF i.t. after NS s.c. PPF therapy group, rats received CFA incubation after PPF i.t. (concentrations were 2.5, 5 and 10μg/10μl, respectively). PPF or NS daily via lumbar puncture at the L4～L5 level half an hour before CFA incubate. Measure the change of paw TWL from the first day to the seventh day and fourteenth day after CFA sc. Part two: 30 SD rats were randomly divided into 6 groups (n=5 each). Choice 3 groups randomly and pretreated NS half an hour before CFA incubate. Killed inflammated rats after injected CFA 5h in the first, third and seventh day (that is model group, CFA5h, CFA3d, CFA7d), choice another 3 groups pretreated with PPF (10μg/10μl, i.t.), before injected CFA half an hour and killed 5h later in the first, third and seventh day (that is PPF therapy group, PPF5h, PPF3d, PPF7d), Five rats of NS group were used as the blank control. The change of GFAP expression in L4～L5 segments of spinal cord was accessed by immunohistochemistry analysis. Results PPF (10μg/10μl, i.t.) solely had no effect on the TWLs of normal rats. PPF (2.5μg/μl, i.t.) had no effect on the TWL of inflamed hind paw during the experiment except the first day and the second day (P>0.05, n=8). At the dosage of 5 and 10μg/μl, PPF produced marked anti-hyperalgesia in inflamed hind paw respectively (P<0.05, n=8). Both dosages inhibited the induction of hyperalgesia in both acute and persistent paradigms. The TWL of right hind paw was significantly higher in the PPF groups than model group (P<0.001). Astrocytes marker GFAP were deeply stained in spinal cord dorsal horn of model group , PPF i.t.10μg significantly attenuated the activation of GFAP in the spinal cord dorsal horn in group PPF (P<0.01). Conclusion The result suggests that PPF have antihyperalgesia properties. The antihyperalgesia effect of PPF is closely related to suppress the astrocytes activation in spinal cord in CFA-induced inflammation pain progress.Part two: The spinal antinociceptive mechanism of intrathecal administration of propentofylline in inflammatory ratsObjective To investigate the effects of intrathecal injections(i.t.) propentofylline (PPF) in established Complete Freunds Adjuvant (CFA)-induced peripheral hyperalgesia in spinal cord. Methods The experiment was performed in two parts. In part one 32 male adult SD rats (180-220 g) were randomly divided into 4 groups (n=8 each): in groupⅠ, normal rats received sterilities cerebrospinal fluid (SCF) and normal saline (NS) subcutaneously (sc), in groupⅡinflammatory rats received sterilities cerebrospinal fluid i.t., in groupⅢnormal rats received. PPF i.t. after NS sc, in groupⅣinflammatory rats received PPF i.t. or SCF i.t. daily via lumbar puncture at the L4～L5 level 5 hours after CFA incubated. Measure the change of TWL from the second day to the seventh day and fourteenth day after CFA subcutaneous injected. In part two, 30 inflammatory rats were randomly divided into 6 groups (n=5 each group): in group C1～C7 rats were killed after incubated CFA 1d, 3d, 7d respectively; in group P1～P7 animals were killed after PPF i.t. 5h in 1d, 3d, 7d respectively. Five rats in groupⅠwere used as the blank control. The change of GFAP expression in L4～L5 segments of spinal cord was accessed by immunohistochemistry analysis. Results CFA produced marked inflammation (edema and erythema) and thermal hyperalgesia in the injected paw, which peaked at 8h after injection and showed little change in magnitude for continuous 3d. PPF i.t. (10μg/10μl) had no effect on the TWL of normal rats, but significantly reversed the thermal hyperalgesia induced by CFA in subacute and persistent paradigms (P<0.001, n=8). The TWL of right hind paw was significantly higher in groupⅣthan groupⅡ(P<0.001). Astrocytes activation mareker GFAP were deeply stained in spinal cord dorsal horn of group C, intrathecal PPF 10μg significantly attenuated the activation of GFAP in the spinal cord dorsal horn in group P (P<0.01). Conclusion PPF have anti-nociceptive property. The anti-nociceptive effect of PPF is probably related to the astrocytes activation in spinal cord of inflammatory rats.