Neuroprotective effects of magnesium sulfate on spinal cord injury in rats

Yonggang MA; Shiqing LIU; Hao PENG; Gang WANG

ABSTRACT

BACKGROUND:

Available evidence suggests that following spinal cord injury, obvious reduction of Mg2+ level occurs in both the serum and the injured spinal cord, which has significant effects on cell membrane permeability, vascular regulation as well as secondary spinal cord injury.

OBJECTIVE:

To investigate the protective effects of magnesium sulfate (Mg2SO4) administered via intraperitoneal injection on the injured spinal cord of SD rats.

DESIGN:

A randomized controlled experiment.

SETTING:

Department of Orthopedics, Renmin Hospital of Wuhan UniversityMATERIALS Forty-eight adult male SD rats were allocated randomly into experiment group and control group with 24 rats in each.

INTERVENTIONS:

The experiment was conducted in the Laboratory of Department of Orthopedics, Renmin Hospital of Wuhan University from April to August 2002. One hour after establishment of spinal cord injury models, the rats in the controlled group were injected intraperitoneally with normal saline, while those in the experiment group were given intraperitoneal injection of 300 mg/kg Mg2SO4. At each time point of 4, 8 and 24 hours after the treatment, 6 rats were selected from each group for measuring free Ca2+ concentration in the cells at the site of injury with spectrofluorometer . The activities of superoxide dismutase (SOD) in the spinal cord were detected by means of xanthine oxidation and thiobarbituric acid was used to determine the concentration of malondialdehyde (MDA). Lowered SOD activity and decreased MDA level were considered to suggest the protective effect of Mg2SO4 against spinal cord injury. Inclined plane test was used to assess the spinal cord function at 8, 24 hours and 1 week after the injury, in which the rat was made to stand on an inclined plate covered by a piece of rubber and the plate was inclined gradually until the rat was no longer able to stay in the original position for 5 s, and the inclination of the plate was recorded. The test was performed 3 times for each rat and the plate inclinations were averaged. An increased inclination indicated improvement of the spinal cord function.MAIN OUTCOME

MEASURES:

① Intracellular Ca2+ concentration at the injury site. ② Changes in SOD activity and MDA concentration in the spinal cord. ③ Results of spinal cord function evaluation of the rats.

RESULTS:

Intracellular Ca2+ concentration at 8 and 24 hours after the injury was significantly lower in the experimental group than in the control group [(376.5±36.2)×10-9vs (425.9±32.7)×10-9 mol/L and (316.3±13.9)×10-9vs (350.2±29.4)×10-9 mol/L, respectively, P ＜ 0.05]. Compared with the control group at each time point, MDA concentration was significantly decreased, while SOD activity of SOD was increased in the experiment group (P ＜ 0.01). The improvement of spinal cord injury was not obvious in the experiment group and was significantly higher than that in the control group until I week after the injury [(53.3±4.3)° vs (44.3±5.7)°, P ＜ 0.05].

CONCLUSION:

Intraperitoneal Mg2SO4 injection may significantly lower the concentration of intracellular Ca2+ at the injury site and alters the product of lipid peroxidation, suggesting its neuroprotective effect against spinal injury so as to lighten secondary spinal injury in rats.