Effects of Dexamethasone and of Local Hypothermia on Early and Late Tissue Electrolyte Changes in Experimental Spinal Cord Injury
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The current experiment reexamines this laboratory's frequently cited previous experimental conclusion that a mechanism underlying the beneficial effects of glucocorticoids in the treatment of spinal cord injury may be the enhanced preservation of spinal cord tissue potassium. For the first time, similar methodology also has been applied to study the effects of hypothermia. Canine spinal cords were injured at T13 by use of an epidural balloon and then were treated with local hypothermia or intramuscular dexamethasone or both. Motor recovery was assessed using a modified Tarlov scale. At either 6 days or 7 weeks, spinal cords T8 through L4 were removed and divided into 10 ordered blocks, which were analyzed for wet and dry weight, potassium concentration, and sodium concentration. Correlations between clinical motor and chemical results were evaluated. The conclusions drawn are as follows: 1) The canine severe rapid compressive injury model, unlike the previously published less severe feline impact injury model, is not associated with widespread early loss of spinal cord tissue potassium content (dry weight). 2) The dog compressive model, unlike the cat impact model, does not provide evidence that one fundamental mechanism of the confirmed beneficial action of steroids entails enhanced early preservation of tissue potassium content. 3) At 6 days, decrease in the percentage of dry weight and increase in sodium concentration, representing edema, occurred at and adjacent to the direct compression site in all lesioned dog groups except those treated with dexamethasone, demonstrating an antiedema effect of dexamethasone that was nullified by concurrent local hypothermia. 4) This antiedema effect of dexamethasone was associated with superior early motor improvement but did not lead to superior long-term function, in comparison with hypothermia. 5) At 7 weeks, decrease in the percentage of dry weight and potassium concentration, and increase in sodium concentration, all restricted to the directly compressed segment, signify necrosis. 6) This new chemical index of necrosis was highly correlated with clinical motor performance.
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