RESUMO
OBJECTIVE@#To investigate the behavioral and ultrastructural changes of intrathecal administration of different concentrations of ropivacaine for 12 h.@*METHODS@#Thirty male SD rats were randomly divided into 5 groups (6 rats in each group):group N (control), group A (ropivacaine 0.25%), group B (ropivacaine 0.5%), group C (ropivacaine 0.75%),and group D (ropivacaine 1.0%). A polyurethane microcatheter was inserted into the lumbar subarachnoid space 8 cm according to Yakshos intrathecal administration. The rats in group N received saline 0.12 mL/kg for 8 times at 1.5 h interval through the catheter, and the rats in the other groups received different concentrations of ropivacaine in the same way as in group N. The poster paw withdrawal latency to heat (PWHL) and mechanical stimulation (von Fray filament) (PWML) were measured the day before the intrathecal administration and 12 hours after the first intrathecal administration of ropivacaine. Motor function (MF) was measured after the last intrathecal administration. After the behavior test, the rats were sacrificed and the lumber segments of the spinal cord were immediately removed for electron microscopic examination.@*RESULTS@#A total hind limb paralysis was seen at 30 seconds and intramuscular strain gradually came back 10~60 minutes after the intrathecal administration of ropivacaine in group A, B, C, and D, but not in group N. The recovery time of motor block of group A was the shortest (P<0.05), that of group D was the longest,and that of group B and C was between group A and D. Intrathecal administration of different concentrations of ropivacaine did not affect the percent maximum possible effect (%MPE) of PWHL and PWML. Electron microscopic examination showed that the spinal cords were normal in group N and A, slight edema of mitochondria and endoplasmic reticulum (ER) in group B, loosened fibrous layers in medullary sheath, edema and local degeneration of neuraxis in group C,and shrinkage of nuclear membrane, serious edema of ER, vacuolus change of mitochondria and local demyelination in group D.@*CONCLUSION@#Ropivacaine (0.5%, 0.75%, and 1.0%) administered intrathecally for 12 hours causes different degrees of ultrastructural changes in the spinal cord depending on concentrations.