Anti-nociceptive, analgesic and pathohistological effects of intrathecal dexmedetomidine and bupivacaine in rats

Background and objectives: This study investigates analgesic and nociceptive effects of adding dexmedetomidine to bupivacaine neuraxial anesthesia through Tail-flick (TF) and Hot-plate (HP) tests and the pathohistological changes on spinal nerves and nerve roots through light microscopy.

Methods: Forty anesthetized, male Sprague-Dawley rats were intrathecally catheterized. Basal values of TF and HP tests were measured before and after catheterization. Thirty-six successfully catheterized rats were assigned to four groups. Group B received 10 μg bupivacaine, Group BD3 received 10 μg bupivacaine + 3 μg dexmedetomidine, Group BD10 received 10 μg bupivacaine + 10 μg dexmedetomidine and Control group received 10 μL volume of artificial cerebrospinal fluid. TF and HP tests were performed between the 5(th) and 300(th) minutes of drug administration. Twenty-four hours after administration of drugs, rats were sacrificed and spinal cord and nerve roots were removed for pathological investigation.

Results: Baseline values of the TF and HP tests were not statistically different among the groups (6.8±0.15s). TF and HP latencies in the Control group did not change significantly during the study. TF and HP test results showed that adding 3 and 10 μg dexmedetomidine caused a dose-dependent increase in duration and amplitude of analgesic and nociceptive effect of bupivacaine (TF: 37.52±1.08%, 57.86±1.16% respectively, HP: 44.24±1.15%, 68.43±1.24% respectively).

Conclusions: There were no apparent pathohistological changes at least 24 hours after the intrathecal administration of a single dose of dexmedetomidine 3 μg and 10 μg. Dexmedetomidine added to bupivacaine for spinal block improves analgesia and prolongs block duration.