Subarachnoid bupivacaine increases human cerebrospinal fluid concentration of serotonin

Background and Objectives. Serotonin (5-hydroxytryptamine [5-HT]) has antinociceptive properties at the spinal level. Activation of descending serotonergic neurons or topically applied 5-HT at the spinal cord inhibits rostral spread of sensory information. Epidural anesthesia has been shown to increase 5-HT in plasma, and local anesthetics may interfere with 5-HT reuptake and metabolism. For these reasons, the action of subarachnoid local anesthetics on cerebrospinal fluid (CSF) 5-HT concentrations has been studied. Methods. Six volunteers received lumbar spinal anesthesia with 0.5% bupivacaine through subarachnoid catheters, and CSF and plasma 5-HT concentrations were determined radioenzymatically before and after anesthesia. Results. Plasma 5-HT was unchanged, but CSF 5-HT increased by 300% after bupivacaine administration (P < .02). Conclusion. Subarachnoid bupivacaine increases local 5-HT concentration. This may have implications for nociceptive gating as well as for local vasoregulation.