Intrathecal administration of N-methyl-D-aspartate receptor antagonist reduces the minimum alveolar anaesthetic concentration of isoflurane in rats

We have studied the effect of intrathecal administration of N-methyl-D-aspartate (NMDA) receptor antagonists on the minimum alveolar anaestheticconcentration (MAC) of isoflurane in rats. In Wistar rats fitted withindwelling intrathecal catheters, we determined the MAC of isoflurane afteradministration of a competitive NMDA receptor antagonist, APV (0.01, 0.1,1.0, 10, 30 micrograms), a non-competitive NMDA receptor antagonist, MK801(0.1, 1.0, 10, 30 micrograms). NMDA (0.01, 0.1, 1.0, 10, 30 micrograms) andsaline. APV at all doses except 0.01 micrograms decreased MAC by 17.1-32%(P < 0.001 and P < 0.0001). Although MK801 at 10 and 30 microgramsreduced MAC by 24.3-31.7% (P < 0.001 and P < 0.0001), lower doses didnot affect MAC. Intrathecal administration of NMDA reversed these decreasesin MAC, but not to control values with APV 10 and 30 micrograms and MK80130 micrograms. We suspect that NMDA and NMDA receptor antagonists playimportant roles in the spinal cord in determining the MAC of isoflurane.