PENTAMIDINE, AN INHIBITOR OF SPINAL FLEXOR REFLEXES IN RATS, IS A POTENT N-METHYL-D-ASPARTATE (NMDA) ANTAGONIST IN-VIVO

The present study examined whether the antimicrobial agent pentamidine exerts an antagonistic action at the N-methyl-D-aspartate (NMDA) receptor as tested on spinal reflexes in rats in vivo. After intrathecal injection both the specific NMDA antagonist (-)-2-amino-7-phosphonoheptanoate and pentamidine dose-dependently reduced the magnitude of the polysynaptic flexor reflex without affecting the monosynaptic H-reflex. In contrast, the non-NMDA antagonist 6,7-dinitroquinoxaline-2,3-dione depressed the H-reflex in a dose-dependent manner without affecting the flexor reflex. The depressant effect of pentamidine on the flexor reflex was prevented by coadministration with NMDA but not with the non-NMDA agonist alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid. These data suggest that pentamidine exerts an antagonistic action at the NMDA receptor in vivo.