INTRAVENOUS NBQX INHIBITS SPONTANEOUSLY OCCURRING SYMPATHETIC-NERVE ACTIVITY AND REDUCES BLOOD-PRESSURE IN CATS

-Dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX) has been dem onstrated to be a specific and competitive non-N-methyl-D-aspartate (n on-NMDA) glutamate receptor antagonist. Our previous data obtained wit h the NMDA receptor antagonist MK-801 indicate that blockade of the NM DA receptor affects blood pressure. The purpose of this study was to d etermine whether the same is true with blockade of the non-NMDA recept or. For this purpose we administered three doses of NBQX (1, 3 and 10 mg/kg i.v.) to anesthetized, artificially ventilated and paralyzed cat s while monitoring spontaneously occurring cardiac sympathetic nerve a ctivity, arterial blood pressure and heart rate. The 1 mg/kg dose of N BQX i.v. reduced both sympathetic nerve activity (-29 +/- 7%, P < 0.05 , n = 4) and blood pressure (-27 +/- 5 mm Hg, P < 0.05). Injection of 3 mg/kg NBQX produced a greater decrease in sympathetic nerve activity (-78 +/- 11%, P < 0.01, n = 8) and mean arterial pressure (-47 +/- 5 mm Hg) and also reduced heart rate (-11 +/- 2 beats/min, P < 0.01). Th e depressant effects of NBQX on sympathetic nerve activity, blood pres sure and heart rate were similar regardless of whether activity was re corded from pre- or postganglionic cardiac nerves, or from animals sub jected to baroreceptor denervation. Intravenous injection of a total d ose of 10 mg/kg NBQX completely inhibited sympathetic nerve activity ( -100 +/- O%, P < 0.05, n = 3) and this effect was associated with redu ctions in mean arterial pressure (-49 +/- 10 mm Hg, P < 0.05) and hear t rate (-30 +/- 6 beats/min, P < 0.05). The data indicate that NBQX i. v. decreases sympathetic nerve activity, blood pressure and heart rate in a dose-dependent manner and that the primary site of these effects is likely in the central nervous system.