Participation of nitric oxide and N-methyl- d-aspartic acid receptors in the pressor response to intrathecal injected noradrenaline at the spinal cord of the rat

Abstract

In pentobarbital-anesthetized rats, intrathecal injection of noradrenaline (NA; 6, 18 and 60 nmol) induced a dose-dependent increase in the mean blood pressure. The pressor response to NA (18 nmol) was blocked by pretreatment with the selective antagonist for N-methyl- d-aspartic acid (NMDA) receptors, 2-amino-5-phosphonovaleric acid (30 nmol), but not by pretreatment with the selective antagonist for (±)-α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid/kainate receptors, 6,7-dinitroquinoxaline-2,3-dione (50 nmol). The pressor effect of NA was reduced after pretreatment with N G-nitro- l-arginine methyl ester ( l-NAME, 1 μmol). The effect of l-NAME on the pressor response to NA was reverted by the precursor of nitric oxide (NO), l-arginine (5 μmol). The hypertension induced by NA was also reduced by the guanylate cyclase inhibitor methylene blue (0.3 μmol). These results suggest that spinal NMDA receptors and spinal NO are involved in the pressor response to NA.