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  • Title: Clonidine antagonizes pressor effect of N-methyl-D-aspartate in the rostral ventrolateral medulla of rats.
    Author: Lin JC, Liu DM, Wang Y.
    Journal: Clin Exp Hypertens; 1997 Oct; 19(7):1065-78. PubMed ID: 9310204.
    Abstract:
    The purpose of the present study was to investigate the modulatory actions of adrenoreceptor agonists on N-methyl-D-aspartate (NMDA)-induced pressor effect in rostral ventrolateral medulla (RVLM). These drugs were locally applied into RVLM of urethane-anesthetized Sprague-Dawley rats through multibarrel pipettes. Microinjection of NMDA increased the arterial pressure, an effect which was abolished by pretreatment with clonidine, whereas neither the beta-adrenergic agonist isoproterenol nor the alpha 1-adrenergic agonist phenylephrine did alter this pressor response. Previous experiments demonstrated that clonidine binds to noradrenergic alpha 2 and imidazoline receptors in the RVLM. Norepinephrine, which has high affinity for the alpha 2 receptor and low affinity to the imidazoline receptor, partially antagonized NMDA-induced hypertension. On the other hand, administration of selective imidazoline receptor antagonist idazoxan partially reversed clonidine-mediated antagonism of NMDA. Taken together, these results suggest that clonidine may modulate the excitatory amino acid-induced pressor response through noradrenergic alpha 2 and imidazoline receptors in the RVLM.
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