Mivazerol, a selective alpha 2-adrenoceptor agonist, attenuates tachycardia by intrathecal injection of N-methyl-D-aspartate in the rat.

The intravenous (i.v.) infusion of mivazerol, a new selective alpha 2-adrenoceptor agonist, produced a significant decrease in heart rate but not in blood pressure in pentobarbital-anesthetized Sprague-Dawley rats. The tachycardic response to intrathecal (i.t.) injection of N-methyl-D-aspartic acid (NMDA) was significantly attenuated by the i.v. infusion of mivazerol. The i.t. pretreatment with yohimbine significantly attenuated the bradycardic response to i.v. mivazerol and blocked the effect of mivazerol on the tachycardic response to i.t. NMDA. These results suggest that (1) the bradycardic effect of mivazerol is mediated, at least partly, by spinal alpha 2-adrenoceptors; and (2) there is a possibility of functional antagonism between spinal alpha 2-adrenoceptors and NMDA receptors in the regulation of heart rate.