MIVAZEROL, A SELECTIVE ALPHA(2)-ADRENOCEPTOR AGONIST, ATTENUATES TACHYCARDIA BY INTRATHECAL INJECTION OF N-METHYL-D-ASPARATE IN THE RAT

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