Effects of Central Dopaminergic Receptor-Activation on the Cardiovascular System

ABSTRACT

The central dopaminergic receptor is believed to suppress the cardiovascular system So it may be involved in the blood pressure regulation But, it's action is still controversial. Furthermore, the mechanisms involved in the central dopaminergic receptor-induced blood pressure regulation is unclear. So, present study was performed in order to clarify the effects of central dopaminergic receptor and to investigate the mechamisms involved in it. Lisuride a D2-receptor agonist, and clonidine, a alpha2-receptor agonist, were administered into lateral ventricle in rat and the changes of blood pressure were compared The results were as follows; 1. Intracerebroventricular administration of lisuride amd clonidine from 0.3 ug to 10 ug elicited dose related decrease of blood pressure and heart rate. The potencies were similar in both drugs. 2. Centrally administered sulpiride, a D2-antagonist, blocked only the lisuride-induced hypotension while the clonidine induced hypotension was blocked only by centrally adrninistered tolazoline, a alpha2-antagonist. Intravenous administration of both antagonists elicited no or minimal attenuabon of agonists effects. 3. After desipramine pretreatment, which increases the norepinephrine concentration lisuride elicited somewhat further decrease of blood pressure than normal, while clonidine administration caused rather increase in blood pressure. 4. After chemical sympathectomy by 6-hydroxydopamine, lisuride administration still elicited strong suppression of blood pressure. From thses above results, it is concluded that central dopaminergic receptor activation decrease the blood pressure. Suppression of the norepinephrine release at the sympathetic nerve terminal is not related with central dopaminergic receptor induced hypotension.