Effect of the intracerebroventricular injection of dopamine on blood pressure in the spontaneously hypertensive rat

To examine the role of the central dopaminergic system in blood pressure regulation, dopamine was injected into the cerebral lateral ventricles of conscious, unrestrained spontaneously hypertensive rats (SHR), deoxycorticosterone (DOC)-salt hypertensive rats and Wistar-Kyoto normotensive rats (WKY). Intracerebroventricular (i.c.v.) injection of dopamine produced a significant dose-dependent decrease in blood pressure in the SHR as well as in the WKY and DOC-salt hypertensive rats. However, the SHR were significantly more sensitive than were the other 2 groups of rats. In the SHR, this central depressor effect of dopamine was significantly attenuated by pretreatment with i.c.v. metoclopramide, but not by phentolamine, suggesting that central dopamine receptors rather than αadrenoceptors are involved in the mediation of the actions of dopamine in the brain. These results suggest that the central dopaminergic system plays a more important role in the regulation of blood pressure in the SHR than in the WKY and DOC-salt hypertensive rats.