Effects of intracerebroventricular administration of dopamine and metoclopramide on blood pressure in rats.

The intracerebroventricular (i.c.v.) injection of dopamine (50--200 micrograms/kg) produced a dose-dependent decrease in arterial blood pressure in conscious rats. This depressor effect of dopamine was attenuated by the pretreatment with metoclopramide (16.5 micrograms/kg, i.c.v.), a dopamine receptor antagonist. Metoclopramide in higher doses (50 and 150 micrograms/kg), given i.c.v., produced an increase in blood pressure. The pretreatment with dopamine (50 micrograms/kg, i.c.v.) attenuated the pressor effect of metoclopramide. Furthermore, autonomic ganglion blockade with hexamethonium (25 mg/kg, i.v.) almost completely abolished the effects of dopamine and metoclopramide, indicating that these substances were exerting their effects within the central nervous system. These results suggest that the dopaminergic system in the brain is involved in regulation of systemic blood pressure in conscious rats.