Effect of dopamine receptor antagonists on the calcium-dependent central function that reduces blood pressure in spontaneously hypertensive rats

The effects of intracerebroventricular (i.c.v.) administration of dopamine receptor antagonists on the calcium-dependent brain function that reduces b lood pressure were investigated. The systolic blood pressure of spontaneous ly hypertensive rats (SHR; male, 13 weeks of age) was reduced following i.c .v. administration of calcium chloride (100 mu g/rat), and this effect of c alcium chloride was attenuated by i.c.v, injection of eticlopride (dopamine D-2 receptor antagonist, 100 mu g/rat), but not by i.c.v, injection of SCH 23390 (dopamine D-1 receptor antagonist, 30 mu g/rat). Taking into conside ration these results with our previous reports, it is suggested that calciu m enhances dopamine synthesis in the brain through a calmodulin-dependent s ystem, and that the resultant increase in dopamine levels inhibits sympathe tic activity via the dopamine Da receptor in the brain and reduces the bloo d pressure in SHR. (C) 1999 Elsevier Science Ireland Ltd. All rights reserv ed.