Role of brain dopamine in centrally evoked angiotensin ii responses in conscious rats

Because intracerebroventricular (i.c.v.) injection of angiotensin II enhances the activity of brain dopaminergic neurons, the possible role of the brain dopamine neuronal system as a mediator of the pressor, dipsogenic, and neurohormonal effects of centrally administered angiotensin II was examined in this study. In conscious male Sprague-Dawley rats, injections of angiotensin II (125 ng i.c.v.) caused a significant increase in mean arterial pressure (19 ± 1 mm Hg), which was not changed by i.c.v. pretreatment with a subpressor dose of either dopamine (16 ± 1 mm Hg) or the dopamine antagonist metoclopramide (21 ± 1 mm Hg). However, angiotensin II-induced drinking (11.3 ± 0.4 ml/30 min) was partially inhibited by i.c.v. pretreatment with metoclopramide (7.4 ±1.0 ml/30 min, p < 0.01) but not affected by i.c.v. dopamine pretreatment. Intraventricular injections of angiotensin II caused a sixfold increase in plasma arginine vasopressin (10.9 ±1.3 pg/ml vs 1.7 ± 0.7 pg/ml in control rats, p < 0.01), which was enhanced by metoclopramide (17.6 ± 2.3 pg/ml, p < 0.01). Dopamine pretreatment had no significant effect on this increase in plasma arginine vasopressin (7.1 ±1.1 pg/ml) produced by angiotensin II, Angiotensin II-induced suppression of plasma renin activity from 14.7 ± 1.2 to 6.8 ± 1.6 ng/ml/hr was not affected by prior i.c.v. administration of either dopamine or metoclopramide. Central injection of dopamine or metoclopramide alone had no effect on plasma arginine vasopressin or plasma renin activity levels, mean arterial pressure, or water intake. Our results suggest that central dopaminergic neurons interact with centrally administered angiotensin II in the regulation of hydromineral balance and neurohypophysial release of arginine vasopressin but not in the regulation of blood pressure or plasma renin activity.