Rat brain angiotensin II receptors: Effects of intracerebroventricular angiotensin II infusion

Angiotensin II (Ang II) was infused into a lateral cerebral ventricle of male Sprague-Dawley rats and its effects on blood pressure, water balance and specific [125I]Ang II binding to brain and adrenal tissues were studied. The infusion was maintained at a rate of 500 ng/μl/h for 6 days using subcutaneously implanted osmotic minipumps. A control group was infused intracerebroventricularly (i.c.v.) with 0.9% saline at a rate of 1 μl/h for 6 days. Angiotensin II treated rats showed a four-fold increase in water intake and urine volume and a moderate increase in blood pressure; these effects were not observed in rats given saline i.c.v. There was no significant difference in [125I]Ang II binding site density or binding affinity in either the hypothalamus-thalamus-septum-midbrain (HTSM) of the brainstem between Ang II-treated and saline-treated groups. In addition, [125I]Ang II binding sites in the adrenals were also unaffected by i.c.v. infusion of Ang II. The results suggest that brain Ang II receptors are unresponsive to increased Ang II levels in cerebrospinal fluid.