Effect of intraventricular infusion of an angiotensin II antagonist on ¹²⁵I-angiotensin II binding in rats

The effects of chronic (six day) intracerebroventricular (i.c.v.) infusion of an angiotensin II antagonist, sarcosine1, isoleucine8 angiotensin II ([Sar1,Ile8]Ang II), (500 ng/μl per hour) was studied. Specific 125I-Ang II binding site density and binding affinity in the hypothalamus-thalamus-septum-midbrain (H-T-S-M) region of the brain and the adrenal medulla did not differ significantly between [Sar1,Ile8]Ang II treated and control (0.9% saline) rats. However, 125I-Ang II binding to the adrenal cortex was significantly reduced by i.c.v. infusion of [Sar1,Ile8]Ang II. The drinking response to microinjection of Ang II was blunted for up to seven days of [Sar1,Ile8]Ang II infusion. Thus, although [Sar1,Ile8]Ang II effectively blocked the central Ang II receptors, chronic infusion of this Ang II antagonist did not appear to cause alterations in brain H-T-S-M Ang II receptors, suggesting that brain Ang II receptors in normal rats do not undergo homologous regulation.