Angiotensin-(1-7) binding at angiotensin II receptors in the rat brain

Angiotensin-(1-7) (Ang-(1-7)) is reported to be equipotent with angiotensin II (AII) in producing some central biological effects but the receptors responsible for these actions have not been defined. Three classes of receptor have been proposed: AT1, AT2, and a putative Ang-(1-7) selective receptor. This study specifically evaluates Ang-(1-7) competition at AII binding sites (AT1 and AT2) in the rat brain. 125I Sar1 Ile8 AII (269-312 pM) was used to conduct receptor autoradiographic binding assays in brain sections. Competition with Ile5 AII and Val5 AII was similar at nuclei in which either AT1 or AT2 receptor subtypes predominate (Ki = 11-18 nM). Ang-(1-7) competed 150-fold less effectively than native AII at AT1 predominant brain nuclei (Ki = 2.4 microM). At brain regions where AT2 receptors predominate, Ang-(1-7) showed a very low affinity (Ki = 104 microM) for the majority of the 125I Sar1 Ile8 AII binding sites (AT2). A small proportion of 125I Sar1 Ile8 AII binding sites showed an affinity of 2.0 microM, presumably AT1 receptors present in those brain regions. For biological responses where Ang-(1-7) is reported to be equipotent with AII, it is unlikely that these actions are mediated by the widely distributed AT1 or AT2 receptor subtypes which recognize 125I Sar1 Ile8 AII.