In vitro Autoradiography Reveals Predominantly AT<sub>1</sub> Angiotensin II Receptors in Rat Kidney

Abstract

Angiotensin II (Ang II) receptor subtypes in the rat kidney were investigated by using type 1 (AT<sub>1</sub>) and type 2 (AT<sub>2</sub>) Ang II receptor antagonists to discriminate specific <sup>125</sup>I-[Sar<sup>1</sup>, Ile<sup>8</sup>] Ang II binding sites with in vitro autoradiography. DuP 753, a nonpeptide Ang II antagonist specific for the AT<sub>1</sub> sites, potently displaced binding in glomeruli (K<sub>i</sub> = 23.9 ± 3.3 n<i>M</i>) and proximal tubules (K<sub>i</sub> = 43.4 ± 17 n<i>M</i>). By contrast, the AT<sub>2 </sub>antagonists, PD 123177 and CGP 42112A, were very weak in competing for specific <sup>125</sup>I-[Sar<sup>1</sup>, Ile<sup>8</sup>] Ang II binding sites. AT<sub>1</sub> receptors, as determined in the presence of an excess concentration (10 µ<i>M</i>) of the AT<sub>2</sub> antagonist, PD 123177, account for 95% of total renal Ang II receptors, whereas AT<sub>2</sub> receptors, as determined in the presence of an excess concentration (10 µ<i>M</i>) of the AT<sub>1</sub> antagonist, DuP 753, represent approximately 5% of total 0renal Ang II receptors. In addition, the reducing agent, dithiothreitol, produces a dose-dependent inhibition of Ang II receptor binding with an IC<sub>50</sub> of 2 m<i>M</i>, a characteristic of the AT<sub>1</sub> receptors. These findings indicate that the AT<sub>1</sub> receptor is the predominant subtype at multiple anatomical sites in the rat kidney.