Angiotensin II receptors in the kidney

Angiotensin II (AngII) receptors have been localized in rat kidney by using the high-affinity agonist analog 125I-labeled [Sar1]AngII as a probe for in vitro autoradiography. Receptors were associated with four morphologically distinct patterns of distribution. First, a high density of receptors occurs in glomeruli. These are diffusely distributed, consistent with a mesangial localization. AngII receptor density shows a cortical gradient, which is highest in superficial and midcortical glomeruli and lowest in juxtamedullary glomeruli. Receptors associated with both superficial and deep glomeruli show down-regulation during low-sodium intake. Second, low levels of tubular AngII binding were seen in the outer cortex. Third, a very high density of AngII receptors occurs in longitudinal bands in the inner zone of the outer medulla in association with vasa recta bundles. Receptors in this site also show down-regulation during low dietary sodium intake. Fourth, a moderate density of receptors occurs diffusely throughout the inner zone of the outer medulla in the interbundle areas. These results suggest that AngII exerts a number of different intrarenal regulatory actions. In addition to the known vascular, glomerular, and proximal tubular effects of AngII, these findings focus attention on possible actions of AngII in the renal medulla where it could regulate medullary blood flow and thereby modify the function of the countercurrent concentrating system.