Up- and down-regulation of angiotensin II AT1-A and AT1-B receptors in afferent and efferent rat kidney arterioles

Abstract

The contractile effect of angiotensin II via AT1 receptors on the kidney arterioles is a crucial element in the kidney microcirculation. Angiotensin II also plays a role as an inhibitor via the AT1 receptors in the renin granulation of the arterioles. We have previously demonstrated that the AT1 receptors are downregulated in the renin-positive smooth muscle cells (SMCs) in contrast to renin-negative SMCs. In this study, we estimated the numbers of the AT1 receptor sub-types separately in the afferent and efferent arterioles and the renin-positive and renin-negative SMCs. The immunohistochemical signals of the AT1-A and AT1-B receptors were counted by stereological methods. (1) The number of AT1-B receptors in the efferent arterioles (expressed in signals/microm3; mean (CV): 0.32 (0.33)) was significantly higher (78%; p<0.05) as compared with the number in the afferent arterioles (0.18 (0.11)). No differences were found in the AT1-A receptors. In a number of AT1-A receptors, significant differences (p<0.01) were detected between the afferent arteriolar renin-positive SMCs (0.13 (0.36)) and the number in renin-negative SMCs (0.25 (0.34)). The AT1-B receptors did not display any differences. These results indicate that the AT1 receptor sub-types are regulated independently in the SMCs of the normal kidney arterioles.