Up- and down-regulation of angiotensin II AT 1 -A and AT 1 -B receptors in afferent and efferent rat kidney arterioles

Abstract

Introduction. 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.

Methods. The immunohistochemical signals of theAT₁-A and AT₁-B receptors were counted by stereological methods.¹

Results. The number of AT₁-B receptors in the efferent arterioles (expressed in signals/µm ³; 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 ofAT ₁-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.

Conclusions. These results indicate that the AT₁ receptor sub-types are regulated independently in the SMCs of the normal kidney arterioles.