Intrarenal Angiotensin III Infusion Induces Natriuresisand Angiotensin Type 2 Receptor Translocation in Wistar-Kyoto but not in Spontaneously Hypertensive Rats

摘要

In Sprague-Dawley rats, renal angiotensin (Ang) type 2 receptors (AT_2Rs) mediate natriuresis in response to renal interstitial (RI) Drlike receptor stimulation or RI Ang III infusion. After D_1like receptor activation, apical membrane (AM) but not total renal proximal tubule cell AT_2R expression is increased, suggesting that AM AT_2R translocation may be important for natriuresis. The onset of hypertension in spontaneously hypertensive rats (SHRs) is preceded by defects in renal sodium excretion. The present study examines AT_2R-mediated natriuresis in response to RI Ang III infusion in Wistar-Kyoto rats (WKYs) and SHRs. WKYs and SHRs received RI Ang III infusion after 24 hours of systemic AT_1R blockade with candesartan. In WKYs, urine sodium excretion rate increased from 0.043+-0.01 to 0.191 +-0.06 munol/min (P<0.05) in response to Ang III infusion, but identical conditions failed to increase the urine sodium excretion rate in SHRs. The increase in the urine sodium excretion rate was blocked by coinfusion of PD-123319, a selective AT_2R antagonist. On confocal microscopy images, Ang III-infused WKYs demonstrated greater renal proximal tubule cell AM AT_2R fluorescence intensity compared with SHRs (5385+-725 versus 919+-35; P<0.0001), and Western blot analysis demonstrated increased AM (0.050+-0.003 versus 0.038+-0.003; P<0.01) but not total cell AT_2R expression in WKYs. In SHRs, AM AT_2R expression remained unchanged in response to RI Ang III infusion. Thus, RI Ang III infusion elicits natriuresis and renal proximal tubule cell AT_2R translocation in WKYs. Identical manipulations fail to induce natriuresis or AT_2R translocation in SHRs, suggesting that defects in AT_2R-mediated natriuresis and trafficking may be important to the development of hypertension in SHRs.