PS-BPB08-1: ANGIOTENSIN II AT1A RECEPTORS IN THE PROXIMAL TUBULES PLAY A CRITICAL ROLE IN THE DEVELOPMENT OF TWO-KIDNEY, ONE-CLIP GOLDBLATT HYPERTENSION

Abstract

Objective: It is well recognized that the activation of the renin-angiotensin system (RAS) in the clipped kidney plays a critical role in the development of two-kidney, one-clip Goldblatt hypertension (2K1C) in animal models, but the roles of intratubular angiotensin II (Ang II) AT1 (AT1a) receptors and its downstream target, Na+/H+ exchanger 3 (NHE3) in the proximal tubules have not been determined previously. In the present study, we tested the hypothesis that genetic deletion of AT1a receptors selectively in the proximal tubules of the kidney attenuates the development of 2K1C Goldblatt hypertension via AT1a receptor-mediated, Na+/H+ exchanger 3 (NHE3)-dependent mechanisms. Design and Methods: To test the hypothesis, 2K1C Goldblatt hypertension was induced by placing a silver clip, 0.12 mm internal diameter, on the left renal artery for 4 weeks in adult male and female wild-type (WT), global AT1areceptor knockout (Agtr1a-/- ), proximal tubule (PT)-specific Agtr1a-/- (PT-Agtr1a-/- ), or PT-Nhe3-/- mice, respectively. Results: Systolic blood pressure increased in a time-dependent manner reaching a maximal response by Week 2–3 in wild-type mice (Basal: 112 ± 2 vs. 2K1C: 149 ± 4 mmHg, n = 12, P < 0.01). 2K1C Goldblatt hypertension in WT mice was associated with significant increases in renin mRNA expression in the clipped kidney (Control: 2066 ± 255 vs. Clipped: 3144 ± 569 copies/ng RNA, P < 0.01), and decreases in renin mRNA expression in the nonclipped right kidney (1738 ± 341 copies/ng RNA, P < 0.05). Plasma Ang II levels were significantly increased in WT mice with 2K1C Goldblatt hypertension (Control: 50.2 ± 7.2 vs. 2K1C: 109.7 ± 17.2 pg/ml, P < 0.05). Glomerular and tubulointerstitial fibrotic responses were also significantly increased in the clipped kidney (P < 0.01). In contrast to WT mice, the development of 2K1C hypertension was completely attenuated in global Agtr1a-/- (Basal: 88 ± 4 vs. 2K1C: 92 ± 2 mmHg, n = 9, n.s.), PT-Agtr1a-/- mice (Basal: 101 ± 2 vs. 2K1C: 104 ± 4 mmHg, n = 12, n.s.), or PT-Nhe3-/- mice (Basal: 103 ± 3 vs. 109 ± 5 mmHg, n.s.). Renin mRNA expression was not different in clipped and nonclipped kidney of Agtr1a-/- mice, but it was decreased in the nonclipped kidney of PT-Agtr1a-/- mice (P < 0.05). Conclusions: Taken together, our results suggest that the activation of intratubular RAS in the proximal tubules and increase of NHE3-mediated proximal tubular Na+ reabsorption play a key role in the development of 2K1C Goldblatt hypertension in mice.