Abstract 476: Renal AT2 Receptor Activation Prevents Sodium Retention And Lowers Blood Pressure In Angiotensin II-Dependent Hypertension

Abstract

A major proposed mechanism for the initiation of hypertension involves a primary increase in renal tubular sodium (Na+) reabsorption. Activation of intrarenal angiotensin type-2 receptors (AT2R) increases Na+ excretion; however, the role of intrarenal angiotensin type-2 receptors (AT2R) in the development of hypertension is unknown. Sprague-Dawley rats (N=36) underwent uninephrectomy and telemetric blood pressure probe implantation. Following a 72h recovery, two osmotic minipumps were inserted in each rat, one for chronic systemic delivery of 5% dextrose in water (D5W) or angiotensin II (Ang II, 200 ng/kg/min), and one for chronic intrarenal delivery of D5W (0.25 μL/h x 7d), highly selective AT2R agonist Compound 21 (C-21; 60 ng/kg/min x 7d), or specific AT2R antagonist PD-1223319 (PD; 10 ng/kg/min x 7d). Five groups of rats were studied: Group 1 (Control; N=10): systemic D5W + intrarenal D5W; Group 2 (Ang II-induced hypertension; N=8): systemic Ang II + intrarenal D5W; Group 3 (N=6): systemic Ang II + intrarenal C-21; Group 4 (N=6): systemic Ang II + 48h lead-in intrarenal C-21; Group 5 (N=6): systemic Ang II + intrarenal PD. Systemic Ang II infusion increased mean systolic blood pressure from 126±5 to 190±3 mm Hg over a 7d period in Group 2 (ANOVA F=73; P<1 X 10-6). Intrarenal administration of AT2R agonist C-21 (Groups 3 and 4) markedly inhibited the pressor effect of systemic Ang II (P<0.0001). Intrarenal AT2R antagonist PD (Group 5) augmented the pressor action of Ang II (P<0.0001). Consecutive 24h urinary Na+ excretion (UNaV) was reduced from 0.95±0.04 to 0.34±0.07 μmol/min (P<0.0001) on day 1 of Ang II infusion; Ang II-induced antinatriuresis was inhibited by intrarenal C-21 (P<0.0001) and augmented by intrarenal PD (P<0.0001) during the entire 7d infusion, demonstrating that one of the mechanisms to prevent Ang II-induced hypertension during intrarenal AT2R activation is the abolition of the initial increase in Na+ reabsorption that triggers the hypertensive cascade in this model. Thus, renal AT2Rs represent a novel therapeutic target for the prevention of hypertension.