Abstract Body: Bradykinin is a potent vasoactive peptide of the kallikrein-kinin system and activates two different classes of G protein-coupled receptors, B₁ and B₂, in the kidney. In the present study, we tested the hypothesis that deletion of B₂ receptors selectively in renomemdullary interstitial cells (RMICs) of the kidney medulla lowers basal blood pressure and attenuates angiotensin II (Ang II)-induced hypertension. To test the hypothesis, we generated a novel mouse model with deletion of B₂ receptors selectively in RMICs of the medulla (RMIC-Bdkrb2^-/-) using inducible Tenascin-C-CreER2/Bdkrb2^fl/fl recombination approach. Mice with deletion of B₂ receptors selectively in RMICs developed and grew normally without structural abnormalities in the kidney medulla. Basal telemetry systolic (SBP), diastolic, and mean arterial blood pressure were significantly lower in RMIC-Bdkrb2^-/- than WT mice (WT: 123 ± 3 mmHg vs. RMIC-Bdkrb2^-/-: 106 ± 3 mmHg, P<0.01) (n=12-15). The hypotensive phenotype in RMIC-Bdkrb2^-/- mice was associated with significant decreases in 24 h urine output (WT: 1.86 ± 0.15 mL/24 h vs. RMIC-Bdkrb2^-/-: 1.09 ± 0.15 mL/24 h, P<0.05) and urine osmolality (WT: 1893 ± 441 mOsm/Kg H₂O vs. RMIC-Bdkrb2^-/-: 1311 ± 78 mOsm/Kg H₂O, P<0.01) (n=12=15). Deletion of Bdkrb2 receptors in RMICs significantly decreases COX-2, eNOS, ENaC, and AQP2 mRNA expression (P<0.01 vs. WT), but not PGE₂ or prorenin receptor mRNA expression in the kidney medulla (n.s.) (n=6-10). In response to Ang II, SBP increased to 166 ± 6 mmHg in WT mice (P<0.01 vs. Basal), but it increased only to 139 ± 5 mmHg in RMIC-Bdkrb2^-/- mice (P<0.01 vs. WT+Ang II) (n=10-12). Ang II-induced hypertension was completely blocked by oral administration of AT₁ receptor blocker losartan (20 mg/kg/day, p.o.) in WT and RMIC-Bdkrb2^-/- mice (n=10). By comparison, infusion of DDAVP (1-deamino-8-D-arginine vasopressin, ~0.5 mg/kg/day, i.p., for 2 weeks) had no effect on blood pressure in WT and RMIC-Bdkrb2^-/- mice (n.s.) (n=8). Similarly, infusion of Ang II or DDAVP for 2 weeks significantly increased urine osmolality in WT mice (P<0.01), and restored urine osmolality in RMIC-Bdkrb2^-/- mice to the WT basal level (1995 ± 315 mOsm/Kg H₂O, P<0.01) (n=8-12). In conclusion, the present study demonstrates for the 1^st time that bradykinin B₂ receptors in RMICs of the kidney medulla plays an important role in maintaining basal blood pressure and urine osmolality homeostasis and the development of Ang II-induced hypertension.