Deletion of Bradykinin Type 2 Receptors Selectively in the Renomedullary Interstitial Cells of the Kidney Medulla Attenuates Angiotensin Ii-Induced Hypertension in Mice

Objective: The present study tested the hypothesis that deletion of vasoactive peptide bradykinin B2 receptors selectively in the renomemdullary interstitial cells (RMICs) of the kidney medulla attenuates angiotensin II-induced hypertension in mice. Design and method: To test the hypothesis, we employed inducible Tenascin-C-CreER2 and bradykinin B2 receptor-floxed recombination approach to generate a novel mouse model with deletion of B2 receptors selectively in the RMICs of the kidney medulla (RMIC-B2R-/-). Basal blood pressure and urine osmolality and their responses to angiotensin II (Ang II, ∼500 μg/kg/day, i.p., for 2 weeks) were determined in adult male wildtype (WT) and RMIC-B2R-/- mice (n=10 per group), respectively. Results: Mice with deletion of B2 receptors selectively in RMICs of the kidney medulla developed normally without structural abnormalities in the kidney medulla. However, basal telemetry systolic, diastolic, and mean arterial blood pressure were significantly lower in RMIC-B2R-/- than WT mice (WT: 123 ± 3 mmHg vs. RMIC-B2R-/-: 106 ± 3 mmHg, P<0.01). The hypotensive phenotype in RMIC-B2R-/- mice was associated with significant decreases in 24 h urine output (WT: 1.86 ± 0.15 mL/24 h vs. RMIC-B2R-/-: 1.09 ± 0.15 mL/24 h, P<0.05) and urine osmolality (WT: 1893 ± 441 mOsm/Kg H2O vs. RMIC-B2R-/-: 1311 ± 78 mOsm/Kg H2O, P<0.01). In response to Ang II infusion (∼0.5 mg/kg/day, i.p., for 2 weeks), systolic blood pressure increased to 166 ± 6 mmHg in WT mice (P<0.01 vs. Basal), but it increased only to 139 ± 5 mmHg in RMIC-B2R-/- mice (P<0.01 vs. WT). By comparison, infusion of DDAVP (1-deamino-8-D-arginine vasopressin, ∼0.5 mg/kg/day, i.p., for 2 weeks) did not significantly alter blood pressure in WT and RMIC-B2R-/- mice (n.s.). However, infusion of Ang II for 2 weeks significantly increased urine osmolality in WT mice (P<0.01), and restored urine osmolality in RMIC-B2R-/- mice to the WT basal level (1995 ± 315 mOsm/Kg H2O, P<0.01). Conclusions: In conclusion, the present study demonstrates for the 1st time that bradykinin B2 receptors in the 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.