GENETIC DELETION OF AT1A RECEPTORS SELECTIVELY IN THE RENOMEDULLARY INTERSTITIAL CELLS OF THE KIDNEY MEDULLA ATTENUATES ANGIOTENSIN II-INDUCED HYPERTENSION

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Objective: The present study tested the hypothesis that genetic deletion of angiotensin II (Ang II) AT1 (AT1a) receptors selectively in the renomemdullary interstitial cells (RMICs) of the kidney medulla attenuates the development of Ang II-induced hypertension in mice. Design and method: To test the hypothesis, we used inducible Tenascin-C-CreER2 and Agtr1a-floxed recombination approach to generate a novel mouse model with deletion of AT1a receptors selectively in the RMICs of the kidney (RMIC-Agtr1a-/-). Adult male wildtype (WT) and RMIC-Agtr1a-/- mice (n = 10 per group) were implanted with a telemetry probe and infused with or without Ang II via an osmotic minipump (∼500 μg/kg/day, i.p.) for 2 weeks. Results: Mice with deletion of AT1a receptors selectively in RMICs of the kidney medulla were fertile and grew normally without apparent structural or histological abnormality in the kidney medulla. However, telemetry systolic, diastolic, and mean blood pressure were significantly lower in adult male RMIC-Agtr1a-/- than WT mice (WT: 122 ± 4 mmHg vs. RMIC-Agtr1a-/-: 102 ± 3 mmHg, P < 0.01). Interestingly, this hypotensive phenotype in RMIC-Agtr1a-/- mice was associated with significant decreases in 24 h urine output (WT: 1.56 ± 0.15 mL/24 h vs. RMIC-Agtr1a-/-: 0.98 ± 0.13 mL/24 h, P < 0.01), urinary sodium (WT: 207.9 ± 7.3 μmol/24 h vs. RMIC-Agtr1a-/-: 145.2 ± 5.4 μmol/24 h, P < 0.01), and potassium excretion (WT: 221.0 ± 6.7 μmol/24 h vs. RMIC-Agtr1a-/-: 160.8 ± 10.6 μmol/24 h, P < 0.01), respectively. Moreover, urine osmolality was markedly decreased in RMIC-Agtr1a-/-mice (WT: 1724 ± 335 mOsm/Kg H2O vs. RMIC-Agtr1a-/-: 1128 ± 102 mOsm/Kg H2O, P < 0.01). Ang II infusion significantly increased telemetry systolic blood pressure to 148 ± 5 mmHg in WT mice, but it increased systolic blood pressure only to 129 ± 8 mmHg in RMIC-Agtr1a-/- mice (P < 0.01). Furthermore, infusion of Ang II for 2 weeks failed to restore urine osmolality in RMIC-Agtr1a-/- mice (1226 ± 110 mOsm/Kg H2O, n.s.). Conclusions: In conclusion, the results of the present study support the hypothesis that AT1a receptors in the RMICs of the kidney medulla plays a critical role in maintaining basal blood pressure homeostasis and the development of Ang II-induced hypertension.