Deletion of AT1a Receptors Selectively in Renomedullary Interstitial Cells Attenuates Basal, Angiotensin II-, or Vasopressin-induced Vasoactive Factors' mRNA Expression in The Mouse Kidney Medulla

We recently shown that deletion of the vasoactive peptide angiotensin II (Ang II) AT 1a receptors selectively in renomedullary interstitial cells (RMICs) of the kidney medulla significantly lowered basal blood pressure and impaired urine concentration in mice. However, the underlying signaling mechanisms involved remains poorly understood. In the present study, AT 1a receptors were selectively deleted in the RMICs of the mouse kidney medulla using tamoxifen-inducible Tenascin-C-CreER2/Agtr1a f/f approach. Three groups of adult male wild-type (WT) and RMIC- Agtr1a −/− mice (n=6-10) were pretreated with or without tamoxifen (150 mg/kg, i.p., for 5 days) before Ang II was infused to induce Ang II-dependent hypertension (~0.75 mg/kg/day, i.p., for 2 weeks). Systolic, diastolic, and mean arterial blood pressure and urine osmolality were determined before and after Ang II treatment. At the end of the experiment, the kidneys were harvested, and the inner and outer medulla were dissected out for the measurement of the mRNA expression of key vasoactive factors that are associated with the regulation of blood pressure and urine concentration using digital droplet PCR. Deletion of AT 1a receptors in RMICs significantly decreased AT 1a receptor mRNA expression by 41% (WT: 554 ± 49 vs. RMIC- Agtr1a −/− : 327 ± 10 copies/ng RNA; P<0.01) and bradykinin B 2 receptor mRNA expression by 52% (WT: 10.10 ± 0.75 vs. RMIC- Agtr1a −/− : 4.90 ± 0.56 copies/ng RNA; P<0.01), without altering the expression of endothelin ET B (WT: 466 ± 21 vs. RMIC- Agtr1a −/− : 393 ± 24 copies/ng RNA; n.s.) and vasopressin V 2 receptor mRNAs in the kidney medulla (WT: 580 ± 60 vs. RMIC- Agtr1a −/− : 586 ± 61 copies/ng RNA; n.s.). Deletion of AT 1a receptors in RMICs also significantly decreased the expression of eNOS (WT: 87.0 ± 3.0 vs. RMIC- Agtr1a −/− : 61.2 ± 2.8 copies/ng RNA; P<0.01) and aquaporin 2 (AQP2) mRNAs (WT: 12463 ± 2015 vs. RMIC- Agtr1a −/− : 6613 ± 692 copies/ng RNA; P<0.01). Interestingly, deletion of AT 1a receptors in RMICs did not alter the mRNA expression of cyclooxygenase-2 (COX-2, n.s.), prostaglandin E2 (PGE2, n.s.), epithelial sodium channel (ENaC, n.s.) or prorenin receptors (PRR, n.s.) in the kidney medulla. In response to Ang II infusion, deletion of AT 1a receptors in RMICs significantly attenuated Ang II-induced expression of bradykinin B 2 receptors, COX-2, eNOS, and AQP2 mRNAs ( P<0.01), respectively. Furthermore, deletion of AT 1a receptors in RMICs also significantly attenuated vasopressin-induced bradykinin B 2 receptor, eNOS, and AQP2 mRNA expression in the kidney medulla ( P<0.01). We concluded that AT 1a receptors in RMICs in the kidney medulla play an important role in maintaining physiological blood pressure homeostasis and urine concentration process likely via AT 1a receptor/bradykinin B 2 receptor/eNOS/AQP2-mediated signaling pathways. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.