RATIONALE Previous studies identified a defect in Ang III (angiotensin III [des-aspartyl1-angiotensin II])-elicited AT2R (Ang type-2 receptor)-mediated natriuresis in renal proximal tubule cells of spontaneously hypertensive rats (SHR). OBJECTIVE This study aimed to delineate in prehypertensive SHR kidneys the receptor or postreceptor defect causing impaired AT2R signaling and renal sodium (Na+) retention by utilizing the selective AT2R agonist compound-21 (C-21). METHODS AND RESULTS Female 4-week-old Wistar Kyoto and SHR rats were studied after 24-hour systemic AT1R (Ang II type-1 receptor) blockade. Left kidneys received 30-minute renal interstitial infusions of vehicle followed by C-21 (20, 40, and 60 ng/[kg·min], each dose 30 minutes). Right kidneys received vehicle infusions. In Wistar Kyoto, C-21 dose-dependently increased urine Na+ excretion from 0.023±0.01 to 0.064±0.02, 0.087±0.01, and 0.089±0.01 µmol/min (P=0.008, P<0.0001, and P<0.0001, respectively) and renal interstitial fluid levels of AT2R downstream signaling molecule cGMP (cyclic guanosine 3',5' monophosphate) from 0.91±0.3 to 3.1±1.0, 5.9±1.2 and 5.3±0.5 fmol/mL (P=nonsignificant, P<0.0001, and P<0.0001, respectively). In contrast, C-21 did not increase urine Na+ excretion or renal interstitial cGMP in SHR. Mean arterial pressure was slightly higher in SHR but within the normotensive range and unaffected by C-21. In Wistar Kyoto, but not SHR, C-21 induced AT2R translocation to apical plasma membranes of renal proximal tubule cells, internalization/inactivation of NHE-3 (sodium-hydrogen exchanger-3) and Na+/K+ATPase (sodium-potassium-atpase) and phosphorylation of AT2R-cGMP downstream signaling molecules Src (Src family kinase), ERK (extracellular signal-related kinase), and VASP (vasodilator-stimulated phosphoprotein). To test whether cGMP could bypass the natriuretic defect in SHR, we infused 8-bromo-cGMP. This restored natriuresis, Na+ transporter internalization/inactivation, and Src and VASP phosphorylation, but not apical plasma membrane AT2R recruitment. In contrast, 8-bromo-cAMP administration had no effect on natriuresis or AT2R recruitment in SHR. CONCLUSIONS The results demonstrate a primary renal proximal tubule cell AT2R natriuretic defect in SHR that may contribute to the development of hypertension. Since the defect is abrogated by exogenous intrarenal cGMP, the renal cGMP pathway may represent a viable target for the treatment of hypertension. Visual Overview: An online visual overview is available for this article.

中文翻译：

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自发性高血压大鼠中原发性肾脏AT2受体缺陷的鉴定。

以往的研究发现自发性高血压大鼠（SHR）的肾近端小管细胞中由Ang III（血管紧张素III [des-aspartyl1-angiotensin II]）诱导的AT2R（Ang 2受体）介导的利尿功能存在缺陷。目的本研究旨在通过利用选择性AT2R激动剂化合物21（C-21）来描述高血压前期SHR肾脏中导致AT2R信号传导受损和肾钠（Na +）保留的受体或受体缺陷。方法和结果研究了24小时全身AT1R（Ang II 1型受体）阻断后的雌性4周龄Wistar Kyoto和SHR大鼠。左肾接受媒介物的肾间质输注30分钟，然后输注C-21（20、40和60 ng / [kg·min]，每次30分钟）。右肾接受了载体输注。在京都京都维斯塔酒店，C-21剂量依赖性地使尿液Na +排泄从0.023±0.01增加到0.064±0.02、0.087±0.01和0.089±0.01μmol/ min（分别为P = 0.008，P <0.0001和P <0.0001）和肾间质液AT2R下游信号分子cGMP（环状鸟苷3'，5'一磷酸）的水平从0.91±0.3降至3.1±1.0、5.9±1.2和5.3±0.5 fmol / mL（P =无意义，P <0.0001，P <0.0001，分别）。相反，C-21在SHR中并未增加尿液Na +排泄或肾脏间质cGMP。SHR中的平均动脉压略高，但在血压正常范围内，不受C-21的影响。在Wistar Kyoto（但不是SHR）中，C-21诱导AT2R易位至肾近端小管细胞的顶质膜，NHE-3（钠氢交换剂3）和Na + / K + ATPase（钠钾ATP酶）的内在化/失活以及AT2R-cGMP下游信号分子Src（Src家族激酶），ERK（细胞外信号相关）的磷酸化激酶）和VASP（血管扩张剂刺激的磷蛋白）。为了测试cGMP是否可以绕过SHR中的利尿钠缺陷，我们注入了8-溴-cGMP。这样可以恢复利钠，Na +转运蛋白内在化/失活以及Src和VASP磷酸化，但不能恢复顶质膜AT2R募集。相反，在SHR中使用8-溴-cAMP对利尿或AT2R募集没有影响。结论结果表明，SHR中存在原发性肾近端肾小管细胞AT2R利尿钠缺陷，可能有助于高血压的发展。由于该缺陷已被外源性肾内cGMP消除，肾脏cGMP途径可能是治疗高血压的可行靶标。视觉概述：本文提供了在线视觉概述。