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Pathophysiological roles of arginine vasopressin and aquaporin-2 in impaired water excretion and hyponatremia

精氨酸加压素和水通道蛋白-2 在水排泄受损和低钠血症中的病理生理作用

基本信息

批准号：
13671160
负责人：
ISHIKAWA San-e
金额：
$ 2.24万
依托单位：
Jichi Medical School
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13671160/
关键词：
Vasopressin Aquaporin-2 Hyponatremia Transcription SIADH Osmolality プロモーター活性遺伝子発現

项目摘要

We examined the alteration in aquaporin-2 (AQP-2) water channel in pathological state of arginine vasopressin (AVP)-dependent hyponatremia. First, SIADH model was prepared in Sprague-Dawley rats by giving liquid diet and subcutaneous infusion of dDAVP. Serum Na level was decreased to below 120 mmol/l in the experimental SIADH rats, and urinary osmolality remained as low as 800-900 mmol/kg, that was significantly lower than that of 3,000-3,200 mmol/kg in the control rats. Thus, urinary concentrating defect was found, which is called as AVP escape phenomenon. There were marked reduction in AVP receptor binding and AVP V_2 receptor mRNA expression, but they were not different between the two groups. The expression of AQP-2 mRNA in kidney was upregulated in the SIADH rats, and its expression was significantly attenuated as compared to that in the dDAVP-excess rats, which were given solid diet and subcutaneous infusion of dDAVP. Similar results were obtained with kidney AQP-2 protein expression and urinary excretion of AQP-2. These in vivo studies indicate that either extracellular volume expansion or hypoosmolality may directly inhibit kidney AQP-2 mRNA expression, resulting in AVP escape in SIADH. Following in vitro study was carried out to examine whether osmolality directly regulate transcription of 5'-flanking region of AQP-2. The AQP-2 promoter gene (-9.5 kb) was obtained, and its activity was determined by luciferase assay. Cyclic AMP responsive element (CRE) was present until -1.1 kb. Hypertonic pressure of 600 mmol/kg increased the luciferase activity by approximately 2-fold in the AQP-2 promoter (-9.5〜-1.1 kb). Further study determined two osmolality responsive sites in the AQP-2 promoter gene (-9.5〜-7.7 kb and -6.0〜-4.2 kb).

本研究观察了精氨酸加压素（AVP）依赖性低钠血症病理状态下水通道蛋白-2（AQP-2）的变化。首先，通过给予SD大鼠流质饮食和皮下注射dDAVP制备SIADH模型。实验性SIADH大鼠血清钠水平降至120 mmol/l以下，尿渗透压维持在800-900 mmol/kg，明显低于对照组的3,000-3,200 mmol/kg。因此，发现尿浓缩缺陷，这被称为AVP逃逸现象。AVP受体结合率和AVPV_2受体mRNA表达均明显降低，但两组间无显著性差异。SIADH组大鼠肾脏AQP-2 mRNA表达上调，与dDAVP过量组相比，SIADH组大鼠肾脏AQP-2 mRNA表达明显减弱。肾AQP-2蛋白表达和尿AQP-2排泄也得到了类似的结果。这些体内研究表明，无论是细胞外容量扩张或低渗可直接抑制肾脏AQP-2 mRNA的表达，导致AVP逃逸SIADH。随后进行体外研究以检查渗透压是否直接调节AQP-2的5 '侧翼区的转录。获得AQP-2启动子基因（~ 9.5kb），并通过荧光素酶测定法测定其活性。环AMP反应元件（CRE）存在至约1.1kb。600 mmol/kg的高渗压力使AQP-2启动子中的荧光素酶活性增加约2倍（约9.5 kb-1.1 kb）。进一步的研究确定了AQP-2启动子基因中的两个渗透压响应位点（-9.5 kb-7.7 kb和-6.0 kb-4.2 kb）。