Regulation of the Renal Microcirculation by the Connecting Tubule

描述（由申请人提供）：在高血压中，由于肾血管阻力和Na+再吸收的增加，压力钠尿设定点转移到更高的压力。肾血管阻力主要由传入小动脉和传出小动脉引起；它们控制肾小球滤过率（GFR）和小管周围压力，从而控制肾功能。Af-Art抵抗是由与控制其他小动脉相似的因素调节的；此外，Af-Art还受管肾小球反馈（TGF）的控制。TGF通过黄斑致密组织起作用，黄斑致密组织感知到NaCl的增加，并发出信号收缩Af-Art。我们有证据表明，增加连接小管（CNT）的NaCl递送会使Af-Art扩张，并且这种扩张可以被Na+运输抑制剂阻断。我们将CNT和Af-Art之间的串扰称为连接小管肾小球反馈（CTGF）。我们拟对CTGF进行体内外两方面的研究，以确定其生理作用及Na+引起CTGF的机制。我们还将研究一氧化氮（NO）和管状肾素-血管紧张素系统（RAS）对CTGF的调控，因为NO合酶和肾素和血管紧张素原都在肾单位中表达。在体外和体内，我们提出验证连接小管的Na+重吸收诱导花生四烯酸代谢物的释放，这些代谢物扩散到Af-Art并促进其扩张（CTGF反应）的一般假设。因此，CTGF拮抗血管收缩刺激如TGF。管状RAS通过刺激CNT的Na+转运来增强CTGF，而NO通过抑制这一过程来减弱CTGF。我们将用四个目标来检验这个一般假设。目的I将测试CNT中Na+重吸收的增加是否会通过Na+/ Ca++交换器导致细胞内Ca++的增加，从而导致Ca++介导的磷脂酶激活，花生四烯酸的释放，以及扩散到Af-Art并引起扩张的二十烷类化合物的形成。Aim II将检测体内CTGF是否对抗TGF的血管收缩作用，以及在TGF不存在的情况下，CTGF是否引起Af-Art扩张。Aim III将测试CNT中NOS 3产生的NO是否通过阻断ENaC通过guany酰环化酶的转运、增加cGMP、激活cGMP依赖性蛋白激酶和降低cAMP来降低CTGF。Aim IV将测试管状RAS是否通过Ang II和AT1受体直接作用于ENaC，间接通过NADPH氧化酶刺激O2-的释放来增强CTGF。这将是首次确定肾连接小管在调节传入小动脉阻力和肾小球滤过率中的作用的研究。这是一种新的机制，将为肾功能调节提供新的见解。

DESCRIPTION (provided by applicant): In hypertension the pressure natriuresis set point is shifted to a higher pressure, due to an increase in both renal vascular resistance and Na+ reabsorption. The afferent arterioles (Af-Art) and efferent arterioles account for most renal vascular resistance; they control glomerular filtration rate (GFR) and peritubular pressure, and consequently renal function. Af-Art resistance is regulated by factors similar to those that control other arterioles; in addition, the Af-Art is also controlled by tubuloglomerular feedback (TGF). TGF operates via the macula densa, which senses increases in NaCl and sends a signal that constricts the Af-Art. We have evidence that increasing NaCl delivery to the connecting tubule (CNT) dilates the Af-Art, and that this dilatation can be blocked by inhibitors of Na+ transport. We refer to the cross-talk between the CNT and Af-Art as connecting tubule glomerular feedback (CTGF). Here we propose to study CTGF both in vitro and in vivo to determine its physiological role and the mechanisms by which Na+ causes CTGF. We will also study the regulation of CTGF by nitric oxide (NO) and the tubular renin-angiotensin system (RAS), since both NO synthase and renin and angiotensinogen are expressed in the nephron. In vitro and in vivo we propose to test the general hypothesis that Na+ reabsorption by the connecting tubule induces the release of arachidonic acid metabolites that diffuse to and promote dilatation of the Af-Art (CTGF response). Thus CTGF antagonizes vasoconstrictor stimuli such as TGF. The tubular RAS potentiates CTGF by stimulating Na+ transport by the CNT, while NO blunts CTGF by inhibiting this process. We will test this general hypothesis in four Aims. Aim I will test whether an increase in Na+ reabsorption in the CNT causes an increase in intracellular Ca++ via the Na+/ Ca++ exchanger, which results in Ca++-mediated activation of phospholipases, release of arachidonic acid, and formation of eicosanoids which diffuse to the Af-Art and cause dilatation. Aim II will test whether in vivo, CTGF opposes the vasoconstrictor effect of TGF and whether in the absence of TGF, CTGF causes Af-Art dilatation. Aim III will test whether NO produced by NOS 3 in the CNT decreases CTGF by blocking Na+ transport by ENaC via activation of guanylyl cyclase, increasing cGMP, activating cGMP-dependent protein kinase, and reducing cAMP. Aim IV will test whether the tubular RAS via Ang II and the AT1 receptor enhances CTGF directly by acting on ENaC and indirectly by stimulating the release of O2- via NADPH oxidase. This will be the first study to determine the role of the renal connecting tubule in the regulation of afferent arteriole resistance and glomerular filtration rate. This is a novel mechanism that will provide new insights on the regulation of renal function.