Insulin, Renal Sodium Transport and Blood Pressure

描述（由申请人提供）：在动物和人类中，高胰岛素血症与高血压有关。此外，胰岛素已被证明会导致肾脏的钠潴留。在细胞培养中，胰岛素直接增加了通常位于肾连接小管和集管的阿米洛胺敏感钠通道（ENaC）的钠运输能力。钠在小管远端部分的不适当保留可导致细胞外液容量扩大和高血压。然而，高胰岛素血症对钠平衡的直接影响和间接影响尚不清楚。此外，高胰岛素血症对特异性肾钠转运体和/或通道的表达和调节的影响尚未得到充分研究。针对这些蛋白质的抗体直到最近才出现。在本提案中，我们计划测试胰岛素和“胰岛素增敏剂”，如ppar - γ激动剂，作为一个整体，将增加肾脏中几种关键钠转运蛋白的蛋白丰度。我们将通过半定量免疫印迹和免疫组织化学检查这些蛋白质的丰度和细胞位置的慢性和急性变化。针对具体目的1，我们计划评估循环胰岛素水平升高对肾小管黄斑后致密部分两种主要顶端钠转运蛋白相对丰度的直接影响：1)阿米罗胺敏感上皮钠通道（ENaC）；2)噻嗪类药物敏感的Na-CI共转运体（NCC）。在具体目标2中，我们将评估ENaC亚基和NCC蛋白丰度变化与大鼠血压变化的相关性，以及对转运体或通道选择性利尿剂（即阿米洛胺和多噻嗪）的敏感性。在具体目标3中，我们将探讨胰岛素输注观察到的ENaC亚基或NCC蛋白丰度增加的候选细胞机制。在具体目标4中，我们将评估NCC和ENaC亚基在急性和慢性胰岛素暴露下细胞分布的相对变化。最后，在具体目标5中，我们将研究膳食ppar - γ激动剂对正常大鼠和胰岛素抵抗、肥胖Zucker大鼠所有主要肾钠转运蛋白调节的影响。希望这些研究能让我们对胰岛素在钠平衡中的作用有一个开明的理解。

DESCRIPTION (provided by applicant): Hyperinsulinemia has been linked to hypertension in both animals and humans. Furthermore, insulin has been shown to result in sodium retention by the kidney. In cell culture, insulin directly increases sodium transport capacity of the amiloride-sensitive sodium channel (ENaC), normally located in the renal connecting tubule and collecting duct. Inappropriate retention of sodium in the distal portion of the tubule could result in expanded extracellular fluid volume and hypertension. However, it is not clear what are direct versus indirect effects of hyperinsulinemia with regard to sodium balance. Furthermore, the impact of hyperinsulinemia on the expression and regulation of specific renal sodium transporters and/or channels has not been aqequately studied. Antibodies against many of these proteins have only recently become available. In this proposal, we plan to test the overall hypothesis that insulin and "insulin sensitizing agents", such as PPAR-gamma agonists, will, as a whole, increase the protein abundances of several critical sodium transport proteins expressed in the kidney. We will examine both chronic and acute changes in the abundance and cellular location of these proteins by semi-quantitative immunoblotting and immunohistochemistry. For specific aim 1, we plan to assess the direct effect of increased circulating insulin levels on the relative abundances of the two primary apical sodium transport proteins of the postmacula densa portion of the renal tubule: 1) the amiloride-sensitive epithelial sodium channel (ENaC); and 2) the thiazide-sensitive Na-CI cotransporter (NCC). In specific aim 2, we will evaluate the correlation of changes in ENaC subunit and NCC protein abundances with changes in rat blood pressure, and sensitivity to transporter or channel selective diuretics, i.e., amiloride and polythiazide. In specific aim 3, we will address candidate cellular mechanisms for the increase in ENaC subunit or NCC protein abundances observed with insulin infusion. In specific aim 4 we will evaluate relative changes in cellular distribution of both NCC and ENaC subunits in response to acute and chronic insulin exposure. Finally, in specific aim 5, we will investigate the impact of dietary PPAR-gamma agonists on the regulation of all of the major renal sodium transporter proteins in normal rats and insulin resistant, obese Zucker rats. These studies will, hopefully, provide us with an enlightened understanding of the role of insulin in sodium balance.