Mechanisms for Cardiovascular Control Early in Diabetes

描述(申请人提供)：定义糖尿病的变量是葡萄糖和胰岛素，糖尿病的主要并发症：高血压和肾功能不全，彼此之间有着千丝万缕的联系。此外，人们普遍认为，随着患者从代谢综合征发展到明显的II型糖尿病，胰岛素的肾脏作用仍然是导致血压升高的原因之一。然而，没有公布的数据表明，代谢综合征或II型糖尿病患者测量到的胰岛素和葡萄糖的变化是如何在肾脏内发挥作用的，从而控制肾功能和血压。我们开发了一种创新的实验方法，可以在24小时内测量肾脏血流量、肾脏排泄功能和平均动脉压(MAP)，从而为发现这些变量之间的联系机制提供了一个独特的机会。我们将验证中心假设，即代谢综合征患者血浆胰岛素和葡萄糖浓度的增加会导致钠重吸收和GFR增加，如果GFR增加的程度减弱，则会导致高血压。该项目的具体目标是：1.通过确定是否：a.肾内高血糖(~20 mg/dl增加)降低UnaV并增加RBF和GFR；b.肾内高胰岛素血症(~3倍正常)增强葡萄糖的这些肾小管作用；c&d.钠重吸收的刺激不依赖肾素-血管紧张素系统，来验证葡萄糖和胰岛素联合作用可慢性刺激肾小管重吸收和肾血管扩张的假说。2.验证葡萄糖和胰岛素诱导的肾血管扩张需要肾脏COX-2和nNOS活性的假设，以确定：a.代谢综合征肾内抑制COX-2是否会减少RBF和升高MAP；b和c.血管紧张素转换酶抑制剂或TX拮抗剂将阻止COX-2抑制时RVR和MAP增加的反应；D.肾内应用SMTC阻断nNOS将阻止肾血管扩张并提高MAP；E.COX-2和nNOS对RBF和MAP的慢性肾内作用是相加的。3.测试假设：如果GFR不能适当增加，胰岛素和葡萄糖的肾脏作用将导致代谢综合征中的高血压，通过确定是否：a.狗的糖尿病发作需要增加GFR以预防高血压；b.如果GFR不增加，肾内代谢综合征环境将增加MAP；c.持续的肾内代谢综合征的发作将导致肥胖演变过程中喂食脂肪的狗的肾血管扩张和高滤过逐渐减少；以及D.血管紧张素II特别抑制狗肾脏中的胰岛素信号。与公共卫生相关的代谢综合征是II型糖尿病发展的最早阶段，属于这种血糖稳态紊乱的患者处于流行水平。然而，尽管胰岛素和葡萄糖与高血压和肾功能受损有很强的相关性，而且有许多假设认为胰岛素和葡萄糖可能有直接的肾脏作用，可以提高血压，但仍然没有直接的实验证据表明这些作用存在。此外，没有一个实验模型可以让这些假设直接得到检验。我们开发了这样一个模型。我们可以将代谢综合征的血糖和胰岛素水平定位到肾脏，并在每天24小时测量肾脏血流量、肾脏排泄功能和平均动脉压的同时，每天保持这种水平。我们的新假设是，葡萄糖和胰岛素协同作用，促进钠滞留和肾脏血管扩张，而且，血管扩张剂反应受损使钠滞留作用导致高血压。我们的试点数据支持这一点。

DESCRIPTION (provided by applicant): The variables that define diabetes are glucose and insulin, and the major complications of diabetes: hypertension and renal dysfunction, are inextricably linked to one another. Moreover, renal actions of insulin still are widely believed to contribute to the increase in blood pressure as patients progress through metabolic syndrome to overt Type II diabetes. Yet, there are zero published data that show how the changes in insulin and glucose that are measured in metabolic syndrome or Type II diabetes act within the kidney, chronically, to control kidney function and blood pressure. We developed an innovative experimental approach for clamping plasma glucose and insulin concentrations in dog kidneys, chronically, in any combination, and independent of systemic changes, while measuring renal blood flow, renal excretory function, and mean arterial pressure (MAP) 24 hours per day, to provide a unique opportunity to discover the mechanisms linking these variables. We will test the central hypothesis that the increases in plasma insulin and glucose concentrations measured in metabolic syndrome cause sodium reabsorption and increase GFR, and that hypertension ensues if the increase in GFR is attenuated. The specific aims of this project are to: 1. Test the hypothesis that combined renal tubular actions of glucose and insulin chronically stimulate tubular reabsorption and renal vasodilation, by determining whether: a. intrarenal hyperglycemia (~ 20 mg/dl increase) decreases UnaV and increases RBF and GFR; b. intrarenal hyperinsulinemia (~ 3x normal) augments those tubular effects of glucose; c&d. the stimulation of sodium reabsorption is independent of the renin-angiotensin system. 2. Test the hypothesis that glucose and insulin-induced renal vasodilation requires renal COX-2 and nNOS activity, by determining whether: a. intrarenal COX-2 inhibition in metabolic syndrome will decrease RBF and increase MAP; b&c. AngII or Tx blockade will prevent the increased RVR and MAP responses during COX-2 inhibition; d. blockade of intrarenal nNOS with SMTC will prevent the renal vasodilation and raise MAP; e. the chronic intrarenal actions of COX-2 and nNOS inhibition on RBF and MAP are additive. 3. Test the hypothesis that renal actions of insulin and glucose will cause hypertension in metabolic syndrome if GFR is not able to increase appropriately, by determining whether: a. onset of diabetes in dogs requires an increase in GFR to prevent hypertension; b. an intrarenal metabolic syndrome environment will increase MAP if GFR does not increase; c. episodes of sustained intrarenal metabolic syndrome will cause progressively lesser renal vasodilation and hyperfiltration in fat-fed dogs during the evolution of obesity; and d. angiotensin II specifically inhibits insulin signaling in the dog kidney. PUBLIC HEALTH RELEVANCE Metabolic syndrome is the earliest phase in the evolution of Type II diabetes, and patients that fall within this spectrum of deranged glucose homeostasis are at epidemic levels. Yet, despite the strong correlations between insulin and glucose with hypertension and impaired kidney function, and numerous hypotheses that insulin and glucose may have direct renal actions that can increase blood pressure, there remains no direct experimental evidence that these actions exist. Moreover, there is not an experimental model that enables these hypotheses to be tested directly. We developed such a model. We can localize metabolic syndrome levels of plasma glucose and insulin to the kidney, and maintain that for days-to-weeks while measuring renal blood flow, renal excretory function, and mean arterial pressure 24 hrs/day. Our novel hypothesis is that glucose and insulin act in concert to promote sodium retention and renal vasodilation, and, moreover, that an impaired vasodilator response enables the sodium-retaining actions to cause hypertension. Our pilot data support that.