Autoregulation of Glomerular Filtration Rate

描述（由申请人提供）：肾脏在容量稳态中的作用严重依赖于肾小球超滤（GFR）和肾小管重吸收的协调。这是通过肾小球-小管平衡（glomerulotube balance， GTB）和小管-肾小球反馈（tubuloglomerular feedback， TGF）系统的协同作用来实现的。每当管状液中到达MD的盐浓度发生变化时，TGF引起SNGFR的反比变化。然而，TGF系统必须随着时间的推移适应MD NaCl浓度和递送的持续变化，以维持TGF的稳态效率。TGF的重置或TGF的“时间适应”确实通过肾单位血流、传入小动脉阻力和SNGFR的改变而发生，从而导致MD信号与输出血管反应之间的新关系。急性TGF反应发生在30秒内。即时的etgf反应与ATP从MD释放有关，并由ATP和/或腺苷介导，可能通过Al受体。第二持续期血管收缩持续30-40分钟，主要由腺苷介导。TGF的第三阶段时间适应发生在30-40分钟后，需要NOS-1和COX-2产物的活性，可能作为调节剂。TGF的时间适应性机制仍有待阐明。我们将利用微穿刺技术、体外微灌注MD/传入小动脉-肾小球的制备、体外近端小管和酶分析、放射免疫分析、Western blots和代谢评估来回答以下相关问题：具体目标#1-我们将通过体内和体外实验确定时间适应是否发生在a) MD NaCl信号的改变水平，b) TGF信号的传递（可能通过肾小球外系膜细胞到传入小动脉和肾小球）的抑制，或c)通过传出血管阻力的反应性改变。具体目标#2 -我们提出，在TGF适应后，滤过负荷的主要变化会使小管重吸收适应并增加，而这些变化取决于激素的影响，这些激素介导和调节TGF激活和时间适应，例如腺苷、ATP、血管紧张素II （All）和NOS-1中的NO。具体目标#3 -我们将研究TGF重置或时间适应的3种情况，即1)饮食NaCl和慢性体积扩张（DOCA和高NaCl）的变化，2)急性体积扩张和3)对侧肾切除术后。这些条件是否允许并表现出TGF进一步的时间适应性？在上述条件下，阻止TGF的时间适应性的生理后果是什么？TGF的时间适应性是维持TGF随生理条件变化的稳态效率所必需的。TGF适应是生命对多种条件的要求；正常生长，饮食中NaCl的改变，肾元质量的减少，近端肾小管重吸收的改变，急性高血压等。明确TGF的时间适应机制是全面了解肾脏对体积稳态的长期贡献的必要条件。这些研究还将明确嘌呤能（ATP）和腺苷介导的TGF在TGF的所有3个阶段中的作用。

DESCRIPTION (provided by applicant): The role of the kidney in volume homeostasis critically depends upon coordination of glomerular ultrafiltration (GFR) and tubular reabsorption. This is achieved through the coordinated actions of glomerulotubular balance (GTB) and the tubuloglomerular feedback (TGF) system. Whenever there is a change in concentration of salt in tubular fluid reaching the MD, TGF elicits a reciprocal change in SNGFR. However, the TGF system must adapt over time to sustained changes in MD NaCl concentration and delivery in order to maintain homeostatic efficiency of TGF. Resetting of TGF or 'temporal adaptation' of TGF does occur by changes in nephron blood flow, afferent arteriolar resistance and alteration in SNGFR leading to a new relationship between the MD signal and the efferent vascular response. The acute TGF response occurs within 30 seconds. The immediateTGF response is associated with ATP release from the MD and is mediated by ATP and/or adenosine, possibly via the Al receptor. A second sustained phase of vasoconstriction continues for 30-40 minutes primarily mediated by adenosine. A third phase of temporal adaptation of TGF occurs after 30-40 minutes and requires activity of NOS-1 and COX-2 products, probably as modulators. The mechanisms of temporal adaptation of TGF remain to be elucidated. We will utilize micropuncture techniques, the in vitro microperfused MD/ afferent arteriole-glomerulus's preparation, in vitro proximal tubules and enzyme assays, radioimmunoassays, Western blots and metabolic assessments to answer the following pertinent questions: Specific aim #1- We will determine using in vivo and in vitro experiments whether temporal adaptation occurs a) at the level of modification of the MD NaCl signal, b)suppression of transmission of the TGF signal, probably via the extraglomerular mesangial cells to the afferent arteriole and glomerulus or c) via alterations in the responsiveness of efferent vascular resistance. Specific aim #2 - We propose that tubular reabsorption adapts and increases secondarily in response to the major changes in filtered load after TGF adaptation and these changes depend upon hormonal influences which mediate and modulate TGF activation and temporal adaptation, e.g., adenosine, ATP, angiotensin II (All) and NO from NOS-1. Specific aim #3 - We will examine 3 conditions of TGF resetting or temporal adaptation which are 1) variations in dietary NaCl and chronic volume expansion (DOCA and high NaCl), 2) acute volume expansion and 3) following contralateral nephrectomy. Do these conditions permit and exhibit further temporal adaptation of TGF? What are the physiologic consequences of preventing temporal adaptation of TGF in the conditions described? Temporal adaptation of TGF is required to maintain homeostatic efficiency of TGF with transitions in physiologic conditions. TGF adaptation is a requirement for a variety of conditions in life; normal growth, changes in dietary NaCl, loss of nephron mass, alterations in proximal tubular reabsorption, acute hypertension, etc. Defining the mechanism of temporal adaptation of TGF is required for complete understanding of long term kidney contribution to volume homeostasis. These studies will also define the role of purinergic (ATP) and adenosine mediated TGF during all 3 phases of TGF.