URINARY CONCENTRATING MECHANISM: UNIQUE AVIAN MODELS

本提案的总体目标是促进我们对 尿浓缩机制，通过利用从 独特的鸟类肾脏模型。 鸟类和哺乳动物是唯一的脊椎动物 能产生高渗性尿液，但结构和功能 尿液浓缩的逆流系统似乎是 不同. 鸟类肾脏：1）浅层爬行动物型（RT）和 存在髓质的髓型（MT）肾单位; 2）内部髓质， 无乳头; 3）NaCl而不是尿素组成皮质髓质 渗透梯度;和4）RT肾单位的低渗引流改变尿液 流量和浓度。 基于这些特点，我们建议进行两次 项目使用鹌鹑体外灌流小管，Coturnix 鹌鹑 项目一是确定一个简单的逆流 基于NaCl运输的倍增模型在TAL和 MT肾单位的降支（DL）。 我们将在DL中测量 扩散势、渗透率和Na、Cl和 水 肾单位Na-K-ATP酶活性与肾细胞构筑 将检查髓质。 项目二旨在确定 通过收集管的体积流率的减小将 在没有精氨酸催产素的情况下提高尿浓缩能力 (AVT禽类抗利尿激素）。 首先，我们将测量AVT是否 增加渗透性水渗透性和腺苷酸环化酶活性， 第二，灌注流速的降低是否 改变了净液体运输和渗透水的渗透性， AVT。 禽尿沉渣分析仪操作特性的确定 浓缩机制，与哺乳动物系统相比， （1）帮助澄清基本问题， 哺乳动物肾脏的浓缩机制，27提供了新的 关于调整《公约》所需共同特征的见解 原始脊椎动物的肾脏，能形成浓缩的尿。

The overall aim of this proposal is to advance our understanding of the urinary concentrating mechanism by exploiting the knowledge obtained from the unique avian kidney model. Birds and mammals are the only vertebrates that can produce urine hyperosmotic to plasma, but structure and function of the countercurrent system for urine concentration appear to be different. In bird kidneys: 1) superficial reptilian-type (RT) and medullary mammalian-type (MT) nephrons exist; 2) an inner medulla and papilla are absent; 3) NaCl but not urea composes a corticomedullary osmotic gradient; and 4) hyposmotic drainage from RT nephrons alters urine flow and concentration. Based on these features, we propose to conduct two projects using the in vitro perfused tubule from the quail, Coturnix coturnix. Project I is to determine whether a simpler counter-current multiplication model based on NaCl transport operates between the TAL and the descending limb (DL) of the MT nephron. We will measure in the DL diffusional potentials, and permeabilities and fluxes for Na, Cl, and water. Na-K-ATPase activity of nephrons and architectural organization of the medulla will be examined. Project II aims to determine whether reductions in the volume flow rate through the collecting duct would improve urine concentrating ability in the absence of arginine vasotocin (AVT, avian antidiuretic hormone). We will measure, first, whether AVT increases osmotic water permeability and adenylate cyclase activity of the collecting duct and, second, whether a reduction of the perfusion flow rate alters net fluid transport and osmotic water permeability in the absence of AVT. Definition of the operational characteristics of the avian urinary concentrating mechanism, as compared to those of the mammalian system, will: 1) aid in clarifying fundamental problems underlying the concentrating mechanism of the mammalian kidney, and 27 provide new insights concerning common features that were necessary to adapt the primitive vertebrate kidney to permit formation of concentrated urine.