URINARY CONCENTRATING MECHANISM: UNIQUE AVIAN MODELS

这项建议的总体目标是增进我们对 利用从以下方面获得的知识探讨尿液浓缩机制 独特的禽类肾脏模型。鸟类和哺乳动物是唯一的脊椎动物 可使尿液对血浆产生高渗，但结构和功能 用于尿液浓缩的逆流系统的 不一样。鸟类肾脏：1)浅层爬行动物类型(RT)和 延髓哺乳动物型(MT)肾单位存在；2)内髓和 没有乳突；3)氯化钠而不是尿素构成皮髓 4)RT肾单位低渗引流改变尿液 流动和集中。基于这些特点，我们建议开展两项工作 使用体外灌流的鹌鹑Coturnix小管的项目 Coturnix。第一个项目是确定一种更简单的逆流 基于氯化钠转运的增殖模型在TAL和 甲状旁腺肾单位降支。我们将在DL中进行测量 钠、氯和氯的扩散势、渗透率和通量 水。肾单位Na-K-ATPase活性与神经细胞的构筑组织 对髓质进行检查。项目二旨在确定是否 通过收集管道的体积流量的减少将 在不使用精氨酸催产素的情况下提高尿液浓缩能力 (AVT，禽类抗利尿激素)。我们将首先衡量AVT是否 增加渗透水通透性和腺苷环化酶活性 收集管，第二，是否降低了灌注率 改变液体的净传输和渗透水的渗透率 AVT。禽类尿液操作特性的界定 与哺乳动物系统的浓缩机制相比， 威尔：1)帮助澄清潜在的根本问题 哺乳动物肾脏的浓缩机制，27提供了新的 关于必要的公共功能的见解 原始脊椎动物的肾脏，允许形成浓缩的尿液。

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.