HEPATIC UREAGENESIS--STUDIES WITH 15-N GC-MS AND 13C NMR

这项建议要求全面审查各种机制， 控制肝脏尿素生成和氨解毒， 分离的肝细胞和分离的灌注肝脏。 工作 将讨论四个主要主题：（1）确定 氨基酸作为氨和尿素氮的前体， 代谢条件;（2）嘌呤核苷酸的作用 循环提供用于合成 谷氨酰胺的尿素;（3）各种效应物的作用和/或 尿素生成抑制剂在确定尿素来源中的应用 氮;和（4）氢离子浓度的影响， 调节氮通过肝脏的流量。 后一主题将 通过对肝脏氮代谢的研究， 急性或慢性酸中毒或缺氧的大鼠。 这部作品的一个独特之处是使用了生理媒介 含有大多数通常存在于 细胞外液，其中只有一个将标记有15 N 或13 C。 通过利用气相色谱-质谱法和 核磁共振定量稳定同位素富集 在氨、尿素、氨基酸和腺嘌呤核苷酸中， 可以测量代谢物通量，并确定重要的 以一种迄今为止 不可能的 所获得的数据将具有重要的科学意义， 加深我们对尿素生成和肝氮的理解 新陈代谢. 急性脑梗死患者的合理临床管理 肝病就有这样的科学基础。

This proposal entails a comprehensive examination of the mechanisms controlling hepatic ureagenesis and ammonia detoxification in isolated hepatocytes and the isolated perfused liver. The work will address four primary themes: (1) identification of those amino acids serving as precursor to ammonia and urea N in a variety of metabolic conditions; (2) the role of the purine nucleotide cycle in furnishing the nitrogen utilized for the synthesis of either urea of glutamine; (3) the role of various effectors and/or inhibitors of ureagenesis in determining the sources of urea nitrogen; and (4) the effect(s) of hydrogen ion concentration in regulating nitrogen flux through the liver. The latter theme will receive special attention through the study of hepatic N metabolism in rats made acutely or chronically acidotic or alkalotic. A unique feature of the work is the use of physiologic medium containing most of the amino acids normally present in the extracellular fluid, only one of which will be labelled with 15N or 13C. By utilizing both gas chromatography-mass spectrometry and nuclear magnetic resonance to quantify stable isotopic enrichment in ammonia, urea, amino acids and adenine nucleotides, it will be possible to measure metabolite flux and to identify important precursor-product relationships in a manner which has been hitherto impossible. The data do obtained will be of scientific import by deepening our understanding of ureagenesis and of hepatic nitrogen metabolism. The rational clinical management of patients with liver disease presupposes such a scientific foundation.