Levillain O, Hus-Citharel A, Morel F, Bankir L
Institut National de la Santé et de la Recherche Médicale Unité 90, Hôpital Necker, Paris, France.
Am J Physiol. 1990 Dec;259(6 Pt 2):F916-23. doi: 10.1152/ajprenal.1990.259.6.F916.
Arginine production was measured in isolated rat nephron segments. Segments were incubated with 0.3 mM aspartate and 0.1 mM L-[ureido-14C]-citrulline in a sealed chamber. Arginase and urease were added to the medium to hydrolyze arginine and to release 14CO2, which was trapped in KOH and counted. Arginine synthesis was found only in the proximal tubule, with decreasing intensity from proximal convoluted (PCT) to proximal straight tubule (PST). Results were as follows (in fmol.min-1.mm tubule length-1): PCT, 122 +/- 15; cortical PST, 71 +/- 6; outer medullary PST, 41 +/- 4; all other segments, less than 6. Arginine synthesis changed almost proportionally with precursor concentration of less than or equal to 0.4 mM. We had shown previously that PST but not PCT was able to hydrolyze arginine into urea and ornithine. In this study arginine was further hydrolyzed in cortical (40%) and medullary (64%) PST but not in PCT. These observations suggest that the arginine formed in PCT contributes to the maintenance of the whole body arginine pool, whereas most of the arginine formed in PST might contribute, by its conversion to urea, to the process of urine concentration.
在分离的大鼠肾单位节段中测定精氨酸的生成。将节段在密封小室中与0.3 mM天冬氨酸和0.1 mM L-[脲基-¹⁴C]-瓜氨酸一起孵育。向培养基中加入精氨酸酶和脲酶以水解精氨酸并释放¹⁴CO₂，¹⁴CO₂被捕获在KOH中并进行计数。仅在近端小管中发现精氨酸合成，从近端曲管（PCT）到近端直小管（PST）强度逐渐降低。结果如下（以fmol·min⁻¹·mm小管长度⁻¹计）：PCT，122±15；皮质PST，71±6；外髓质PST，41±4；所有其他节段，小于6。当前体浓度小于或等于0.4 mM时，精氨酸合成几乎成比例变化。我们之前已经表明，PST而非PCT能够将精氨酸水解为尿素和鸟氨酸。在本研究中，精氨酸在皮质（40%）和髓质（64%）PST中进一步水解，但在PCT中不水解。这些观察结果表明，在PCT中形成的精氨酸有助于维持全身精氨酸池，而在PST中形成的大部分精氨酸可能通过转化为尿素，对尿液浓缩过程有贡献。
