Noiret Lorette, Baigent Stephen, Jalan Rajiv, Thomas S Randall
CoMPLEX, University College London (UCL), London, United Kingdom.
CoMPLEX, University College London (UCL), London, United Kingdom; Mathematics, UCL, London, United Kingdom.
PLoS One. 2015 Aug 17;10(8):e0134477. doi: 10.1371/journal.pone.0134477. eCollection 2015.
The kidney is one of the main organs that produces ammonia and release it into the circulation. Under normal conditions, between 30 and 50% of the ammonia produced in the kidney is excreted in the urine, the rest being absorbed into the systemic circulation via the renal vein. In acidosis and in some pathological conditions, the proportion of urinary excretion can increase to 70% of the ammonia produced in the kidney. Mechanisms regulating the balance between urinary excretion and renal vein release are not fully understood. We developed a mathematical model that reflects current thinking about renal ammonia handling in order to investigate the role of each tubular segment and identify some of the components which might control this balance. The model treats the movements of water, sodium chloride, urea, NH3 and [Formula: see text], and non-reabsorbable solute in an idealized renal medulla of the rat at steady state. A parameter study was performed to identify the transport parameters and microenvironmental conditions that most affect the rate of urinary ammonia excretion. Our results suggest that urinary ammonia excretion is mainly determined by those parameters that affect ammonia recycling in the loops of Henle. In particular, our results suggest a critical role for interstitial pH in the outer medulla and for luminal pH along the inner medullary collecting ducts.
肾脏是产生氨并将其释放到循环系统中的主要器官之一。在正常情况下，肾脏产生的氨中有30%至50%通过尿液排出，其余则通过肾静脉吸收进入体循环。在酸中毒和某些病理状态下，尿液排泄的比例可增加至肾脏产生氨的70%。调节尿液排泄和肾静脉释放之间平衡的机制尚未完全明了。我们建立了一个反映当前关于肾脏氨处理的数学模型，以研究每个肾小管节段的作用，并确定一些可能控制这种平衡的成分。该模型处理了大鼠理想化肾髓质中稳态下的水、氯化钠、尿素、NH3和[化学式：见原文]以及不可重吸收溶质的运动。进行了参数研究以确定对尿氨排泄速率影响最大的转运参数和微环境条件。我们的结果表明，尿氨排泄主要由影响髓袢中氨再循环的那些参数决定。特别是，我们的结果表明外髓质中的间质pH值以及沿内髓集合管的管腔pH值起着关键作用。
