Veeneman Jorden M, Kingma Hermi A, Stellaard Frans, de Jong Paul E, Reijngoud Dirk-Jan, Huisman Roel M
Department of Internal Medicine, Division of Nephrology, University Hospital Groningen and Groningen University Institute of Drug Exploration, The Netherlands.
Nephrol Dial Transplant. 2004 Jun;19(6):1533-41. doi: 10.1093/ndt/gfh236. Epub 2004 Apr 6.
The PNA (protein equivalent of nitrogen appearance) is used to calculate protein intake from urea kinetics. One of the essential assumptions in the calculation of PNA is that urea accumulation in haemodialysis (HD) patients is equivalent to amino acid oxidation. However, urea is hydrolysed in the intestine and the resulting ammonia could be used metabolically. The magnitude and dependence on protein intake of this process are unknown in HD patients.
Seven HD patients were studied twice, 1 week apart, on a similar protocol. After an overnight fast, patients fasted in the morning and received meals in the afternoon. On one day, amino acid oxidation was measured by infusion of L-[1-(13)C]valine. Urea production, measured from the dilution of [(13)C]urea, and urea accumulation, calculated from the increase in plasma urea concentration multiplied by the urea dilution volume, were measured during the other day. PNA was calculated using standard equations.
Amino acid oxidation and urea production were not significantly different during fasting. Urea accumulation during fasting was significantly lower than both amino acid oxidation and urea production. Urea accumulation during feeding remained significantly lower than amino acid oxidation. PNA was equal to the average of the urea accumulation values during fasting and feeding.
We conclude that during fasting, urea accumulation is not associated with amino acid oxidation or urea production. During meal intake, amino acid oxidation, urea production and urea accumulation show acutely an almost identical increase. PNA represents the average of fasting and fed urea accumulation and is lower than average amino acid oxidation or urea production.
蛋白质氮呈现量（PNA）用于根据尿素动力学计算蛋白质摄入量。计算PNA的一个基本假设是血液透析（HD）患者体内尿素的蓄积等同于氨基酸氧化。然而，尿素在肠道中会被水解，生成的氨可用于代谢。HD患者中这一过程的程度及其对蛋白质摄入量的依赖性尚不清楚。
对7例HD患者进行了两次研究，间隔1周，采用相似的方案。患者过夜禁食后，上午继续禁食，下午进食。一天通过输注L-[1-(13)C]缬氨酸测量氨基酸氧化。另一天测量[(13)C]尿素稀释法测得的尿素生成量，以及根据血浆尿素浓度升高乘以尿素稀释体积计算得出的尿素蓄积量。使用标准公式计算PNA。
禁食期间氨基酸氧化和尿素生成无显著差异。禁食期间的尿素蓄积显著低于氨基酸氧化和尿素生成。进食期间的尿素蓄积仍显著低于氨基酸氧化。PNA等于禁食和进食期间尿素蓄积值的平均值。
我们得出结论，禁食期间，尿素蓄积与氨基酸氧化或尿素生成无关。进餐期间，氨基酸氧化、尿素生成和尿素蓄积急剧增加，几乎相同。PNA代表禁食和进食时尿素蓄积的平均值，低于平均氨基酸氧化或尿素生成。
