Hamada Y, Taniguchi J, Imai M
Laboratory for Neural Modeling, Forefront Research Program, Saitama, Japan.
Nephron. 1996;74(3):600-6. doi: 10.1159/000189459.
Although the accumulation of urea in the renal medulla is essential for the formation of concentrated urine, it is also necessary for the kidney to excrete considerable amounts of urea into the urine as a waste product of protein degradation. Thus, the urine concentrating capacity is attained by the interaction with the efficiency of urea excretion. To seek the best condition for this phenomenon, we developed an objective function for evaluating urea excreting capacity relative to urine concentrating capacity by using a mathematical model consisting of components of the countercurrent multiplication system: the ascending thin limb, capillary network, and inner medullary collecting duct. The values of the objective functions were calculated as three-dimensional functions of transport parameters for the inner medullary collecting duct, including hydraulic conductivity, urea permeability, and reflection coefficient for urea. The results of the computer analysis revealed that the maximum value of the objective function was attained when values for transport parameters of the inner medullary collecting duct corresponded to those experimentally obtained values reported previously. We conclude that the maximum urine concentrating capacity is limited by the efficiency of urea excreting capacity of the kidney, and vice versa.
尽管肾髓质中尿素的蓄积对于浓缩尿的形成至关重要，但肾脏将大量尿素作为蛋白质降解的废物排泄到尿液中也是必要的。因此，尿液浓缩能力是通过与尿素排泄效率的相互作用来实现的。为了探寻这种现象的最佳条件，我们通过使用一个由逆流倍增系统的组成部分（升支细段、毛细血管网和髓质内集合管）构成的数学模型，开发了一个用于评估相对于尿液浓缩能力的尿素排泄能力的目标函数。目标函数的值作为髓质内集合管转运参数的三维函数进行计算，这些参数包括水力传导率、尿素通透性和尿素的反射系数。计算机分析结果表明，当髓质内集合管转运参数的值与先前报道的实验获得值相对应时，目标函数达到最大值。我们得出结论，最大尿液浓缩能力受到肾脏尿素排泄能力效率的限制，反之亦然。
