Baines A D, Basmadjian D, Wang B C
Biophys J. 1979 Jul;27(1):21-38. doi: 10.1016/S0006-3495(79)85200-5.
With computer simulation we examined the extent to which current theories and experimental data explain function of single microperfused superficial Henle's loops in rats. In the model standard phenomenological equations describe transport; two sets of transport parameters labeled rat and rabbit were taken from published experiments; Michaelis-Menten kinetics in the ascending thick limb were adjusted arbitrarily; tubular radius is either constant or depends on luminal pressure with compliance based on experimental observations; the interstitium is an infinite sink with salt and urea concentrations constant in the cortex and exponentially increasing in the outer medulla; concentrations resemble those found in hydropenic or saline diuretic rats. The following predictions were obtained. The model with rabbit parameters does not recirculate urea and will not operate with high medullary urea concentrations; with rat parameters too much urea recirculates an the results of perfusion with equilibrium solution are not reproduced. Using a compromise between rat and rabbit parameters, the model reproduces water absorption, salt reabsorption, and urea recirculation as observed in vivo in rat loops perfused at 5-40 nl/min. It also simulates perfusion with saline, equilibrium solution, saline plus furosemide, and 300 mM mannitol. When the model includes a short early distal segment, effluent salt concentration reaches a minimum at a 15 nl/min perfusion rate as observed in vivo; however, concentration at the macula densa is a monotonically increasing function of flow. When permeation rate is a function of wall surface area and thickness a better fit to experimental results is produced. However, the effect is small: water absorption alters by 4% or less and effluent salt concentration is reduced by up to 10% at low perfusion rates. Comparison of rigid and compliant loops shows no relationship between transit time per se and reabsorption.
通过计算机模拟，我们研究了当前理论和实验数据对大鼠单个微灌流浅表髓袢功能的解释程度。在该模型中，标准现象学方程描述转运过程；两组标记为大鼠和兔子的转运参数取自已发表的实验；对升支粗段的米氏动力学进行了任意调整；肾小管半径要么恒定，要么根据实验观察结果的顺应性取决于管腔内压力；间质是一个无限的汇，皮质中的盐和尿素浓度恒定，外髓质中呈指数增加；浓度类似于禁水或盐水利尿大鼠中的浓度。得到了以下预测结果。具有兔子参数的模型不会使尿素再循环，并且在高髓质尿素浓度下无法运行；具有大鼠参数时，尿素再循环过多，且无法重现平衡溶液灌注的结果。采用大鼠和兔子参数之间的折衷方案，该模型能够重现以5 - 40 nl/min灌注的大鼠髓袢在体内观察到的水吸收、盐重吸收和尿素再循环情况。它还模拟了用盐水、平衡溶液、盐水加呋塞米和300 mM甘露醇进行的灌注。当模型包括一个短的早期远曲小管段时，流出液盐浓度在15 nl/min的灌注速率下达到最小值，这与体内观察结果一致；然而，致密斑处的浓度是流量的单调递增函数。当渗透速率是壁表面积和厚度的函数时，能更好地拟合实验结果。然而，这种影响很小：在低灌注速率下，水吸收变化4%或更小，流出液盐浓度最多降低10%。刚性和顺应性髓袢的比较表明，转运时间本身与重吸收之间没有关系。
