Beuchat C A
Department of Physiology, University of Arizona, Tucson 85724.
J Theor Biol. 1990 Mar 8;143(1):113-22. doi: 10.1016/s0022-5193(05)80291-7.
Currently accepted theories of the urine concentrating mechanism of the mammalian kidney predict that concentrating ability should increase with increasing length of the loop of Henle. However, larger mammals have longer nephrons than do smaller ones, yet concentrating ability declines with increasing body mass (M, in kg) as M-0.097. Greenwald & Stetson (1988, News Physiol. Sci. 3, 46-49) have suggested that the diminished concentrating ability of large mammals reflects their lower mass-specific metabolic rate. They propose that, because the urine concentrating mechanism depends upon the energy-dependent transport of sodium chloride, concentrating ability should be closely related to mass-specific metabolic rate. Examination of the allometric scalings with body mass of medullary thickness and metabolic rate indicate that the rate of increase in length of the loop of Henle with body size (M0.129) is insufficient to offset the decline in mass-specific metabolism (M-0.24). The residual product of these scalings (M-0.11) indicates that urine concentrating ability should be inversely related to body size and is similar to the observed allometry of concentrating ability (M-0.097). The decline in concentrating ability of the kidney with body size is probably not a result of inability of the kidney to adapt physiologically or structurally to changes in size, but rather reflects the scaling of the need to conserve water. Small mammals, because of their high rates of evaporative and respiratory water loss, have a much higher rate of water turnover than do large mammals (Vwater.kg-1 alpha M-0.20). Because the need to concentrate the urine diminishes with increasing body size, the increase in loop length need only partially compensate for the simultaneous decline in metabolism.
目前被广泛接受的哺乳动物肾脏尿液浓缩机制理论预测，浓缩能力应随着亨利氏袢长度的增加而增强。然而，大型哺乳动物的肾单位比小型哺乳动物的更长，但浓缩能力却随着体重（M，单位为千克）的增加而下降，其关系为M^-0.097。格林沃尔德和斯特森（1988年，《生理学新闻》3卷，46 - 49页）提出，大型哺乳动物浓缩能力的下降反映了它们较低的单位体重代谢率。他们认为，由于尿液浓缩机制依赖于氯化钠的能量依赖性转运，浓缩能力应与单位体重代谢率密切相关。对髓质厚度和代谢率与体重的异速生长关系进行研究表明，亨利氏袢长度随体型（M^0.129）的增加速率不足以抵消单位体重代谢的下降（M^-0.24）。这些异速生长关系的剩余产物（M^-0.11）表明，尿液浓缩能力应与体型呈负相关，这与观察到的浓缩能力异速生长关系（M^-0.097）相似。肾脏浓缩能力随体型下降可能不是因为肾脏在生理或结构上无法适应大小变化，而是反映了对节约用水需求的缩放关系。小型哺乳动物由于其蒸发和呼吸失水率较高，其水分周转率比大型哺乳动物高得多（Vwater.kg^-1 ∝ M^-0.20）。由于随着体型增大，浓缩尿液的需求减少，袢长度的增加只需部分补偿同时出现的代谢下降。
