Beuchat C A
Department of Biology, San Diego State University, California 92182-4614, USA.
Am J Physiol. 1996 Jul;271(1 Pt 2):R157-79. doi: 10.1152/ajpregu.1996.271.1.R157.
Mammals with relatively long loops of Henle for their body size tend to have greater than average urinary concentrating ability, but the relationship between urine osmolality (Uosm) and absolute length of the loop of Henle (generally estimated as medullary thickness) is neither proportional nor direct. Uosm is independent of the thickness of the outer medulla (corresponding to the length of the medullary thick ascending limb), which scales similarly with body mass in animals from mesic, arid, and freshwater environments. After adjustment for the effect of body size, there is a significant relationship between the thickness of the inner medulla (corresponding to length of the thin ascending limb) and concentrating ability, but only in species from mesic environments; for these, the thickness of the inner medulla accounts for only 16% of the interspecific variability in Uosm. In marine mammals, both the cortex and medulla are surprisingly thin, yet these animals produce very concentrated urine for their size. A functional dependence of urinary concentrating ability on the length of the loop of Henle is a central tenet of countercurrent multiplier theory, but the correlation of maximum urine concentration with loop length is weak at best and largely reflects the influence of the thin ascending limb.
对于体型而言，具有相对较长亨利氏袢的哺乳动物往往具有高于平均水平的尿液浓缩能力，但尿渗透压（Uosm）与亨利氏袢的绝对长度（通常以髓质厚度来估算）之间的关系既不成比例也不直接。Uosm与外髓质的厚度无关（外髓质厚度对应于髓质厚升支的长度），在来自中生境、干旱环境和淡水环境的动物中，外髓质厚度与体重的比例关系相似。在调整体型的影响后，内髓质厚度（对应于细升支的长度）与浓缩能力之间存在显著关系，但仅在来自中生境的物种中如此；对于这些物种，内髓质厚度仅占Uosm种间变异性的16%。在海洋哺乳动物中，皮质和髓质都出奇地薄，但这些动物却能针对其体型产生非常浓缩的尿液。尿液浓缩能力对亨利氏袢长度的功能依赖性是逆流倍增理论的核心原则，但最大尿浓度与袢长度之间的相关性充其量很弱，并且在很大程度上反映了细升支的影响。
