Kleinman L I, Banks R O
Proc Soc Exp Biol Med. 1983 Jun;173(2):231-7. doi: 10.3181/00379727-173-41637.
Studies were carried out in 23 anesthetized neonatal dogs aged 2 to 20 days and in 16 adult dogs to compare the effects of saline volume expansion on renal tubular Na and K reabsorption between newborn and adult animals. Proximal- and distal-tubule function was estimated by the distal-nephron-blockade technique using ethacrynic acid and amiloride. During saline infusion, which increased extracellular volume by approximately 30% for both age groups, total nephron fractional Na reabsorption was 0.91 for the adult but 0.98 for the puppy (P less than 0.01). However, proximal tubule fractional Na reabsorption was greater in the adult (0.64) than in the puppy (0.48, P less than 0.01) whereas distal nephron fractional Na reabsorption was much greater in the newborn (0.51) than in the adult (0.26, P less than 0.01). Sodium reabsorption normalized to kidney weight was lower in all segments of the neonatal kidney than in the adult kidney. The filtered sodium load was lower in the newborn (27.0 mueq min-1g-1) than in the adult (105.0, P less than 0.01), and the Na load to the distal nephron was also lower in the newborn (14.0 mueq min-1g-1) than in the adult (37.2, P less than 0.01). Fractional K excretion was similar in both age groups even though the fraction of filtered K escaping proximal-tubule reabsorption was greater in the newborn than in the adult, indicating greater net K fractional reabsorption in the distal nephron of the newborn than in the adult kidney. These results indicate that in response to saline expansion there is a greater proximal tubule natriuresis in the neonate than in the adult but overall renal Na excretion is less in the newborn animal due to enhanced fractional Na reabsorption in the neonatal distal nephron, particularly in Henle's Loop. This increase in distal nephron fractional sodium reabsorption may be related in part to the relatively small absolute Na load presented to the distal nephron of the neonatal kidney.
对23只2至20日龄的麻醉新生犬和16只成年犬进行了研究，以比较生理盐水扩容对新生动物和成年动物肾小管钠和钾重吸收的影响。使用依他尼酸和阿米洛利通过远曲小管阻断技术评估近端和远端小管功能。在生理盐水输注期间，两个年龄组的细胞外液量均增加了约30%，成年犬的总肾单位钠重吸收率为0.91，幼犬为0.98（P<0.01）。然而，成年犬近端小管钠重吸收率（0.64）高于幼犬（0.48，P<0.01），而新生犬远曲小管钠重吸收率（0.51）远高于成年犬（0.26，P<0.01）。新生犬肾脏所有节段中按肾脏重量归一化的钠重吸收均低于成年犬肾脏。新生犬的滤过钠负荷（27.0μeq·min⁻¹·g⁻¹）低于成年犬（105.0，P<0.01），新生犬远曲小管的钠负荷（14.0μeq·min⁻¹·g⁻¹）也低于成年犬（37.2，P<0.01）。两个年龄组的钾排泄分数相似，尽管新生犬滤过钾逃脱近端小管重吸收的分数高于成年犬，这表明新生犬远曲小管的净钾重吸收分数高于成年犬肾脏。这些结果表明，对生理盐水扩容的反应中，新生儿近端小管排钠作用比成年犬更大，但由于新生动物远曲小管尤其是髓袢钠重吸收分数增加，新生动物的总体肾脏钠排泄较少。远曲小管钠重吸收分数的这种增加可能部分与新生犬肾脏远曲小管相对较小的绝对钠负荷有关。
