Dantzler W H, Silbernagl S
Department of Physiology, College of Medicine, University of Arizona, Tucson 85724.
Am J Physiol. 1988 Sep;255(3 Pt 2):F397-407. doi: 10.1152/ajprenal.1988.255.3.F397.
Amino acid transport by juxtamedullary (JM) nephrons and its relationship to transport by superficial cortical (SC) nephrons and to function of vasa recta and collecting ducts were examined in vivo and in situ by free-flow micropuncture of Henle's loops, collecting ducts, and vasa recta and by continuous microinfusion of Henle's loops in exposed rat papillae. Fractional deliveries (FDs) of six neutral amino acids, two acidic amino acids, and taurine to tips of Henle's loops of JM nephrons could be substantially below those to early distal loops of SC nephrons, indicating that reabsorption before loop tips could be greater in JM than in SC nephrons. FDs to collecting ducts lower than to JM loop tips suggested reabsorption distal to loop tips. This was confirmed by continuous microinfusion of ascending limbs of Henle's loops. Distal site of reabsorption is unknown, but amino acids may move passively out of the thin ascending limb and be recycled into vasa recta and descending limb. Recycling of amino acids was supported by high FDs to tips of Henle's loops (sometimes greater than 1.0), higher concentrations in ascending than in descending vasa recta at same papilla level, and high mean concentrations in vasa recta.
通过对亨利袢、集合管和直小血管进行自由流微穿刺，并对暴露的大鼠乳头中的亨利袢进行连续微量灌注，在体内和原位研究了近髓肾单位的氨基酸转运及其与浅表皮质肾单位转运以及直小血管和集合管功能的关系。六种中性氨基酸、两种酸性氨基酸和牛磺酸向近髓肾单位亨利袢尖端的分数输送量可能显著低于向浅表皮质肾单位早期远曲袢的分数输送量，这表明近髓肾单位在袢尖端之前的重吸收可能比浅表皮质肾单位更强。向集合管的分数输送量低于向近髓袢尖端的分数输送量，提示在袢尖端远端存在重吸收。通过对亨利袢升支进行连续微量灌注证实了这一点。重吸收的远端部位尚不清楚，但氨基酸可能被动地从小的升支中移出，并被再循环到直小血管和降支中。氨基酸的再循环得到了向亨利袢尖端的高分率输送量（有时大于1.0）、在同一乳头水平升支直小血管中比降支直小血管中更高的浓度以及直小血管中的高平均浓度的支持。
