Fleck C
Institute of Pharmacology and Toxicology, Friedrich Schiller University of Jena, FRG.
Ren Physiol Biochem. 1992 Sep-Oct;15(5):257-65.
In the late neonatal period of male Wistar rats (10 days old) concentrations in plasma were higher for 5 of 24 amino acids compared to adult animals (2 months old): beta-alanine, tyrosine, glycine, histidine, and the dipeptide anserine. The plasma concentrations of tryptophan, valine and leucine were lower in young than in adult rats. The renal clearances of amino acids were lower in young rats, both in relation to 1 g b.w. and related to 1 g kidney weight. In the latter case the differences became more distinct because the relative kidney weight was higher in young than in adult animals (1.17 +/- 0.07 vs. 0.82 +/- 0.03 g/100 g b.w.) and significant age differences in renal water content did not exist. The apparently more effective tubular reabsorption capacity in young rats can be explained as follows: Because of the significantly lower GFR in 10-day-old rats compared with adults (0.46 +/- 0.03 vs. 1.10 +/- 0.09 ml/min/1 g kidney), the glomerularly filtered load of amino acids is generally lower in young rats (exceptions: tyrosine, glycine). Therefore, the amino acid transporting carrier systems are able to reabsorb the absolutely lower amounts of amino acids from the ultrafiltrate in immature animals. This hypothesis is supported if one relates the renal amino acid clearance to the clearance of inulin. In this way it is possible to show that there are absolutely no differences between both age groups indicating mature transport systems for endogenous amino acids as early as in 10-day-old rats.(ABSTRACT TRUNCATED AT 250 WORDS)
在雄性Wistar大鼠的新生儿后期（10日龄），与成年动物（2月龄）相比，24种氨基酸中有5种在血浆中的浓度更高：β-丙氨酸、酪氨酸、甘氨酸、组氨酸和二肽鹅肌肽。幼鼠血浆中色氨酸、缬氨酸和亮氨酸的浓度低于成年大鼠。幼鼠的氨基酸肾清除率较低，无论是相对于1g体重还是相对于1g肾脏重量而言。在后一种情况下，差异变得更加明显，因为幼鼠的相对肾脏重量高于成年动物（1.17±0.07 vs. 0.82±0.03g/100g体重），并且肾脏含水量不存在显著的年龄差异。幼鼠肾小管重吸收能力明显更强可解释如下：由于10日龄大鼠的肾小球滤过率（GFR）显著低于成年大鼠（0.46±0.03 vs. 1.10±0.09ml/min/1g肾脏），幼鼠氨基酸的肾小球滤过负荷通常较低（例外：酪氨酸、甘氨酸）。因此，氨基酸转运载体系统能够从不成熟动物的超滤液中重吸收绝对量较低的氨基酸。如果将肾脏氨基酸清除率与菊粉清除率相关联，这一假设将得到支持。通过这种方式可以表明，两个年龄组之间绝对没有差异，这表明早在10日龄大鼠中就存在成熟的内源性氨基酸转运系统。（摘要截断于250字）
