Lönnerholm G, Wistrand P J
Pediatr Res. 1983 May;17(5):390-7. doi: 10.1203/00006450-198305000-00015.
Kidney tissue from human fetuses of gestational ages ranging 12--26 wk were studied by histochemical and biochemical methods. Clear staining for carbonic anhydrase activity was found in both proximal and distal parts of some nephrons already at gestational age of 12--15 wk. The staining pattern in the inner cortex of the fetuses of 24 and 26 wk did not differ markedly from that in adult renal cortex, except for the absence of capillary staining; proximal and distal convoluted tubules as well as initial collecting tubules exhibited distinct enzyme activity. In the outer cortex, where the nephronogenic zone is located, newly formed nephrons with no or little staining were found in all kidneys. Loops of Henle were absent or sparse in the medulla of the fetuses of 12--17 wk. Fully developed loops of Henle were relatively few also in the fetuses of 24 and 25 wk; the thick ascending limb and part of the thin limb were stained in such loops. The collecting ducts in all kidneys contained a varying number of intensely stained cells interspersed among unstained or weakly stained ones. The catalytic activity and the immunoassayable amount of carbonic anhydrase were determined in homogenates of renal cortex from three fetuses (19, 21, and 26 wk). The kidney from the fetus of 26 wk showed the highest values with an enzyme activity and an immunoassayable amount of HCA-C corresponding to 204 enzyme units and 0.14 mg enzyme per g wet weight of tissue, respectively. These values are similar to those of adult renal cortex and indicate that all of antigenically determined HCA-C is also catalytically active in the kidney at this gestational age. As judged from their content of carbonic anhydrase many nephrons might be fully able to reabsorb bicarbonate and secrete hydrogen ions in human fetuses of 24--26 wk. Other nephrons are much less developed at this stage, however. This nephronic heterogeneity might at least partly explain the reduced capacity for urinary acidification which has been reported for premature newborn infants.
采用组织化学和生物化学方法研究了孕龄为12 - 26周的人类胎儿的肾组织。在孕龄12 - 15周时，在一些肾单位的近端和远端部分已发现碳酸酐酶活性的清晰染色。24周和26周胎儿的肾内皮质的染色模式与成人肾皮质的染色模式没有明显差异，只是没有毛细血管染色；近端和远端曲管以及初始集合管表现出明显的酶活性。在肾单位生成区所在的肾外皮质，在所有肾脏中均发现新形成的肾单位染色缺失或很少。12 - 17周胎儿的髓质中没有或仅有稀疏的髓袢。在24周和25周的胎儿中，完全发育的髓袢也相对较少；在这些髓袢中，厚升支和部分细段被染色。所有肾脏的集合管中都含有数量不等的强染色细胞，散布于未染色或弱染色的细胞之间。测定了三个胎儿（19周、21周和26周）肾皮质匀浆中碳酸酐酶的催化活性和免疫可测定量。26周胎儿的肾脏显示出最高值，酶活性和免疫可测定的HCA - C量分别相当于每克湿组织204个酶单位和0.14毫克酶。这些值与成人肾皮质的值相似，表明在这个孕龄时，所有抗原性确定的HCA - C在肾脏中也具有催化活性。从碳酸酐酶的含量判断，在孕龄24 - 26周的人类胎儿中，许多肾单位可能完全能够重吸收碳酸氢盐并分泌氢离子。然而，在这个阶段，其他肾单位发育程度要低得多。这种肾单位的异质性可能至少部分解释了早产儿报道的尿酸化能力降低的现象。
