Transepithelial ammonia concentration gradients in inner medulla of the rat.
Transepithelial ammonia concentration gradients in inner medulla of the rat.
复制标题
大鼠髓内跨上皮氨浓度梯度。
DOI：
10.1152/ajprenal.1987.252.3.f491
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发表时间：
1987
期刊：
影响因子：
--
通讯作者：
DuBoseJr,TD
中科院分区：
文献类型：
--
作者：
Good,DW;Caflisch,CR;DuBoseJr,TD
NH3从Henle袢转运到髓质收集管已被认为在肾氨排泄中起重要作用。为了确定髓质内是否存在能够驱动这种转运的经上皮氨浓度梯度，我们在对照大鼠和慢性代谢性酸中毒大鼠中进行了微穿刺实验。测定原位pH值和总氨浓度，计算碱基和尖端收集管、Henle袢和直肠血管的NH3浓度（[NH3]）。在对照组和酸中毒大鼠中，Henle环中的[NH3]明显大于集管中的[NH3]。[NH3]在两组大鼠的Henle袢和邻近的直血管中没有差异，说明袢和集管之间的NH3浓度梯度代表了髓质间质和集管之间存在的NH3浓度梯度。在酸中毒过程中，收集管氨分泌的增加与收集管之间的NH3浓度差的增加有关，但在收集管ph没有下降的情况下发生。酸中毒过程中，有利于NH3向收集管扩散的NH3浓度梯度增加，因为Henle袢和髓质间质中的[NH3]比收集管中的[NH3]增加得更多。这些结果表明，参与髓质氨积累的转运过程在体内调节氨分泌到髓内收集管中起重要作用，慢性代谢性酸中毒时，髓内收集管pH值的下降并不一定会导致该段氨分泌增加。
Transport of NH3 from loops of Henle to medullary collecting ducts has been proposed to play an important role in renal ammonia excretion. To determine whether transepithelial ammonia concentration gradients capable of driving this transport are present in the inner medulla, micropuncture experiments were performed in control rats and in rats with chronic metabolic acidosis. In situ pH and total ammonia concentrations were measured to calculate NH3 concentrations ([NH3]) for base and tip collecting duct, loop of Henle, and vasa recta. In control and acidotic rats, [NH3] in the loop of Henle was significantly greater than [NH3] in the collecting ducts. [NH3] did not differ in loop of Henle and adjacent vasa recta in either group of rats, indicating that NH3 concentration gradients between loop and collecting duct represent NH3 gradients that are present between medullary interstitium and collecting duct. During acidosis, an increase in collecting duct ammonia secretion was associated with an increase in the NH3 concentration difference between loop of Henle and collecting duct but occurred in the absence of a fall in collecting duct pH. The NH3 concentration gradient favoring diffusion of NH3 into the collecting ducts increased during acidosis because [NH3] in the loop of Henle and medullary interstitium increased more than [NH3] in the collecting duct. These findings indicate that transport processes involved in medullary ammonia accumulation play an important role in regulating ammonia secretion into the inner medullary collecting duct in vivo and that a fall in inner medullary collecting duct pH is not necessarily required for ammonia secretion by this segment to increase during chronic metabolic acidosis.