Imig J D, Navar G L, Zou L X, O'Reilly K C, Allen P L, Kaysen J H, Hammond T G, Navar L G
Department of Physiology and Division of Nephrology, Tulane University School of Medicine, New Orleans, Louisiana 70112, USA.
Am J Physiol. 1999 Aug;277(2):F303-11. doi: 10.1152/ajprenal.1999.277.2.F303.
Kidney cortex and proximal tubular angiotensin II (ANG II) levels are greater than can be explained on the basis of circulating ANG II, suggesting intrarenal compartmentalization of these peptides. One possible site of intracellular accumulation is the endosomes. In the present study, we tested for endosomal ANG I, ANG II, angiotensin type 1A receptor (AT(1A)), and angiotensin converting enzyme (ACE) activity and determined whether these levels are regulated by salt intake. Male Sprague-Dawley rats were fed chow containing either high or low dietary sodium for 10-14 days. Blood and kidneys were harvested and processed for measurement of plasma, kidney, and renal intermicrovillar cleft and endosomal angiotensin levels. Kidney ANG I averaged 179 +/- 20 fmol/g and ANG II averaged 258 +/- 36 fmol/g in rats fed a high-sodium diet and were significantly higher, averaging 347 +/- 58 fmol/g and 386 +/- 55 fmol/g, respectively, in rats fed a low-salt diet. Renal intermicrovillar clefts and endosomes contained ANG I and ANG II. Intermicrovillar cleft ANG I and ANG II levels averaged 8.4 +/- 2.6 and 74 +/- 26 fmol/mg, respectively, in rats fed a high-salt diet and 7.6 +/- 1.7 and 70 +/- 25 fmol/mg in rats fed a low-salt diet. Endosomal ANG I and ANG II levels averaged 12.3 +/- 4.4 and 43 +/- 19 fmol/mg, respectively, in rats fed a high-salt diet, and these levels were similar to those observed in rats fed a low-salt diet. Renal endosomes from rats fed a low-salt diet demonstrated significantly more AT(1A) receptor binding compared with rats fed a high-salt diet. ACE activity was detectable in renal intermicrovillar clefts and was 2.5-fold higher than the levels observed in renal endosomes. Acute enalaprilat treatment decreased ACE activity in renal intermicrovillar clefts by 90% and in renal endosomes by 84%. Likewise, intermicrovillar cleft and endosomal ANG II levels decreased by 61% and 52%, respectively, in enalaprilat-treated animals. These data demonstrate the presence of intact angiotensin peptides and ACE activity in renal intermicrovillar clefts and endosomes, indicating that intact angiotensin peptides are formed and/or trafficked through intracellular endosomal compartments and are dependent on ACE activity.
肾皮质和近端肾小管中的血管紧张素II（ANG II）水平高于基于循环ANG II所能解释的水平，这表明这些肽在肾内存在区室化。细胞内积累的一个可能部位是内体。在本研究中，我们检测了内体中的血管紧张素I（ANG I）、ANG II、1A型血管紧张素受体（AT(1A)）和血管紧张素转换酶（ACE）活性，并确定这些水平是否受盐摄入量的调节。将雄性Sprague-Dawley大鼠喂以高钠或低钠饮食10 - 14天。采集血液和肾脏并进行处理，以测量血浆、肾脏、肾微绒毛间裂和内体中的血管紧张素水平。高钠饮食喂养的大鼠肾脏中ANG I平均为179±20 fmol/g，ANG II平均为258±36 fmol/g，而低钠饮食喂养的大鼠中ANG I和ANG II水平显著更高，分别平均为347±58 fmol/g和386±55 fmol/g。肾微绒毛间裂和内体中含有ANG I和ANG II。高钠饮食喂养的大鼠微绒毛间裂中ANG I和ANG II水平分别平均为8.4±2.6和74±26 fmol/mg，低钠饮食喂养的大鼠中分别为7.6±1.7和70±25 fmol/mg。高钠饮食喂养的大鼠内体中ANG I和ANG II水平分别平均为12.3±4.4和43±19 fmol/mg，这些水平与低钠饮食喂养的大鼠中观察到的水平相似。与高钠饮食喂养的大鼠相比，低钠饮食喂养的大鼠肾内体显示出明显更多的AT(1A)受体结合。在肾微绒毛间裂中可检测到ACE活性，其比肾内体中观察到的水平高2.5倍。急性依那普利拉治疗使肾微绒毛间裂中的ACE活性降低90%，肾内体中的降低84%。同样，在依那普利拉治疗的动物中，微绒毛间裂和内体中的ANG II水平分别降低了61%和52%。这些数据表明肾微绒毛间裂和内体中存在完整的血管紧张素肽和ACE活性，表明完整的血管紧张素肽在内细胞内体区室中形成和/或运输，并且依赖于ACE活性。
