Shaltout Hossam A, Westwood Brian M, Averill David B, Ferrario Carlos M, Figueroa Jorge P, Diz Debra I, Rose James C, Chappell Mark C
Department of Obstetrics and Gynecology, Hypertension and Vascular Disease Center, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157-1095, USA.
Am J Physiol Renal Physiol. 2007 Jan;292(1):F82-91. doi: 10.1152/ajprenal.00139.2006. Epub 2006 Aug 8.
Despite the evidence that angiotensin-converting enzyme (ACE)2 is a component of the renin-angiotensin system (RAS), the influence of ACE2 on angiotensin metabolism within the kidney is not well known, particularly in experimental models other than rats or mice. Therefore, we investigated the metabolism of the angiotensins in isolated proximal tubules, urine, and serum from sheep. Radiolabeled [(125)I]ANG I was hydrolyzed primarily to ANG II and ANG-(1-7) by ACE and neprilysin, respectively, in sheep proximal tubules. The ACE2 product ANG-(1-9) from ANG I was not detected in the absence or presence of ACE and neprilysin inhibition. In contrast, the proximal tubules contained robust ACE2 activity that converted ANG II to ANG-(1-7). Immunoblots utilizing an NH(2) terminal-directed ACE2 antibody revealed a single 120-kDa band in proximal tubule membranes. ANG-(1-7) was not a stable product in the tubule preparation and was rapidly hydrolyzed to ANG-(1-5) and ANG-(1-4) by ACE and neprilysin, respectively. Comparison of activities in the proximal tubules with nonsaturating concentrations of substrate revealed equivalent activities for ACE (ANG I to ANG II: 248 +/- 17 fmol x mg(-1) x min(-1)) and ACE2 [ANG II to ANG-(1-7): 253 +/- 11 fmol x mg(-1) x min(-1)], but lower neprilysin activity [ANG II to ANG-(1-4): 119 +/- 24 fmol x mg(-1) x min(-1); P < 0.05 vs. ACE or ACE2]. Urinary metabolism of ANG I and ANG II was similar to the proximal tubules; soluble ACE2 activity was also detectable in sheep serum. In conclusion, sheep tissues contain abundant ACE2 activity that converts ANG II to ANG-(1-7) but does not participate in the processing of ANG I into ANG-(1-9).
尽管有证据表明血管紧张素转换酶（ACE）2是肾素-血管紧张素系统（RAS）的一个组成部分，但ACE2对肾脏内血管紧张素代谢的影响尚不清楚，尤其是在大鼠或小鼠以外的实验模型中。因此，我们研究了绵羊离体近端小管、尿液和血清中血管紧张素的代谢。在绵羊近端小管中，放射性标记的[(125)I]ANG I分别被ACE和中性内肽酶主要水解为ANG II和ANG-(1-7)。在不存在或存在ACE和中性内肽酶抑制的情况下，均未检测到ANG I产生的ACE2产物ANG-(1-9)。相反，近端小管含有强大的ACE2活性，可将ANG II转化为ANG-(1-7)。利用氨基末端定向的ACE2抗体进行的免疫印迹显示，近端小管膜中有一条单一的120 kDa条带。ANG-(1-7)在小管制剂中不是稳定产物，分别被ACE和中性内肽酶迅速水解为ANG-(1-5)和ANG-(1-4)。用非饱和底物浓度比较近端小管中的活性，发现ACE（ANG I转化为ANG II：248±17 fmol·mg(-1)·min(-1)）和ACE2 [ANG II转化为ANG-(1-7)：253±11 fmol·mg(-1)·min(-1)]的活性相当，但中性内肽酶活性较低[ANG II转化为ANG-(1-4)：119±24 fmol·mg(-1)·min(-1)；与ACE或ACE2相比，P<0.05]。ANG I和ANG II的尿液代谢与近端小管相似；在绵羊血清中也可检测到可溶性ACE2活性。总之，绵羊组织含有丰富的ACE2活性，可将ANG II转化为ANG-(1-7)，但不参与ANG I加工成ANG-(1-9)的过程。
