Purdon A D, Loh A Y, Osmond D H
Department of Physiology, Faculty of Medicine, University of Toronto, Ont., Canada.
Can J Physiol Pharmacol. 1987 Nov;65(11):2319-28. doi: 10.1139/y87-368.
Standard methods for determining prorenin-renin concentrations in plasma (PRC) and other tissues require the addition of exogenous renin substrate (angiotensinogen) to improve the kinetics of the renin reaction. We studied the effects of substrate prepared from normal human plasma fraction Cohn IV-4, or from nephrectomized (2NX) sheep plasma, on PRC of normal and 2NX human plasmas before and after prorenin activation by acid, cold, and trypsin, and compared the results with plasma renin activities (PRA, no added substrate). Plasmas from 2NX men exhibited negligible basal PRA, indicating that very little, if any, renin had been formed from the extrarenal prorenin they contained, and suggesting the lack of an endogenous prorenin activating mechanism, or "convertase," of probable renal origin. Prorenin was demonstrable by tryptic activation, more than by acid or cold, at up to about 30% of normal. Addition of Cohn IV-4 substrate to 2NX plasma unexpectedly produced (i) a basal PRC value higher than in normal plasma, (ii) total renin values after activation by acid, cold, and trypsin that were much closer to normal values than reflected by PRA methodology, without a commensurate increase (if anything a decrease) in prorenin as a percentage of total renin estimated by all activation methods, and (iii) substantial equalization of activation effects such that trypsin was no longer more effective than acid and cold (and this was also noted with normal plasma). The skewing effect of adding Cohn IV-4 substrate on the PRC of 2NX plasma was much greater than in normal plasma, even though 2NX plasma already had an above normal level of endogenous substrate and should have been influenced less. Enhancement of PRC was very pronounced even when Cohn IV-4 was added to make up only 9% of total (endogenous + exogenous) substrate in the incubation system, suggesting that it was not the added substrate but a renin-generating contaminant that inflated the PRC. Such inflation could be blocked by adding protease inhibitors, suggesting that the responsible protease(s) acted as a prorenin "convertase" that generated new renin from renal and (or) extrarenal prorenin contributed by the added substrate, as well as by the plasma being assayed. One component of convertase could be kallikrein, which was identified by chromogenic assay, the importance of which relative to total convertase activity is unknown.(ABSTRACT TRUNCATED AT 400 WORDS)
测定血浆（PRC）和其他组织中前肾素 - 肾素浓度的标准方法需要添加外源性肾素底物（血管紧张素原）来改善肾素反应的动力学。我们研究了从正常人血浆组分Cohn IV - 4或肾切除（2NX）绵羊血浆制备的底物对正常人和2NX人血浆在酸、冷和胰蛋白酶激活前肾素前后PRC的影响，并将结果与血浆肾素活性（PRA，未添加底物）进行比较。2NX男性的血浆显示出可忽略不计的基础PRA，这表明他们所含的肾外前肾素极少形成肾素，提示可能缺乏源自肾脏的内源性前肾素激活机制或“转化酶”。通过胰蛋白酶激活可检测到前肾素，其检测效果比酸或冷激活更明显，可达正常水平的约30%。向2NX血浆中添加Cohn IV - 4底物意外产生了以下结果：（i）基础PRC值高于正常血浆；（ii）经酸、冷和胰蛋白酶激活后的总肾素值比PRA方法所反映的更接近正常水平，且所有激活方法估计的前肾素占总肾素的百分比没有相应增加（甚至有所下降）；（iii）激活效果基本均衡，使得胰蛋白酶不再比酸和冷更有效（正常血浆也有此现象）。添加Cohn IV - 4底物对2NX血浆PRC的偏差影响比正常血浆大得多，尽管2NX血浆内源性底物水平已高于正常，本应受影响较小。即使在孵育系统中添加Cohn IV - 4仅占总（内源性 + 外源性）底物的9%时，PRC的增强也非常明显，这表明使PRC升高的不是添加的底物，而是一种产生肾素的污染物。添加蛋白酶抑制剂可阻断这种升高，这表明相关蛋白酶作为前肾素“转化酶”，从添加底物以及被测血浆中所含的肾脏和（或）肾外前肾素产生新的肾素。转化酶的一个成分可能是激肽释放酶，通过显色测定法已鉴定出激肽释放酶，但其相对于总转化酶活性的重要性尚不清楚。
