Kokkonen J O, Saarinen J, Kovanen P T
Wihuri Research Institute, Helsinki, Finland.
Circulation. 1997 Mar 18;95(6):1455-63. doi: 10.1161/01.cir.95.6.1455.
Data from in vitro studies suggest that both chymase and ACE contribute to the local generation of angiotensin (Ang) II in the heart. The enzyme kinetics under in vivo conditions are unclear. We thus studied the generation of Ang II by cardiac tissue in the presence of interstitial fluid (IF) that contains a variety of naturally occurring protease inhibitors.
Ang I was incubated with heart homogenate in the presence of IF. IF obtained from human skin contained substantial amounts of protease inhibitors and ACE activity, the concentration of alpha 1-antitrypsin being 35% and the activity of ACE 24% of the corresponding serum values. When heart homogenate was incubated with Ang I, three enzymes were responsible for its metabolism: heart chymase and heart ACE converted Ang I to Ang II, and heart carboxypeptidase A (CPA)-like activity degraded Ang I to Ang-(1-9). Incubation of heart homogenate in the presence of IF led to practically full inhibition of heart chymase-mediated Ang II formation by the natural protease inhibitors present in IF. In contrast, heart CPA-like activity was not blocked, as reflected by the continued generation of Ang-(1-9). In addition, both heart ACE- and IF ACE-mediated Ang II formation were strongly inhibited. This inhibition was shown to be due to the Ang-(1-9) formed.
The present experimental study defines two novel inhibitory mechanisms of Ang II formation in the human heart interstitium. Heart chymase-mediated Ang II formation is strongly inhibited by the natural protease inhibitors present in the IF. Similarly, both heart ACE- and IF ACE-mediated Ang II formation appear to be inhibited by the endogenous inhibitor Ang-(1-9) formed by heart CPA-like activity. These inhibitory mechanisms provide additional information about how the Ang II concentration in the heart interstitium may be controlled.
体外研究数据表明，糜酶和血管紧张素转换酶（ACE）均参与心脏局部血管紧张素（Ang）II的生成。体内条件下的酶动力学尚不清楚。因此，我们研究了在含有多种天然存在的蛋白酶抑制剂的间质液（IF）存在的情况下，心脏组织中Ang II的生成情况。
在IF存在的情况下，将Ang I与心脏匀浆一起孵育。从人皮肤获得的IF含有大量的蛋白酶抑制剂和ACE活性，α1-抗胰蛋白酶的浓度为相应血清值的35%，ACE的活性为24%。当心脏匀浆与Ang I孵育时，三种酶参与其代谢：心脏糜酶和心脏ACE将Ang I转化为Ang II，心脏羧肽酶A（CPA）样活性将Ang I降解为Ang-(1-9)。在IF存在的情况下孵育心脏匀浆，IF中存在的天然蛋白酶抑制剂几乎完全抑制了心脏糜酶介导的Ang II形成。相比之下，心脏CPA样活性未被阻断，这可通过Ang-(1-9)的持续生成反映出来。此外，心脏ACE和IF ACE介导的Ang II形成均受到强烈抑制。这种抑制作用被证明是由于形成的Ang-(1-9)所致。
本实验研究确定了人心脏间质中Ang II形成的两种新的抑制机制。心脏糜酶介导的Ang II形成受到IF中存在的天然蛋白酶抑制剂的强烈抑制。同样，心脏ACE和IF ACE介导的Ang II形成似乎均受到心脏CPA样活性形成的内源性抑制剂Ang-(1-9)的抑制。这些抑制机制为心脏间质中Ang II浓度如何受到控制提供了更多信息。
