Production of Angiotensin-(l-7) by Human Vascular Endothelium

The heptapeptide angiotensin-(l-7) is a circulating biologically active product of the reninangiotensin system. In this study, we evaluated the role of the vascular endothelium in the formation of angiotensin-(l-7). Metabolism of I-angiotensin I was investigated using confluent cultured bovine and human aortic and umbilical vein endothelial cells. The fetal calf serum-supplemented medium was replaced by serum-free medium containing 0.2% bovine serum albumin. One hour later, this medium was replaced by serum-free medium containing I-angiotensin I. After incubation of I-angiotensin I for various intervals at 37°C, the medium was collected and analyzed for formed products by high-performance liquid chromatography. Products of angiotensin I metabolism were identified by comparison of their retention times with those of radiolabeled standards. The contribution of proteases released into the medium was evaluated by incubation of '"I-angiotensin I with medium previously incubated for 1 hour with endothelial cells. Incubation of I-angiotensin I with bovine and human endothelial cells produced a time-dependent generation of I-angiotensin-(l-7)>I-angiotensin II>I-angiotensin-(l-4). Generation of angiotensin peptides was not due to the presence of proteases in the medium. When human umbilical endothelial cells were incubated in the presence of the angiotensin converting enzyme inhibitor enalaprilat (1 /tM), generation of angiotensin II was undetectable. In contrast, angiotensin-(1-7) production increased by an average of 30%. Experiments in which the metabolism of I-angiotensin I was determined in the presence of the prolyl endopeptidase inhibitor Z-pro-prolinal are consistent with the presence of a membrane-bound form of this endopeptidase being in part responsible for the production of angiotensin-(1-7) from labeled angiotensin I. The data showed that generation of angjotensin-(l-7) by an angiotensin converting enzyme-independent route is a major metabolic pathway for the processing of angiotensin I by human endothelium. (Hypertension 1992;19[suppl II] :II-56-11-61)