The heptapeptide angiotensin-(1-7) is a circulating biologically active product of the renin-angiotensin system. In this study, we evaluated the role of the vascular endothelium in the formation of angiotensin-(1-7). Metabolism of 125I-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 125I-angiotensin I. After incubation of 125I-angiotensin I for various intervals at 37 degrees 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 125I-angiotensin I with medium previously incubated for 1 hour with endothelial cells. Incubation of 125I-angiotensin I with bovine and human endothelial cells produced a time-dependent generation of 125I-angiotensin-(1-7) greater than 125I-angiotensin II greater than 125I-angiotensin-(1-4). 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 microM), generation of angiotensin II was undetectable. In contrast, angiotensin-(1-7) production increased by an average of 30%.(ABSTRACT TRUNCATED AT 250 WORDS)