The activity of angiotensin converting enzyme (ACE) released into the culture medium of human umbilical cord vein endothelial cells in culture (HUVEC) for 24-hour incubation with or without various serotypes of lipopolysaccharide (LPS) was unchanged. ACE activity, however, in cell lysate or monolayer HUVEC after 24-hour incubation of various serotypes of LPS except LPS from E. coli, 026:B6, showed significant decrease, compared with no LPS treatment. Cell lysate contained much higher ACE

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... y than monolayer HUVEC after 24-hour incubation with or without LPS. These findings give rise to speculation that ACE or ACE-like substance might be located not only on the luminal surface, but also in cytoplasm of HUVEC, and also that decrease of ACE activity in the serum of septic adult respiratory distress syndrome (ARDS) patients might be due to reduced synthesis by vascular endothelial cells.